text: /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
   * All rights reserved.
   *
   * This package is an SSL implementation written
   * by Eric Young (eay@cryptsoft.com).
   * The implementation was written so as to conform with Netscapes SSL.
   *
   * This library is free for commercial and non-commercial use as long as
   * the following conditions are aheared to.  The following conditions
   * apply to all code found in this distribution, be it the RC4, RSA,
   * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
   * included with this distribution is covered by the same copyright terms
   * except that the holder is Tim Hudson (tjh@cryptsoft.com).
   *
   * Copyright remains Eric Young's, and as such any Copyright notices in
   * the code are not to be removed.
   * If this package is used in a product, Eric Young should be given attribution
   * as the author of the parts of the library used.
   * This can be in the form of a textual message at program startup or
   * in documentation (online or textual) provided with the package.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. All advertising materials mentioning features or use of this software
   *    must display the following acknowledgement:
   *    "This product includes cryptographic software written by
   *     Eric Young (eay@cryptsoft.com)"
   *    The word 'cryptographic' can be left out if the rouines from the library
   *    being used are not cryptographic related :-).
   * 4. If you include any Windows specific code (or a derivative thereof) from
   *    the apps directory (application code) you must include an acknowledgement:
   *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
   *
   * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   * The licence and distribution terms for any publically available version or
   * derivative of this code cannot be changed.  i.e. this code cannot simply be
   * copied and put under another distribution licence
   * [including the GNU Public Licence.]
   */
  /* ====================================================================
   * Copyright (c) 1998-2007 The OpenSSL Project.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   *
   * 3. All advertising materials mentioning features or use of this
   *    software must display the following acknowledgment:
   *    "This product includes software developed by the OpenSSL Project
   *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
   *
   * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
   *    endorse or promote products derived from this software without
   *    prior written permission. For written permission, please contact
   *    openssl-core@openssl.org.
   *
   * 5. Products derived from this software may not be called "OpenSSL"
   *    nor may "OpenSSL" appear in their names without prior written
   *    permission of the OpenSSL Project.
   *
   * 6. Redistributions of any form whatsoever must retain the following
   *    acknowledgment:
   *    "This product includes software developed by the OpenSSL Project
   *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
   *
   * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
   * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
   * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
   * OF THE POSSIBILITY OF SUCH DAMAGE.
   * ====================================================================
   *
   * This product includes cryptographic software written by Eric Young
   * (eay@cryptsoft.com).  This product includes software written by Tim
   * Hudson (tjh@cryptsoft.com).
   *
   */
  /* ====================================================================
   * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED.
   * ECC cipher suite support in OpenSSL originally developed by
   * SUN MICROSYSTEMS, INC., and contributed to the OpenSSL project.
   */
  /* ====================================================================
   * Copyright 2005 Nokia. All rights reserved.
   *
   * The portions of the attached software ("Contribution") is developed by
   * Nokia Corporation and is licensed pursuant to the OpenSSL open source
   * license.
   *
   * The Contribution, originally written by Mika Kousa and Pasi Eronen of
   * Nokia Corporation, consists of the "PSK" (Pre-Shared Key) ciphersuites
   * support (see RFC 4279) to OpenSSL.
   *
   * No patent licenses or other rights except those expressly stated in
   * the OpenSSL open source license shall be deemed granted or received
   * expressly, by implication, estoppel, or otherwise.
   *
   * No assurances are provided by Nokia that the Contribution does not
   * infringe the patent or other intellectual property rights of any third
   * party or that the license provides you with all the necessary rights
   * to make use of the Contribution.
   *
   * THE SOFTWARE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. IN
   * ADDITION TO THE DISCLAIMERS INCLUDED IN THE LICENSE, NOKIA
   * SPECIFICALLY DISCLAIMS ANY LIABILITY FOR CLAIMS BROUGHT BY YOU OR ANY
   * OTHER ENTITY BASED ON INFRINGEMENT OF INTELLECTUAL PROPERTY RIGHTS OR
   * OTHERWISE.
   */
  
  #ifndef OPENSSL_HEADER_SSL_H
  #define OPENSSL_HEADER_SSL_H
  
  #include <openssl/base.h>
  
  #include <openssl/bio.h>
  #include <openssl/buf.h>
  #include <openssl/pem.h>
  #include <openssl/span.h>
  #include <openssl/ssl3.h>
  #include <openssl/thread.h>
  #include <openssl/tls1.h>
  #include <openssl/x509.h>
  
  #if !defined(OPENSSL_WINDOWS)
  #include <sys/time.h>
  #endif
  
  // NGINX needs this #include. Consider revisiting this after NGINX 1.14.0 has
  // been out for a year or so (assuming that they fix it in that release.) See
  // https://boringssl-review.googlesource.com/c/boringssl/+/21664.
  #include <openssl/hmac.h>
  
  // Forward-declare struct timeval. On Windows, it is defined in winsock2.h and
  // Windows headers define too many macros to be included in public headers.
  // However, only a forward declaration is needed.
  struct timeval;
  
  #if defined(__cplusplus)
  extern "C" {
  #endif
  
  
  // SSL implementation.
  
  
  // SSL contexts.
  //
  // |SSL_CTX| objects manage shared state and configuration between multiple TLS
  // or DTLS connections. Whether the connections are TLS or DTLS is selected by
  // an |SSL_METHOD| on creation.
  //
  // |SSL_CTX| are reference-counted and may be shared by connections across
  // multiple threads. Once shared, functions which change the |SSL_CTX|'s
  // configuration may not be used.
  
  // TLS_method is the |SSL_METHOD| used for TLS (and SSLv3) connections.
  OPENSSL_EXPORT const SSL_METHOD *TLS_method(void);
  
  // DTLS_method is the |SSL_METHOD| used for DTLS connections.
  OPENSSL_EXPORT const SSL_METHOD *DTLS_method(void);
  
  // TLS_with_buffers_method is like |TLS_method|, but avoids all use of
  // crypto/x509. All client connections created with |TLS_with_buffers_method|
  // will fail unless a certificate verifier is installed with
  // |SSL_set_custom_verify| or |SSL_CTX_set_custom_verify|.
  OPENSSL_EXPORT const SSL_METHOD *TLS_with_buffers_method(void);
  
  // DTLS_with_buffers_method is like |DTLS_method|, but avoids all use of
  // crypto/x509.
  OPENSSL_EXPORT const SSL_METHOD *DTLS_with_buffers_method(void);
  
  // SSL_CTX_new returns a newly-allocated |SSL_CTX| with default settings or NULL
  // on error.
  OPENSSL_EXPORT SSL_CTX *SSL_CTX_new(const SSL_METHOD *method);
  
  // SSL_CTX_up_ref increments the reference count of |ctx|. It returns one.
  OPENSSL_EXPORT int SSL_CTX_up_ref(SSL_CTX *ctx);
  
  // SSL_CTX_free releases memory associated with |ctx|.
  OPENSSL_EXPORT void SSL_CTX_free(SSL_CTX *ctx);
  
  
  // SSL connections.
  //
  // An |SSL| object represents a single TLS or DTLS connection. Although the
  // shared |SSL_CTX| is thread-safe, an |SSL| is not thread-safe and may only be
  // used on one thread at a time.
  
  // SSL_new returns a newly-allocated |SSL| using |ctx| or NULL on error. The new
  // connection inherits settings from |ctx| at the time of creation. Settings may
  // also be individually configured on the connection.
  //
  // On creation, an |SSL| is not configured to be either a client or server. Call
  // |SSL_set_connect_state| or |SSL_set_accept_state| to set this.
  OPENSSL_EXPORT SSL *SSL_new(SSL_CTX *ctx);
  
  // SSL_free releases memory associated with |ssl|.
  OPENSSL_EXPORT void SSL_free(SSL *ssl);
  
  // SSL_get_SSL_CTX returns the |SSL_CTX| associated with |ssl|. If
  // |SSL_set_SSL_CTX| is called, it returns the new |SSL_CTX|, not the initial
  // one.
  OPENSSL_EXPORT SSL_CTX *SSL_get_SSL_CTX(const SSL *ssl);
  
  // SSL_set_connect_state configures |ssl| to be a client.
  OPENSSL_EXPORT void SSL_set_connect_state(SSL *ssl);
  
  // SSL_set_accept_state configures |ssl| to be a server.
  OPENSSL_EXPORT void SSL_set_accept_state(SSL *ssl);
  
  // SSL_is_server returns one if |ssl| is configured as a server and zero
  // otherwise.
  OPENSSL_EXPORT int SSL_is_server(const SSL *ssl);
  
  // SSL_is_dtls returns one if |ssl| is a DTLS connection and zero otherwise.
  OPENSSL_EXPORT int SSL_is_dtls(const SSL *ssl);
  
  // SSL_set_bio configures |ssl| to read from |rbio| and write to |wbio|. |ssl|
  // takes ownership of the two |BIO|s. If |rbio| and |wbio| are the same, |ssl|
  // only takes ownership of one reference.
  //
  // In DTLS, |rbio| must be non-blocking to properly handle timeouts and
  // retransmits.
  //
  // If |rbio| is the same as the currently configured |BIO| for reading, that
  // side is left untouched and is not freed.
  //
  // If |wbio| is the same as the currently configured |BIO| for writing AND |ssl|
  // is not currently configured to read from and write to the same |BIO|, that
  // side is left untouched and is not freed. This asymmetry is present for
  // historical reasons.
  //
  // Due to the very complex historical behavior of this function, calling this
  // function if |ssl| already has |BIO|s configured is deprecated. Prefer
  // |SSL_set0_rbio| and |SSL_set0_wbio| instead.
  OPENSSL_EXPORT void SSL_set_bio(SSL *ssl, BIO *rbio, BIO *wbio);
  
  // SSL_set0_rbio configures |ssl| to write to |rbio|. It takes ownership of
  // |rbio|.
  //
  // Note that, although this function and |SSL_set0_wbio| may be called on the
  // same |BIO|, each call takes a reference. Use |BIO_up_ref| to balance this.
  OPENSSL_EXPORT void SSL_set0_rbio(SSL *ssl, BIO *rbio);
  
  // SSL_set0_wbio configures |ssl| to write to |wbio|. It takes ownership of
  // |wbio|.
  //
  // Note that, although this function and |SSL_set0_rbio| may be called on the
  // same |BIO|, each call takes a reference. Use |BIO_up_ref| to balance this.
  OPENSSL_EXPORT void SSL_set0_wbio(SSL *ssl, BIO *wbio);
  
  // SSL_get_rbio returns the |BIO| that |ssl| reads from.
  OPENSSL_EXPORT BIO *SSL_get_rbio(const SSL *ssl);
  
  // SSL_get_wbio returns the |BIO| that |ssl| writes to.
  OPENSSL_EXPORT BIO *SSL_get_wbio(const SSL *ssl);
  
  // SSL_get_fd calls |SSL_get_rfd|.
  OPENSSL_EXPORT int SSL_get_fd(const SSL *ssl);
  
  // SSL_get_rfd returns the file descriptor that |ssl| is configured to read
  // from. If |ssl|'s read |BIO| is not configured or doesn't wrap a file
  // descriptor then it returns -1.
  //
  // Note: On Windows, this may return either a file descriptor or a socket (cast
  // to int), depending on whether |ssl| was configured with a file descriptor or
  // socket |BIO|.
  OPENSSL_EXPORT int SSL_get_rfd(const SSL *ssl);
  
  // SSL_get_wfd returns the file descriptor that |ssl| is configured to write
  // to. If |ssl|'s write |BIO| is not configured or doesn't wrap a file
  // descriptor then it returns -1.
  //
  // Note: On Windows, this may return either a file descriptor or a socket (cast
  // to int), depending on whether |ssl| was configured with a file descriptor or
  // socket |BIO|.
  OPENSSL_EXPORT int SSL_get_wfd(const SSL *ssl);
  
  // SSL_set_fd configures |ssl| to read from and write to |fd|. It returns one
  // on success and zero on allocation error. The caller retains ownership of
  // |fd|.
  //
  // On Windows, |fd| is cast to a |SOCKET| and used with Winsock APIs.
  OPENSSL_EXPORT int SSL_set_fd(SSL *ssl, int fd);
  
  // SSL_set_rfd configures |ssl| to read from |fd|. It returns one on success and
  // zero on allocation error. The caller retains ownership of |fd|.
  //
  // On Windows, |fd| is cast to a |SOCKET| and used with Winsock APIs.
  OPENSSL_EXPORT int SSL_set_rfd(SSL *ssl, int fd);
  
  // SSL_set_wfd configures |ssl| to write to |fd|. It returns one on success and
  // zero on allocation error. The caller retains ownership of |fd|.
  //
  // On Windows, |fd| is cast to a |SOCKET| and used with Winsock APIs.
  OPENSSL_EXPORT int SSL_set_wfd(SSL *ssl, int fd);
  
  // SSL_do_handshake continues the current handshake. If there is none or the
  // handshake has completed or False Started, it returns one. Otherwise, it
  // returns <= 0. The caller should pass the value into |SSL_get_error| to
  // determine how to proceed.
  //
  // In DTLS, the caller must drive retransmissions. Whenever |SSL_get_error|
  // signals |SSL_ERROR_WANT_READ|, use |DTLSv1_get_timeout| to determine the
  // current timeout. If it expires before the next retry, call
  // |DTLSv1_handle_timeout|. Note that DTLS handshake retransmissions use fresh
  // sequence numbers, so it is not sufficient to replay packets at the transport.
  //
  // TODO(davidben): Ensure 0 is only returned on transport EOF.
  // https://crbug.com/466303.
  OPENSSL_EXPORT int SSL_do_handshake(SSL *ssl);
  
  // SSL_connect configures |ssl| as a client, if unconfigured, and calls
  // |SSL_do_handshake|.
  OPENSSL_EXPORT int SSL_connect(SSL *ssl);
  
  // SSL_accept configures |ssl| as a server, if unconfigured, and calls
  // |SSL_do_handshake|.
  OPENSSL_EXPORT int SSL_accept(SSL *ssl);
  
  // SSL_read reads up to |num| bytes from |ssl| into |buf|. It implicitly runs
  // any pending handshakes, including renegotiations when enabled. On success, it
  // returns the number of bytes read. Otherwise, it returns <= 0. The caller
  // should pass the value into |SSL_get_error| to determine how to proceed.
  //
  // TODO(davidben): Ensure 0 is only returned on transport EOF.
  // https://crbug.com/466303.
  OPENSSL_EXPORT int SSL_read(SSL *ssl, void *buf, int num);
  
  // SSL_peek behaves like |SSL_read| but does not consume any bytes returned.
  OPENSSL_EXPORT int SSL_peek(SSL *ssl, void *buf, int num);
  
  // SSL_pending returns the number of bytes available in |ssl|. It does not read
  // from the transport.
  OPENSSL_EXPORT int SSL_pending(const SSL *ssl);
  
  // SSL_write writes up to |num| bytes from |buf| into |ssl|. It implicitly runs
  // any pending handshakes, including renegotiations when enabled. On success, it
  // returns the number of bytes written. Otherwise, it returns <= 0. The caller
  // should pass the value into |SSL_get_error| to determine how to proceed.
  //
  // In TLS, a non-blocking |SSL_write| differs from non-blocking |write| in that
  // a failed |SSL_write| still commits to the data passed in. When retrying, the
  // caller must supply the original write buffer (or a larger one containing the
  // original as a prefix). By default, retries will fail if they also do not
  // reuse the same |buf| pointer. This may be relaxed with
  // |SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER|, but the buffer contents still must be
  // unchanged.
  //
  // By default, in TLS, |SSL_write| will not return success until all |num| bytes
  // are written. This may be relaxed with |SSL_MODE_ENABLE_PARTIAL_WRITE|. It
  // allows |SSL_write| to complete with a partial result when only part of the
  // input was written in a single record.
  //
  // In DTLS, neither |SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER| and
  // |SSL_MODE_ENABLE_PARTIAL_WRITE| do anything. The caller may retry with a
  // different buffer freely. A single call to |SSL_write| only ever writes a
  // single record in a single packet, so |num| must be at most
  // |SSL3_RT_MAX_PLAIN_LENGTH|.
  //
  // TODO(davidben): Ensure 0 is only returned on transport EOF.
  // https://crbug.com/466303.
  OPENSSL_EXPORT int SSL_write(SSL *ssl, const void *buf, int num);
  
  // SSL_shutdown shuts down |ssl|. On success, it completes in two stages. First,
  // it returns 0 if |ssl| completed uni-directional shutdown; close_notify has
  // been sent, but the peer's close_notify has not been received. Most callers
  // may stop at this point. For bi-directional shutdown, call |SSL_shutdown|
  // again. It returns 1 if close_notify has been both sent and received.
  //
  // If the peer's close_notify arrived first, the first stage is skipped.
  // |SSL_shutdown| will return 1 once close_notify is sent and skip 0. Callers
  // only interested in uni-directional shutdown must therefore allow for the
  // first stage returning either 0 or 1.
  //
  // |SSL_shutdown| returns -1 on failure. The caller should pass the return value
  // into |SSL_get_error| to determine how to proceed. If the underlying |BIO| is
  // non-blocking, both stages may require retry.
  OPENSSL_EXPORT int SSL_shutdown(SSL *ssl);
  
  // SSL_CTX_set_quiet_shutdown sets quiet shutdown on |ctx| to |mode|. If
  // enabled, |SSL_shutdown| will not send a close_notify alert or wait for one
  // from the peer. It will instead synchronously return one.
  OPENSSL_EXPORT void SSL_CTX_set_quiet_shutdown(SSL_CTX *ctx, int mode);
  
  // SSL_CTX_get_quiet_shutdown returns whether quiet shutdown is enabled for
  // |ctx|.
  OPENSSL_EXPORT int SSL_CTX_get_quiet_shutdown(const SSL_CTX *ctx);
  
  // SSL_set_quiet_shutdown sets quiet shutdown on |ssl| to |mode|. If enabled,
  // |SSL_shutdown| will not send a close_notify alert or wait for one from the
  // peer. It will instead synchronously return one.
  OPENSSL_EXPORT void SSL_set_quiet_shutdown(SSL *ssl, int mode);
  
  // SSL_get_quiet_shutdown returns whether quiet shutdown is enabled for
  // |ssl|.
  OPENSSL_EXPORT int SSL_get_quiet_shutdown(const SSL *ssl);
  
  // SSL_get_error returns a |SSL_ERROR_*| value for the most recent operation on
  // |ssl|. It should be called after an operation failed to determine whether the
  // error was fatal and, if not, when to retry.
  OPENSSL_EXPORT int SSL_get_error(const SSL *ssl, int ret_code);
  
  // SSL_ERROR_NONE indicates the operation succeeded.
  #define SSL_ERROR_NONE 0
  
  // SSL_ERROR_SSL indicates the operation failed within the library. The caller
  // may inspect the error queue for more information.
  #define SSL_ERROR_SSL 1
  
  // SSL_ERROR_WANT_READ indicates the operation failed attempting to read from
  // the transport. The caller may retry the operation when the transport is ready
  // for reading.
  //
  // If signaled by a DTLS handshake, the caller must also call
  // |DTLSv1_get_timeout| and |DTLSv1_handle_timeout| as appropriate. See
  // |SSL_do_handshake|.
  #define SSL_ERROR_WANT_READ 2
  
  // SSL_ERROR_WANT_WRITE indicates the operation failed attempting to write to
  // the transport. The caller may retry the operation when the transport is ready
  // for writing.
  #define SSL_ERROR_WANT_WRITE 3
  
  // SSL_ERROR_WANT_X509_LOOKUP indicates the operation failed in calling the
  // |cert_cb| or |client_cert_cb|. The caller may retry the operation when the
  // callback is ready to return a certificate or one has been configured
  // externally.
  //
  // See also |SSL_CTX_set_cert_cb| and |SSL_CTX_set_client_cert_cb|.
  #define SSL_ERROR_WANT_X509_LOOKUP 4
  
  // SSL_ERROR_SYSCALL indicates the operation failed externally to the library.
  // The caller should consult the system-specific error mechanism. This is
  // typically |errno| but may be something custom if using a custom |BIO|. It
  // may also be signaled if the transport returned EOF, in which case the
  // operation's return value will be zero.
  #define SSL_ERROR_SYSCALL 5
  
  // SSL_ERROR_ZERO_RETURN indicates the operation failed because the connection
  // was cleanly shut down with a close_notify alert.
  #define SSL_ERROR_ZERO_RETURN 6
  
  // SSL_ERROR_WANT_CONNECT indicates the operation failed attempting to connect
  // the transport (the |BIO| signaled |BIO_RR_CONNECT|). The caller may retry the
  // operation when the transport is ready.
  #define SSL_ERROR_WANT_CONNECT 7
  
  // SSL_ERROR_WANT_ACCEPT indicates the operation failed attempting to accept a
  // connection from the transport (the |BIO| signaled |BIO_RR_ACCEPT|). The
  // caller may retry the operation when the transport is ready.
  //
  // TODO(davidben): Remove this. It's used by accept BIOs which are bizarre.
  #define SSL_ERROR_WANT_ACCEPT 8
  
  // SSL_ERROR_WANT_CHANNEL_ID_LOOKUP indicates the operation failed looking up
  // the Channel ID key. The caller may retry the operation when |channel_id_cb|
  // is ready to return a key or one has been configured with
  // |SSL_set1_tls_channel_id|.
  //
  // See also |SSL_CTX_set_channel_id_cb|.
  #define SSL_ERROR_WANT_CHANNEL_ID_LOOKUP 9
  
  // SSL_ERROR_PENDING_SESSION indicates the operation failed because the session
  // lookup callback indicated the session was unavailable. The caller may retry
  // the operation when lookup has completed.
  //
  // See also |SSL_CTX_sess_set_get_cb| and |SSL_magic_pending_session_ptr|.
  #define SSL_ERROR_PENDING_SESSION 11
  
  // SSL_ERROR_PENDING_CERTIFICATE indicates the operation failed because the
  // early callback indicated certificate lookup was incomplete. The caller may
  // retry the operation when lookup has completed.
  //
  // See also |SSL_CTX_set_select_certificate_cb|.
  #define SSL_ERROR_PENDING_CERTIFICATE 12
  
  // SSL_ERROR_WANT_PRIVATE_KEY_OPERATION indicates the operation failed because
  // a private key operation was unfinished. The caller may retry the operation
  // when the private key operation is complete.
  //
  // See also |SSL_set_private_key_method| and
  // |SSL_CTX_set_private_key_method|.
  #define SSL_ERROR_WANT_PRIVATE_KEY_OPERATION 13
  
  // SSL_ERROR_PENDING_TICKET indicates that a ticket decryption is pending. The
  // caller may retry the operation when the decryption is ready.
  //
  // See also |SSL_CTX_set_ticket_aead_method|.
  #define SSL_ERROR_PENDING_TICKET 14
  
  // SSL_ERROR_EARLY_DATA_REJECTED indicates that early data was rejected. The
  // caller should treat this as a connection failure and retry any operations
  // associated with the rejected early data. |SSL_reset_early_data_reject| may be
  // used to reuse the underlying connection for the retry.
  #define SSL_ERROR_EARLY_DATA_REJECTED 15
  
  // SSL_ERROR_WANT_CERTIFICATE_VERIFY indicates the operation failed because
  // certificate verification was incomplete. The caller may retry the operation
  // when certificate verification is complete.
  //
  // See also |SSL_CTX_set_custom_verify|.
  #define SSL_ERROR_WANT_CERTIFICATE_VERIFY 16
  
  #define SSL_ERROR_HANDOFF 17
  
  // SSL_set_mtu sets the |ssl|'s MTU in DTLS to |mtu|. It returns one on success
  // and zero on failure.
  OPENSSL_EXPORT int SSL_set_mtu(SSL *ssl, unsigned mtu);
  
  // DTLSv1_set_initial_timeout_duration sets the initial duration for a DTLS
  // handshake timeout.
  //
  // This duration overrides the default of 1 second, which is the strong
  // recommendation of RFC 6347 (see section 4.2.4.1). However, there may exist
  // situations where a shorter timeout would be beneficial, such as for
  // time-sensitive applications.
  OPENSSL_EXPORT void DTLSv1_set_initial_timeout_duration(SSL *ssl,
                                                          unsigned duration_ms);
  
  // DTLSv1_get_timeout queries the next DTLS handshake timeout. If there is a
  // timeout in progress, it sets |*out| to the time remaining and returns one.
  // Otherwise, it returns zero.
  //
  // When the timeout expires, call |DTLSv1_handle_timeout| to handle the
  // retransmit behavior.
  //
  // NOTE: This function must be queried again whenever the handshake state
  // machine changes, including when |DTLSv1_handle_timeout| is called.
  OPENSSL_EXPORT int DTLSv1_get_timeout(const SSL *ssl, struct timeval *out);
  
  // DTLSv1_handle_timeout is called when a DTLS handshake timeout expires. If no
  // timeout had expired, it returns 0. Otherwise, it retransmits the previous
  // flight of handshake messages and returns 1. If too many timeouts had expired
  // without progress or an error occurs, it returns -1.
  //
  // The caller's external timer should be compatible with the one |ssl| queries
  // within some fudge factor. Otherwise, the call will be a no-op, but
  // |DTLSv1_get_timeout| will return an updated timeout.
  //
  // If the function returns -1, checking if |SSL_get_error| returns
  // |SSL_ERROR_WANT_WRITE| may be used to determine if the retransmit failed due
  // to a non-fatal error at the write |BIO|. However, the operation may not be
  // retried until the next timeout fires.
  //
  // WARNING: This function breaks the usual return value convention.
  //
  // TODO(davidben): This |SSL_ERROR_WANT_WRITE| behavior is kind of bizarre.
  OPENSSL_EXPORT int DTLSv1_handle_timeout(SSL *ssl);
  
  
  // Protocol versions.
  
  #define DTLS1_VERSION_MAJOR 0xfe
  #define SSL3_VERSION_MAJOR 0x03
  
  #define SSL3_VERSION 0x0300
  #define TLS1_VERSION 0x0301
  #define TLS1_1_VERSION 0x0302
  #define TLS1_2_VERSION 0x0303
  #define TLS1_3_VERSION 0x0304
  
  #define DTLS1_VERSION 0xfeff
  #define DTLS1_2_VERSION 0xfefd
  
  #define TLS1_3_DRAFT23_VERSION 0x7f17
  
  // SSL_CTX_set_min_proto_version sets the minimum protocol version for |ctx| to
  // |version|. If |version| is zero, the default minimum version is used. It
  // returns one on success and zero if |version| is invalid.
  OPENSSL_EXPORT int SSL_CTX_set_min_proto_version(SSL_CTX *ctx,
                                                   uint16_t version);
  
  // SSL_CTX_set_max_proto_version sets the maximum protocol version for |ctx| to
  // |version|. If |version| is zero, the default maximum version is used. It
  // returns one on success and zero if |version| is invalid.
  OPENSSL_EXPORT int SSL_CTX_set_max_proto_version(SSL_CTX *ctx,
                                                   uint16_t version);
  
  // SSL_set_min_proto_version sets the minimum protocol version for |ssl| to
  // |version|. If |version| is zero, the default minimum version is used. It
  // returns one on success and zero if |version| is invalid.
  OPENSSL_EXPORT int SSL_set_min_proto_version(SSL *ssl, uint16_t version);
  
  // SSL_set_max_proto_version sets the maximum protocol version for |ssl| to
  // |version|. If |version| is zero, the default maximum version is used. It
  // returns one on success and zero if |version| is invalid.
  OPENSSL_EXPORT int SSL_set_max_proto_version(SSL *ssl, uint16_t version);
  
  // SSL_version returns the TLS or DTLS protocol version used by |ssl|, which is
  // one of the |*_VERSION| values. (E.g. |TLS1_2_VERSION|.) Before the version
  // is negotiated, the result is undefined.
  OPENSSL_EXPORT int SSL_version(const SSL *ssl);
  
  
  // Options.
  //
  // Options configure protocol behavior.
  
  // SSL_OP_NO_QUERY_MTU, in DTLS, disables querying the MTU from the underlying
  // |BIO|. Instead, the MTU is configured with |SSL_set_mtu|.
  #define SSL_OP_NO_QUERY_MTU 0x00001000L
  
  // SSL_OP_NO_TICKET disables session ticket support (RFC 5077).
  #define SSL_OP_NO_TICKET 0x00004000L
  
  // SSL_OP_CIPHER_SERVER_PREFERENCE configures servers to select ciphers and
  // ECDHE curves according to the server's preferences instead of the
  // client's.
  #define SSL_OP_CIPHER_SERVER_PREFERENCE 0x00400000L
  
  // The following flags toggle individual protocol versions. This is deprecated.
  // Use |SSL_CTX_set_min_proto_version| and |SSL_CTX_set_max_proto_version|
  // instead.
  #define SSL_OP_NO_SSLv3 0x02000000L
  #define SSL_OP_NO_TLSv1 0x04000000L
  #define SSL_OP_NO_TLSv1_2 0x08000000L
  #define SSL_OP_NO_TLSv1_1 0x10000000L
  #define SSL_OP_NO_TLSv1_3 0x20000000L
  #define SSL_OP_NO_DTLSv1 SSL_OP_NO_TLSv1
  #define SSL_OP_NO_DTLSv1_2 SSL_OP_NO_TLSv1_2
  
  // SSL_CTX_set_options enables all options set in |options| (which should be one
  // or more of the |SSL_OP_*| values, ORed together) in |ctx|. It returns a
  // bitmask representing the resulting enabled options.
  OPENSSL_EXPORT uint32_t SSL_CTX_set_options(SSL_CTX *ctx, uint32_t options);
  
  // SSL_CTX_clear_options disables all options set in |options| (which should be
  // one or more of the |SSL_OP_*| values, ORed together) in |ctx|. It returns a
  // bitmask representing the resulting enabled options.
  OPENSSL_EXPORT uint32_t SSL_CTX_clear_options(SSL_CTX *ctx, uint32_t options);
  
  // SSL_CTX_get_options returns a bitmask of |SSL_OP_*| values that represent all
  // the options enabled for |ctx|.
  OPENSSL_EXPORT uint32_t SSL_CTX_get_options(const SSL_CTX *ctx);
  
  // SSL_set_options enables all options set in |options| (which should be one or
  // more of the |SSL_OP_*| values, ORed together) in |ssl|. It returns a bitmask
  // representing the resulting enabled options.
  OPENSSL_EXPORT uint32_t SSL_set_options(SSL *ssl, uint32_t options);
  
  // SSL_clear_options disables all options set in |options| (which should be one
  // or more of the |SSL_OP_*| values, ORed together) in |ssl|. It returns a
  // bitmask representing the resulting enabled options.
  OPENSSL_EXPORT uint32_t SSL_clear_options(SSL *ssl, uint32_t options);
  
  // SSL_get_options returns a bitmask of |SSL_OP_*| values that represent all the
  // options enabled for |ssl|.
  OPENSSL_EXPORT uint32_t SSL_get_options(const SSL *ssl);
  
  
  // Modes.
  //
  // Modes configure API behavior.
  
  // SSL_MODE_ENABLE_PARTIAL_WRITE, in TLS, allows |SSL_write| to complete with a
  // partial result when the only part of the input was written in a single
  // record. In DTLS, it does nothing.
  #define SSL_MODE_ENABLE_PARTIAL_WRITE 0x00000001L
  
  // SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER, in TLS, allows retrying an incomplete
  // |SSL_write| with a different buffer. However, |SSL_write| still assumes the
  // buffer contents are unchanged. This is not the default to avoid the
  // misconception that non-blocking |SSL_write| behaves like non-blocking
  // |write|. In DTLS, it does nothing.
  #define SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER 0x00000002L
  
  // SSL_MODE_NO_AUTO_CHAIN disables automatically building a certificate chain
  // before sending certificates to the peer. This flag is set (and the feature
  // disabled) by default.
  // TODO(davidben): Remove this behavior. https://crbug.com/boringssl/42.
  #define SSL_MODE_NO_AUTO_CHAIN 0x00000008L
  
  // SSL_MODE_ENABLE_FALSE_START allows clients to send application data before
  // receipt of ChangeCipherSpec and Finished. This mode enables full handshakes
  // to 'complete' in one RTT. See RFC 7918.
  //
  // When False Start is enabled, |SSL_do_handshake| may succeed before the
  // handshake has completely finished. |SSL_write| will function at this point,
  // and |SSL_read| will transparently wait for the final handshake leg before
  // returning application data. To determine if False Start occurred or when the
  // handshake is completely finished, see |SSL_in_false_start|, |SSL_in_init|,
  // and |SSL_CB_HANDSHAKE_DONE| from |SSL_CTX_set_info_callback|.
  #define SSL_MODE_ENABLE_FALSE_START 0x00000080L
  
  // SSL_MODE_CBC_RECORD_SPLITTING causes multi-byte CBC records in SSL 3.0 and
  // TLS 1.0 to be split in two: the first record will contain a single byte and
  // the second will contain the remainder. This effectively randomises the IV and
  // prevents BEAST attacks.
  #define SSL_MODE_CBC_RECORD_SPLITTING 0x00000100L
  
  // SSL_MODE_NO_SESSION_CREATION will cause any attempts to create a session to
  // fail with SSL_R_SESSION_MAY_NOT_BE_CREATED. This can be used to enforce that
  // session resumption is used for a given SSL*.
  #define SSL_MODE_NO_SESSION_CREATION 0x00000200L
  
  // SSL_MODE_SEND_FALLBACK_SCSV sends TLS_FALLBACK_SCSV in the ClientHello.
  // To be set only by applications that reconnect with a downgraded protocol
  // version; see RFC 7507 for details.
  //
  // DO NOT ENABLE THIS if your application attempts a normal handshake. Only use
  // this in explicit fallback retries, following the guidance in RFC 7507.
  #define SSL_MODE_SEND_FALLBACK_SCSV 0x00000400L
  
  // SSL_CTX_set_mode enables all modes set in |mode| (which should be one or more
  // of the |SSL_MODE_*| values, ORed together) in |ctx|. It returns a bitmask
  // representing the resulting enabled modes.
  OPENSSL_EXPORT uint32_t SSL_CTX_set_mode(SSL_CTX *ctx, uint32_t mode);
  
  // SSL_CTX_clear_mode disables all modes set in |mode| (which should be one or
  // more of the |SSL_MODE_*| values, ORed together) in |ctx|. It returns a
  // bitmask representing the resulting enabled modes.
  OPENSSL_EXPORT uint32_t SSL_CTX_clear_mode(SSL_CTX *ctx, uint32_t mode);
  
  // SSL_CTX_get_mode returns a bitmask of |SSL_MODE_*| values that represent all
  // the modes enabled for |ssl|.
  OPENSSL_EXPORT uint32_t SSL_CTX_get_mode(const SSL_CTX *ctx);
  
  // SSL_set_mode enables all modes set in |mode| (which should be one or more of
  // the |SSL_MODE_*| values, ORed together) in |ssl|. It returns a bitmask
  // representing the resulting enabled modes.
  OPENSSL_EXPORT uint32_t SSL_set_mode(SSL *ssl, uint32_t mode);
  
  // SSL_clear_mode disables all modes set in |mode| (which should be one or more
  // of the |SSL_MODE_*| values, ORed together) in |ssl|. It returns a bitmask
  // representing the resulting enabled modes.
  OPENSSL_EXPORT uint32_t SSL_clear_mode(SSL *ssl, uint32_t mode);
  
  // SSL_get_mode returns a bitmask of |SSL_MODE_*| values that represent all the
  // modes enabled for |ssl|.
  OPENSSL_EXPORT uint32_t SSL_get_mode(const SSL *ssl);
  
  // SSL_CTX_set0_buffer_pool sets a |CRYPTO_BUFFER_POOL| that will be used to
  // store certificates. This can allow multiple connections to share
  // certificates and thus save memory.
  //
  // The SSL_CTX does not take ownership of |pool| and the caller must ensure
  // that |pool| outlives |ctx| and all objects linked to it, including |SSL|,
  // |X509| and |SSL_SESSION| objects. Basically, don't ever free |pool|.
  OPENSSL_EXPORT void SSL_CTX_set0_buffer_pool(SSL_CTX *ctx,
                                               CRYPTO_BUFFER_POOL *pool);
  
  
  // Configuring certificates and private keys.
  //
  // These functions configure the connection's leaf certificate, private key, and
  // certificate chain. The certificate chain is ordered leaf to root (as sent on
  // the wire) but does not include the leaf. Both client and server certificates
  // use these functions.
  //
  // Certificates and keys may be configured before the handshake or dynamically
  // in the early callback and certificate callback.
  
  // SSL_CTX_use_certificate sets |ctx|'s leaf certificate to |x509|. It returns
  // one on success and zero on failure.
  OPENSSL_EXPORT int SSL_CTX_use_certificate(SSL_CTX *ctx, X509 *x509);
  
  // SSL_use_certificate sets |ssl|'s leaf certificate to |x509|. It returns one
  // on success and zero on failure.
  OPENSSL_EXPORT int SSL_use_certificate(SSL *ssl, X509 *x509);
  
  // SSL_CTX_use_PrivateKey sets |ctx|'s private key to |pkey|. It returns one on
  // success and zero on failure.
  OPENSSL_EXPORT int SSL_CTX_use_PrivateKey(SSL_CTX *ctx, EVP_PKEY *pkey);
  
  // SSL_use_PrivateKey sets |ssl|'s private key to |pkey|. It returns one on
  // success and zero on failure.
  OPENSSL_EXPORT int SSL_use_PrivateKey(SSL *ssl, EVP_PKEY *pkey);
  
  // SSL_CTX_set0_chain sets |ctx|'s certificate chain, excluding the leaf, to
  // |chain|. On success, it returns one and takes ownership of |chain|.
  // Otherwise, it returns zero.
  OPENSSL_EXPORT int SSL_CTX_set0_chain(SSL_CTX *ctx, STACK_OF(X509) *chain);
  
  // SSL_CTX_set1_chain sets |ctx|'s certificate chain, excluding the leaf, to
  // |chain|. It returns one on success and zero on failure. The caller retains
  // ownership of |chain| and may release it freely.
  OPENSSL_EXPORT int SSL_CTX_set1_chain(SSL_CTX *ctx, STACK_OF(X509) *chain);
  
  // SSL_set0_chain sets |ssl|'s certificate chain, excluding the leaf, to
  // |chain|. On success, it returns one and takes ownership of |chain|.
  // Otherwise, it returns zero.
  OPENSSL_EXPORT int SSL_set0_chain(SSL *ssl, STACK_OF(X509) *chain);
  
  // SSL_set1_chain sets |ssl|'s certificate chain, excluding the leaf, to
  // |chain|. It returns one on success and zero on failure. The caller retains
  // ownership of |chain| and may release it freely.
  OPENSSL_EXPORT int SSL_set1_chain(SSL *ssl, STACK_OF(X509) *chain);
  
  // SSL_CTX_add0_chain_cert appends |x509| to |ctx|'s certificate chain. On
  // success, it returns one and takes ownership of |x509|. Otherwise, it returns
  // zero.
  OPENSSL_EXPORT int SSL_CTX_add0_chain_cert(SSL_CTX *ctx, X509 *x509);
  
  // SSL_CTX_add1_chain_cert appends |x509| to |ctx|'s certificate chain. It
  // returns one on success and zero on failure. The caller retains ownership of
  // |x509| and may release it freely.
  OPENSSL_EXPORT int SSL_CTX_add1_chain_cert(SSL_CTX *ctx, X509 *x509);
  
  // SSL_add0_chain_cert appends |x509| to |ctx|'s certificate chain. On success,
  // it returns one and takes ownership of |x509|. Otherwise, it returns zero.
  OPENSSL_EXPORT int SSL_add0_chain_cert(SSL *ssl, X509 *x509);
  
  // SSL_CTX_add_extra_chain_cert calls |SSL_CTX_add0_chain_cert|.
  OPENSSL_EXPORT int SSL_CTX_add_extra_chain_cert(SSL_CTX *ctx, X509 *x509);
  
  // SSL_add1_chain_cert appends |x509| to |ctx|'s certificate chain. It returns
  // one on success and zero on failure. The caller retains ownership of |x509|
  // and may release it freely.
  OPENSSL_EXPORT int SSL_add1_chain_cert(SSL *ssl, X509 *x509);
  
  // SSL_CTX_clear_chain_certs clears |ctx|'s certificate chain and returns
  // one.
  OPENSSL_EXPORT int SSL_CTX_clear_chain_certs(SSL_CTX *ctx);
  
  // SSL_CTX_clear_extra_chain_certs calls |SSL_CTX_clear_chain_certs|.
  OPENSSL_EXPORT int SSL_CTX_clear_extra_chain_certs(SSL_CTX *ctx);
  
  // SSL_clear_chain_certs clears |ssl|'s certificate chain and returns one.
  OPENSSL_EXPORT int SSL_clear_chain_certs(SSL *ssl);
  
  // SSL_CTX_set_cert_cb sets a callback that is called to select a certificate.
  // The callback returns one on success, zero on internal error, and a negative
  // number on failure or to pause the handshake. If the handshake is paused,
  // |SSL_get_error| will return |SSL_ERROR_WANT_X509_LOOKUP|.
  //
  // On the client, the callback may call |SSL_get0_certificate_types| and
  // |SSL_get_client_CA_list| for information on the server's certificate
  // request.
  //
  // On the server, the callback will be called on non-resumption handshakes,
  // after extensions have been processed.
  OPENSSL_EXPORT void SSL_CTX_set_cert_cb(SSL_CTX *ctx,
                                          int (*cb)(SSL *ssl, void *arg),
                                          void *arg);
  
  // SSL_set_cert_cb sets a callback that is called to select a certificate. The
  // callback returns one on success, zero on internal error, and a negative
  // number on failure or to pause the handshake. If the handshake is paused,
  // |SSL_get_error| will return |SSL_ERROR_WANT_X509_LOOKUP|.
  //
  // On the client, the callback may call |SSL_get0_certificate_types| and
  // |SSL_get_client_CA_list| for information on the server's certificate
  // request.
  OPENSSL_EXPORT void SSL_set_cert_cb(SSL *ssl, int (*cb)(SSL *ssl, void *arg),
                                      void *arg);
  
  // SSL_get0_certificate_types, for a client, sets |*out_types| to an array
  // containing the client certificate types requested by a server. It returns the
  // length of the array.
  //
  // The behavior of this function is undefined except during the callbacks set by
  // by |SSL_CTX_set_cert_cb| and |SSL_CTX_set_client_cert_cb| or when the
  // handshake is paused because of them.
  OPENSSL_EXPORT size_t SSL_get0_certificate_types(SSL *ssl,
                                                   const uint8_t **out_types);
  
  // SSL_certs_clear resets the private key, leaf certificate, and certificate
  // chain of |ssl|.
  OPENSSL_EXPORT void SSL_certs_clear(SSL *ssl);
  
  // SSL_CTX_check_private_key returns one if the certificate and private key
  // configured in |ctx| are consistent and zero otherwise.
  OPENSSL_EXPORT int SSL_CTX_check_private_key(const SSL_CTX *ctx);
  
  // SSL_check_private_key returns one if the certificate and private key
  // configured in |ssl| are consistent and zero otherwise.
  OPENSSL_EXPORT int SSL_check_private_key(const SSL *ssl);
  
  // SSL_CTX_get0_certificate returns |ctx|'s leaf certificate.
  OPENSSL_EXPORT X509 *SSL_CTX_get0_certificate(const SSL_CTX *ctx);
  
  // SSL_get_certificate returns |ssl|'s leaf certificate.
  OPENSSL_EXPORT X509 *SSL_get_certificate(const SSL *ssl);
  
  // SSL_CTX_get0_privatekey returns |ctx|'s private key.
  OPENSSL_EXPORT EVP_PKEY *SSL_CTX_get0_privatekey(const SSL_CTX *ctx);
  
  // SSL_get_privatekey returns |ssl|'s private key.
  OPENSSL_EXPORT EVP_PKEY *SSL_get_privatekey(const SSL *ssl);
  
  // SSL_CTX_get0_chain_certs sets |*out_chain| to |ctx|'s certificate chain and
  // returns one.
  OPENSSL_EXPORT int SSL_CTX_get0_chain_certs(const SSL_CTX *ctx,
                                              STACK_OF(X509) **out_chain);
  
  // SSL_CTX_get_extra_chain_certs calls |SSL_CTX_get0_chain_certs|.
  OPENSSL_EXPORT int SSL_CTX_get_extra_chain_certs(const SSL_CTX *ctx,
                                                   STACK_OF(X509) **out_chain);
  
  // SSL_get0_chain_certs sets |*out_chain| to |ssl|'s certificate chain and
  // returns one.
  OPENSSL_EXPORT int SSL_get0_chain_certs(const SSL *ssl,
                                          STACK_OF(X509) **out_chain);
  
  // SSL_CTX_set_signed_cert_timestamp_list sets the list of signed certificate
  // timestamps that is sent to clients that request it. The |list| argument must
  // contain one or more SCT structures serialised as a SignedCertificateTimestamp
  // List (see https://tools.ietf.org/html/rfc6962#section-3.3) – i.e. each SCT
  // is prefixed by a big-endian, uint16 length and the concatenation of one or
  // more such prefixed SCTs are themselves also prefixed by a uint16 length. It
  // returns one on success and zero on error. The caller retains ownership of
  // |list|.
  OPENSSL_EXPORT int SSL_CTX_set_signed_cert_timestamp_list(SSL_CTX *ctx,
                                                            const uint8_t *list,
                                                            size_t list_len);
  
  // SSL_set_signed_cert_timestamp_list sets the list of signed certificate
  // timestamps that is sent to clients that request is. The same format as the
  // one used for |SSL_CTX_set_signed_cert_timestamp_list| applies. The caller
  // retains ownership of |list|.
  OPENSSL_EXPORT int SSL_set_signed_cert_timestamp_list(SSL *ctx,
                                                        const uint8_t *list,
                                                        size_t list_len);
  
  // SSL_CTX_set_ocsp_response sets the OCSP response that is sent to clients
  // which request it. It returns one on success and zero on error. The caller
  // retains ownership of |response|.
  OPENSSL_EXPORT int SSL_CTX_set_ocsp_response(SSL_CTX *ctx,
                                               const uint8_t *response,
                                               size_t response_len);
  
  // SSL_set_ocsp_response sets the OCSP response that is sent to clients which
  // request it. It returns one on success and zero on error. The caller retains
  // ownership of |response|.
  OPENSSL_EXPORT int SSL_set_ocsp_response(SSL *ssl,
                                           const uint8_t *response,
                                           size_t response_len);
  
  // SSL_SIGN_* are signature algorithm values as defined in TLS 1.3.
  #define SSL_SIGN_RSA_PKCS1_SHA1 0x0201
  #define SSL_SIGN_RSA_PKCS1_SHA256 0x0401
  #define SSL_SIGN_RSA_PKCS1_SHA384 0x0501
  #define SSL_SIGN_RSA_PKCS1_SHA512 0x0601
  #define SSL_SIGN_ECDSA_SHA1 0x0203
  #define SSL_SIGN_ECDSA_SECP256R1_SHA256 0x0403
  #define SSL_SIGN_ECDSA_SECP384R1_SHA384 0x0503
  #define SSL_SIGN_ECDSA_SECP521R1_SHA512 0x0603
  #define SSL_SIGN_RSA_PSS_SHA256 0x0804
  #define SSL_SIGN_RSA_PSS_SHA384 0x0805
  #define SSL_SIGN_RSA_PSS_SHA512 0x0806
  #define SSL_SIGN_ED25519 0x0807
  
  // SSL_SIGN_RSA_PKCS1_MD5_SHA1 is an internal signature algorithm used to
  // specify raw RSASSA-PKCS1-v1_5 with an MD5/SHA-1 concatenation, as used in TLS
  // before TLS 1.2.
  #define SSL_SIGN_RSA_PKCS1_MD5_SHA1 0xff01
  
  // SSL_get_signature_algorithm_name returns a human-readable name for |sigalg|,
  // or NULL if unknown. If |include_curve| is one, the curve for ECDSA algorithms
  // is included as in TLS 1.3. Otherwise, it is excluded as in TLS 1.2.
  OPENSSL_EXPORT const char *SSL_get_signature_algorithm_name(uint16_t sigalg,
                                                              int include_curve);
  
  // SSL_get_signature_algorithm_key_type returns the key type associated with
  // |sigalg| as an |EVP_PKEY_*| constant or |EVP_PKEY_NONE| if unknown.
  OPENSSL_EXPORT int SSL_get_signature_algorithm_key_type(uint16_t sigalg);
  
  // SSL_get_signature_algorithm_digest returns the digest function associated
  // with |sigalg| or |NULL| if |sigalg| has no prehash (Ed25519) or is unknown.
  OPENSSL_EXPORT const EVP_MD *SSL_get_signature_algorithm_digest(
      uint16_t sigalg);
  
  // SSL_is_signature_algorithm_rsa_pss returns one if |sigalg| is an RSA-PSS
  // signature algorithm and zero otherwise.
  OPENSSL_EXPORT int SSL_is_signature_algorithm_rsa_pss(uint16_t sigalg);
  
  // SSL_CTX_set_signing_algorithm_prefs configures |ctx| to use |prefs| as the
  // preference list when signing with |ctx|'s private key. It returns one on
  // success and zero on error. |prefs| should not include the internal-only value
  // |SSL_SIGN_RSA_PKCS1_MD5_SHA1|.
  OPENSSL_EXPORT int SSL_CTX_set_signing_algorithm_prefs(SSL_CTX *ctx,
                                                         const uint16_t *prefs,
                                                         size_t num_prefs);
  
  // SSL_set_signing_algorithm_prefs configures |ssl| to use |prefs| as the
  // preference list when signing with |ssl|'s private key. It returns one on
  // success and zero on error. |prefs| should not include the internal-only value
  // |SSL_SIGN_RSA_PKCS1_MD5_SHA1|.
  OPENSSL_EXPORT int SSL_set_signing_algorithm_prefs(SSL *ssl,
                                                     const uint16_t *prefs,
                                                     size_t num_prefs);
  
  
  // Certificate and private key convenience functions.
  
  // SSL_CTX_set_chain_and_key sets the certificate chain and private key for a
  // TLS client or server. References to the given |CRYPTO_BUFFER| and |EVP_PKEY|
  // objects are added as needed. Exactly one of |privkey| or |privkey_method|
  // may be non-NULL. Returns one on success and zero on error.
  OPENSSL_EXPORT int SSL_CTX_set_chain_and_key(
      SSL_CTX *ctx, CRYPTO_BUFFER *const *certs, size_t num_certs,
      EVP_PKEY *privkey, const SSL_PRIVATE_KEY_METHOD *privkey_method);
  
  // SSL_set_chain_and_key sets the certificate chain and private key for a TLS
  // client or server. References to the given |CRYPTO_BUFFER| and |EVP_PKEY|
  // objects are added as needed. Exactly one of |privkey| or |privkey_method|
  // may be non-NULL. Returns one on success and zero on error.
  OPENSSL_EXPORT int SSL_set_chain_and_key(
      SSL *ssl, CRYPTO_BUFFER *const *certs, size_t num_certs, EVP_PKEY *privkey,
      const SSL_PRIVATE_KEY_METHOD *privkey_method);
  
  // SSL_CTX_use_RSAPrivateKey sets |ctx|'s private key to |rsa|. It returns one
  // on success and zero on failure.
  OPENSSL_EXPORT int SSL_CTX_use_RSAPrivateKey(SSL_CTX *ctx, RSA *rsa);
  
  // SSL_use_RSAPrivateKey sets |ctx|'s private key to |rsa|. It returns one on
  // success and zero on failure.
  OPENSSL_EXPORT int SSL_use_RSAPrivateKey(SSL *ssl, RSA *rsa);
  
  // The following functions configure certificates or private keys but take as
  // input DER-encoded structures. They return one on success and zero on
  // failure.
  
  OPENSSL_EXPORT int SSL_CTX_use_certificate_ASN1(SSL_CTX *ctx, size_t der_len,
                                                  const uint8_t *der);
  OPENSSL_EXPORT int SSL_use_certificate_ASN1(SSL *ssl, const uint8_t *der,
                                              size_t der_len);
  
  OPENSSL_EXPORT int SSL_CTX_use_PrivateKey_ASN1(int pk, SSL_CTX *ctx,
                                                 const uint8_t *der,
                                                 size_t der_len);
  OPENSSL_EXPORT int SSL_use_PrivateKey_ASN1(int type, SSL *ssl,
                                             const uint8_t *der, size_t der_len);
  
  OPENSSL_EXPORT int SSL_CTX_use_RSAPrivateKey_ASN1(SSL_CTX *ctx,
                                                    const uint8_t *der,
                                                    size_t der_len);
  OPENSSL_EXPORT int SSL_use_RSAPrivateKey_ASN1(SSL *ssl, const uint8_t *der,
                                                size_t der_len);
  
  // The following functions configure certificates or private keys but take as
  // input files to read from. They return one on success and zero on failure. The
  // |type| parameter is one of the |SSL_FILETYPE_*| values and determines whether
  // the file's contents are read as PEM or DER.
  
  #define SSL_FILETYPE_PEM 1
  #define SSL_FILETYPE_ASN1 2
  
  OPENSSL_EXPORT int SSL_CTX_use_RSAPrivateKey_file(SSL_CTX *ctx,
                                                    const char *file,
                                                    int type);
  OPENSSL_EXPORT int SSL_use_RSAPrivateKey_file(SSL *ssl, const char *file,
                                                int type);
  
  OPENSSL_EXPORT int SSL_CTX_use_certificate_file(SSL_CTX *ctx, const char *file,
                                                  int type);
  OPENSSL_EXPORT int SSL_use_certificate_file(SSL *ssl, const char *file,
                                              int type);
  
  OPENSSL_EXPORT int SSL_CTX_use_PrivateKey_file(SSL_CTX *ctx, const char *file,
                                                 int type);
  OPENSSL_EXPORT int SSL_use_PrivateKey_file(SSL *ssl, const char *file,
                                             int type);
  
  // SSL_CTX_use_certificate_chain_file configures certificates for |ctx|. It
  // reads the contents of |file| as a PEM-encoded leaf certificate followed
  // optionally by the certificate chain to send to the peer. It returns one on
  // success and zero on failure.
  OPENSSL_EXPORT int SSL_CTX_use_certificate_chain_file(SSL_CTX *ctx,
                                                        const char *file);
  
  // SSL_CTX_set_default_passwd_cb sets the password callback for PEM-based
  // convenience functions called on |ctx|.
  OPENSSL_EXPORT void SSL_CTX_set_default_passwd_cb(SSL_CTX *ctx,
                                                    pem_password_cb *cb);
  
  // SSL_CTX_get_default_passwd_cb returns the callback set by
  // |SSL_CTX_set_default_passwd_cb|.
  OPENSSL_EXPORT pem_password_cb *SSL_CTX_get_default_passwd_cb(
      const SSL_CTX *ctx);
  
  // SSL_CTX_set_default_passwd_cb_userdata sets the userdata parameter for
  // |ctx|'s password callback.
  OPENSSL_EXPORT void SSL_CTX_set_default_passwd_cb_userdata(SSL_CTX *ctx,
                                                             void *data);
  
  // SSL_CTX_get_default_passwd_cb_userdata returns the userdata parameter set by
  // |SSL_CTX_set_default_passwd_cb_userdata|.
  OPENSSL_EXPORT void *SSL_CTX_get_default_passwd_cb_userdata(const SSL_CTX *ctx);
  
  
  // Custom private keys.
  
  enum ssl_private_key_result_t {
    ssl_private_key_success,
    ssl_private_key_retry,
    ssl_private_key_failure,
  };
  
  // ssl_private_key_method_st (aka |SSL_PRIVATE_KEY_METHOD|) describes private
  // key hooks. This is used to off-load signing operations to a custom,
  // potentially asynchronous, backend. Metadata about the key such as the type
  // and size are parsed out of the certificate.
  struct ssl_private_key_method_st {
    // sign signs the message |in| in using the specified signature algorithm. On
    // success, it returns |ssl_private_key_success| and writes at most |max_out|
    // bytes of signature data to |out| and sets |*out_len| to the number of bytes
    // written. On failure, it returns |ssl_private_key_failure|. If the operation
    // has not completed, it returns |ssl_private_key_retry|. |sign| should
    // arrange for the high-level operation on |ssl| to be retried when the
    // operation is completed. This will result in a call to |complete|.
    //
    // |signature_algorithm| is one of the |SSL_SIGN_*| values, as defined in TLS
    // 1.3. Note that, in TLS 1.2, ECDSA algorithms do not require that curve
    // sizes match hash sizes, so the curve portion of |SSL_SIGN_ECDSA_*| values
    // must be ignored. BoringSSL will internally handle the curve matching logic
    // where appropriate.
    //
    // It is an error to call |sign| while another private key operation is in
    // progress on |ssl|.
    enum ssl_private_key_result_t (*sign)(SSL *ssl, uint8_t *out, size_t *out_len,
                                          size_t max_out,
                                          uint16_t signature_algorithm,
                                          const uint8_t *in, size_t in_len);
  
    // decrypt decrypts |in_len| bytes of encrypted data from |in|. On success it
    // returns |ssl_private_key_success|, writes at most |max_out| bytes of
    // decrypted data to |out| and sets |*out_len| to the actual number of bytes
    // written. On failure it returns |ssl_private_key_failure|. If the operation
    // has not completed, it returns |ssl_private_key_retry|. The caller should
    // arrange for the high-level operation on |ssl| to be retried when the
    // operation is completed, which will result in a call to |complete|. This
    // function only works with RSA keys and should perform a raw RSA decryption
    // operation with no padding.
    //
    // It is an error to call |decrypt| while another private key operation is in
    // progress on |ssl|.
    enum ssl_private_key_result_t (*decrypt)(SSL *ssl, uint8_t *out,
                                             size_t *out_len, size_t max_out,
                                             const uint8_t *in, size_t in_len);
  
    // complete completes a pending operation. If the operation has completed, it
    // returns |ssl_private_key_success| and writes the result to |out| as in
    // |sign|. Otherwise, it returns |ssl_private_key_failure| on failure and
    // |ssl_private_key_retry| if the operation is still in progress.
    //
    // |complete| may be called arbitrarily many times before completion, but it
    // is an error to call |complete| if there is no pending operation in progress
    // on |ssl|.
    enum ssl_private_key_result_t (*complete)(SSL *ssl, uint8_t *out,
                                              size_t *out_len, size_t max_out);
  };
  
  // SSL_set_private_key_method configures a custom private key on |ssl|.
  // |key_method| must remain valid for the lifetime of |ssl|.
  OPENSSL_EXPORT void SSL_set_private_key_method(
      SSL *ssl, const SSL_PRIVATE_KEY_METHOD *key_method);
  
  // SSL_CTX_set_private_key_method configures a custom private key on |ctx|.
  // |key_method| must remain valid for the lifetime of |ctx|.
  OPENSSL_EXPORT void SSL_CTX_set_private_key_method(
      SSL_CTX *ctx, const SSL_PRIVATE_KEY_METHOD *key_method);
  
  
  // Cipher suites.
  //
  // |SSL_CIPHER| objects represent cipher suites.
  
  DEFINE_CONST_STACK_OF(SSL_CIPHER)
  
  // SSL_get_cipher_by_value returns the structure representing a TLS cipher
  // suite based on its assigned number, or NULL if unknown. See
  // https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-4.
  OPENSSL_EXPORT const SSL_CIPHER *SSL_get_cipher_by_value(uint16_t value);
  
  // SSL_CIPHER_get_id returns |cipher|'s id. It may be cast to a |uint16_t| to
  // get the cipher suite value.
  OPENSSL_EXPORT uint32_t SSL_CIPHER_get_id(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_is_aead returns one if |cipher| uses an AEAD cipher.
  OPENSSL_EXPORT int SSL_CIPHER_is_aead(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_is_block_cipher returns one if |cipher| is a block cipher.
  OPENSSL_EXPORT int SSL_CIPHER_is_block_cipher(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_get_cipher_nid returns the NID for |cipher|'s bulk
  // cipher. Possible values are |NID_aes_128_gcm|, |NID_aes_256_gcm|,
  // |NID_chacha20_poly1305|, |NID_aes_128_cbc|, |NID_aes_256_cbc|, and
  // |NID_des_ede3_cbc|.
  OPENSSL_EXPORT int SSL_CIPHER_get_cipher_nid(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_get_digest_nid returns the NID for |cipher|'s HMAC if it is a
  // legacy cipher suite. For modern AEAD-based ciphers (see
  // |SSL_CIPHER_is_aead|), it returns |NID_undef|.
  //
  // Note this function only returns the legacy HMAC digest, not the PRF hash.
  OPENSSL_EXPORT int SSL_CIPHER_get_digest_nid(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_get_kx_nid returns the NID for |cipher|'s key exchange. This may
  // be |NID_kx_rsa|, |NID_kx_ecdhe|, or |NID_kx_psk| for TLS 1.2. In TLS 1.3,
  // cipher suites do not specify the key exchange, so this function returns
  // |NID_kx_any|.
  OPENSSL_EXPORT int SSL_CIPHER_get_kx_nid(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_get_auth_nid returns the NID for |cipher|'s authentication
  // type. This may be |NID_auth_rsa|, |NID_auth_ecdsa|, or |NID_auth_psk| for TLS
  // 1.2. In TLS 1.3, cipher suites do not specify authentication, so this
  // function returns |NID_auth_any|.
  OPENSSL_EXPORT int SSL_CIPHER_get_auth_nid(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_get_prf_nid retuns the NID for |cipher|'s PRF hash. If |cipher| is
  // a pre-TLS-1.2 cipher, it returns |NID_md5_sha1| but note these ciphers use
  // SHA-256 in TLS 1.2. Other return values may be treated uniformly in all
  // applicable versions.
  OPENSSL_EXPORT int SSL_CIPHER_get_prf_nid(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_get_min_version returns the minimum protocol version required
  // for |cipher|.
  OPENSSL_EXPORT uint16_t SSL_CIPHER_get_min_version(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_get_max_version returns the maximum protocol version that
  // supports |cipher|.
  OPENSSL_EXPORT uint16_t SSL_CIPHER_get_max_version(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_standard_name returns the standard IETF name for |cipher|. For
  // example, "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256".
  OPENSSL_EXPORT const char *SSL_CIPHER_standard_name(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_get_name returns the OpenSSL name of |cipher|. For example,
  // "ECDHE-RSA-AES128-GCM-SHA256".
  OPENSSL_EXPORT const char *SSL_CIPHER_get_name(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_get_kx_name returns a string that describes the key-exchange
  // method used by |cipher|. For example, "ECDHE_ECDSA". TLS 1.3 AEAD-only
  // ciphers return the string "GENERIC".
  OPENSSL_EXPORT const char *SSL_CIPHER_get_kx_name(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_get_bits returns the strength, in bits, of |cipher|. If
  // |out_alg_bits| is not NULL, it writes the number of bits consumed by the
  // symmetric algorithm to |*out_alg_bits|.
  OPENSSL_EXPORT int SSL_CIPHER_get_bits(const SSL_CIPHER *cipher,
                                         int *out_alg_bits);
  
  
  // Cipher suite configuration.
  //
  // OpenSSL uses a mini-language to configure cipher suites. The language
  // maintains an ordered list of enabled ciphers, along with an ordered list of
  // disabled but available ciphers. Initially, all ciphers are disabled with a
  // default ordering. The cipher string is then interpreted as a sequence of
  // directives, separated by colons, each of which modifies this state.
  //
  // Most directives consist of a one character or empty opcode followed by a
  // selector which matches a subset of available ciphers.
  //
  // Available opcodes are:
  //
  //   The empty opcode enables and appends all matching disabled ciphers to the
  //   end of the enabled list. The newly appended ciphers are ordered relative to
  //   each other matching their order in the disabled list.
  //
  //   |-| disables all matching enabled ciphers and prepends them to the disabled
  //   list, with relative order from the enabled list preserved. This means the
  //   most recently disabled ciphers get highest preference relative to other
  //   disabled ciphers if re-enabled.
  //
  //   |+| moves all matching enabled ciphers to the end of the enabled list, with
  //   relative order preserved.
  //
  //   |!| deletes all matching ciphers, enabled or not, from either list. Deleted
  //   ciphers will not matched by future operations.
  //
  // A selector may be a specific cipher (using either the standard or OpenSSL
  // name for the cipher) or one or more rules separated by |+|. The final
  // selector matches the intersection of each rule. For instance, |AESGCM+aECDSA|
  // matches ECDSA-authenticated AES-GCM ciphers.
  //
  // Available cipher rules are:
  //
  //   |ALL| matches all ciphers.
  //
  //   |kRSA|, |kDHE|, |kECDHE|, and |kPSK| match ciphers using plain RSA, DHE,
  //   ECDHE, and plain PSK key exchanges, respectively. Note that ECDHE_PSK is
  //   matched by |kECDHE| and not |kPSK|.
  //
  //   |aRSA|, |aECDSA|, and |aPSK| match ciphers authenticated by RSA, ECDSA, and
  //   a pre-shared key, respectively.
  //
  //   |RSA|, |DHE|, |ECDHE|, |PSK|, |ECDSA|, and |PSK| are aliases for the
  //   corresponding |k*| or |a*| cipher rule. |RSA| is an alias for |kRSA|, not
  //   |aRSA|.
  //
  //   |3DES|, |AES128|, |AES256|, |AES|, |AESGCM|, |CHACHA20| match ciphers
  //   whose bulk cipher use the corresponding encryption scheme. Note that
  //   |AES|, |AES128|, and |AES256| match both CBC and GCM ciphers.
  //
  //   |SHA1|, |SHA256|, and |SHA384| match legacy cipher suites using the
  //   corresponding hash function in their MAC. AEADs are matched by none of
  //   these.
  //
  //   |SHA| is an alias for |SHA1|.
  //
  // Although implemented, authentication-only ciphers match no rules and must be
  // explicitly selected by name.
  //
  // Deprecated cipher rules:
  //
  //   |kEDH|, |EDH|, |kEECDH|, and |EECDH| are legacy aliases for |kDHE|, |DHE|,
  //   |kECDHE|, and |ECDHE|, respectively.
  //
  //   |HIGH| is an alias for |ALL|.
  //
  //   |FIPS| is an alias for |HIGH|.
  //
  //   |SSLv3| and |TLSv1| match ciphers available in TLS 1.1 or earlier.
  //   |TLSv1_2| matches ciphers new in TLS 1.2. This is confusing and should not
  //   be used.
  //
  // Unknown rules are silently ignored by legacy APIs, and rejected by APIs with
  // "strict" in the name, which should be preferred. Cipher lists can be long
  // and it's easy to commit typos. Strict functions will also reject the use of
  // spaces, semi-colons and commas as alternative separators.
  //
  // The special |@STRENGTH| directive will sort all enabled ciphers by strength.
  //
  // The |DEFAULT| directive, when appearing at the front of the string, expands
  // to the default ordering of available ciphers.
  //
  // If configuring a server, one may also configure equal-preference groups to
  // partially respect the client's preferences when
  // |SSL_OP_CIPHER_SERVER_PREFERENCE| is enabled. Ciphers in an equal-preference
  // group have equal priority and use the client order. This may be used to
  // enforce that AEADs are preferred but select AES-GCM vs. ChaCha20-Poly1305
  // based on client preferences. An equal-preference is specified with square
  // brackets, combining multiple selectors separated by |. For example:
  //
  //   [ECDHE-ECDSA-CHACHA20-POLY1305|ECDHE-ECDSA-AES128-GCM-SHA256]
  //
  // Once an equal-preference group is used, future directives must be
  // opcode-less. Inside an equal-preference group, spaces are not allowed.
  //
  // TLS 1.3 ciphers do not participate in this mechanism and instead have a
  // built-in preference order. Functions to set cipher lists do not affect TLS
  // 1.3, and functions to query the cipher list do not include TLS 1.3
  // ciphers.
  
  // SSL_DEFAULT_CIPHER_LIST is the default cipher suite configuration. It is
  // substituted when a cipher string starts with 'DEFAULT'.
  #define SSL_DEFAULT_CIPHER_LIST "ALL"
  
  // SSL_CTX_set_strict_cipher_list configures the cipher list for |ctx|,
  // evaluating |str| as a cipher string and returning error if |str| contains
  // anything meaningless. It returns one on success and zero on failure.
  OPENSSL_EXPORT int SSL_CTX_set_strict_cipher_list(SSL_CTX *ctx,
                                                    const char *str);
  
  // SSL_CTX_set_cipher_list configures the cipher list for |ctx|, evaluating
  // |str| as a cipher string. It returns one on success and zero on failure.
  //
  // Prefer to use |SSL_CTX_set_strict_cipher_list|. This function tolerates
  // garbage inputs, unless an empty cipher list results.
  OPENSSL_EXPORT int SSL_CTX_set_cipher_list(SSL_CTX *ctx, const char *str);
  
  // SSL_set_strict_cipher_list configures the cipher list for |ssl|, evaluating
  // |str| as a cipher string and returning error if |str| contains anything
  // meaningless. It returns one on success and zero on failure.
  OPENSSL_EXPORT int SSL_set_strict_cipher_list(SSL *ssl, const char *str);
  
  // SSL_set_cipher_list configures the cipher list for |ssl|, evaluating |str| as
  // a cipher string. It returns one on success and zero on failure.
  //
  // Prefer to use |SSL_set_strict_cipher_list|. This function tolerates garbage
  // inputs, unless an empty cipher list results.
  OPENSSL_EXPORT int SSL_set_cipher_list(SSL *ssl, const char *str);
  
  // SSL_CTX_get_ciphers returns the cipher list for |ctx|, in order of
  // preference.
  OPENSSL_EXPORT STACK_OF(SSL_CIPHER) *SSL_CTX_get_ciphers(const SSL_CTX *ctx);
  
  // SSL_CTX_cipher_in_group returns one if the |i|th cipher (see
  // |SSL_CTX_get_ciphers|) is in the same equipreference group as the one
  // following it and zero otherwise.
  OPENSSL_EXPORT int SSL_CTX_cipher_in_group(const SSL_CTX *ctx, size_t i);
  
  // SSL_get_ciphers returns the cipher list for |ssl|, in order of preference.
  OPENSSL_EXPORT STACK_OF(SSL_CIPHER) *SSL_get_ciphers(const SSL *ssl);
  
  
  // Connection information.
  
  // SSL_is_init_finished returns one if |ssl| has completed its initial handshake
  // and has no pending handshake. It returns zero otherwise.
  OPENSSL_EXPORT int SSL_is_init_finished(const SSL *ssl);
  
  // SSL_in_init returns one if |ssl| has a pending handshake and zero
  // otherwise.
  OPENSSL_EXPORT int SSL_in_init(const SSL *ssl);
  
  // SSL_in_false_start returns one if |ssl| has a pending handshake that is in
  // False Start. |SSL_write| may be called at this point without waiting for the
  // peer, but |SSL_read| will complete the handshake before accepting application
  // data.
  //
  // See also |SSL_MODE_ENABLE_FALSE_START|.
  OPENSSL_EXPORT int SSL_in_false_start(const SSL *ssl);
  
  // SSL_get_peer_certificate returns the peer's leaf certificate or NULL if the
  // peer did not use certificates. The caller must call |X509_free| on the
  // result to release it.
  OPENSSL_EXPORT X509 *SSL_get_peer_certificate(const SSL *ssl);
  
  // SSL_get_peer_cert_chain returns the peer's certificate chain or NULL if
  // unavailable or the peer did not use certificates. This is the unverified list
  // of certificates as sent by the peer, not the final chain built during
  // verification. The caller does not take ownership of the result.
  //
  // WARNING: This function behaves differently between client and server. If
  // |ssl| is a server, the returned chain does not include the leaf certificate.
  // If a client, it does.
  OPENSSL_EXPORT STACK_OF(X509) *SSL_get_peer_cert_chain(const SSL *ssl);
  
  // SSL_get_peer_full_cert_chain returns the peer's certificate chain, or NULL if
  // unavailable or the peer did not use certificates. This is the unverified list
  // of certificates as sent by the peer, not the final chain built during
  // verification. The caller does not take ownership of the result.
  //
  // This is the same as |SSL_get_peer_cert_chain| except that this function
  // always returns the full chain, i.e. the first element of the return value
  // (if any) will be the leaf certificate. In constrast,
  // |SSL_get_peer_cert_chain| returns only the intermediate certificates if the
  // |ssl| is a server.
  OPENSSL_EXPORT STACK_OF(X509) *SSL_get_peer_full_cert_chain(const SSL *ssl);
  
  // SSL_get0_peer_certificates returns the peer's certificate chain, or NULL if
  // unavailable or the peer did not use certificates. This is the unverified list
  // of certificates as sent by the peer, not the final chain built during
  // verification. The caller does not take ownership of the result.
  //
  // This is the |CRYPTO_BUFFER| variant of |SSL_get_peer_full_cert_chain|.
  OPENSSL_EXPORT STACK_OF(CRYPTO_BUFFER) *
      SSL_get0_peer_certificates(const SSL *ssl);
  
  // SSL_get0_signed_cert_timestamp_list sets |*out| and |*out_len| to point to
  // |*out_len| bytes of SCT information from the server. This is only valid if
  // |ssl| is a client. The SCT information is a SignedCertificateTimestampList
  // (including the two leading length bytes).
  // See https://tools.ietf.org/html/rfc6962#section-3.3
  // If no SCT was received then |*out_len| will be zero on return.
  //
  // WARNING: the returned data is not guaranteed to be well formed.
  OPENSSL_EXPORT void SSL_get0_signed_cert_timestamp_list(const SSL *ssl,
                                                          const uint8_t **out,
                                                          size_t *out_len);
  
  // SSL_get0_ocsp_response sets |*out| and |*out_len| to point to |*out_len|
  // bytes of an OCSP response from the server. This is the DER encoding of an
  // OCSPResponse type as defined in RFC 2560.
  //
  // WARNING: the returned data is not guaranteed to be well formed.
  OPENSSL_EXPORT void SSL_get0_ocsp_response(const SSL *ssl, const uint8_t **out,
                                             size_t *out_len);
  
  // SSL_get_tls_unique writes at most |max_out| bytes of the tls-unique value
  // for |ssl| to |out| and sets |*out_len| to the number of bytes written. It
  // returns one on success or zero on error. In general |max_out| should be at
  // least 12.
  //
  // This function will always fail if the initial handshake has not completed.
  // The tls-unique value will change after a renegotiation but, since
  // renegotiations can be initiated by the server at any point, the higher-level
  // protocol must either leave them disabled or define states in which the
  // tls-unique value can be read.
  //
  // The tls-unique value is defined by
  // https://tools.ietf.org/html/rfc5929#section-3.1. Due to a weakness in the
  // TLS protocol, tls-unique is broken for resumed connections unless the
  // Extended Master Secret extension is negotiated. Thus this function will
  // return zero if |ssl| performed session resumption unless EMS was used when
  // negotiating the original session.
  OPENSSL_EXPORT int SSL_get_tls_unique(const SSL *ssl, uint8_t *out,
                                        size_t *out_len, size_t max_out);
  
  // SSL_get_extms_support returns one if the Extended Master Secret extension or
  // TLS 1.3 was negotiated. Otherwise, it returns zero.
  OPENSSL_EXPORT int SSL_get_extms_support(const SSL *ssl);
  
  // SSL_get_current_cipher returns the cipher used in the current outgoing
  // connection state, or NULL if the null cipher is active.
  OPENSSL_EXPORT const SSL_CIPHER *SSL_get_current_cipher(const SSL *ssl);
  
  // SSL_session_reused returns one if |ssl| performed an abbreviated handshake
  // and zero otherwise.
  //
  // TODO(davidben): Hammer down the semantics of this API while a handshake,
  // initial or renego, is in progress.
  OPENSSL_EXPORT int SSL_session_reused(const SSL *ssl);
  
  // SSL_get_secure_renegotiation_support returns one if the peer supports secure
  // renegotiation (RFC 5746) or TLS 1.3. Otherwise, it returns zero.
  OPENSSL_EXPORT int SSL_get_secure_renegotiation_support(const SSL *ssl);
  
  // SSL_export_keying_material exports a value derived from the master secret, as
  // specified in RFC 5705. It writes |out_len| bytes to |out| given a label and
  // optional context. (Since a zero length context is allowed, the |use_context|
  // flag controls whether a context is included.)
  //
  // It returns one on success and zero otherwise.
  OPENSSL_EXPORT int SSL_export_keying_material(
      SSL *ssl, uint8_t *out, size_t out_len, const char *label, size_t label_len,
      const uint8_t *context, size_t context_len, int use_context);
  
  
  // Custom extensions.
  //
  // The custom extension functions allow TLS extensions to be added to
  // ClientHello and ServerHello messages.
  
  // SSL_custom_ext_add_cb is a callback function that is called when the
  // ClientHello (for clients) or ServerHello (for servers) is constructed. In
  // the case of a server, this callback will only be called for a given
  // extension if the ClientHello contained that extension – it's not possible to
  // inject extensions into a ServerHello that the client didn't request.
  //
  // When called, |extension_value| will contain the extension number that is
  // being considered for addition (so that a single callback can handle multiple
  // extensions). If the callback wishes to include the extension, it must set
  // |*out| to point to |*out_len| bytes of extension contents and return one. In
  // this case, the corresponding |SSL_custom_ext_free_cb| callback will later be
  // called with the value of |*out| once that data has been copied.
  //
  // If the callback does not wish to add an extension it must return zero.
  //
  // Alternatively, the callback can abort the connection by setting
  // |*out_alert_value| to a TLS alert number and returning -1.
  typedef int (*SSL_custom_ext_add_cb)(SSL *ssl, unsigned extension_value,
                                       const uint8_t **out, size_t *out_len,
                                       int *out_alert_value, void *add_arg);
  
  // SSL_custom_ext_free_cb is a callback function that is called by OpenSSL iff
  // an |SSL_custom_ext_add_cb| callback previously returned one. In that case,
  // this callback is called and passed the |out| pointer that was returned by
  // the add callback. This is to free any dynamically allocated data created by
  // the add callback.
  typedef void (*SSL_custom_ext_free_cb)(SSL *ssl, unsigned extension_value,
                                         const uint8_t *out, void *add_arg);
  
  // SSL_custom_ext_parse_cb is a callback function that is called by OpenSSL to
  // parse an extension from the peer: that is from the ServerHello for a client
  // and from the ClientHello for a server.
  //
  // When called, |extension_value| will contain the extension number and the
  // contents of the extension are |contents_len| bytes at |contents|.
  //
  // The callback must return one to continue the handshake. Otherwise, if it
  // returns zero, a fatal alert with value |*out_alert_value| is sent and the
  // handshake is aborted.
  typedef int (*SSL_custom_ext_parse_cb)(SSL *ssl, unsigned extension_value,
                                         const uint8_t *contents,
                                         size_t contents_len,
                                         int *out_alert_value, void *parse_arg);
  
  // SSL_extension_supported returns one iff OpenSSL internally handles
  // extensions of type |extension_value|. This can be used to avoid registering
  // custom extension handlers for extensions that a future version of OpenSSL
  // may handle internally.
  OPENSSL_EXPORT int SSL_extension_supported(unsigned extension_value);
  
  // SSL_CTX_add_client_custom_ext registers callback functions for handling
  // custom TLS extensions for client connections.
  //
  // If |add_cb| is NULL then an empty extension will be added in each
  // ClientHello. Otherwise, see the comment for |SSL_custom_ext_add_cb| about
  // this callback.
  //
  // The |free_cb| may be NULL if |add_cb| doesn't dynamically allocate data that
  // needs to be freed.
  //
  // It returns one on success or zero on error. It's always an error to register
  // callbacks for the same extension twice, or to register callbacks for an
  // extension that OpenSSL handles internally. See |SSL_extension_supported| to
  // discover, at runtime, which extensions OpenSSL handles internally.
  OPENSSL_EXPORT int SSL_CTX_add_client_custom_ext(
      SSL_CTX *ctx, unsigned extension_value, SSL_custom_ext_add_cb add_cb,
      SSL_custom_ext_free_cb free_cb, void *add_arg,
      SSL_custom_ext_parse_cb parse_cb, void *parse_arg);
  
  // SSL_CTX_add_server_custom_ext is the same as
  // |SSL_CTX_add_client_custom_ext|, but for server connections.
  //
  // Unlike on the client side, if |add_cb| is NULL no extension will be added.
  // The |add_cb|, if any, will only be called if the ClientHello contained a
  // matching extension.
  OPENSSL_EXPORT int SSL_CTX_add_server_custom_ext(
      SSL_CTX *ctx, unsigned extension_value, SSL_custom_ext_add_cb add_cb,
      SSL_custom_ext_free_cb free_cb, void *add_arg,
      SSL_custom_ext_parse_cb parse_cb, void *parse_arg);
  
  
  // Sessions.
  //
  // An |SSL_SESSION| represents an SSL session that may be resumed in an
  // abbreviated handshake. It is reference-counted and immutable. Once
  // established, an |SSL_SESSION| may be shared by multiple |SSL| objects on
  // different threads and must not be modified.
  
  DECLARE_PEM_rw(SSL_SESSION, SSL_SESSION)
  
  // SSL_SESSION_new returns a newly-allocated blank |SSL_SESSION| or NULL on
  // error. This may be useful when writing tests but should otherwise not be
  // used.
  OPENSSL_EXPORT SSL_SESSION *SSL_SESSION_new(const SSL_CTX *ctx);
  
  // SSL_SESSION_up_ref increments the reference count of |session| and returns
  // one.
  OPENSSL_EXPORT int SSL_SESSION_up_ref(SSL_SESSION *session);
  
  // SSL_SESSION_free decrements the reference count of |session|. If it reaches
  // zero, all data referenced by |session| and |session| itself are released.
  OPENSSL_EXPORT void SSL_SESSION_free(SSL_SESSION *session);
  
  // SSL_SESSION_to_bytes serializes |in| into a newly allocated buffer and sets
  // |*out_data| to that buffer and |*out_len| to its length. The caller takes
  // ownership of the buffer and must call |OPENSSL_free| when done. It returns
  // one on success and zero on error.
  OPENSSL_EXPORT int SSL_SESSION_to_bytes(const SSL_SESSION *in,
                                          uint8_t **out_data, size_t *out_len);
  
  // SSL_SESSION_to_bytes_for_ticket serializes |in|, but excludes the session
  // identification information, namely the session ID and ticket.
  OPENSSL_EXPORT int SSL_SESSION_to_bytes_for_ticket(const SSL_SESSION *in,
                                                     uint8_t **out_data,
                                                     size_t *out_len);
  
  // SSL_SESSION_from_bytes parses |in_len| bytes from |in| as an SSL_SESSION. It
  // returns a newly-allocated |SSL_SESSION| on success or NULL on error.
  OPENSSL_EXPORT SSL_SESSION *SSL_SESSION_from_bytes(
      const uint8_t *in, size_t in_len, const SSL_CTX *ctx);
  
  // SSL_SESSION_get_version returns a string describing the TLS or DTLS version
  // |session| was established at. For example, "TLSv1.2" or "SSLv3".
  OPENSSL_EXPORT const char *SSL_SESSION_get_version(const SSL_SESSION *session);
  
  // SSL_SESSION_get_protocol_version returns the TLS or DTLS version |session|
  // was established at.
  OPENSSL_EXPORT uint16_t
  SSL_SESSION_get_protocol_version(const SSL_SESSION *session);
  
  // SSL_SESSION_set_protocol_version sets |session|'s TLS or DTLS version to
  // |version|. This may be useful when writing tests but should otherwise not be
  // used. It returns one on success and zero on error.
  OPENSSL_EXPORT int SSL_SESSION_set_protocol_version(SSL_SESSION *session,
                                                      uint16_t version);
  
  // SSL_SESSION_get_id returns a pointer to a buffer containing |session|'s
  // session ID and sets |*out_len| to its length.
  OPENSSL_EXPORT const uint8_t *SSL_SESSION_get_id(const SSL_SESSION *session,
                                                   unsigned *out_len);
  
  // SSL_SESSION_get_time returns the time at which |session| was established in
  // seconds since the UNIX epoch.
  OPENSSL_EXPORT uint64_t SSL_SESSION_get_time(const SSL_SESSION *session);
  
  // SSL_SESSION_get_timeout returns the lifetime of |session| in seconds.
  OPENSSL_EXPORT uint32_t SSL_SESSION_get_timeout(const SSL_SESSION *session);
  
  // SSL_SESSION_get0_peer returns the peer leaf certificate stored in
  // |session|.
  //
  // TODO(davidben): This should return a const X509 *.
  OPENSSL_EXPORT X509 *SSL_SESSION_get0_peer(const SSL_SESSION *session);
  
  // SSL_SESSION_get_master_key writes up to |max_out| bytes of |session|'s master
  // secret to |out| and returns the number of bytes written. If |max_out| is
  // zero, it returns the size of the master secret.
  OPENSSL_EXPORT size_t SSL_SESSION_get_master_key(const SSL_SESSION *session,
                                                   uint8_t *out, size_t max_out);
  
  // SSL_SESSION_set_time sets |session|'s creation time to |time| and returns
  // |time|. This function may be useful in writing tests but otherwise should not
  // be used.
  OPENSSL_EXPORT uint64_t SSL_SESSION_set_time(SSL_SESSION *session,
                                               uint64_t time);
  
  // SSL_SESSION_set_timeout sets |session|'s timeout to |timeout| and returns
  // one. This function may be useful in writing tests but otherwise should not
  // be used.
  OPENSSL_EXPORT uint32_t SSL_SESSION_set_timeout(SSL_SESSION *session,
                                                  uint32_t timeout);
  
  // SSL_SESSION_set1_id_context sets |session|'s session ID context (see
  // |SSL_CTX_set_session_id_context|) to |sid_ctx|. It returns one on success and
  // zero on error. This function may be useful in writing tests but otherwise
  // should not be used.
  OPENSSL_EXPORT int SSL_SESSION_set1_id_context(SSL_SESSION *session,
                                                 const uint8_t *sid_ctx,
                                                 size_t sid_ctx_len);
  
  // SSL_SESSION_should_be_single_use returns one if |session| should be
  // single-use (TLS 1.3 and later) and zero otherwise.
  //
  // If this function returns one, clients retain multiple sessions and use each
  // only once. This prevents passive observers from correlating connections with
  // tickets. See draft-ietf-tls-tls13-18, appendix B.5. If it returns zero,
  // |session| cannot be used without leaking a correlator.
  OPENSSL_EXPORT int SSL_SESSION_should_be_single_use(const SSL_SESSION *session);
  
  // SSL_SESSION_is_resumable returns one if |session| is resumable and zero
  // otherwise.
  OPENSSL_EXPORT int SSL_SESSION_is_resumable(const SSL_SESSION *session);
  
  // SSL_SESSION_has_ticket returns one if |session| has a ticket and zero
  // otherwise.
  OPENSSL_EXPORT int SSL_SESSION_has_ticket(const SSL_SESSION *session);
  
  // SSL_SESSION_get0_ticket sets |*out_ticket| and |*out_len| to |session|'s
  // ticket, or NULL and zero if it does not have one. |out_ticket| may be NULL
  // if only the ticket length is needed.
  OPENSSL_EXPORT void SSL_SESSION_get0_ticket(const SSL_SESSION *session,
                                              const uint8_t **out_ticket,
                                              size_t *out_len);
  
  // SSL_SESSION_get_ticket_lifetime_hint returns ticket lifetime hint of
  // |session| in seconds or zero if none was set.
  OPENSSL_EXPORT uint32_t
  SSL_SESSION_get_ticket_lifetime_hint(const SSL_SESSION *session);
  
  
  // Session caching.
  //
  // Session caching allows connections to be established more efficiently based
  // on saved parameters from a previous connection, called a session (see
  // |SSL_SESSION|). The client offers a saved session, using an opaque identifier
  // from a previous connection. The server may accept the session, if it has the
  // parameters available. Otherwise, it will decline and continue with a full
  // handshake.
  //
  // This requires both the client and the server to retain session state. A
  // client does so with a stateful session cache. A server may do the same or, if
  // supported by both sides, statelessly using session tickets. For more
  // information on the latter, see the next section.
  //
  // For a server, the library implements a built-in internal session cache as an
  // in-memory hash table. Servers may also use |SSL_CTX_sess_set_get_cb| and
  // |SSL_CTX_sess_set_new_cb| to implement a custom external session cache. In
  // particular, this may be used to share a session cache between multiple
  // servers in a large deployment. An external cache may be used in addition to
  // or instead of the internal one. Use |SSL_CTX_set_session_cache_mode| to
  // toggle the internal cache.
  //
  // For a client, the only option is an external session cache. Clients may use
  // |SSL_CTX_sess_set_new_cb| to register a callback for when new sessions are
  // available. These may be cached and, in subsequent compatible connections,
  // configured with |SSL_set_session|.
  //
  // Note that offering or accepting a session short-circuits certificate
  // verification and most parameter negotiation. Resuming sessions across
  // different contexts may result in security failures and surprising
  // behavior. For a typical client, this means sessions for different hosts must
  // be cached under different keys. A client that connects to the same host with,
  // e.g., different cipher suite settings or client certificates should also use
  // separate session caches between those contexts. Servers should also partition
  // session caches between SNI hosts with |SSL_CTX_set_session_id_context|.
  //
  // Note also, in TLS 1.2 and earlier, offering sessions allows passive observers
  // to correlate different client connections. TLS 1.3 and later fix this,
  // provided clients use sessions at most once. Session caches are managed by the
  // caller in BoringSSL, so this must be implemented externally. See
  // |SSL_SESSION_should_be_single_use| for details.
  
  // SSL_SESS_CACHE_OFF disables all session caching.
  #define SSL_SESS_CACHE_OFF 0x0000
  
  // SSL_SESS_CACHE_CLIENT enables session caching for a client. The internal
  // cache is never used on a client, so this only enables the callbacks.
  #define SSL_SESS_CACHE_CLIENT 0x0001
  
  // SSL_SESS_CACHE_SERVER enables session caching for a server.
  #define SSL_SESS_CACHE_SERVER 0x0002
  
  // SSL_SESS_CACHE_BOTH enables session caching for both client and server.
  #define SSL_SESS_CACHE_BOTH (SSL_SESS_CACHE_CLIENT | SSL_SESS_CACHE_SERVER)
  
  // SSL_SESS_CACHE_NO_AUTO_CLEAR disables automatically calling
  // |SSL_CTX_flush_sessions| every 255 connections.
  #define SSL_SESS_CACHE_NO_AUTO_CLEAR 0x0080
  
  // SSL_SESS_CACHE_NO_INTERNAL_LOOKUP, on a server, disables looking up a session
  // from the internal session cache.
  #define SSL_SESS_CACHE_NO_INTERNAL_LOOKUP 0x0100
  
  // SSL_SESS_CACHE_NO_INTERNAL_STORE, on a server, disables storing sessions in
  // the internal session cache.
  #define SSL_SESS_CACHE_NO_INTERNAL_STORE 0x0200
  
  // SSL_SESS_CACHE_NO_INTERNAL, on a server, disables the internal session
  // cache.
  #define SSL_SESS_CACHE_NO_INTERNAL \
      (SSL_SESS_CACHE_NO_INTERNAL_LOOKUP | SSL_SESS_CACHE_NO_INTERNAL_STORE)
  
  // SSL_CTX_set_session_cache_mode sets the session cache mode bits for |ctx| to
  // |mode|. It returns the previous value.
  OPENSSL_EXPORT int SSL_CTX_set_session_cache_mode(SSL_CTX *ctx, int mode);
  
  // SSL_CTX_get_session_cache_mode returns the session cache mode bits for
  // |ctx|
  OPENSSL_EXPORT int SSL_CTX_get_session_cache_mode(const SSL_CTX *ctx);
  
  // SSL_set_session, for a client, configures |ssl| to offer to resume |session|
  // in the initial handshake and returns one. The caller retains ownership of
  // |session|.
  //
  // It is an error to call this function after the handshake has begun.
  OPENSSL_EXPORT int SSL_set_session(SSL *ssl, SSL_SESSION *session);
  
  // SSL_DEFAULT_SESSION_TIMEOUT is the default lifetime, in seconds, of a
  // session in TLS 1.2 or earlier. This is how long we are willing to use the
  // secret to encrypt traffic without fresh key material.
  #define SSL_DEFAULT_SESSION_TIMEOUT (2 * 60 * 60)
  
  // SSL_DEFAULT_SESSION_PSK_DHE_TIMEOUT is the default lifetime, in seconds, of a
  // session for TLS 1.3 psk_dhe_ke. This is how long we are willing to use the
  // secret as an authenticator.
  #define SSL_DEFAULT_SESSION_PSK_DHE_TIMEOUT (2 * 24 * 60 * 60)
  
  // SSL_DEFAULT_SESSION_AUTH_TIMEOUT is the default non-renewable lifetime, in
  // seconds, of a TLS 1.3 session. This is how long we are willing to trust the
  // signature in the initial handshake.
  #define SSL_DEFAULT_SESSION_AUTH_TIMEOUT (7 * 24 * 60 * 60)
  
  // SSL_CTX_set_timeout sets the lifetime, in seconds, of TLS 1.2 (or earlier)
  // sessions created in |ctx| to |timeout|.
  OPENSSL_EXPORT uint32_t SSL_CTX_set_timeout(SSL_CTX *ctx, uint32_t timeout);
  
  // SSL_CTX_set_session_psk_dhe_timeout sets the lifetime, in seconds, of TLS 1.3
  // sessions created in |ctx| to |timeout|.
  OPENSSL_EXPORT void SSL_CTX_set_session_psk_dhe_timeout(SSL_CTX *ctx,
                                                          uint32_t timeout);
  
  // SSL_CTX_get_timeout returns the lifetime, in seconds, of TLS 1.2 (or earlier)
  // sessions created in |ctx|.
  OPENSSL_EXPORT uint32_t SSL_CTX_get_timeout(const SSL_CTX *ctx);
  
  // SSL_CTX_set_session_id_context sets |ctx|'s session ID context to |sid_ctx|.
  // It returns one on success and zero on error. The session ID context is an
  // application-defined opaque byte string. A session will not be used in a
  // connection without a matching session ID context.
  //
  // For a server, if |SSL_VERIFY_PEER| is enabled, it is an error to not set a
  // session ID context.
  OPENSSL_EXPORT int SSL_CTX_set_session_id_context(SSL_CTX *ctx,
                                                    const uint8_t *sid_ctx,
                                                    size_t sid_ctx_len);
  
  // SSL_set_session_id_context sets |ssl|'s session ID context to |sid_ctx|. It
  // returns one on success and zero on error. See also
  // |SSL_CTX_set_session_id_context|.
  OPENSSL_EXPORT int SSL_set_session_id_context(SSL *ssl, const uint8_t *sid_ctx,
                                                size_t sid_ctx_len);
  
  // SSL_get0_session_id_context returns a pointer to |ssl|'s session ID context
  // and sets |*out_len| to its length.
  OPENSSL_EXPORT const uint8_t *SSL_get0_session_id_context(const SSL *ssl,
                                                            size_t *out_len);
  
  // SSL_SESSION_CACHE_MAX_SIZE_DEFAULT is the default maximum size of a session
  // cache.
  #define SSL_SESSION_CACHE_MAX_SIZE_DEFAULT (1024 * 20)
  
  // SSL_CTX_sess_set_cache_size sets the maximum size of |ctx|'s internal session
  // cache to |size|. It returns the previous value.
  OPENSSL_EXPORT unsigned long SSL_CTX_sess_set_cache_size(SSL_CTX *ctx,
                                                           unsigned long size);
  
  // SSL_CTX_sess_get_cache_size returns the maximum size of |ctx|'s internal
  // session cache.
  OPENSSL_EXPORT unsigned long SSL_CTX_sess_get_cache_size(const SSL_CTX *ctx);
  
  // SSL_CTX_sess_number returns the number of sessions in |ctx|'s internal
  // session cache.
  OPENSSL_EXPORT size_t SSL_CTX_sess_number(const SSL_CTX *ctx);
  
  // SSL_CTX_add_session inserts |session| into |ctx|'s internal session cache. It
  // returns one on success and zero on error or if |session| is already in the
  // cache. The caller retains its reference to |session|.
  OPENSSL_EXPORT int SSL_CTX_add_session(SSL_CTX *ctx, SSL_SESSION *session);
  
  // SSL_CTX_remove_session removes |session| from |ctx|'s internal session cache.
  // It returns one on success and zero if |session| was not in the cache.
  OPENSSL_EXPORT int SSL_CTX_remove_session(SSL_CTX *ctx, SSL_SESSION *session);
  
  // SSL_CTX_flush_sessions removes all sessions from |ctx| which have expired as
  // of time |time|. If |time| is zero, all sessions are removed.
  OPENSSL_EXPORT void SSL_CTX_flush_sessions(SSL_CTX *ctx, uint64_t time);
  
  // SSL_CTX_sess_set_new_cb sets the callback to be called when a new session is
  // established and ready to be cached. If the session cache is disabled (the
  // appropriate one of |SSL_SESS_CACHE_CLIENT| or |SSL_SESS_CACHE_SERVER| is
  // unset), the callback is not called.
  //
  // The callback is passed a reference to |session|. It returns one if it takes
  // ownership (and then calls |SSL_SESSION_free| when done) and zero otherwise. A
  // consumer which places |session| into an in-memory cache will likely return
  // one, with the cache calling |SSL_SESSION_free|. A consumer which serializes
  // |session| with |SSL_SESSION_to_bytes| may not need to retain |session| and
  // will likely return zero. Returning one is equivalent to calling
  // |SSL_SESSION_up_ref| and then returning zero.
  //
  // Note: For a client, the callback may be called on abbreviated handshakes if a
  // ticket is renewed. Further, it may not be called until some time after
  // |SSL_do_handshake| or |SSL_connect| completes if False Start is enabled. Thus
  // it's recommended to use this callback over calling |SSL_get_session| on
  // handshake completion.
  OPENSSL_EXPORT void SSL_CTX_sess_set_new_cb(
      SSL_CTX *ctx, int (*new_session_cb)(SSL *ssl, SSL_SESSION *session));
  
  // SSL_CTX_sess_get_new_cb returns the callback set by
  // |SSL_CTX_sess_set_new_cb|.
  OPENSSL_EXPORT int (*SSL_CTX_sess_get_new_cb(SSL_CTX *ctx))(
      SSL *ssl, SSL_SESSION *session);
  
  // SSL_CTX_sess_set_remove_cb sets a callback which is called when a session is
  // removed from the internal session cache.
  //
  // TODO(davidben): What is the point of this callback? It seems useless since it
  // only fires on sessions in the internal cache.
  OPENSSL_EXPORT void SSL_CTX_sess_set_remove_cb(
      SSL_CTX *ctx,
      void (*remove_session_cb)(SSL_CTX *ctx, SSL_SESSION *session));
  
  // SSL_CTX_sess_get_remove_cb returns the callback set by
  // |SSL_CTX_sess_set_remove_cb|.
  OPENSSL_EXPORT void (*SSL_CTX_sess_get_remove_cb(SSL_CTX *ctx))(
      SSL_CTX *ctx, SSL_SESSION *session);
  
  // SSL_CTX_sess_set_get_cb sets a callback to look up a session by ID for a
  // server. The callback is passed the session ID and should return a matching
  // |SSL_SESSION| or NULL if not found. It should set |*out_copy| to zero and
  // return a new reference to the session. This callback is not used for a
  // client.
  //
  // For historical reasons, if |*out_copy| is set to one (default), the SSL
  // library will take a new reference to the returned |SSL_SESSION|, expecting
  // the callback to return a non-owning pointer. This is not recommended. If
  // |ctx| and thus the callback is used on multiple threads, the session may be
  // removed and invalidated before the SSL library calls |SSL_SESSION_up_ref|,
  // whereas the callback may synchronize internally.
  //
  // To look up a session asynchronously, the callback may return
  // |SSL_magic_pending_session_ptr|. See the documentation for that function and
  // |SSL_ERROR_PENDING_SESSION|.
  //
  // If the internal session cache is enabled, the callback is only consulted if
  // the internal cache does not return a match.
  OPENSSL_EXPORT void SSL_CTX_sess_set_get_cb(
      SSL_CTX *ctx, SSL_SESSION *(*get_session_cb)(SSL *ssl, const uint8_t *id,
                                                   int id_len, int *out_copy));
  
  // SSL_CTX_sess_get_get_cb returns the callback set by
  // |SSL_CTX_sess_set_get_cb|.
  OPENSSL_EXPORT SSL_SESSION *(*SSL_CTX_sess_get_get_cb(SSL_CTX *ctx))(
      SSL *ssl, const uint8_t *id, int id_len, int *out_copy);
  
  // SSL_magic_pending_session_ptr returns a magic |SSL_SESSION|* which indicates
  // that the session isn't currently unavailable. |SSL_get_error| will then
  // return |SSL_ERROR_PENDING_SESSION| and the handshake can be retried later
  // when the lookup has completed.
  OPENSSL_EXPORT SSL_SESSION *SSL_magic_pending_session_ptr(void);
  
  
  // Session tickets.
  //
  // Session tickets, from RFC 5077, allow session resumption without server-side
  // state. The server maintains a secret ticket key and sends the client opaque
  // encrypted session parameters, called a ticket. When offering the session, the
  // client sends the ticket which the server decrypts to recover session state.
  // Session tickets are enabled by default but may be disabled with
  // |SSL_OP_NO_TICKET|.
  //
  // On the client, ticket-based sessions use the same APIs as ID-based tickets.
  // Callers do not need to handle them differently.
  //
  // On the server, tickets are encrypted and authenticated with a secret key. By
  // default, an |SSL_CTX| generates a key on creation and uses it for the
  // lifetime of the |SSL_CTX|. Tickets are minted and processed
  // transparently. The following functions may be used to configure a persistent
  // key or implement more custom behavior, including key rotation and sharing
  // keys between multiple servers in a large deployment. There are three levels
  // of customisation possible:
  //
  // 1) One can simply set the keys with |SSL_CTX_set_tlsext_ticket_keys|.
  // 2) One can configure an |EVP_CIPHER_CTX| and |HMAC_CTX| directly for
  //    encryption and authentication.
  // 3) One can configure an |SSL_TICKET_AEAD_METHOD| to have more control
  //    and the option of asynchronous decryption.
  //
  // An attacker that compromises a server's session ticket key can impersonate
  // the server and, prior to TLS 1.3, retroactively decrypt all application
  // traffic from sessions using that ticket key. Thus ticket keys must be
  // regularly rotated for forward secrecy. Note the default key is rotated
  // automatically once every 48 hours but manually configured keys are not.
  
  // SSL_DEFAULT_TICKET_KEY_ROTATION_INTERVAL is the interval with which the
  // default session ticket encryption key is rotated, if in use. If any
  // non-default ticket encryption mechanism is configured, automatic rotation is
  // disabled.
  #define SSL_DEFAULT_TICKET_KEY_ROTATION_INTERVAL (2 * 24 * 60 * 60)
  
  // SSL_CTX_get_tlsext_ticket_keys writes |ctx|'s session ticket key material to
  // |len| bytes of |out|. It returns one on success and zero if |len| is not
  // 48. If |out| is NULL, it returns 48 instead.
  OPENSSL_EXPORT int SSL_CTX_get_tlsext_ticket_keys(SSL_CTX *ctx, void *out,
                                                    size_t len);
  
  // SSL_CTX_set_tlsext_ticket_keys sets |ctx|'s session ticket key material to
  // |len| bytes of |in|. It returns one on success and zero if |len| is not
  // 48. If |in| is NULL, it returns 48 instead.
  OPENSSL_EXPORT int SSL_CTX_set_tlsext_ticket_keys(SSL_CTX *ctx, const void *in,
                                                    size_t len);
  
  // SSL_TICKET_KEY_NAME_LEN is the length of the key name prefix of a session
  // ticket.
  #define SSL_TICKET_KEY_NAME_LEN 16
  
  // SSL_CTX_set_tlsext_ticket_key_cb sets the ticket callback to |callback| and
  // returns one. |callback| will be called when encrypting a new ticket and when
  // decrypting a ticket from the client.
  //
  // In both modes, |ctx| and |hmac_ctx| will already have been initialized with
  // |EVP_CIPHER_CTX_init| and |HMAC_CTX_init|, respectively. |callback|
  // configures |hmac_ctx| with an HMAC digest and key, and configures |ctx|
  // for encryption or decryption, based on the mode.
  //
  // When encrypting a new ticket, |encrypt| will be one. It writes a public
  // 16-byte key name to |key_name| and a fresh IV to |iv|. The output IV length
  // must match |EVP_CIPHER_CTX_iv_length| of the cipher selected. In this mode,
  // |callback| returns 1 on success and -1 on error.
  //
  // When decrypting a ticket, |encrypt| will be zero. |key_name| will point to a
  // 16-byte key name and |iv| points to an IV. The length of the IV consumed must
  // match |EVP_CIPHER_CTX_iv_length| of the cipher selected. In this mode,
  // |callback| returns -1 to abort the handshake, 0 if decrypting the ticket
  // failed, and 1 or 2 on success. If it returns 2, the ticket will be renewed.
  // This may be used to re-key the ticket.
  //
  // WARNING: |callback| wildly breaks the usual return value convention and is
  // called in two different modes.
  OPENSSL_EXPORT int SSL_CTX_set_tlsext_ticket_key_cb(
      SSL_CTX *ctx, int (*callback)(SSL *ssl, uint8_t *key_name, uint8_t *iv,
                                    EVP_CIPHER_CTX *ctx, HMAC_CTX *hmac_ctx,
                                    int encrypt));
  
  // ssl_ticket_aead_result_t enumerates the possible results from decrypting a
  // ticket with an |SSL_TICKET_AEAD_METHOD|.
  enum ssl_ticket_aead_result_t {
    // ssl_ticket_aead_success indicates that the ticket was successfully
    // decrypted.
    ssl_ticket_aead_success,
    // ssl_ticket_aead_retry indicates that the operation could not be
    // immediately completed and must be reattempted, via |open|, at a later
    // point.
    ssl_ticket_aead_retry,
    // ssl_ticket_aead_ignore_ticket indicates that the ticket should be ignored
    // (i.e. is corrupt or otherwise undecryptable).
    ssl_ticket_aead_ignore_ticket,
    // ssl_ticket_aead_error indicates that a fatal error occured and the
    // handshake should be terminated.
    ssl_ticket_aead_error,
  };
  
  // ssl_ticket_aead_method_st (aka |SSL_TICKET_AEAD_METHOD|) contains methods
  // for encrypting and decrypting session tickets.
  struct ssl_ticket_aead_method_st {
    // max_overhead returns the maximum number of bytes of overhead that |seal|
    // may add.
    size_t (*max_overhead)(SSL *ssl);
  
    // seal encrypts and authenticates |in_len| bytes from |in|, writes, at most,
    // |max_out_len| bytes to |out|, and puts the number of bytes written in
    // |*out_len|. The |in| and |out| buffers may be equal but will not otherwise
    // alias. It returns one on success or zero on error.
    int (*seal)(SSL *ssl, uint8_t *out, size_t *out_len, size_t max_out_len,
                const uint8_t *in, size_t in_len);
  
    // open authenticates and decrypts |in_len| bytes from |in|, writes, at most,
    // |max_out_len| bytes of plaintext to |out|, and puts the number of bytes
    // written in |*out_len|. The |in| and |out| buffers may be equal but will
    // not otherwise alias. See |ssl_ticket_aead_result_t| for details of the
    // return values. In the case that a retry is indicated, the caller should
    // arrange for the high-level operation on |ssl| to be retried when the
    // operation is completed, which will result in another call to |open|.
    enum ssl_ticket_aead_result_t (*open)(SSL *ssl, uint8_t *out, size_t *out_len,
                                          size_t max_out_len, const uint8_t *in,
                                          size_t in_len);
  };
  
  // SSL_CTX_set_ticket_aead_method configures a custom ticket AEAD method table
  // on |ctx|. |aead_method| must remain valid for the lifetime of |ctx|.
  OPENSSL_EXPORT void SSL_CTX_set_ticket_aead_method(
      SSL_CTX *ctx, const SSL_TICKET_AEAD_METHOD *aead_method);
  
  
  // Elliptic curve Diffie-Hellman.
  //
  // Cipher suites using an ECDHE key exchange perform Diffie-Hellman over an
  // elliptic curve negotiated by both endpoints. See RFC 4492. Only named curves
  // are supported. ECDHE is always enabled, but the curve preferences may be
  // configured with these functions.
  //
  // Note that TLS 1.3 renames these from curves to groups. For consistency, we
  // currently use the TLS 1.2 name in the API.
  
  // SSL_CTX_set1_curves sets the preferred curves for |ctx| to be |curves|. Each
  // element of |curves| should be a curve nid. It returns one on success and
  // zero on failure.
  //
  // Note that this API uses nid values from nid.h and not the |SSL_CURVE_*|
  // values defined below.
  OPENSSL_EXPORT int SSL_CTX_set1_curves(SSL_CTX *ctx, const int *curves,
                                         size_t curves_len);
  
  // SSL_set1_curves sets the preferred curves for |ssl| to be |curves|. Each
  // element of |curves| should be a curve nid. It returns one on success and
  // zero on failure.
  //
  // Note that this API uses nid values from nid.h and not the |SSL_CURVE_*|
  // values defined below.
  OPENSSL_EXPORT int SSL_set1_curves(SSL *ssl, const int *curves,
                                     size_t curves_len);
  
  // SSL_CTX_set1_curves_list sets the preferred curves for |ctx| to be the
  // colon-separated list |curves|. Each element of |curves| should be a curve
  // name (e.g. P-256, X25519, ...). It returns one on success and zero on
  // failure.
  OPENSSL_EXPORT int SSL_CTX_set1_curves_list(SSL_CTX *ctx, const char *curves);
  
  // SSL_set1_curves_list sets the preferred curves for |ssl| to be the
  // colon-separated list |curves|. Each element of |curves| should be a curve
  // name (e.g. P-256, X25519, ...). It returns one on success and zero on
  // failure.
  OPENSSL_EXPORT int SSL_set1_curves_list(SSL *ssl, const char *curves);
  
  // SSL_CURVE_* define TLS curve IDs.
  #define SSL_CURVE_SECP224R1 21
  #define SSL_CURVE_SECP256R1 23
  #define SSL_CURVE_SECP384R1 24
  #define SSL_CURVE_SECP521R1 25
  #define SSL_CURVE_X25519 29
  
  // SSL_get_curve_id returns the ID of the curve used by |ssl|'s most recently
  // completed handshake or 0 if not applicable.
  //
  // TODO(davidben): This API currently does not work correctly if there is a
  // renegotiation in progress. Fix this.
  OPENSSL_EXPORT uint16_t SSL_get_curve_id(const SSL *ssl);
  
  // SSL_get_curve_name returns a human-readable name for the curve specified by
  // the given TLS curve id, or NULL if the curve is unknown.
  OPENSSL_EXPORT const char *SSL_get_curve_name(uint16_t curve_id);
  
  
  // Certificate verification.
  //
  // SSL may authenticate either endpoint with an X.509 certificate. Typically
  // this is used to authenticate the server to the client. These functions
  // configure certificate verification.
  //
  // WARNING: By default, certificate verification errors on a client are not
  // fatal. See |SSL_VERIFY_NONE| This may be configured with
  // |SSL_CTX_set_verify|.
  //
  // By default clients are anonymous but a server may request a certificate from
  // the client by setting |SSL_VERIFY_PEER|.
  //
  // Many of these functions use OpenSSL's legacy X.509 stack which is
  // underdocumented and deprecated, but the replacement isn't ready yet. For
  // now, consumers may use the existing stack or bypass it by performing
  // certificate verification externally. This may be done with
  // |SSL_CTX_set_cert_verify_callback| or by extracting the chain with
  // |SSL_get_peer_cert_chain| after the handshake. In the future, functions will
  // be added to use the SSL stack without dependency on any part of the legacy
  // X.509 and ASN.1 stack.
  //
  // To augment certificate verification, a client may also enable OCSP stapling
  // (RFC 6066) and Certificate Transparency (RFC 6962) extensions.
  
  // SSL_VERIFY_NONE, on a client, verifies the server certificate but does not
  // make errors fatal. The result may be checked with |SSL_get_verify_result|. On
  // a server it does not request a client certificate. This is the default.
  #define SSL_VERIFY_NONE 0x00
  
  // SSL_VERIFY_PEER, on a client, makes server certificate errors fatal. On a
  // server it requests a client certificate and makes errors fatal. However,
  // anonymous clients are still allowed. See
  // |SSL_VERIFY_FAIL_IF_NO_PEER_CERT|.
  #define SSL_VERIFY_PEER 0x01
  
  // SSL_VERIFY_FAIL_IF_NO_PEER_CERT configures a server to reject connections if
  // the client declines to send a certificate. This flag must be used together
  // with |SSL_VERIFY_PEER|, otherwise it won't work.
  #define SSL_VERIFY_FAIL_IF_NO_PEER_CERT 0x02
  
  // SSL_VERIFY_PEER_IF_NO_OBC configures a server to request a client certificate
  // if and only if Channel ID is not negotiated.
  #define SSL_VERIFY_PEER_IF_NO_OBC 0x04
  
  // SSL_CTX_set_verify configures certificate verification behavior. |mode| is
  // one of the |SSL_VERIFY_*| values defined above. |callback|, if not NULL, is
  // used to customize certificate verification. See the behavior of
  // |X509_STORE_CTX_set_verify_cb|.
  //
  // The callback may use |SSL_get_ex_data_X509_STORE_CTX_idx| with
  // |X509_STORE_CTX_get_ex_data| to look up the |SSL| from |store_ctx|.
  OPENSSL_EXPORT void SSL_CTX_set_verify(
      SSL_CTX *ctx, int mode, int (*callback)(int ok, X509_STORE_CTX *store_ctx));
  
  // SSL_set_verify configures certificate verification behavior. |mode| is one of
  // the |SSL_VERIFY_*| values defined above. |callback|, if not NULL, is used to
  // customize certificate verification. See the behavior of
  // |X509_STORE_CTX_set_verify_cb|.
  //
  // The callback may use |SSL_get_ex_data_X509_STORE_CTX_idx| with
  // |X509_STORE_CTX_get_ex_data| to look up the |SSL| from |store_ctx|.
  OPENSSL_EXPORT void SSL_set_verify(SSL *ssl, int mode,
                                     int (*callback)(int ok,
                                                     X509_STORE_CTX *store_ctx));
  
  enum ssl_verify_result_t {
    ssl_verify_ok,
    ssl_verify_invalid,
    ssl_verify_retry,
  };
  
  // SSL_CTX_set_custom_verify configures certificate verification. |mode| is one
  // of the |SSL_VERIFY_*| values defined above. |callback| performs the
  // certificate verification.
  //
  // The callback may call |SSL_get0_peer_certificates| for the certificate chain
  // to validate. The callback should return |ssl_verify_ok| if the certificate is
  // valid. If the certificate is invalid, the callback should return
  // |ssl_verify_invalid| and optionally set |*out_alert| to an alert to send to
  // the peer. Some useful alerts include |SSL_AD_CERTIFICATE_EXPIRED|,
  // |SSL_AD_CERTIFICATE_REVOKED|, |SSL_AD_UNKNOWN_CA|, |SSL_AD_BAD_CERTIFICATE|,
  // |SSL_AD_CERTIFICATE_UNKNOWN|, and |SSL_AD_INTERNAL_ERROR|. See RFC 5246
  // section 7.2.2 for their precise meanings. If unspecified,
  // |SSL_AD_CERTIFICATE_UNKNOWN| will be sent by default.
  //
  // To verify a certificate asynchronously, the callback may return
  // |ssl_verify_retry|. The handshake will then pause with |SSL_get_error|
  // returning |SSL_ERROR_WANT_CERTIFICATE_VERIFY|.
  OPENSSL_EXPORT void SSL_CTX_set_custom_verify(
      SSL_CTX *ctx, int mode,
      enum ssl_verify_result_t (*callback)(SSL *ssl, uint8_t *out_alert));
  
  // SSL_set_custom_verify behaves like |SSL_CTX_set_custom_verify| but configures
  // an individual |SSL|.
  OPENSSL_EXPORT void SSL_set_custom_verify(
      SSL *ssl, int mode,
      enum ssl_verify_result_t (*callback)(SSL *ssl, uint8_t *out_alert));
  
  // SSL_CTX_get_verify_mode returns |ctx|'s verify mode, set by
  // |SSL_CTX_set_verify|.
  OPENSSL_EXPORT int SSL_CTX_get_verify_mode(const SSL_CTX *ctx);
  
  // SSL_get_verify_mode returns |ssl|'s verify mode, set by |SSL_CTX_set_verify|
  // or |SSL_set_verify|.
  OPENSSL_EXPORT int SSL_get_verify_mode(const SSL *ssl);
  
  // SSL_CTX_get_verify_callback returns the callback set by
  // |SSL_CTX_set_verify|.
  OPENSSL_EXPORT int (*SSL_CTX_get_verify_callback(const SSL_CTX *ctx))(
      int ok, X509_STORE_CTX *store_ctx);
  
  // SSL_get_verify_callback returns the callback set by |SSL_CTX_set_verify| or
  // |SSL_set_verify|.
  OPENSSL_EXPORT int (*SSL_get_verify_callback(const SSL *ssl))(
      int ok, X509_STORE_CTX *store_ctx);
  
  // SSL_CTX_set_verify_depth sets the maximum depth of a certificate chain
  // accepted in verification. This number does not include the leaf, so a depth
  // of 1 allows the leaf and one CA certificate.
  OPENSSL_EXPORT void SSL_CTX_set_verify_depth(SSL_CTX *ctx, int depth);
  
  // SSL_set_verify_depth sets the maximum depth of a certificate chain accepted
  // in verification. This number does not include the leaf, so a depth of 1
  // allows the leaf and one CA certificate.
  OPENSSL_EXPORT void SSL_set_verify_depth(SSL *ssl, int depth);
  
  // SSL_CTX_get_verify_depth returns the maximum depth of a certificate accepted
  // in verification.
  OPENSSL_EXPORT int SSL_CTX_get_verify_depth(const SSL_CTX *ctx);
  
  // SSL_get_verify_depth returns the maximum depth of a certificate accepted in
  // verification.
  OPENSSL_EXPORT int SSL_get_verify_depth(const SSL *ssl);
  
  // SSL_CTX_set1_param sets verification parameters from |param|. It returns one
  // on success and zero on failure. The caller retains ownership of |param|.
  OPENSSL_EXPORT int SSL_CTX_set1_param(SSL_CTX *ctx,
                                        const X509_VERIFY_PARAM *param);
  
  // SSL_set1_param sets verification parameters from |param|. It returns one on
  // success and zero on failure. The caller retains ownership of |param|.
  OPENSSL_EXPORT int SSL_set1_param(SSL *ssl,
                                    const X509_VERIFY_PARAM *param);
  
  // SSL_CTX_get0_param returns |ctx|'s |X509_VERIFY_PARAM| for certificate
  // verification. The caller must not release the returned pointer but may call
  // functions on it to configure it.
  OPENSSL_EXPORT X509_VERIFY_PARAM *SSL_CTX_get0_param(SSL_CTX *ctx);
  
  // SSL_get0_param returns |ssl|'s |X509_VERIFY_PARAM| for certificate
  // verification. The caller must not release the returned pointer but may call
  // functions on it to configure it.
  OPENSSL_EXPORT X509_VERIFY_PARAM *SSL_get0_param(SSL *ssl);
  
  // SSL_CTX_set_purpose sets |ctx|'s |X509_VERIFY_PARAM|'s 'purpose' parameter to
  // |purpose|. It returns one on success and zero on error.
  OPENSSL_EXPORT int SSL_CTX_set_purpose(SSL_CTX *ctx, int purpose);
  
  // SSL_set_purpose sets |ssl|'s |X509_VERIFY_PARAM|'s 'purpose' parameter to
  // |purpose|. It returns one on success and zero on error.
  OPENSSL_EXPORT int SSL_set_purpose(SSL *ssl, int purpose);
  
  // SSL_CTX_set_trust sets |ctx|'s |X509_VERIFY_PARAM|'s 'trust' parameter to
  // |trust|. It returns one on success and zero on error.
  OPENSSL_EXPORT int SSL_CTX_set_trust(SSL_CTX *ctx, int trust);
  
  // SSL_set_trust sets |ssl|'s |X509_VERIFY_PARAM|'s 'trust' parameter to
  // |trust|. It returns one on success and zero on error.
  OPENSSL_EXPORT int SSL_set_trust(SSL *ssl, int trust);
  
  // SSL_CTX_set_cert_store sets |ctx|'s certificate store to |store|. It takes
  // ownership of |store|. The store is used for certificate verification.
  //
  // The store is also used for the auto-chaining feature, but this is deprecated.
  // See also |SSL_MODE_NO_AUTO_CHAIN|.
  OPENSSL_EXPORT void SSL_CTX_set_cert_store(SSL_CTX *ctx, X509_STORE *store);
  
  // SSL_CTX_get_cert_store returns |ctx|'s certificate store.
  OPENSSL_EXPORT X509_STORE *SSL_CTX_get_cert_store(const SSL_CTX *ctx);
  
  // SSL_CTX_set_default_verify_paths loads the OpenSSL system-default trust
  // anchors into |ctx|'s store. It returns one on success and zero on failure.
  OPENSSL_EXPORT int SSL_CTX_set_default_verify_paths(SSL_CTX *ctx);
  
  // SSL_CTX_load_verify_locations loads trust anchors into |ctx|'s store from
  // |ca_file| and |ca_dir|, either of which may be NULL. If |ca_file| is passed,
  // it is opened and PEM-encoded CA certificates are read. If |ca_dir| is passed,
  // it is treated as a directory in OpenSSL's hashed directory format. It returns
  // one on success and zero on failure.
  //
  // See
  // https://www.openssl.org/docs/manmaster/ssl/SSL_CTX_load_verify_locations.html
  // for documentation on the directory format.
  OPENSSL_EXPORT int SSL_CTX_load_verify_locations(SSL_CTX *ctx,
                                                   const char *ca_file,
                                                   const char *ca_dir);
  
  // SSL_get_verify_result returns the result of certificate verification. It is
  // either |X509_V_OK| or a |X509_V_ERR_*| value.
  OPENSSL_EXPORT long SSL_get_verify_result(const SSL *ssl);
  
  // SSL_alert_from_verify_result returns the SSL alert code, such as
  // |SSL_AD_CERTIFICATE_EXPIRED|, that corresponds to an |X509_V_ERR_*| value.
  // The return value is always an alert, even when |result| is |X509_V_OK|.
  OPENSSL_EXPORT int SSL_alert_from_verify_result(long result);
  
  // SSL_get_ex_data_X509_STORE_CTX_idx returns the ex_data index used to look up
  // the |SSL| associated with an |X509_STORE_CTX| in the verify callback.
  OPENSSL_EXPORT int SSL_get_ex_data_X509_STORE_CTX_idx(void);
  
  // SSL_CTX_set_cert_verify_callback sets a custom callback to be called on
  // certificate verification rather than |X509_verify_cert|. |store_ctx| contains
  // the verification parameters. The callback should return one on success and
  // zero on fatal error. It may use |X509_STORE_CTX_set_error| to set a
  // verification result.
  //
  // The callback may use |SSL_get_ex_data_X509_STORE_CTX_idx| to recover the
  // |SSL| object from |store_ctx|.
  OPENSSL_EXPORT void SSL_CTX_set_cert_verify_callback(
      SSL_CTX *ctx, int (*callback)(X509_STORE_CTX *store_ctx, void *arg),
      void *arg);
  
  // SSL_enable_signed_cert_timestamps causes |ssl| (which must be the client end
  // of a connection) to request SCTs from the server. See
  // https://tools.ietf.org/html/rfc6962.
  //
  // Call |SSL_get0_signed_cert_timestamp_list| to recover the SCT after the
  // handshake.
  OPENSSL_EXPORT void SSL_enable_signed_cert_timestamps(SSL *ssl);
  
  // SSL_CTX_enable_signed_cert_timestamps enables SCT requests on all client SSL
  // objects created from |ctx|.
  //
  // Call |SSL_get0_signed_cert_timestamp_list| to recover the SCT after the
  // handshake.
  OPENSSL_EXPORT void SSL_CTX_enable_signed_cert_timestamps(SSL_CTX *ctx);
  
  // SSL_enable_ocsp_stapling causes |ssl| (which must be the client end of a
  // connection) to request a stapled OCSP response from the server.
  //
  // Call |SSL_get0_ocsp_response| to recover the OCSP response after the
  // handshake.
  OPENSSL_EXPORT void SSL_enable_ocsp_stapling(SSL *ssl);
  
  // SSL_CTX_enable_ocsp_stapling enables OCSP stapling on all client SSL objects
  // created from |ctx|.
  //
  // Call |SSL_get0_ocsp_response| to recover the OCSP response after the
  // handshake.
  OPENSSL_EXPORT void SSL_CTX_enable_ocsp_stapling(SSL_CTX *ctx);
  
  // SSL_CTX_set0_verify_cert_store sets an |X509_STORE| that will be used
  // exclusively for certificate verification and returns one. Ownership of
  // |store| is transferred to the |SSL_CTX|.
  OPENSSL_EXPORT int SSL_CTX_set0_verify_cert_store(SSL_CTX *ctx,
                                                    X509_STORE *store);
  
  // SSL_CTX_set1_verify_cert_store sets an |X509_STORE| that will be used
  // exclusively for certificate verification and returns one. An additional
  // reference to |store| will be taken.
  OPENSSL_EXPORT int SSL_CTX_set1_verify_cert_store(SSL_CTX *ctx,
                                                    X509_STORE *store);
  
  // SSL_set0_verify_cert_store sets an |X509_STORE| that will be used
  // exclusively for certificate verification and returns one. Ownership of
  // |store| is transferred to the |SSL|.
  OPENSSL_EXPORT int SSL_set0_verify_cert_store(SSL *ssl, X509_STORE *store);
  
  // SSL_set1_verify_cert_store sets an |X509_STORE| that will be used
  // exclusively for certificate verification and returns one. An additional
  // reference to |store| will be taken.
  OPENSSL_EXPORT int SSL_set1_verify_cert_store(SSL *ssl, X509_STORE *store);
  
  // SSL_CTX_set_ed25519_enabled configures whether |ctx| advertises support for
  // the Ed25519 signature algorithm when using the default preference list.
  OPENSSL_EXPORT void SSL_CTX_set_ed25519_enabled(SSL_CTX *ctx, int enabled);
  
  // SSL_CTX_set_verify_algorithm_prefs confingures |ctx| to use |prefs| as the
  // preference list when verifying signature's from the peer's long-term key. It
  // returns one on zero on error. |prefs| should not include the internal-only
  // value |SSL_SIGN_RSA_PKCS1_MD5_SHA1|.
  OPENSSL_EXPORT int SSL_CTX_set_verify_algorithm_prefs(SSL_CTX *ctx,
                                                        const uint16_t *prefs,
                                                        size_t num_prefs);
  
  
  // Client certificate CA list.
  //
  // When requesting a client certificate, a server may advertise a list of
  // certificate authorities which are accepted. These functions may be used to
  // configure this list.
  
  // SSL_set_client_CA_list sets |ssl|'s client certificate CA list to
  // |name_list|. It takes ownership of |name_list|.
  OPENSSL_EXPORT void SSL_set_client_CA_list(SSL *ssl,
                                             STACK_OF(X509_NAME) *name_list);
  
  // SSL_CTX_set_client_CA_list sets |ctx|'s client certificate CA list to
  // |name_list|. It takes ownership of |name_list|.
  OPENSSL_EXPORT void SSL_CTX_set_client_CA_list(SSL_CTX *ctx,
                                                 STACK_OF(X509_NAME) *name_list);
  
  // SSL_set0_client_CAs sets |ssl|'s client certificate CA list to |name_list|,
  // which should contain DER-encoded distinguished names (RFC 5280). It takes
  // ownership of |name_list|.
  OPENSSL_EXPORT void SSL_set0_client_CAs(SSL *ssl,
                                          STACK_OF(CRYPTO_BUFFER) *name_list);
  
  // SSL_CTX_set0_client_CAs sets |ctx|'s client certificate CA list to
  // |name_list|, which should contain DER-encoded distinguished names (RFC 5280).
  // It takes ownership of |name_list|.
  OPENSSL_EXPORT void SSL_CTX_set0_client_CAs(SSL_CTX *ctx,
                                              STACK_OF(CRYPTO_BUFFER) *name_list);
  
  // SSL_get_client_CA_list returns |ssl|'s client certificate CA list. If |ssl|
  // has not been configured as a client, this is the list configured by
  // |SSL_CTX_set_client_CA_list|.
  //
  // If configured as a client, it returns the client certificate CA list sent by
  // the server. In this mode, the behavior is undefined except during the
  // callbacks set by |SSL_CTX_set_cert_cb| and |SSL_CTX_set_client_cert_cb| or
  // when the handshake is paused because of them.
  OPENSSL_EXPORT STACK_OF(X509_NAME) *SSL_get_client_CA_list(const SSL *ssl);
  
  // SSL_get0_server_requested_CAs returns the CAs sent by a server to guide a
  // client in certificate selection. They are a series of DER-encoded X.509
  // names. This function may only be called during a callback set by
  // |SSL_CTX_set_cert_cb| or when the handshake is paused because of it.
  //
  // The returned stack is owned by |ssl|, as are its contents. It should not be
  // used past the point where the handshake is restarted after the callback.
  OPENSSL_EXPORT STACK_OF(CRYPTO_BUFFER) *SSL_get0_server_requested_CAs(
      const SSL *ssl);
  
  // SSL_CTX_get_client_CA_list returns |ctx|'s client certificate CA list.
  OPENSSL_EXPORT STACK_OF(X509_NAME) *
      SSL_CTX_get_client_CA_list(const SSL_CTX *ctx);
  
  // SSL_add_client_CA appends |x509|'s subject to the client certificate CA list.
  // It returns one on success or zero on error. The caller retains ownership of
  // |x509|.
  OPENSSL_EXPORT int SSL_add_client_CA(SSL *ssl, X509 *x509);
  
  // SSL_CTX_add_client_CA appends |x509|'s subject to the client certificate CA
  // list. It returns one on success or zero on error. The caller retains
  // ownership of |x509|.
  OPENSSL_EXPORT int SSL_CTX_add_client_CA(SSL_CTX *ctx, X509 *x509);
  
  // SSL_load_client_CA_file opens |file| and reads PEM-encoded certificates from
  // it. It returns a newly-allocated stack of the certificate subjects or NULL
  // on error.
  OPENSSL_EXPORT STACK_OF(X509_NAME) *SSL_load_client_CA_file(const char *file);
  
  // SSL_dup_CA_list makes a deep copy of |list|. It returns the new list on
  // success or NULL on allocation error.
  OPENSSL_EXPORT STACK_OF(X509_NAME) *SSL_dup_CA_list(STACK_OF(X509_NAME) *list);
  
  // SSL_add_file_cert_subjects_to_stack behaves like |SSL_load_client_CA_file|
  // but appends the result to |out|. It returns one on success or zero on
  // error.
  OPENSSL_EXPORT int SSL_add_file_cert_subjects_to_stack(STACK_OF(X509_NAME) *out,
                                                         const char *file);
  
  
  // Server name indication.
  //
  // The server_name extension (RFC 3546) allows the client to advertise the name
  // of the server it is connecting to. This is used in virtual hosting
  // deployments to select one of a several certificates on a single IP. Only the
  // host_name name type is supported.
  
  #define TLSEXT_NAMETYPE_host_name 0
  
  // SSL_set_tlsext_host_name, for a client, configures |ssl| to advertise |name|
  // in the server_name extension. It returns one on success and zero on error.
  OPENSSL_EXPORT int SSL_set_tlsext_host_name(SSL *ssl, const char *name);
  
  // SSL_get_servername, for a server, returns the hostname supplied by the
  // client or NULL if there was none. The |type| argument must be
  // |TLSEXT_NAMETYPE_host_name|.
  OPENSSL_EXPORT const char *SSL_get_servername(const SSL *ssl, const int type);
  
  // SSL_get_servername_type, for a server, returns |TLSEXT_NAMETYPE_host_name|
  // if the client sent a hostname and -1 otherwise.
  OPENSSL_EXPORT int SSL_get_servername_type(const SSL *ssl);
  
  // SSL_CTX_set_tlsext_servername_callback configures |callback| to be called on
  // the server after ClientHello extensions have been parsed and returns one.
  // The callback may use |SSL_get_servername| to examine the server_name
  // extension and returns a |SSL_TLSEXT_ERR_*| value. The value of |arg| may be
  // set by calling |SSL_CTX_set_tlsext_servername_arg|.
  //
  // If the callback returns |SSL_TLSEXT_ERR_NOACK|, the server_name extension is
  // not acknowledged in the ServerHello. If the return value is
  // |SSL_TLSEXT_ERR_ALERT_FATAL|, then |*out_alert| is the alert to send,
  // defaulting to |SSL_AD_UNRECOGNIZED_NAME|. |SSL_TLSEXT_ERR_ALERT_WARNING| is
  // ignored and treated as |SSL_TLSEXT_ERR_OK|.
  OPENSSL_EXPORT int SSL_CTX_set_tlsext_servername_callback(
      SSL_CTX *ctx, int (*callback)(SSL *ssl, int *out_alert, void *arg));
  
  // SSL_CTX_set_tlsext_servername_arg sets the argument to the servername
  // callback and returns one. See |SSL_CTX_set_tlsext_servername_callback|.
  OPENSSL_EXPORT int SSL_CTX_set_tlsext_servername_arg(SSL_CTX *ctx, void *arg);
  
  // SSL_TLSEXT_ERR_* are values returned by some extension-related callbacks.
  #define SSL_TLSEXT_ERR_OK 0
  #define SSL_TLSEXT_ERR_ALERT_WARNING 1
  #define SSL_TLSEXT_ERR_ALERT_FATAL 2
  #define SSL_TLSEXT_ERR_NOACK 3
  
  // SSL_set_SSL_CTX changes |ssl|'s |SSL_CTX|. |ssl| will use the
  // certificate-related settings from |ctx|, and |SSL_get_SSL_CTX| will report
  // |ctx|. This function may be used during the callbacks registered by
  // |SSL_CTX_set_select_certificate_cb|,
  // |SSL_CTX_set_tlsext_servername_callback|, and |SSL_CTX_set_cert_cb| or when
  // the handshake is paused from them. It is typically used to switch
  // certificates based on SNI.
  //
  // Note the session cache and related settings will continue to use the initial
  // |SSL_CTX|. Callers should use |SSL_CTX_set_session_id_context| to partition
  // the session cache between different domains.
  //
  // TODO(davidben): Should other settings change after this call?
  OPENSSL_EXPORT SSL_CTX *SSL_set_SSL_CTX(SSL *ssl, SSL_CTX *ctx);
  
  
  // Application-layer protocol negotiation.
  //
  // The ALPN extension (RFC 7301) allows negotiating different application-layer
  // protocols over a single port. This is used, for example, to negotiate
  // HTTP/2.
  
  // SSL_CTX_set_alpn_protos sets the client ALPN protocol list on |ctx| to
  // |protos|. |protos| must be in wire-format (i.e. a series of non-empty, 8-bit
  // length-prefixed strings). It returns zero on success and one on failure.
  // Configuring this list enables ALPN on a client.
  //
  // WARNING: this function is dangerous because it breaks the usual return value
  // convention.
  OPENSSL_EXPORT int SSL_CTX_set_alpn_protos(SSL_CTX *ctx, const uint8_t *protos,
                                             unsigned protos_len);
  
  // SSL_set_alpn_protos sets the client ALPN protocol list on |ssl| to |protos|.
  // |protos| must be in wire-format (i.e. a series of non-empty, 8-bit
  // length-prefixed strings). It returns zero on success and one on failure.
  // Configuring this list enables ALPN on a client.
  //
  // WARNING: this function is dangerous because it breaks the usual return value
  // convention.
  OPENSSL_EXPORT int SSL_set_alpn_protos(SSL *ssl, const uint8_t *protos,
                                         unsigned protos_len);
  
  // SSL_CTX_set_alpn_select_cb sets a callback function on |ctx| that is called
  // during ClientHello processing in order to select an ALPN protocol from the
  // client's list of offered protocols. Configuring this callback enables ALPN on
  // a server.
  //
  // The callback is passed a wire-format (i.e. a series of non-empty, 8-bit
  // length-prefixed strings) ALPN protocol list in |in|. It should set |*out| and
  // |*out_len| to the selected protocol and return |SSL_TLSEXT_ERR_OK| on
  // success. It does not pass ownership of the buffer. Otherwise, it should
  // return |SSL_TLSEXT_ERR_NOACK|. Other |SSL_TLSEXT_ERR_*| values are
  // unimplemented and will be treated as |SSL_TLSEXT_ERR_NOACK|.
  //
  // The cipher suite is selected before negotiating ALPN. The callback may use
  // |SSL_get_pending_cipher| to query the cipher suite.
  OPENSSL_EXPORT void SSL_CTX_set_alpn_select_cb(
      SSL_CTX *ctx, int (*cb)(SSL *ssl, const uint8_t **out, uint8_t *out_len,
                              const uint8_t *in, unsigned in_len, void *arg),
      void *arg);
  
  // SSL_get0_alpn_selected gets the selected ALPN protocol (if any) from |ssl|.
  // On return it sets |*out_data| to point to |*out_len| bytes of protocol name
  // (not including the leading length-prefix byte). If the server didn't respond
  // with a negotiated protocol then |*out_len| will be zero.
  OPENSSL_EXPORT void SSL_get0_alpn_selected(const SSL *ssl,
                                             const uint8_t **out_data,
                                             unsigned *out_len);
  
  // SSL_CTX_set_allow_unknown_alpn_protos configures client connections on |ctx|
  // to allow unknown ALPN protocols from the server. Otherwise, by default, the
  // client will require that the protocol be advertised in
  // |SSL_CTX_set_alpn_protos|.
  OPENSSL_EXPORT void SSL_CTX_set_allow_unknown_alpn_protos(SSL_CTX *ctx,
                                                            int enabled);
  
  
  // Next protocol negotiation.
  //
  // The NPN extension (draft-agl-tls-nextprotoneg-03) is the predecessor to ALPN
  // and deprecated in favor of it.
  
  // SSL_CTX_set_next_protos_advertised_cb sets a callback that is called when a
  // TLS server needs a list of supported protocols for Next Protocol
  // Negotiation. The returned list must be in wire format. The list is returned
  // by setting |*out| to point to it and |*out_len| to its length. This memory
  // will not be modified, but one should assume that |ssl| keeps a reference to
  // it.
  //
  // The callback should return |SSL_TLSEXT_ERR_OK| if it wishes to advertise.
  // Otherwise, no such extension will be included in the ServerHello.
  OPENSSL_EXPORT void SSL_CTX_set_next_protos_advertised_cb(
      SSL_CTX *ctx,
      int (*cb)(SSL *ssl, const uint8_t **out, unsigned *out_len, void *arg),
      void *arg);
  
  // SSL_CTX_set_next_proto_select_cb sets a callback that is called when a client
  // needs to select a protocol from the server's provided list. |*out| must be
  // set to point to the selected protocol (which may be within |in|). The length
  // of the protocol name must be written into |*out_len|. The server's advertised
  // protocols are provided in |in| and |in_len|. The callback can assume that
  // |in| is syntactically valid.
  //
  // The client must select a protocol. It is fatal to the connection if this
  // callback returns a value other than |SSL_TLSEXT_ERR_OK|.
  //
  // Configuring this callback enables NPN on a client.
  OPENSSL_EXPORT void SSL_CTX_set_next_proto_select_cb(
      SSL_CTX *ctx, int (*cb)(SSL *ssl, uint8_t **out, uint8_t *out_len,
                              const uint8_t *in, unsigned in_len, void *arg),
      void *arg);
  
  // SSL_get0_next_proto_negotiated sets |*out_data| and |*out_len| to point to
  // the client's requested protocol for this connection. If the client didn't
  // request any protocol, then |*out_data| is set to NULL.
  //
  // Note that the client can request any protocol it chooses. The value returned
  // from this function need not be a member of the list of supported protocols
  // provided by the server.
  OPENSSL_EXPORT void SSL_get0_next_proto_negotiated(const SSL *ssl,
                                                     const uint8_t **out_data,
                                                     unsigned *out_len);
  
  // SSL_select_next_proto implements the standard protocol selection. It is
  // expected that this function is called from the callback set by
  // |SSL_CTX_set_next_proto_select_cb|.
  //
  // |peer| and |supported| must be vectors of 8-bit, length-prefixed byte strings
  // containing the peer and locally-configured protocols, respectively. The
  // length byte itself is not included in the length. A byte string of length 0
  // is invalid. No byte string may be truncated. |supported| is assumed to be
  // non-empty.
  //
  // This function finds the first protocol in |peer| which is also in
  // |supported|. If one was found, it sets |*out| and |*out_len| to point to it
  // and returns |OPENSSL_NPN_NEGOTIATED|. Otherwise, it returns
  // |OPENSSL_NPN_NO_OVERLAP| and sets |*out| and |*out_len| to the first
  // supported protocol.
  OPENSSL_EXPORT int SSL_select_next_proto(uint8_t **out, uint8_t *out_len,
                                           const uint8_t *peer, unsigned peer_len,
                                           const uint8_t *supported,
                                           unsigned supported_len);
  
  #define OPENSSL_NPN_UNSUPPORTED 0
  #define OPENSSL_NPN_NEGOTIATED 1
  #define OPENSSL_NPN_NO_OVERLAP 2
  
  
  // Channel ID.
  //
  // See draft-balfanz-tls-channelid-01.
  
  // SSL_CTX_set_tls_channel_id_enabled configures whether connections associated
  // with |ctx| should enable Channel ID.
  OPENSSL_EXPORT void SSL_CTX_set_tls_channel_id_enabled(SSL_CTX *ctx,
                                                         int enabled);
  
  // SSL_set_tls_channel_id_enabled configures whether |ssl| should enable Channel
  // ID.
  OPENSSL_EXPORT void SSL_set_tls_channel_id_enabled(SSL *ssl, int enabled);
  
  // SSL_CTX_set1_tls_channel_id configures a TLS client to send a TLS Channel ID
  // to compatible servers. |private_key| must be a P-256 EC key. It returns one
  // on success and zero on error.
  OPENSSL_EXPORT int SSL_CTX_set1_tls_channel_id(SSL_CTX *ctx,
                                                 EVP_PKEY *private_key);
  
  // SSL_set1_tls_channel_id configures a TLS client to send a TLS Channel ID to
  // compatible servers. |private_key| must be a P-256 EC key. It returns one on
  // success and zero on error.
  OPENSSL_EXPORT int SSL_set1_tls_channel_id(SSL *ssl, EVP_PKEY *private_key);
  
  // SSL_get_tls_channel_id gets the client's TLS Channel ID from a server |SSL*|
  // and copies up to the first |max_out| bytes into |out|. The Channel ID
  // consists of the client's P-256 public key as an (x,y) pair where each is a
  // 32-byte, big-endian field element. It returns 0 if the client didn't offer a
  // Channel ID and the length of the complete Channel ID otherwise.
  OPENSSL_EXPORT size_t SSL_get_tls_channel_id(SSL *ssl, uint8_t *out,
                                               size_t max_out);
  
  // SSL_CTX_set_channel_id_cb sets a callback to be called when a TLS Channel ID
  // is requested. The callback may set |*out_pkey| to a key, passing a reference
  // to the caller. If none is returned, the handshake will pause and
  // |SSL_get_error| will return |SSL_ERROR_WANT_CHANNEL_ID_LOOKUP|.
  //
  // See also |SSL_ERROR_WANT_CHANNEL_ID_LOOKUP|.
  OPENSSL_EXPORT void SSL_CTX_set_channel_id_cb(
      SSL_CTX *ctx, void (*channel_id_cb)(SSL *ssl, EVP_PKEY **out_pkey));
  
  // SSL_CTX_get_channel_id_cb returns the callback set by
  // |SSL_CTX_set_channel_id_cb|.
  OPENSSL_EXPORT void (*SSL_CTX_get_channel_id_cb(SSL_CTX *ctx))(
      SSL *ssl, EVP_PKEY **out_pkey);
  
  
  // Token Binding.
  //
  // See draft-ietf-tokbind-protocol-16.
  
  // SSL_set_token_binding_params sets |params| as the Token Binding Key
  // parameters (section 3 of draft-ietf-tokbind-protocol-16) to negotiate on the
  // connection. If this function is not called, or if |len| is 0, then this
  // endpoint will not attempt to negotiate Token Binding. |params| are provided
  // in preference order, with the more preferred parameters at the beginning of
  // the list. This function returns 1 on success and 0 on failure.
  OPENSSL_EXPORT int SSL_set_token_binding_params(SSL *ssl, const uint8_t *params,
                                                  size_t len);
  
  // SSL_is_token_binding_negotiated returns 1 if Token Binding was negotiated
  // on this connection and 0 otherwise. On a server, it is possible for this
  // function to return 1 when the client's view of the connection is that Token
  // Binding was not negotiated. This occurs when the server indicates a version
  // of Token Binding less than the client's minimum version.
  OPENSSL_EXPORT int SSL_is_token_binding_negotiated(const SSL *ssl);
  
  // SSL_get_negotiated_token_binding_param returns the TokenBindingKeyParameters
  // enum value that was negotiated. It is only valid to call this function if
  // SSL_is_token_binding_negotiated returned 1, otherwise this function returns
  // an undefined value.
  OPENSSL_EXPORT uint8_t SSL_get_negotiated_token_binding_param(const SSL *ssl);
  
  
  // DTLS-SRTP.
  //
  // See RFC 5764.
  
  // srtp_protection_profile_st (aka |SRTP_PROTECTION_PROFILE|) is an SRTP
  // profile for use with the use_srtp extension.
  struct srtp_protection_profile_st {
    const char *name;
    unsigned long id;
  } /* SRTP_PROTECTION_PROFILE */;
  
  DEFINE_CONST_STACK_OF(SRTP_PROTECTION_PROFILE)
  
  // SRTP_* define constants for SRTP profiles.
  #define SRTP_AES128_CM_SHA1_80 0x0001
  #define SRTP_AES128_CM_SHA1_32 0x0002
  #define SRTP_AES128_F8_SHA1_80 0x0003
  #define SRTP_AES128_F8_SHA1_32 0x0004
  #define SRTP_NULL_SHA1_80      0x0005
  #define SRTP_NULL_SHA1_32      0x0006
  #define SRTP_AEAD_AES_128_GCM  0x0007
  #define SRTP_AEAD_AES_256_GCM  0x0008
  
  // SSL_CTX_set_srtp_profiles enables SRTP for all SSL objects created from
  // |ctx|. |profile| contains a colon-separated list of profile names. It returns
  // one on success and zero on failure.
  OPENSSL_EXPORT int SSL_CTX_set_srtp_profiles(SSL_CTX *ctx,
                                               const char *profiles);
  
  // SSL_set_srtp_profiles enables SRTP for |ssl|.  |profile| contains a
  // colon-separated list of profile names. It returns one on success and zero on
  // failure.
  OPENSSL_EXPORT int SSL_set_srtp_profiles(SSL *ssl, const char *profiles);
  
  // SSL_get_srtp_profiles returns the SRTP profiles supported by |ssl|.
  OPENSSL_EXPORT STACK_OF(SRTP_PROTECTION_PROFILE) *SSL_get_srtp_profiles(
      SSL *ssl);
  
  // SSL_get_selected_srtp_profile returns the selected SRTP profile, or NULL if
  // SRTP was not negotiated.
  OPENSSL_EXPORT const SRTP_PROTECTION_PROFILE *SSL_get_selected_srtp_profile(
      SSL *ssl);
  
  
  // Pre-shared keys.
  //
  // Connections may be configured with PSK (Pre-Shared Key) cipher suites. These
  // authenticate using out-of-band pre-shared keys rather than certificates. See
  // RFC 4279.
  //
  // This implementation uses NUL-terminated C strings for identities and identity
  // hints, so values with a NUL character are not supported. (RFC 4279 does not
  // specify the format of an identity.)
  
  // PSK_MAX_IDENTITY_LEN is the maximum supported length of a PSK identity,
  // excluding the NUL terminator.
  #define PSK_MAX_IDENTITY_LEN 128
  
  // PSK_MAX_PSK_LEN is the maximum supported length of a pre-shared key.
  #define PSK_MAX_PSK_LEN 256
  
  // SSL_CTX_set_psk_client_callback sets the callback to be called when PSK is
  // negotiated on the client. This callback must be set to enable PSK cipher
  // suites on the client.
  //
  // The callback is passed the identity hint in |hint| or NULL if none was
  // provided. It should select a PSK identity and write the identity and the
  // corresponding PSK to |identity| and |psk|, respectively. The identity is
  // written as a NUL-terminated C string of length (excluding the NUL terminator)
  // at most |max_identity_len|. The PSK's length must be at most |max_psk_len|.
  // The callback returns the length of the PSK or 0 if no suitable identity was
  // found.
  OPENSSL_EXPORT void SSL_CTX_set_psk_client_callback(
      SSL_CTX *ctx, unsigned (*cb)(SSL *ssl, const char *hint, char *identity,
                                   unsigned max_identity_len, uint8_t *psk,
                                   unsigned max_psk_len));
  
  // SSL_set_psk_client_callback sets the callback to be called when PSK is
  // negotiated on the client. This callback must be set to enable PSK cipher
  // suites on the client. See also |SSL_CTX_set_psk_client_callback|.
  OPENSSL_EXPORT void SSL_set_psk_client_callback(
      SSL *ssl, unsigned (*cb)(SSL *ssl, const char *hint, char *identity,
                               unsigned max_identity_len, uint8_t *psk,
                               unsigned max_psk_len));
  
  // SSL_CTX_set_psk_server_callback sets the callback to be called when PSK is
  // negotiated on the server. This callback must be set to enable PSK cipher
  // suites on the server.
  //
  // The callback is passed the identity in |identity|. It should write a PSK of
  // length at most |max_psk_len| to |psk| and return the number of bytes written
  // or zero if the PSK identity is unknown.
  OPENSSL_EXPORT void SSL_CTX_set_psk_server_callback(
      SSL_CTX *ctx, unsigned (*cb)(SSL *ssl, const char *identity, uint8_t *psk,
                                   unsigned max_psk_len));
  
  // SSL_set_psk_server_callback sets the callback to be called when PSK is
  // negotiated on the server. This callback must be set to enable PSK cipher
  // suites on the server. See also |SSL_CTX_set_psk_server_callback|.
  OPENSSL_EXPORT void SSL_set_psk_server_callback(
      SSL *ssl, unsigned (*cb)(SSL *ssl, const char *identity, uint8_t *psk,
                               unsigned max_psk_len));
  
  // SSL_CTX_use_psk_identity_hint configures server connections to advertise an
  // identity hint of |identity_hint|. It returns one on success and zero on
  // error.
  OPENSSL_EXPORT int SSL_CTX_use_psk_identity_hint(SSL_CTX *ctx,
                                                   const char *identity_hint);
  
  // SSL_use_psk_identity_hint configures server connections to advertise an
  // identity hint of |identity_hint|. It returns one on success and zero on
  // error.
  OPENSSL_EXPORT int SSL_use_psk_identity_hint(SSL *ssl,
                                               const char *identity_hint);
  
  // SSL_get_psk_identity_hint returns the PSK identity hint advertised for |ssl|
  // or NULL if there is none.
  OPENSSL_EXPORT const char *SSL_get_psk_identity_hint(const SSL *ssl);
  
  // SSL_get_psk_identity, after the handshake completes, returns the PSK identity
  // that was negotiated by |ssl| or NULL if PSK was not used.
  OPENSSL_EXPORT const char *SSL_get_psk_identity(const SSL *ssl);
  
  
  // Dummy post-quantum padding.
  //
  // Dummy post-quantum padding invovles the client (and later server) sending
  // useless, random-looking bytes in an extension in their ClientHello or
  // ServerHello. These extensions are sized to simulate a post-quantum
  // key-exchange and so enable measurement of the latency impact of the
  // additional bandwidth.
  
  // SSL_set_dummy_pq_padding_size enables the sending of a dummy PQ padding
  // extension and configures its size. This is only effective for a client: a
  // server will echo an extension with one of equal length when we get to that
  // phase of the experiment. It returns one for success and zero otherwise.
  OPENSSL_EXPORT int SSL_set_dummy_pq_padding_size(SSL *ssl, size_t num_bytes);
  
  // SSL_dummy_pq_padding_used returns one if the server echoed a dummy PQ padding
  // extension and zero otherwise. It may only be called on a client connection
  // once the handshake has completed, otherwise it'll return zero.
  OPENSSL_EXPORT int SSL_dummy_pq_padding_used(SSL *ssl);
  
  
  // QUIC Transport Parameters.
  //
  // draft-ietf-quic-tls defines a new TLS extension quic_transport_parameters
  // used by QUIC for each endpoint to unilaterally declare its supported
  // transport parameters. draft-ietf-quic-transport (section 7.4) defines the
  // contents of that extension (a TransportParameters struct) and describes how
  // to handle it and its semantic meaning.
  //
  // BoringSSL handles this extension as an opaque byte string. The caller is
  // responsible for serializing and parsing it.
  
  // SSL_set_quic_transport_params configures |ssl| to send |params| (of length
  // |params_len|) in the quic_transport_parameters extension in either the
  // ClientHello or EncryptedExtensions handshake message. This extension will
  // only be sent if the TLS version is at least 1.3, and for a server, only if
  // the client sent the extension. The buffer pointed to by |params| only need be
  // valid for the duration of the call to this function. This function returns 1
  // on success and 0 on failure.
  OPENSSL_EXPORT int SSL_set_quic_transport_params(SSL *ssl,
                                                   const uint8_t *params,
                                                   size_t params_len);
  
  // SSL_get_peer_quic_transport_params provides the caller with the value of the
  // quic_transport_parameters extension sent by the peer. A pointer to the buffer
  // containing the TransportParameters will be put in |*out_params|, and its
  // length in |*params_len|. This buffer will be valid for the lifetime of the
  // |SSL|. If no params were received from the peer, |*out_params_len| will be 0.
  OPENSSL_EXPORT void SSL_get_peer_quic_transport_params(const SSL *ssl,
                                                         const uint8_t **out_params,
                                                         size_t *out_params_len);
  
  
  // Early data.
  //
  // WARNING: 0-RTT support in BoringSSL is currently experimental and not fully
  // implemented. It may cause interoperability or security failures when used.
  //
  // Early data, or 0-RTT, is a feature in TLS 1.3 which allows clients to send
  // data on the first flight during a resumption handshake. This can save a
  // round-trip in some application protocols.
  //
  // WARNING: A 0-RTT handshake has different security properties from normal
  // handshake, so it is off by default unless opted in. In particular, early data
  // is replayable by a network attacker. Callers must account for this when
  // sending or processing data before the handshake is confirmed. See
  // draft-ietf-tls-tls13-18 for more information.
  //
  // As a server, if early data is accepted, |SSL_do_handshake| will complete as
  // soon as the ClientHello is processed and server flight sent. |SSL_write| may
  // be used to send half-RTT data. |SSL_read| will consume early data and
  // transition to 1-RTT data as appropriate. Prior to the transition,
  // |SSL_in_init| will report the handshake is still in progress. Callers may use
  // it or |SSL_in_early_data| to defer or reject requests as needed.
  //
  // Early data as a client is more complex. If the offered session (see
  // |SSL_set_session|) is 0-RTT-capable, the handshake will return after sending
  // the ClientHello. The predicted peer certificates and ALPN protocol will be
  // available via the usual APIs. |SSL_write| will write early data, up to the
  // session's limit. Writes past this limit and |SSL_read| will complete the
  // handshake before continuing. Callers may also call |SSL_do_handshake| again
  // to complete the handshake sooner.
  //
  // If the server accepts early data, the handshake will succeed. |SSL_read| and
  // |SSL_write| will then act as in a 1-RTT handshake. The peer certificates and
  // ALPN protocol will be as predicted and need not be re-queried.
  //
  // If the server rejects early data, |SSL_do_handshake| (and thus |SSL_read| and
  // |SSL_write|) will then fail with |SSL_get_error| returning
  // |SSL_ERROR_EARLY_DATA_REJECTED|. The caller should treat this as a connection
  // error and most likely perform a high-level retry. Note the server may still
  // have processed the early data due to attacker replays.
  //
  // To then continue the handshake on the original connection, use
  // |SSL_reset_early_data_reject|. The connection will then behave as one which
  // had not yet completed the handshake. This allows a faster retry than making a
  // fresh connection. |SSL_do_handshake| will complete the full handshake,
  // possibly resulting in different peer certificates, ALPN protocol, and other
  // properties. The caller must disregard any values from before the reset and
  // query again.
  //
  // Finally, to implement the fallback described in draft-ietf-tls-tls13-18
  // appendix C.3, retry on a fresh connection without 0-RTT if the handshake
  // fails with |SSL_R_WRONG_VERSION_ON_EARLY_DATA|.
  
  // SSL_CTX_set_early_data_enabled sets whether early data is allowed to be used
  // with resumptions using |ctx|.
  OPENSSL_EXPORT void SSL_CTX_set_early_data_enabled(SSL_CTX *ctx, int enabled);
  
  // SSL_set_early_data_enabled sets whether early data is allowed to be used
  // with resumptions using |ssl|. See |SSL_CTX_set_early_data_enabled| for more
  // information.
  OPENSSL_EXPORT void SSL_set_early_data_enabled(SSL *ssl, int enabled);
  
  // SSL_in_early_data returns one if |ssl| has a pending handshake that has
  // progressed enough to send or receive early data. Clients may call |SSL_write|
  // to send early data, but |SSL_read| will complete the handshake before
  // accepting application data. Servers may call |SSL_read| to read early data
  // and |SSL_write| to send half-RTT data.
  OPENSSL_EXPORT int SSL_in_early_data(const SSL *ssl);
  
  // SSL_early_data_accepted returns whether early data was accepted on the
  // handshake performed by |ssl|.
  OPENSSL_EXPORT int SSL_early_data_accepted(const SSL *ssl);
  
  // SSL_reset_early_data_reject resets |ssl| after an early data reject. All
  // 0-RTT state is discarded, including any pending |SSL_write| calls. The caller
  // should treat |ssl| as a logically fresh connection, usually by driving the
  // handshake to completion using |SSL_do_handshake|.
  //
  // It is an error to call this function on an |SSL| object that is not signaling
  // |SSL_ERROR_EARLY_DATA_REJECTED|.
  OPENSSL_EXPORT void SSL_reset_early_data_reject(SSL *ssl);
  
  // SSL_export_early_keying_material behaves like |SSL_export_keying_material|,
  // but it uses the early exporter. The operation will fail if |ssl| did not
  // negotiate TLS 1.3 or 0-RTT.
  OPENSSL_EXPORT int SSL_export_early_keying_material(
      SSL *ssl, uint8_t *out, size_t out_len, const char *label, size_t label_len,
      const uint8_t *context, size_t context_len);
  
  
  // Alerts.
  //
  // TLS and SSL 3.0 use alerts to signal error conditions. Alerts have a type
  // (warning or fatal) and description. OpenSSL internally handles fatal alerts
  // with dedicated error codes (see |SSL_AD_REASON_OFFSET|). Except for
  // close_notify, warning alerts are silently ignored and may only be surfaced
  // with |SSL_CTX_set_info_callback|.
  
  // SSL_AD_REASON_OFFSET is the offset between error reasons and |SSL_AD_*|
  // values. Any error code under |ERR_LIB_SSL| with an error reason above this
  // value corresponds to an alert description. Consumers may add or subtract
  // |SSL_AD_REASON_OFFSET| to convert between them.
  //
  // make_errors.go reserves error codes above 1000 for manually-assigned errors.
  // This value must be kept in sync with reservedReasonCode in make_errors.h
  #define SSL_AD_REASON_OFFSET 1000
  
  // SSL_AD_* are alert descriptions for SSL 3.0 and TLS.
  #define SSL_AD_CLOSE_NOTIFY SSL3_AD_CLOSE_NOTIFY
  #define SSL_AD_UNEXPECTED_MESSAGE SSL3_AD_UNEXPECTED_MESSAGE
  #define SSL_AD_BAD_RECORD_MAC SSL3_AD_BAD_RECORD_MAC
  #define SSL_AD_DECRYPTION_FAILED TLS1_AD_DECRYPTION_FAILED
  #define SSL_AD_RECORD_OVERFLOW TLS1_AD_RECORD_OVERFLOW
  #define SSL_AD_DECOMPRESSION_FAILURE SSL3_AD_DECOMPRESSION_FAILURE
  #define SSL_AD_HANDSHAKE_FAILURE SSL3_AD_HANDSHAKE_FAILURE
  #define SSL_AD_NO_CERTIFICATE SSL3_AD_NO_CERTIFICATE  // Not used in TLS
  #define SSL_AD_BAD_CERTIFICATE SSL3_AD_BAD_CERTIFICATE
  #define SSL_AD_UNSUPPORTED_CERTIFICATE SSL3_AD_UNSUPPORTED_CERTIFICATE
  #define SSL_AD_CERTIFICATE_REVOKED SSL3_AD_CERTIFICATE_REVOKED
  #define SSL_AD_CERTIFICATE_EXPIRED SSL3_AD_CERTIFICATE_EXPIRED
  #define SSL_AD_CERTIFICATE_UNKNOWN SSL3_AD_CERTIFICATE_UNKNOWN
  #define SSL_AD_ILLEGAL_PARAMETER SSL3_AD_ILLEGAL_PARAMETER
  #define SSL_AD_UNKNOWN_CA TLS1_AD_UNKNOWN_CA
  #define SSL_AD_ACCESS_DENIED TLS1_AD_ACCESS_DENIED
  #define SSL_AD_DECODE_ERROR TLS1_AD_DECODE_ERROR
  #define SSL_AD_DECRYPT_ERROR TLS1_AD_DECRYPT_ERROR
  #define SSL_AD_EXPORT_RESTRICTION TLS1_AD_EXPORT_RESTRICTION
  #define SSL_AD_PROTOCOL_VERSION TLS1_AD_PROTOCOL_VERSION
  #define SSL_AD_INSUFFICIENT_SECURITY TLS1_AD_INSUFFICIENT_SECURITY
  #define SSL_AD_INTERNAL_ERROR TLS1_AD_INTERNAL_ERROR
  #define SSL_AD_INAPPROPRIATE_FALLBACK SSL3_AD_INAPPROPRIATE_FALLBACK
  #define SSL_AD_USER_CANCELLED TLS1_AD_USER_CANCELLED
  #define SSL_AD_NO_RENEGOTIATION TLS1_AD_NO_RENEGOTIATION
  #define SSL_AD_MISSING_EXTENSION TLS1_AD_MISSING_EXTENSION
  #define SSL_AD_UNSUPPORTED_EXTENSION TLS1_AD_UNSUPPORTED_EXTENSION
  #define SSL_AD_CERTIFICATE_UNOBTAINABLE TLS1_AD_CERTIFICATE_UNOBTAINABLE
  #define SSL_AD_UNRECOGNIZED_NAME TLS1_AD_UNRECOGNIZED_NAME
  #define SSL_AD_BAD_CERTIFICATE_STATUS_RESPONSE \
    TLS1_AD_BAD_CERTIFICATE_STATUS_RESPONSE
  #define SSL_AD_BAD_CERTIFICATE_HASH_VALUE TLS1_AD_BAD_CERTIFICATE_HASH_VALUE
  #define SSL_AD_UNKNOWN_PSK_IDENTITY TLS1_AD_UNKNOWN_PSK_IDENTITY
  #define SSL_AD_CERTIFICATE_REQUIRED TLS1_AD_CERTIFICATE_REQUIRED
  
  // SSL_alert_type_string_long returns a string description of |value| as an
  // alert type (warning or fatal).
  OPENSSL_EXPORT const char *SSL_alert_type_string_long(int value);
  
  // SSL_alert_desc_string_long returns a string description of |value| as an
  // alert description or "unknown" if unknown.
  OPENSSL_EXPORT const char *SSL_alert_desc_string_long(int value);
  
  // SSL_send_fatal_alert sends a fatal alert over |ssl| of the specified type,
  // which should be one of the |SSL_AD_*| constants. It returns one on success
  // and <= 0 on error. The caller should pass the return value into
  // |SSL_get_error| to determine how to proceed. Once this function has been
  // called, future calls to |SSL_write| will fail.
  //
  // If retrying a failed operation due to |SSL_ERROR_WANT_WRITE|, subsequent
  // calls must use the same |alert| parameter.
  OPENSSL_EXPORT int SSL_send_fatal_alert(SSL *ssl, uint8_t alert);
  
  
  // ex_data functions.
  //
  // See |ex_data.h| for details.
  
  OPENSSL_EXPORT int SSL_set_ex_data(SSL *ssl, int idx, void *data);
  OPENSSL_EXPORT void *SSL_get_ex_data(const SSL *ssl, int idx);
  OPENSSL_EXPORT int SSL_get_ex_new_index(long argl, void *argp,
                                          CRYPTO_EX_unused *unused,
                                          CRYPTO_EX_dup *dup_unused,
                                          CRYPTO_EX_free *free_func);
  
  OPENSSL_EXPORT int SSL_SESSION_set_ex_data(SSL_SESSION *session, int idx,
                                             void *data);
  OPENSSL_EXPORT void *SSL_SESSION_get_ex_data(const SSL_SESSION *session,
                                               int idx);
  OPENSSL_EXPORT int SSL_SESSION_get_ex_new_index(long argl, void *argp,
                                                  CRYPTO_EX_unused *unused,
                                                  CRYPTO_EX_dup *dup_unused,
                                                  CRYPTO_EX_free *free_func);
  
  OPENSSL_EXPORT int SSL_CTX_set_ex_data(SSL_CTX *ctx, int idx, void *data);
  OPENSSL_EXPORT void *SSL_CTX_get_ex_data(const SSL_CTX *ctx, int idx);
  OPENSSL_EXPORT int SSL_CTX_get_ex_new_index(long argl, void *argp,
                                              CRYPTO_EX_unused *unused,
                                              CRYPTO_EX_dup *dup_unused,
                                              CRYPTO_EX_free *free_func);
  
  
  // Low-level record-layer state.
  
  // SSL_get_ivs sets |*out_iv_len| to the length of the IVs for the ciphers
  // underlying |ssl| and sets |*out_read_iv| and |*out_write_iv| to point to the
  // current IVs for the read and write directions. This is only meaningful for
  // connections with implicit IVs (i.e. CBC mode with SSLv3 or TLS 1.0).
  //
  // It returns one on success or zero on error.
  OPENSSL_EXPORT int SSL_get_ivs(const SSL *ssl, const uint8_t **out_read_iv,
                                 const uint8_t **out_write_iv,
                                 size_t *out_iv_len);
  
  // SSL_get_key_block_len returns the length of |ssl|'s key block.
  OPENSSL_EXPORT size_t SSL_get_key_block_len(const SSL *ssl);
  
  // SSL_generate_key_block generates |out_len| bytes of key material for |ssl|'s
  // current connection state.
  OPENSSL_EXPORT int SSL_generate_key_block(const SSL *ssl, uint8_t *out,
                                            size_t out_len);
  
  // SSL_get_read_sequence returns, in TLS, the expected sequence number of the
  // next incoming record in the current epoch. In DTLS, it returns the maximum
  // sequence number received in the current epoch and includes the epoch number
  // in the two most significant bytes.
  OPENSSL_EXPORT uint64_t SSL_get_read_sequence(const SSL *ssl);
  
  // SSL_get_write_sequence returns the sequence number of the next outgoing
  // record in the current epoch. In DTLS, it includes the epoch number in the
  // two most significant bytes.
  OPENSSL_EXPORT uint64_t SSL_get_write_sequence(const SSL *ssl);
  
  
  // Obscure functions.
  
  // SSL_get_structure_sizes returns the sizes of the SSL, SSL_CTX and
  // SSL_SESSION structures so that a test can ensure that outside code agrees on
  // these values.
  OPENSSL_EXPORT void SSL_get_structure_sizes(size_t *ssl_size,
                                              size_t *ssl_ctx_size,
                                              size_t *ssl_session_size);
  
  // SSL_CTX_set_msg_callback installs |cb| as the message callback for |ctx|.
  // This callback will be called when sending or receiving low-level record
  // headers, complete handshake messages, ChangeCipherSpec, and alerts.
  // |write_p| is one for outgoing messages and zero for incoming messages.
  //
  // For each record header, |cb| is called with |version| = 0 and |content_type|
  // = |SSL3_RT_HEADER|. The |len| bytes from |buf| contain the header. Note that
  // this does not include the record body. If the record is sealed, the length
  // in the header is the length of the ciphertext.
  //
  // For each handshake message, ChangeCipherSpec, and alert, |version| is the
  // protocol version and |content_type| is the corresponding record type. The
  // |len| bytes from |buf| contain the handshake message, one-byte
  // ChangeCipherSpec body, and two-byte alert, respectively.
  //
  // For a V2ClientHello, |version| is |SSL2_VERSION|, |content_type| is zero, and
  // the |len| bytes from |buf| contain the V2ClientHello structure.
  OPENSSL_EXPORT void SSL_CTX_set_msg_callback(
      SSL_CTX *ctx, void (*cb)(int write_p, int version, int content_type,
                               const void *buf, size_t len, SSL *ssl, void *arg));
  
  // SSL_CTX_set_msg_callback_arg sets the |arg| parameter of the message
  // callback.
  OPENSSL_EXPORT void SSL_CTX_set_msg_callback_arg(SSL_CTX *ctx, void *arg);
  
  // SSL_set_msg_callback installs |cb| as the message callback of |ssl|. See
  // |SSL_CTX_set_msg_callback| for when this callback is called.
  OPENSSL_EXPORT void SSL_set_msg_callback(
      SSL *ssl, void (*cb)(int write_p, int version, int content_type,
                           const void *buf, size_t len, SSL *ssl, void *arg));
  
  // SSL_set_msg_callback_arg sets the |arg| parameter of the message callback.
  OPENSSL_EXPORT void SSL_set_msg_callback_arg(SSL *ssl, void *arg);
  
  // SSL_CTX_set_keylog_callback configures a callback to log key material. This
  // is intended for debugging use with tools like Wireshark. The |cb| function
  // should log |line| followed by a newline, synchronizing with any concurrent
  // access to the log.
  //
  // The format is described in
  // https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/Key_Log_Format.
  OPENSSL_EXPORT void SSL_CTX_set_keylog_callback(
      SSL_CTX *ctx, void (*cb)(const SSL *ssl, const char *line));
  
  // SSL_CTX_get_keylog_callback returns the callback configured by
  // |SSL_CTX_set_keylog_callback|.
  OPENSSL_EXPORT void (*SSL_CTX_get_keylog_callback(const SSL_CTX *ctx))(
      const SSL *ssl, const char *line);
  
  // SSL_CTX_set_current_time_cb configures a callback to retrieve the current
  // time, which should be set in |*out_clock|. This can be used for testing
  // purposes; for example, a callback can be configured that returns a time
  // set explicitly by the test. The |ssl| pointer passed to |cb| is always null.
  OPENSSL_EXPORT void SSL_CTX_set_current_time_cb(
      SSL_CTX *ctx, void (*cb)(const SSL *ssl, struct timeval *out_clock));
  
  enum ssl_renegotiate_mode_t {
    ssl_renegotiate_never = 0,
    ssl_renegotiate_once,
    ssl_renegotiate_freely,
    ssl_renegotiate_ignore,
  };
  
  // SSL_set_renegotiate_mode configures how |ssl|, a client, reacts to
  // renegotiation attempts by a server. If |ssl| is a server, peer-initiated
  // renegotiations are *always* rejected and this function does nothing.
  //
  // The renegotiation mode defaults to |ssl_renegotiate_never|, but may be set
  // at any point in a connection's lifetime. Set it to |ssl_renegotiate_once| to
  // allow one renegotiation, |ssl_renegotiate_freely| to allow all
  // renegotiations or |ssl_renegotiate_ignore| to ignore HelloRequest messages.
  // Note that ignoring HelloRequest messages may cause the connection to stall
  // if the server waits for the renegotiation to complete.
  //
  // There is no support in BoringSSL for initiating renegotiations as a client
  // or server.
  OPENSSL_EXPORT void SSL_set_renegotiate_mode(SSL *ssl,
                                               enum ssl_renegotiate_mode_t mode);
  
  // SSL_renegotiate_pending returns one if |ssl| is in the middle of a
  // renegotiation.
  OPENSSL_EXPORT int SSL_renegotiate_pending(SSL *ssl);
  
  // SSL_total_renegotiations returns the total number of renegotiation handshakes
  // performed by |ssl|. This includes the pending renegotiation, if any.
  OPENSSL_EXPORT int SSL_total_renegotiations(const SSL *ssl);
  
  enum tls13_variant_t {
    tls13_default = 0,
  };
  
  // SSL_CTX_set_tls13_variant sets which variant of TLS 1.3 we negotiate. On the
  // server, if |variant| is not |tls13_default|, all variants are enabled. On the
  // client, only the configured variant is enabled.
  OPENSSL_EXPORT void SSL_CTX_set_tls13_variant(SSL_CTX *ctx,
                                                enum tls13_variant_t variant);
  
  // SSL_set_tls13_variant sets which variant of TLS 1.3 we negotiate. On the
  // server, if |variant| is not |tls13_default|, all variants are enabled. On the
  // client, only the configured variant is enabled.
  OPENSSL_EXPORT void SSL_set_tls13_variant(SSL *ssl,
                                            enum tls13_variant_t variant);
  
  // SSL_MAX_CERT_LIST_DEFAULT is the default maximum length, in bytes, of a peer
  // certificate chain.
  #define SSL_MAX_CERT_LIST_DEFAULT (1024 * 100)
  
  // SSL_CTX_get_max_cert_list returns the maximum length, in bytes, of a peer
  // certificate chain accepted by |ctx|.
  OPENSSL_EXPORT size_t SSL_CTX_get_max_cert_list(const SSL_CTX *ctx);
  
  // SSL_CTX_set_max_cert_list sets the maximum length, in bytes, of a peer
  // certificate chain to |max_cert_list|. This affects how much memory may be
  // consumed during the handshake.
  OPENSSL_EXPORT void SSL_CTX_set_max_cert_list(SSL_CTX *ctx,
                                                size_t max_cert_list);
  
  // SSL_get_max_cert_list returns the maximum length, in bytes, of a peer
  // certificate chain accepted by |ssl|.
  OPENSSL_EXPORT size_t SSL_get_max_cert_list(const SSL *ssl);
  
  // SSL_set_max_cert_list sets the maximum length, in bytes, of a peer
  // certificate chain to |max_cert_list|. This affects how much memory may be
  // consumed during the handshake.
  OPENSSL_EXPORT void SSL_set_max_cert_list(SSL *ssl, size_t max_cert_list);
  
  // SSL_CTX_set_max_send_fragment sets the maximum length, in bytes, of records
  // sent by |ctx|. Beyond this length, handshake messages and application data
  // will be split into multiple records. It returns one on success or zero on
  // error.
  OPENSSL_EXPORT int SSL_CTX_set_max_send_fragment(SSL_CTX *ctx,
                                                   size_t max_send_fragment);
  
  // SSL_set_max_send_fragment sets the maximum length, in bytes, of records sent
  // by |ssl|. Beyond this length, handshake messages and application data will
  // be split into multiple records. It returns one on success or zero on
  // error.
  OPENSSL_EXPORT int SSL_set_max_send_fragment(SSL *ssl,
                                               size_t max_send_fragment);
  
  // ssl_early_callback_ctx (aka |SSL_CLIENT_HELLO|) is passed to certain
  // callbacks that are called very early on during the server handshake. At this
  // point, much of the SSL* hasn't been filled out and only the ClientHello can
  // be depended on.
  typedef struct ssl_early_callback_ctx {
    SSL *ssl;
    const uint8_t *client_hello;
    size_t client_hello_len;
    uint16_t version;
    const uint8_t *random;
    size_t random_len;
    const uint8_t *session_id;
    size_t session_id_len;
    const uint8_t *cipher_suites;
    size_t cipher_suites_len;
    const uint8_t *compression_methods;
    size_t compression_methods_len;
    const uint8_t *extensions;
    size_t extensions_len;
  } SSL_CLIENT_HELLO;
  
  // ssl_select_cert_result_t enumerates the possible results from selecting a
  // certificate with |select_certificate_cb|.
  enum ssl_select_cert_result_t {
    // ssl_select_cert_success indicates that the certificate selection was
    // successful.
    ssl_select_cert_success = 1,
    // ssl_select_cert_retry indicates that the operation could not be
    // immediately completed and must be reattempted at a later point.
    ssl_select_cert_retry = 0,
    // ssl_select_cert_error indicates that a fatal error occured and the
    // handshake should be terminated.
    ssl_select_cert_error = -1,
  };
  
  // SSL_early_callback_ctx_extension_get searches the extensions in
  // |client_hello| for an extension of the given type. If not found, it returns
  // zero. Otherwise it sets |out_data| to point to the extension contents (not
  // including the type and length bytes), sets |out_len| to the length of the
  // extension contents and returns one.
  OPENSSL_EXPORT int SSL_early_callback_ctx_extension_get(
      const SSL_CLIENT_HELLO *client_hello, uint16_t extension_type,
      const uint8_t **out_data, size_t *out_len);
  
  // SSL_CTX_set_select_certificate_cb sets a callback that is called before most
  // ClientHello processing and before the decision whether to resume a session
  // is made. The callback may inspect the ClientHello and configure the
  // connection. See |ssl_select_cert_result_t| for details of the return values.
  //
  // In the case that a retry is indicated, |SSL_get_error| will return
  // |SSL_ERROR_PENDING_CERTIFICATE| and the caller should arrange for the
  // high-level operation on |ssl| to be retried at a later time, which will
  // result in another call to |cb|.
  //
  // Note: The |SSL_CLIENT_HELLO| is only valid for the duration of the callback
  // and is not valid while the handshake is paused.
  OPENSSL_EXPORT void SSL_CTX_set_select_certificate_cb(
      SSL_CTX *ctx,
      enum ssl_select_cert_result_t (*cb)(const SSL_CLIENT_HELLO *));
  
  // SSL_CTX_set_dos_protection_cb sets a callback that is called once the
  // resumption decision for a ClientHello has been made. It can return one to
  // allow the handshake to continue or zero to cause the handshake to abort.
  OPENSSL_EXPORT void SSL_CTX_set_dos_protection_cb(
      SSL_CTX *ctx, int (*cb)(const SSL_CLIENT_HELLO *));
  
  // SSL_ST_* are possible values for |SSL_state| and the bitmasks that make them
  // up.
  #define SSL_ST_CONNECT 0x1000
  #define SSL_ST_ACCEPT 0x2000
  #define SSL_ST_MASK 0x0FFF
  #define SSL_ST_INIT (SSL_ST_CONNECT | SSL_ST_ACCEPT)
  #define SSL_ST_OK 0x03
  #define SSL_ST_RENEGOTIATE (0x04 | SSL_ST_INIT)
  
  // SSL_CB_* are possible values for the |type| parameter in the info
  // callback and the bitmasks that make them up.
  #define SSL_CB_LOOP 0x01
  #define SSL_CB_EXIT 0x02
  #define SSL_CB_READ 0x04
  #define SSL_CB_WRITE 0x08
  #define SSL_CB_ALERT 0x4000
  #define SSL_CB_READ_ALERT (SSL_CB_ALERT | SSL_CB_READ)
  #define SSL_CB_WRITE_ALERT (SSL_CB_ALERT | SSL_CB_WRITE)
  #define SSL_CB_ACCEPT_LOOP (SSL_ST_ACCEPT | SSL_CB_LOOP)
  #define SSL_CB_ACCEPT_EXIT (SSL_ST_ACCEPT | SSL_CB_EXIT)
  #define SSL_CB_CONNECT_LOOP (SSL_ST_CONNECT | SSL_CB_LOOP)
  #define SSL_CB_CONNECT_EXIT (SSL_ST_CONNECT | SSL_CB_EXIT)
  #define SSL_CB_HANDSHAKE_START 0x10
  #define SSL_CB_HANDSHAKE_DONE 0x20
  
  // SSL_CTX_set_info_callback configures a callback to be run when various
  // events occur during a connection's lifetime. The |type| argument determines
  // the type of event and the meaning of the |value| argument. Callbacks must
  // ignore unexpected |type| values.
  //
  // |SSL_CB_READ_ALERT| is signaled for each alert received, warning or fatal.
  // The |value| argument is a 16-bit value where the alert level (either
  // |SSL3_AL_WARNING| or |SSL3_AL_FATAL|) is in the most-significant eight bits
  // and the alert type (one of |SSL_AD_*|) is in the least-significant eight.
  //
  // |SSL_CB_WRITE_ALERT| is signaled for each alert sent. The |value| argument
  // is constructed as with |SSL_CB_READ_ALERT|.
  //
  // |SSL_CB_HANDSHAKE_START| is signaled when a handshake begins. The |value|
  // argument is always one.
  //
  // |SSL_CB_HANDSHAKE_DONE| is signaled when a handshake completes successfully.
  // The |value| argument is always one. If a handshake False Starts, this event
  // may be used to determine when the Finished message is received.
  //
  // The following event types expose implementation details of the handshake
  // state machine. Consuming them is deprecated.
  //
  // |SSL_CB_ACCEPT_LOOP| (respectively, |SSL_CB_CONNECT_LOOP|) is signaled when
  // a server (respectively, client) handshake progresses. The |value| argument
  // is always one.
  //
  // |SSL_CB_ACCEPT_EXIT| (respectively, |SSL_CB_CONNECT_EXIT|) is signaled when
  // a server (respectively, client) handshake completes, fails, or is paused.
  // The |value| argument is one if the handshake succeeded and <= 0
  // otherwise.
  OPENSSL_EXPORT void SSL_CTX_set_info_callback(
      SSL_CTX *ctx, void (*cb)(const SSL *ssl, int type, int value));
  
  // SSL_CTX_get_info_callback returns the callback set by
  // |SSL_CTX_set_info_callback|.
  OPENSSL_EXPORT void (*SSL_CTX_get_info_callback(SSL_CTX *ctx))(const SSL *ssl,
                                                                 int type,
                                                                 int value);
  
  // SSL_set_info_callback configures a callback to be run at various events
  // during a connection's lifetime. See |SSL_CTX_set_info_callback|.
  OPENSSL_EXPORT void SSL_set_info_callback(
      SSL *ssl, void (*cb)(const SSL *ssl, int type, int value));
  
  // SSL_get_info_callback returns the callback set by |SSL_set_info_callback|.
  OPENSSL_EXPORT void (*SSL_get_info_callback(const SSL *ssl))(const SSL *ssl,
                                                               int type,
                                                               int value);
  
  // SSL_state_string_long returns the current state of the handshake state
  // machine as a string. This may be useful for debugging and logging.
  OPENSSL_EXPORT const char *SSL_state_string_long(const SSL *ssl);
  
  #define SSL_SENT_SHUTDOWN 1
  #define SSL_RECEIVED_SHUTDOWN 2
  
  // SSL_get_shutdown returns a bitmask with a subset of |SSL_SENT_SHUTDOWN| and
  // |SSL_RECEIVED_SHUTDOWN| to query whether close_notify was sent or received,
  // respectively.
  OPENSSL_EXPORT int SSL_get_shutdown(const SSL *ssl);
  
  // SSL_get_peer_signature_algorithm returns the signature algorithm used by the
  // peer. If not applicable, it returns zero.
  OPENSSL_EXPORT uint16_t SSL_get_peer_signature_algorithm(const SSL *ssl);
  
  // SSL_get_client_random writes up to |max_out| bytes of the most recent
  // handshake's client_random to |out| and returns the number of bytes written.
  // If |max_out| is zero, it returns the size of the client_random.
  OPENSSL_EXPORT size_t SSL_get_client_random(const SSL *ssl, uint8_t *out,
                                              size_t max_out);
  
  // SSL_get_server_random writes up to |max_out| bytes of the most recent
  // handshake's server_random to |out| and returns the number of bytes written.
  // If |max_out| is zero, it returns the size of the server_random.
  OPENSSL_EXPORT size_t SSL_get_server_random(const SSL *ssl, uint8_t *out,
                                              size_t max_out);
  
  // SSL_get_pending_cipher returns the cipher suite for the current handshake or
  // NULL if one has not been negotiated yet or there is no pending handshake.
  OPENSSL_EXPORT const SSL_CIPHER *SSL_get_pending_cipher(const SSL *ssl);
  
  // SSL_set_retain_only_sha256_of_client_certs, on a server, sets whether only
  // the SHA-256 hash of peer's certificate should be saved in memory and in the
  // session. This can save memory, ticket size and session cache space. If
  // enabled, |SSL_get_peer_certificate| will return NULL after the handshake
  // completes. See the |peer_sha256| field of |SSL_SESSION| for the hash.
  OPENSSL_EXPORT void SSL_set_retain_only_sha256_of_client_certs(SSL *ssl,
                                                                 int enable);
  
  // SSL_CTX_set_retain_only_sha256_of_client_certs, on a server, sets whether
  // only the SHA-256 hash of peer's certificate should be saved in memory and in
  // the session. This can save memory, ticket size and session cache space. If
  // enabled, |SSL_get_peer_certificate| will return NULL after the handshake
  // completes. See the |peer_sha256| field of |SSL_SESSION| for the hash.
  OPENSSL_EXPORT void SSL_CTX_set_retain_only_sha256_of_client_certs(SSL_CTX *ctx,
                                                                     int enable);
  
  // SSL_CTX_set_grease_enabled configures whether sockets on |ctx| should enable
  // GREASE. See draft-davidben-tls-grease-01.
  OPENSSL_EXPORT void SSL_CTX_set_grease_enabled(SSL_CTX *ctx, int enabled);
  
  // SSL_max_seal_overhead returns the maximum overhead, in bytes, of sealing a
  // record with |ssl|.
  OPENSSL_EXPORT size_t SSL_max_seal_overhead(const SSL *ssl);
  
  // SSL_get_ticket_age_skew returns the difference, in seconds, between the
  // client-sent ticket age and the server-computed value in TLS 1.3 server
  // connections which resumed a session.
  OPENSSL_EXPORT int32_t SSL_get_ticket_age_skew(const SSL *ssl);
  
  // SSL_CTX_set_false_start_allowed_without_alpn configures whether connections
  // on |ctx| may use False Start (if |SSL_MODE_ENABLE_FALSE_START| is enabled)
  // without negotiating ALPN.
  OPENSSL_EXPORT void SSL_CTX_set_false_start_allowed_without_alpn(SSL_CTX *ctx,
                                                                   int allowed);
  
  // SSL_is_draft_downgrade returns one if the TLS 1.3 anti-downgrade mechanism
  // would have aborted |ssl|'s handshake and zero otherwise.
  OPENSSL_EXPORT int SSL_is_draft_downgrade(const SSL *ssl);
  
  
  // Deprecated functions.
  
  // SSL_library_init calls |CRYPTO_library_init| and returns one.
  OPENSSL_EXPORT int SSL_library_init(void);
  
  // SSL_CIPHER_description writes a description of |cipher| into |buf| and
  // returns |buf|. If |buf| is NULL, it returns a newly allocated string, to be
  // freed with |OPENSSL_free|, or NULL on error.
  //
  // The description includes a trailing newline and has the form:
  // AES128-SHA              Kx=RSA      Au=RSA  Enc=AES(128)  Mac=SHA1
  //
  // Consider |SSL_CIPHER_standard_name| or |SSL_CIPHER_get_name| instead.
  OPENSSL_EXPORT const char *SSL_CIPHER_description(const SSL_CIPHER *cipher,
                                                    char *buf, int len);
  
  // SSL_CIPHER_get_version returns the string "TLSv1/SSLv3".
  OPENSSL_EXPORT const char *SSL_CIPHER_get_version(const SSL_CIPHER *cipher);
  
  // SSL_CIPHER_get_rfc_name returns a newly-allocated string containing the
  // result of |SSL_CIPHER_standard_name| or NULL on error. The caller is
  // responsible for calling |OPENSSL_free| on the result.
  //
  // Use |SSL_CIPHER_standard_name| instead.
  OPENSSL_EXPORT char *SSL_CIPHER_get_rfc_name(const SSL_CIPHER *cipher);
  
  typedef void COMP_METHOD;
  
  // SSL_COMP_get_compression_methods returns NULL.
  OPENSSL_EXPORT STACK_OF(SSL_COMP) *SSL_COMP_get_compression_methods(void);
  
  // SSL_COMP_add_compression_method returns one.
  OPENSSL_EXPORT int SSL_COMP_add_compression_method(int id, COMP_METHOD *cm);
  
  // SSL_COMP_get_name returns NULL.
  OPENSSL_EXPORT const char *SSL_COMP_get_name(const COMP_METHOD *comp);
  
  // SSL_COMP_free_compression_methods does nothing.
  OPENSSL_EXPORT void SSL_COMP_free_compression_methods(void);
  
  // SSLv23_method calls |TLS_method|.
  OPENSSL_EXPORT const SSL_METHOD *SSLv23_method(void);
  
  // These version-specific methods behave exactly like |TLS_method| and
  // |DTLS_method| except they also call |SSL_CTX_set_min_proto_version| and
  // |SSL_CTX_set_max_proto_version| to lock connections to that protocol
  // version.
  OPENSSL_EXPORT const SSL_METHOD *TLSv1_method(void);
  OPENSSL_EXPORT const SSL_METHOD *TLSv1_1_method(void);
  OPENSSL_EXPORT const SSL_METHOD *TLSv1_2_method(void);
  OPENSSL_EXPORT const SSL_METHOD *DTLSv1_method(void);
  OPENSSL_EXPORT const SSL_METHOD *DTLSv1_2_method(void);
  
  // These client- and server-specific methods call their corresponding generic
  // methods.
  OPENSSL_EXPORT const SSL_METHOD *TLS_server_method(void);
  OPENSSL_EXPORT const SSL_METHOD *TLS_client_method(void);
  OPENSSL_EXPORT const SSL_METHOD *SSLv23_server_method(void);
  OPENSSL_EXPORT const SSL_METHOD *SSLv23_client_method(void);
  OPENSSL_EXPORT const SSL_METHOD *TLSv1_server_method(void);
  OPENSSL_EXPORT const SSL_METHOD *TLSv1_client_method(void);
  OPENSSL_EXPORT const SSL_METHOD *TLSv1_1_server_method(void);
  OPENSSL_EXPORT const SSL_METHOD *TLSv1_1_client_method(void);
  OPENSSL_EXPORT const SSL_METHOD *TLSv1_2_server_method(void);
  OPENSSL_EXPORT const SSL_METHOD *TLSv1_2_client_method(void);
  OPENSSL_EXPORT const SSL_METHOD *DTLS_server_method(void);
  OPENSSL_EXPORT const SSL_METHOD *DTLS_client_method(void);
  OPENSSL_EXPORT const SSL_METHOD *DTLSv1_server_method(void);
  OPENSSL_EXPORT const SSL_METHOD *DTLSv1_client_method(void);
  OPENSSL_EXPORT const SSL_METHOD *DTLSv1_2_server_method(void);
  OPENSSL_EXPORT const SSL_METHOD *DTLSv1_2_client_method(void);
  
  // SSL_clear resets |ssl| to allow another connection and returns one on success
  // or zero on failure. It returns most configuration state but releases memory
  // associated with the current connection.
  //
  // Free |ssl| and create a new one instead.
  OPENSSL_EXPORT int SSL_clear(SSL *ssl);
  
  // SSL_CTX_set_tmp_rsa_callback does nothing.
  OPENSSL_EXPORT void SSL_CTX_set_tmp_rsa_callback(
      SSL_CTX *ctx, RSA *(*cb)(SSL *ssl, int is_export, int keylength));
  
  // SSL_set_tmp_rsa_callback does nothing.
  OPENSSL_EXPORT void SSL_set_tmp_rsa_callback(SSL *ssl,
                                               RSA *(*cb)(SSL *ssl, int is_export,
                                                          int keylength));
  
  // SSL_CTX_sess_connect returns zero.
  OPENSSL_EXPORT int SSL_CTX_sess_connect(const SSL_CTX *ctx);
  
  // SSL_CTX_sess_connect_good returns zero.
  OPENSSL_EXPORT int SSL_CTX_sess_connect_good(const SSL_CTX *ctx);
  
  // SSL_CTX_sess_connect_renegotiate returns zero.
  OPENSSL_EXPORT int SSL_CTX_sess_connect_renegotiate(const SSL_CTX *ctx);
  
  // SSL_CTX_sess_accept returns zero.
  OPENSSL_EXPORT int SSL_CTX_sess_accept(const SSL_CTX *ctx);
  
  // SSL_CTX_sess_accept_renegotiate returns zero.
  OPENSSL_EXPORT int SSL_CTX_sess_accept_renegotiate(const SSL_CTX *ctx);
  
  // SSL_CTX_sess_accept_good returns zero.
  OPENSSL_EXPORT int SSL_CTX_sess_accept_good(const SSL_CTX *ctx);
  
  // SSL_CTX_sess_hits returns zero.
  OPENSSL_EXPORT int SSL_CTX_sess_hits(const SSL_CTX *ctx);
  
  // SSL_CTX_sess_cb_hits returns zero.
  OPENSSL_EXPORT int SSL_CTX_sess_cb_hits(const SSL_CTX *ctx);
  
  // SSL_CTX_sess_misses returns zero.
  OPENSSL_EXPORT int SSL_CTX_sess_misses(const SSL_CTX *ctx);
  
  // SSL_CTX_sess_timeouts returns zero.
  OPENSSL_EXPORT int SSL_CTX_sess_timeouts(const SSL_CTX *ctx);
  
  // SSL_CTX_sess_cache_full returns zero.
  OPENSSL_EXPORT int SSL_CTX_sess_cache_full(const SSL_CTX *ctx);
  
  // SSL_cutthrough_complete calls |SSL_in_false_start|.
  OPENSSL_EXPORT int SSL_cutthrough_complete(const SSL *ssl);
  
  // SSL_num_renegotiations calls |SSL_total_renegotiations|.
  OPENSSL_EXPORT int SSL_num_renegotiations(const SSL *ssl);
  
  // SSL_CTX_need_tmp_RSA returns zero.
  OPENSSL_EXPORT int SSL_CTX_need_tmp_RSA(const SSL_CTX *ctx);
  
  // SSL_need_tmp_RSA returns zero.
  OPENSSL_EXPORT int SSL_need_tmp_RSA(const SSL *ssl);
  
  // SSL_CTX_set_tmp_rsa returns one.
  OPENSSL_EXPORT int SSL_CTX_set_tmp_rsa(SSL_CTX *ctx, const RSA *rsa);
  
  // SSL_set_tmp_rsa returns one.
  OPENSSL_EXPORT int SSL_set_tmp_rsa(SSL *ssl, const RSA *rsa);
  
  // SSL_CTX_get_read_ahead returns zero.
  OPENSSL_EXPORT int SSL_CTX_get_read_ahead(const SSL_CTX *ctx);
  
  // SSL_CTX_set_read_ahead does nothing.
  OPENSSL_EXPORT void SSL_CTX_set_read_ahead(SSL_CTX *ctx, int yes);
  
  // SSL_get_read_ahead returns zero.
  OPENSSL_EXPORT int SSL_get_read_ahead(const SSL *ssl);
  
  // SSL_set_read_ahead does nothing.
  OPENSSL_EXPORT void SSL_set_read_ahead(SSL *ssl, int yes);
  
  // SSL_renegotiate put an error on the error queue and returns zero.
  OPENSSL_EXPORT int SSL_renegotiate(SSL *ssl);
  
  // SSL_set_state does nothing.
  OPENSSL_EXPORT void SSL_set_state(SSL *ssl, int state);
  
  // SSL_get_shared_ciphers writes an empty string to |buf| and returns a
  // pointer to |buf|, or NULL if |len| is less than or equal to zero.
  OPENSSL_EXPORT char *SSL_get_shared_ciphers(const SSL *ssl, char *buf, int len);
  
  // SSL_MODE_HANDSHAKE_CUTTHROUGH is the same as SSL_MODE_ENABLE_FALSE_START.
  #define SSL_MODE_HANDSHAKE_CUTTHROUGH SSL_MODE_ENABLE_FALSE_START
  
  // i2d_SSL_SESSION serializes |in| to the bytes pointed to by |*pp|. On success,
  // it returns the number of bytes written and advances |*pp| by that many bytes.
  // On failure, it returns -1. If |pp| is NULL, no bytes are written and only the
  // length is returned.
  //
  // Use |SSL_SESSION_to_bytes| instead.
  OPENSSL_EXPORT int i2d_SSL_SESSION(SSL_SESSION *in, uint8_t **pp);
  
  // d2i_SSL_SESSION parses a serialized session from the |length| bytes pointed
  // to by |*pp|. It returns the new |SSL_SESSION| and advances |*pp| by the
  // number of bytes consumed on success and NULL on failure. The caller takes
  // ownership of the new session and must call |SSL_SESSION_free| when done.
  //
  // If |a| is non-NULL, |*a| is released and set the new |SSL_SESSION|.
  //
  // Use |SSL_SESSION_from_bytes| instead.
  OPENSSL_EXPORT SSL_SESSION *d2i_SSL_SESSION(SSL_SESSION **a, const uint8_t **pp,
                                              long length);
  
  // i2d_SSL_SESSION_bio serializes |session| and writes the result to |bio|. It
  // returns the number of bytes written on success and <= 0 on error.
  OPENSSL_EXPORT int i2d_SSL_SESSION_bio(BIO *bio, const SSL_SESSION *session);
  
  // d2i_SSL_SESSION_bio reads a serialized |SSL_SESSION| from |bio| and returns a
  // newly-allocated |SSL_SESSION| or NULL on error. If |out| is not NULL, it also
  // frees |*out| and sets |*out| to the new |SSL_SESSION|.
  OPENSSL_EXPORT SSL_SESSION *d2i_SSL_SESSION_bio(BIO *bio, SSL_SESSION **out);
  
  // ERR_load_SSL_strings does nothing.
  OPENSSL_EXPORT void ERR_load_SSL_strings(void);
  
  // SSL_load_error_strings does nothing.
  OPENSSL_EXPORT void SSL_load_error_strings(void);
  
  // SSL_CTX_set_tlsext_use_srtp calls |SSL_CTX_set_srtp_profiles|. It returns
  // zero on success and one on failure.
  //
  // WARNING: this function is dangerous because it breaks the usual return value
  // convention. Use |SSL_CTX_set_srtp_profiles| instead.
  OPENSSL_EXPORT int SSL_CTX_set_tlsext_use_srtp(SSL_CTX *ctx,
                                                 const char *profiles);
  
  // SSL_set_tlsext_use_srtp calls |SSL_set_srtp_profiles|. It returns zero on
  // success and one on failure.
  //
  // WARNING: this function is dangerous because it breaks the usual return value
  // convention. Use |SSL_set_srtp_profiles| instead.
  OPENSSL_EXPORT int SSL_set_tlsext_use_srtp(SSL *ssl, const char *profiles);
  
  // SSL_get_current_compression returns NULL.
  OPENSSL_EXPORT const COMP_METHOD *SSL_get_current_compression(SSL *ssl);
  
  // SSL_get_current_expansion returns NULL.
  OPENSSL_EXPORT const COMP_METHOD *SSL_get_current_expansion(SSL *ssl);
  
  // SSL_get_server_tmp_key returns zero.
  OPENSSL_EXPORT int *SSL_get_server_tmp_key(SSL *ssl, EVP_PKEY **out_key);
  
  // SSL_CTX_set_tmp_dh returns 1.
  OPENSSL_EXPORT int SSL_CTX_set_tmp_dh(SSL_CTX *ctx, const DH *dh);
  
  // SSL_set_tmp_dh returns 1.
  OPENSSL_EXPORT int SSL_set_tmp_dh(SSL *ssl, const DH *dh);
  
  // SSL_CTX_set_tmp_dh_callback does nothing.
  OPENSSL_EXPORT void SSL_CTX_set_tmp_dh_callback(
      SSL_CTX *ctx, DH *(*cb)(SSL *ssl, int is_export, int keylength));
  
  // SSL_set_tmp_dh_callback does nothing.
  OPENSSL_EXPORT void SSL_set_tmp_dh_callback(SSL *ssl,
                                              DH *(*cb)(SSL *ssl, int is_export,
                                                        int keylength));
  
  
  #define SSL_set_app_data(s, arg) (SSL_set_ex_data(s, 0, (char *)(arg)))
  #define SSL_get_app_data(s) (SSL_get_ex_data(s, 0))
  #define SSL_SESSION_set_app_data(s, a) \
    (SSL_SESSION_set_ex_data(s, 0, (char *)(a)))
  #define SSL_SESSION_get_app_data(s) (SSL_SESSION_get_ex_data(s, 0))
  #define SSL_CTX_get_app_data(ctx) (SSL_CTX_get_ex_data(ctx, 0))
  #define SSL_CTX_set_app_data(ctx, arg) \
    (SSL_CTX_set_ex_data(ctx, 0, (char *)(arg)))
  
  #define OpenSSL_add_ssl_algorithms() SSL_library_init()
  #define SSLeay_add_ssl_algorithms() SSL_library_init()
  
  #define SSL_get_cipher(ssl) SSL_CIPHER_get_name(SSL_get_current_cipher(ssl))
  #define SSL_get_cipher_bits(ssl, out_alg_bits) \
      SSL_CIPHER_get_bits(SSL_get_current_cipher(ssl), out_alg_bits)
  #define SSL_get_cipher_version(ssl) \
      SSL_CIPHER_get_version(SSL_get_current_cipher(ssl))
  #define SSL_get_cipher_name(ssl) \
      SSL_CIPHER_get_name(SSL_get_current_cipher(ssl))
  #define SSL_get_time(session) SSL_SESSION_get_time(session)
  #define SSL_set_time(session, time) SSL_SESSION_set_time((session), (time))
  #define SSL_get_timeout(session) SSL_SESSION_get_timeout(session)
  #define SSL_set_timeout(session, timeout) \
      SSL_SESSION_set_timeout((session), (timeout))
  
  typedef struct ssl_comp_st SSL_COMP;
  
  struct ssl_comp_st {
    int id;
    const char *name;
    char *method;
  };
  
  DEFINE_STACK_OF(SSL_COMP)
  
  // The following flags do nothing and are included only to make it easier to
  // compile code with BoringSSL.
  #define SSL_MODE_AUTO_RETRY 0
  #define SSL_MODE_RELEASE_BUFFERS 0
  #define SSL_MODE_SEND_CLIENTHELLO_TIME 0
  #define SSL_MODE_SEND_SERVERHELLO_TIME 0
  #define SSL_OP_ALL 0
  #define SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION 0
  #define SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS 0
  #define SSL_OP_EPHEMERAL_RSA 0
  #define SSL_OP_LEGACY_SERVER_CONNECT 0
  #define SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER 0
  #define SSL_OP_MICROSOFT_SESS_ID_BUG 0
  #define SSL_OP_MSIE_SSLV2_RSA_PADDING 0
  #define SSL_OP_NETSCAPE_CA_DN_BUG 0
  #define SSL_OP_NETSCAPE_CHALLENGE_BUG 0
  #define SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG 0
  #define SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG 0
  #define SSL_OP_NO_COMPRESSION 0
  #define SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION 0
  #define SSL_OP_NO_SSLv2 0
  #define SSL_OP_PKCS1_CHECK_1 0
  #define SSL_OP_PKCS1_CHECK_2 0
  #define SSL_OP_SINGLE_DH_USE 0
  #define SSL_OP_SINGLE_ECDH_USE 0
  #define SSL_OP_SSLEAY_080_CLIENT_DH_BUG 0
  #define SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG 0
  #define SSL_OP_TLS_BLOCK_PADDING_BUG 0
  #define SSL_OP_TLS_D5_BUG 0
  #define SSL_OP_TLS_ROLLBACK_BUG 0
  #define SSL_VERIFY_CLIENT_ONCE 0
  
  // SSL_cache_hit calls |SSL_session_reused|.
  OPENSSL_EXPORT int SSL_cache_hit(SSL *ssl);
  
  // SSL_get_default_timeout returns |SSL_DEFAULT_SESSION_TIMEOUT|.
  OPENSSL_EXPORT long SSL_get_default_timeout(const SSL *ssl);
  
  // SSL_get_version returns a string describing the TLS version used by |ssl|.
  // For example, "TLSv1.2" or "SSLv3".
  OPENSSL_EXPORT const char *SSL_get_version(const SSL *ssl);
  
  // SSL_get_cipher_list returns the name of the |n|th cipher in the output of
  // |SSL_get_ciphers| or NULL if out of range. Use |SSL_get_ciphers| instead.
  OPENSSL_EXPORT const char *SSL_get_cipher_list(const SSL *ssl, int n);
  
  // SSL_CTX_set_client_cert_cb sets a callback which is called on the client if
  // the server requests a client certificate and none is configured. On success,
  // the callback should return one and set |*out_x509| to |*out_pkey| to a leaf
  // certificate and private key, respectively, passing ownership. It should
  // return zero to send no certificate and -1 to fail or pause the handshake. If
  // the handshake is paused, |SSL_get_error| will return
  // |SSL_ERROR_WANT_X509_LOOKUP|.
  //
  // The callback may call |SSL_get0_certificate_types| and
  // |SSL_get_client_CA_list| for information on the server's certificate request.
  //
  // Use |SSL_CTX_set_cert_cb| instead. Configuring intermediate certificates with
  // this function is confusing. This callback may not be registered concurrently
  // with |SSL_CTX_set_cert_cb| or |SSL_set_cert_cb|.
  OPENSSL_EXPORT void SSL_CTX_set_client_cert_cb(
      SSL_CTX *ctx, int (*cb)(SSL *ssl, X509 **out_x509, EVP_PKEY **out_pkey));
  
  #define SSL_NOTHING 1
  #define SSL_WRITING 2
  #define SSL_READING 3
  #define SSL_X509_LOOKUP 4
  #define SSL_CHANNEL_ID_LOOKUP 5
  #define SSL_PENDING_SESSION 7
  #define SSL_CERTIFICATE_SELECTION_PENDING 8
  #define SSL_PRIVATE_KEY_OPERATION 9
  #define SSL_PENDING_TICKET 10
  #define SSL_EARLY_DATA_REJECTED 11
  #define SSL_CERTIFICATE_VERIFY 12
  #define SSL_HANDOFF 13
  
  // SSL_want returns one of the above values to determine what the most recent
  // operation on |ssl| was blocked on. Use |SSL_get_error| instead.
  OPENSSL_EXPORT int SSL_want(const SSL *ssl);
  
  #define SSL_want_read(ssl) (SSL_want(ssl) == SSL_READING)
  #define SSL_want_write(ssl) (SSL_want(ssl) == SSL_WRITING)
  
   // SSL_get_finished writes up to |count| bytes of the Finished message sent by
   // |ssl| to |buf|. It returns the total untruncated length or zero if none has
   // been sent yet. At SSL 3.0 or TLS 1.3 and later, it returns zero.
   //
   // Use |SSL_get_tls_unique| instead.
  OPENSSL_EXPORT size_t SSL_get_finished(const SSL *ssl, void *buf, size_t count);
  
   // SSL_get_peer_finished writes up to |count| bytes of the Finished message
   // received from |ssl|'s peer to |buf|. It returns the total untruncated length
   // or zero if none has been received yet. At SSL 3.0 or TLS 1.3 and later, it
   // returns zero.
   //
   // Use |SSL_get_tls_unique| instead.
  OPENSSL_EXPORT size_t SSL_get_peer_finished(const SSL *ssl, void *buf,
                                              size_t count);
  
  // SSL_alert_type_string returns "!". Use |SSL_alert_type_string_long|
  // instead.
  OPENSSL_EXPORT const char *SSL_alert_type_string(int value);
  
  // SSL_alert_desc_string returns "!!". Use |SSL_alert_desc_string_long|
  // instead.
  OPENSSL_EXPORT const char *SSL_alert_desc_string(int value);
  
  // SSL_state_string returns "!!!!!!". Use |SSL_state_string_long| for a more
  // intelligible string.
  OPENSSL_EXPORT const char *SSL_state_string(const SSL *ssl);
  
  // SSL_TXT_* expand to strings.
  #define SSL_TXT_MEDIUM "MEDIUM"
  #define SSL_TXT_HIGH "HIGH"
  #define SSL_TXT_FIPS "FIPS"
  #define SSL_TXT_kRSA "kRSA"
  #define SSL_TXT_kDHE "kDHE"
  #define SSL_TXT_kEDH "kEDH"
  #define SSL_TXT_kECDHE "kECDHE"
  #define SSL_TXT_kEECDH "kEECDH"
  #define SSL_TXT_kPSK "kPSK"
  #define SSL_TXT_aRSA "aRSA"
  #define SSL_TXT_aECDSA "aECDSA"
  #define SSL_TXT_aPSK "aPSK"
  #define SSL_TXT_DH "DH"
  #define SSL_TXT_DHE "DHE"
  #define SSL_TXT_EDH "EDH"
  #define SSL_TXT_RSA "RSA"
  #define SSL_TXT_ECDH "ECDH"
  #define SSL_TXT_ECDHE "ECDHE"
  #define SSL_TXT_EECDH "EECDH"
  #define SSL_TXT_ECDSA "ECDSA"
  #define SSL_TXT_PSK "PSK"
  #define SSL_TXT_3DES "3DES"
  #define SSL_TXT_RC4 "RC4"
  #define SSL_TXT_AES128 "AES128"
  #define SSL_TXT_AES256 "AES256"
  #define SSL_TXT_AES "AES"
  #define SSL_TXT_AES_GCM "AESGCM"
  #define SSL_TXT_CHACHA20 "CHACHA20"
  #define SSL_TXT_MD5 "MD5"
  #define SSL_TXT_SHA1 "SHA1"
  #define SSL_TXT_SHA "SHA"
  #define SSL_TXT_SHA256 "SHA256"
  #define SSL_TXT_SHA384 "SHA384"
  #define SSL_TXT_SSLV3 "SSLv3"
  #define SSL_TXT_TLSV1 "TLSv1"
  #define SSL_TXT_TLSV1_1 "TLSv1.1"
  #define SSL_TXT_TLSV1_2 "TLSv1.2"
  #define SSL_TXT_TLSV1_3 "TLSv1.3"
  #define SSL_TXT_ALL "ALL"
  #define SSL_TXT_CMPDEF "COMPLEMENTOFDEFAULT"
  
  typedef struct ssl_conf_ctx_st SSL_CONF_CTX;
  
  // SSL_state returns |SSL_ST_INIT| if a handshake is in progress and |SSL_ST_OK|
  // otherwise.
  //
  // Use |SSL_is_init| instead.
  OPENSSL_EXPORT int SSL_state(const SSL *ssl);
  
  #define SSL_get_state(ssl) SSL_state(ssl)
  
  // SSL_set_shutdown causes |ssl| to behave as if the shutdown bitmask (see
  // |SSL_get_shutdown|) were |mode|. This may be used to skip sending or
  // receiving close_notify in |SSL_shutdown| by causing the implementation to
  // believe the events already happened.
  //
  // It is an error to use |SSL_set_shutdown| to unset a bit that has already been
  // set. Doing so will trigger an |assert| in debug builds and otherwise be
  // ignored.
  //
  // Use |SSL_CTX_set_quiet_shutdown| instead.
  OPENSSL_EXPORT void SSL_set_shutdown(SSL *ssl, int mode);
  
  // SSL_CTX_set_tmp_ecdh calls |SSL_CTX_set1_curves| with a one-element list
  // containing |ec_key|'s curve.
  OPENSSL_EXPORT int SSL_CTX_set_tmp_ecdh(SSL_CTX *ctx, const EC_KEY *ec_key);
  
  // SSL_set_tmp_ecdh calls |SSL_set1_curves| with a one-element list containing
  // |ec_key|'s curve.
  OPENSSL_EXPORT int SSL_set_tmp_ecdh(SSL *ssl, const EC_KEY *ec_key);
  
  // SSL_add_dir_cert_subjects_to_stack lists files in directory |dir|. It calls
  // |SSL_add_file_cert_subjects_to_stack| on each file and returns one on success
  // or zero on error. This function is only available from the libdecrepit
  // library.
  OPENSSL_EXPORT int SSL_add_dir_cert_subjects_to_stack(STACK_OF(X509_NAME) *out,
                                                        const char *dir);
  
  // SSL_set_verify_result calls |abort| unless |result| is |X509_V_OK|.
  //
  // TODO(davidben): Remove this function once it has been removed from
  // netty-tcnative.
  OPENSSL_EXPORT void SSL_set_verify_result(SSL *ssl, long result);
  
  // SSL_CTX_enable_tls_channel_id calls |SSL_CTX_set_tls_channel_id_enabled|.
  OPENSSL_EXPORT int SSL_CTX_enable_tls_channel_id(SSL_CTX *ctx);
  
  // SSL_enable_tls_channel_id calls |SSL_set_tls_channel_id_enabled|.
  OPENSSL_EXPORT int SSL_enable_tls_channel_id(SSL *ssl);
  
  // BIO_f_ssl returns a |BIO_METHOD| that can wrap an |SSL*| in a |BIO*|. Note
  // that this has quite different behaviour from the version in OpenSSL (notably
  // that it doesn't try to auto renegotiate).
  //
  // IMPORTANT: if you are not curl, don't use this.
  OPENSSL_EXPORT const BIO_METHOD *BIO_f_ssl(void);
  
  // BIO_set_ssl sets |ssl| as the underlying connection for |bio|, which must
  // have been created using |BIO_f_ssl|. If |take_owership| is true, |bio| will
  // call |SSL_free| on |ssl| when closed. It returns one on success or something
  // other than one on error.
  OPENSSL_EXPORT long BIO_set_ssl(BIO *bio, SSL *ssl, int take_owership);
  
  // SSL_CTX_set_ecdh_auto returns one.
  #define SSL_CTX_set_ecdh_auto(ctx, onoff) 1
  
  // SSL_set_ecdh_auto returns one.
  #define SSL_set_ecdh_auto(ssl, onoff) 1
  
  // SSL_get_session returns a non-owning pointer to |ssl|'s session. For
  // historical reasons, which session it returns depends on |ssl|'s state.
  //
  // Prior to the start of the initial handshake, it returns the session the
  // caller set with |SSL_set_session|. After the initial handshake has finished
  // and if no additional handshakes are in progress, it returns the currently
  // active session. Its behavior is undefined while a handshake is in progress.
  //
  // If trying to add new sessions to an external session cache, use
  // |SSL_CTX_sess_set_new_cb| instead. In particular, using the callback is
  // required as of TLS 1.3. For compatibility, this function will return an
  // unresumable session which may be cached, but will never be resumed.
  //
  // If querying properties of the connection, use APIs on the |SSL| object.
  OPENSSL_EXPORT SSL_SESSION *SSL_get_session(const SSL *ssl);
  
  // SSL_get0_session is an alias for |SSL_get_session|.
  #define SSL_get0_session SSL_get_session
  
  // SSL_get1_session acts like |SSL_get_session| but returns a new reference to
  // the session.
  OPENSSL_EXPORT SSL_SESSION *SSL_get1_session(SSL *ssl);
  
  #define OPENSSL_INIT_NO_LOAD_SSL_STRINGS 0
  #define OPENSSL_INIT_LOAD_SSL_STRINGS 0
  #define OPENSSL_INIT_SSL_DEFAULT 0
  
  // OPENSSL_init_ssl calls |CRYPTO_library_init| and returns one.
  OPENSSL_EXPORT int OPENSSL_init_ssl(uint64_t opts,
                                      const OPENSSL_INIT_SETTINGS *settings);
  
  #if !defined(BORINGSSL_NO_CXX)
  // SSL_CTX_sess_set_get_cb is a legacy C++ overload of |SSL_CTX_sess_set_get_cb|
  // which supports the old callback signature.
  //
  // TODO(davidben): Remove this once Node is compatible with OpenSSL 1.1.0.
  extern "C++" OPENSSL_EXPORT void SSL_CTX_sess_set_get_cb(
      SSL_CTX *ctx, SSL_SESSION *(*get_session_cb)(SSL *ssl, uint8_t *id,
                                                   int id_len, int *out_copy));
  #endif
  
  
  // Private structures.
  //
  // This structures are exposed for historical reasons, but access to them is
  // deprecated.
  
  // TODO(davidben): Remove this forward declaration when |SSL_SESSION| is opaque.
  typedef struct ssl_x509_method_st SSL_X509_METHOD;
  
  #define SSL_MAX_SSL_SESSION_ID_LENGTH 32
  #define SSL_MAX_SID_CTX_LENGTH 32
  #define SSL_MAX_MASTER_KEY_LENGTH 48
  
  struct ssl_session_st {
    CRYPTO_refcount_t references;
    uint16_t ssl_version;  // what ssl version session info is being kept in here?
  
    // group_id is the ID of the ECDH group used to establish this session or zero
    // if not applicable or unknown.
    uint16_t group_id;
  
    // peer_signature_algorithm is the signature algorithm used to authenticate
    // the peer, or zero if not applicable or unknown.
    uint16_t peer_signature_algorithm;
  
    // master_key, in TLS 1.2 and below, is the master secret associated with the
    // session. In TLS 1.3 and up, it is the resumption secret.
    int master_key_length;
    uint8_t master_key[SSL_MAX_MASTER_KEY_LENGTH];
  
    // session_id - valid?
    unsigned int session_id_length;
    uint8_t session_id[SSL_MAX_SSL_SESSION_ID_LENGTH];
    // this is used to determine whether the session is being reused in
    // the appropriate context. It is up to the application to set this,
    // via SSL_new
    uint8_t sid_ctx_length;
    uint8_t sid_ctx[SSL_MAX_SID_CTX_LENGTH];
  
    char *psk_identity;
  
    // certs contains the certificate chain from the peer, starting with the leaf
    // certificate.
    STACK_OF(CRYPTO_BUFFER) *certs;
  
    const SSL_X509_METHOD *x509_method;
  
    // x509_peer is the peer's certificate.
    X509 *x509_peer;
  
    // x509_chain is the certificate chain sent by the peer. NOTE: for historical
    // reasons, when a client (so the peer is a server), the chain includes
    // |peer|, but when a server it does not.
    STACK_OF(X509) *x509_chain;
  
    // x509_chain_without_leaf is a lazily constructed copy of |x509_chain| that
    // omits the leaf certificate. This exists because OpenSSL, historically,
    // didn't include the leaf certificate in the chain for a server, but did for
    // a client. The |x509_chain| always includes it and, if an API call requires
    // a chain without, it is stored here.
    STACK_OF(X509) *x509_chain_without_leaf;
  
    // verify_result is the result of certificate verification in the case of
    // non-fatal certificate errors.
    long verify_result;
  
    // timeout is the lifetime of the session in seconds, measured from |time|.
    // This is renewable up to |auth_timeout|.
    uint32_t timeout;
  
    // auth_timeout is the non-renewable lifetime of the session in seconds,
    // measured from |time|.
    uint32_t auth_timeout;
  
    // time is the time the session was issued, measured in seconds from the UNIX
    // epoch.
    uint64_t time;
  
    const SSL_CIPHER *cipher;
  
    CRYPTO_EX_DATA ex_data;  // application specific data
  
    // These are used to make removal of session-ids more efficient and to
    // implement a maximum cache size.
    SSL_SESSION *prev, *next;
  
    // RFC4507 info
    uint8_t *tlsext_tick;               // Session ticket
    size_t tlsext_ticklen;              // Session ticket length
  
    CRYPTO_BUFFER *signed_cert_timestamp_list;
  
    // The OCSP response that came with the session.
    CRYPTO_BUFFER *ocsp_response;
  
    // peer_sha256 contains the SHA-256 hash of the peer's certificate if
    // |peer_sha256_valid| is true.
    uint8_t peer_sha256[SHA256_DIGEST_LENGTH];
  
    // original_handshake_hash contains the handshake hash (either SHA-1+MD5 or
    // SHA-2, depending on TLS version) for the original, full handshake that
    // created a session. This is used by Channel IDs during resumption.
    uint8_t original_handshake_hash[EVP_MAX_MD_SIZE];
    uint8_t original_handshake_hash_len;
  
    uint32_t tlsext_tick_lifetime_hint;  // Session lifetime hint in seconds
  
    uint32_t ticket_age_add;
  
    // ticket_max_early_data is the maximum amount of data allowed to be sent as
    // early data. If zero, 0-RTT is disallowed.
    uint32_t ticket_max_early_data;
  
    // early_alpn is the ALPN protocol from the initial handshake. This is only
    // stored for TLS 1.3 and above in order to enforce ALPN matching for 0-RTT
    // resumptions.
    uint8_t *early_alpn;
    size_t early_alpn_len;
  
    // extended_master_secret is true if the master secret in this session was
    // generated using EMS and thus isn't vulnerable to the Triple Handshake
    // attack.
    unsigned extended_master_secret:1;
  
    // peer_sha256_valid is non-zero if |peer_sha256| is valid.
    unsigned peer_sha256_valid:1;  // Non-zero if peer_sha256 is valid
  
    // not_resumable is used to indicate that session resumption is disallowed.
    unsigned not_resumable:1;
  
    // ticket_age_add_valid is non-zero if |ticket_age_add| is valid.
    unsigned ticket_age_add_valid:1;
  
    // is_server is true if this session was created by a server.
    unsigned is_server:1;
  };
  
  
  // Nodejs compatibility section (hidden).
  //
  // These defines exist for node.js, with the hope that we can eliminate the
  // need for them over time.
  #define SSLerr(function, reason) \
    ERR_put_error(ERR_LIB_SSL, 0, reason, __FILE__, __LINE__)
  
  
  // Preprocessor compatibility section (hidden).
  //
  // Historically, a number of APIs were implemented in OpenSSL as macros and
  // constants to 'ctrl' functions. To avoid breaking #ifdefs in consumers, this
  // section defines a number of legacy macros.
  //
  // Although using either the CTRL values or their wrapper macros in #ifdefs is
  // still supported, the CTRL values may not be passed to |SSL_ctrl| and
  // |SSL_CTX_ctrl|. Call the functions (previously wrapper macros) instead.
  //
  // See PORTING.md in the BoringSSL source tree for a table of corresponding
  // functions.
  // https://boringssl.googlesource.com/boringssl/+/master/PORTING.md#Replacements-for-values
  
  #define DTLS_CTRL_GET_TIMEOUT doesnt_exist
  #define DTLS_CTRL_HANDLE_TIMEOUT doesnt_exist
  #define SSL_CTRL_CHAIN doesnt_exist
  #define SSL_CTRL_CHAIN_CERT doesnt_exist
  #define SSL_CTRL_CHANNEL_ID doesnt_exist
  #define SSL_CTRL_CLEAR_EXTRA_CHAIN_CERTS doesnt_exist
  #define SSL_CTRL_CLEAR_MODE doesnt_exist
  #define SSL_CTRL_CLEAR_OPTIONS doesnt_exist
  #define SSL_CTRL_EXTRA_CHAIN_CERT doesnt_exist
  #define SSL_CTRL_GET_CHAIN_CERTS doesnt_exist
  #define SSL_CTRL_GET_CHANNEL_ID doesnt_exist
  #define SSL_CTRL_GET_CLIENT_CERT_TYPES doesnt_exist
  #define SSL_CTRL_GET_EXTRA_CHAIN_CERTS doesnt_exist
  #define SSL_CTRL_GET_MAX_CERT_LIST doesnt_exist
  #define SSL_CTRL_GET_NUM_RENEGOTIATIONS doesnt_exist
  #define SSL_CTRL_GET_READ_AHEAD doesnt_exist
  #define SSL_CTRL_GET_RI_SUPPORT doesnt_exist
  #define SSL_CTRL_GET_SESSION_REUSED doesnt_exist
  #define SSL_CTRL_GET_SESS_CACHE_MODE doesnt_exist
  #define SSL_CTRL_GET_SESS_CACHE_SIZE doesnt_exist
  #define SSL_CTRL_GET_TLSEXT_TICKET_KEYS doesnt_exist
  #define SSL_CTRL_GET_TOTAL_RENEGOTIATIONS doesnt_exist
  #define SSL_CTRL_MODE doesnt_exist
  #define SSL_CTRL_NEED_TMP_RSA doesnt_exist
  #define SSL_CTRL_OPTIONS doesnt_exist
  #define SSL_CTRL_SESS_NUMBER doesnt_exist
  #define SSL_CTRL_SET_CURVES doesnt_exist
  #define SSL_CTRL_SET_CURVES_LIST doesnt_exist
  #define SSL_CTRL_SET_ECDH_AUTO doesnt_exist
  #define SSL_CTRL_SET_MAX_CERT_LIST doesnt_exist
  #define SSL_CTRL_SET_MAX_SEND_FRAGMENT doesnt_exist
  #define SSL_CTRL_SET_MSG_CALLBACK doesnt_exist
  #define SSL_CTRL_SET_MSG_CALLBACK_ARG doesnt_exist
  #define SSL_CTRL_SET_MTU doesnt_exist
  #define SSL_CTRL_SET_READ_AHEAD doesnt_exist
  #define SSL_CTRL_SET_SESS_CACHE_MODE doesnt_exist
  #define SSL_CTRL_SET_SESS_CACHE_SIZE doesnt_exist
  #define SSL_CTRL_SET_TLSEXT_HOSTNAME doesnt_exist
  #define SSL_CTRL_SET_TLSEXT_SERVERNAME_ARG doesnt_exist
  #define SSL_CTRL_SET_TLSEXT_SERVERNAME_CB doesnt_exist
  #define SSL_CTRL_SET_TLSEXT_TICKET_KEYS doesnt_exist
  #define SSL_CTRL_SET_TLSEXT_TICKET_KEY_CB doesnt_exist
  #define SSL_CTRL_SET_TMP_DH doesnt_exist
  #define SSL_CTRL_SET_TMP_DH_CB doesnt_exist
  #define SSL_CTRL_SET_TMP_ECDH doesnt_exist
  #define SSL_CTRL_SET_TMP_ECDH_CB doesnt_exist
  #define SSL_CTRL_SET_TMP_RSA doesnt_exist
  #define SSL_CTRL_SET_TMP_RSA_CB doesnt_exist
  
  #define DTLSv1_get_timeout DTLSv1_get_timeout
  #define DTLSv1_handle_timeout DTLSv1_handle_timeout
  #define SSL_CTX_add0_chain_cert SSL_CTX_add0_chain_cert
  #define SSL_CTX_add1_chain_cert SSL_CTX_add1_chain_cert
  #define SSL_CTX_add_extra_chain_cert SSL_CTX_add_extra_chain_cert
  #define SSL_CTX_clear_extra_chain_certs SSL_CTX_clear_extra_chain_certs
  #define SSL_CTX_clear_chain_certs SSL_CTX_clear_chain_certs
  #define SSL_CTX_clear_mode SSL_CTX_clear_mode
  #define SSL_CTX_clear_options SSL_CTX_clear_options
  #define SSL_CTX_get0_chain_certs SSL_CTX_get0_chain_certs
  #define SSL_CTX_get_extra_chain_certs SSL_CTX_get_extra_chain_certs
  #define SSL_CTX_get_max_cert_list SSL_CTX_get_max_cert_list
  #define SSL_CTX_get_mode SSL_CTX_get_mode
  #define SSL_CTX_get_options SSL_CTX_get_options
  #define SSL_CTX_get_read_ahead SSL_CTX_get_read_ahead
  #define SSL_CTX_get_session_cache_mode SSL_CTX_get_session_cache_mode
  #define SSL_CTX_get_tlsext_ticket_keys SSL_CTX_get_tlsext_ticket_keys
  #define SSL_CTX_need_tmp_RSA SSL_CTX_need_tmp_RSA
  #define SSL_CTX_sess_get_cache_size SSL_CTX_sess_get_cache_size
  #define SSL_CTX_sess_number SSL_CTX_sess_number
  #define SSL_CTX_sess_set_cache_size SSL_CTX_sess_set_cache_size
  #define SSL_CTX_set0_chain SSL_CTX_set0_chain
  #define SSL_CTX_set1_chain SSL_CTX_set1_chain
  #define SSL_CTX_set1_curves SSL_CTX_set1_curves
  #define SSL_CTX_set_max_cert_list SSL_CTX_set_max_cert_list
  #define SSL_CTX_set_max_send_fragment SSL_CTX_set_max_send_fragment
  #define SSL_CTX_set_mode SSL_CTX_set_mode
  #define SSL_CTX_set_msg_callback_arg SSL_CTX_set_msg_callback_arg
  #define SSL_CTX_set_options SSL_CTX_set_options
  #define SSL_CTX_set_read_ahead SSL_CTX_set_read_ahead
  #define SSL_CTX_set_session_cache_mode SSL_CTX_set_session_cache_mode
  #define SSL_CTX_set_tlsext_servername_arg SSL_CTX_set_tlsext_servername_arg
  #define SSL_CTX_set_tlsext_servername_callback \
      SSL_CTX_set_tlsext_servername_callback
  #define SSL_CTX_set_tlsext_ticket_key_cb SSL_CTX_set_tlsext_ticket_key_cb
  #define SSL_CTX_set_tlsext_ticket_keys SSL_CTX_set_tlsext_ticket_keys
  #define SSL_CTX_set_tmp_dh SSL_CTX_set_tmp_dh
  #define SSL_CTX_set_tmp_ecdh SSL_CTX_set_tmp_ecdh
  #define SSL_CTX_set_tmp_rsa SSL_CTX_set_tmp_rsa
  #define SSL_add0_chain_cert SSL_add0_chain_cert
  #define SSL_add1_chain_cert SSL_add1_chain_cert
  #define SSL_clear_chain_certs SSL_clear_chain_certs
  #define SSL_clear_mode SSL_clear_mode
  #define SSL_clear_options SSL_clear_options
  #define SSL_get0_certificate_types SSL_get0_certificate_types
  #define SSL_get0_chain_certs SSL_get0_chain_certs
  #define SSL_get_max_cert_list SSL_get_max_cert_list
  #define SSL_get_mode SSL_get_mode
  #define SSL_get_options SSL_get_options
  #define SSL_get_secure_renegotiation_support \
      SSL_get_secure_renegotiation_support
  #define SSL_need_tmp_RSA SSL_need_tmp_RSA
  #define SSL_num_renegotiations SSL_num_renegotiations
  #define SSL_session_reused SSL_session_reused
  #define SSL_set0_chain SSL_set0_chain
  #define SSL_set1_chain SSL_set1_chain
  #define SSL_set1_curves SSL_set1_curves
  #define SSL_set_max_cert_list SSL_set_max_cert_list
  #define SSL_set_max_send_fragment SSL_set_max_send_fragment
  #define SSL_set_mode SSL_set_mode
  #define SSL_set_msg_callback_arg SSL_set_msg_callback_arg
  #define SSL_set_mtu SSL_set_mtu
  #define SSL_set_options SSL_set_options
  #define SSL_set_tlsext_host_name SSL_set_tlsext_host_name
  #define SSL_set_tmp_dh SSL_set_tmp_dh
  #define SSL_set_tmp_ecdh SSL_set_tmp_ecdh
  #define SSL_set_tmp_rsa SSL_set_tmp_rsa
  #define SSL_total_renegotiations SSL_total_renegotiations
  
  
  #if defined(__cplusplus)
  }  // extern C
  
  #if !defined(BORINGSSL_NO_CXX)
  
  extern "C++" {
  
  namespace bssl {
  
  BORINGSSL_MAKE_DELETER(SSL, SSL_free)
  BORINGSSL_MAKE_DELETER(SSL_CTX, SSL_CTX_free)
  BORINGSSL_MAKE_DELETER(SSL_SESSION, SSL_SESSION_free)
  
  enum class OpenRecordResult {
    kOK,
    kDiscard,
    kIncompleteRecord,
    kAlertCloseNotify,
    kError,
  };
  
  //  *** EXPERIMENTAL -- DO NOT USE ***
  //
  // OpenRecord decrypts the first complete SSL record from |in| in-place, sets
  // |out| to the decrypted application data, and |out_record_len| to the length
  // of the encrypted record. Returns:
  // - kOK if an application-data record was successfully decrypted and verified.
  // - kDiscard if a record was sucessfully processed, but should be discarded.
  // - kIncompleteRecord if |in| did not contain a complete record.
  // - kAlertCloseNotify if a record was successfully processed but is a
  //   close_notify alert.
  // - kError if an error occurred or the record is invalid. |*out_alert| will be
  //   set to an alert to emit, or zero if no alert should be emitted.
  OPENSSL_EXPORT OpenRecordResult OpenRecord(SSL *ssl, Span<uint8_t> *out,
                                             size_t *out_record_len,
                                             uint8_t *out_alert,
                                             Span<uint8_t> in);
  
  OPENSSL_EXPORT size_t SealRecordPrefixLen(const SSL *ssl, size_t plaintext_len);
  
  // SealRecordSuffixLen returns the length of the suffix written by |SealRecord|.
  //
  // |plaintext_len| must be equal to the size of the plaintext passed to
  // |SealRecord|.
  //
  // |plaintext_len| must not exceed |SSL3_RT_MAX_PLAINTEXT_LENGTH|. The returned
  // suffix length will not exceed |SSL3_RT_MAX_ENCRYPTED_OVERHEAD|.
  OPENSSL_EXPORT size_t SealRecordSuffixLen(const SSL *ssl, size_t plaintext_len);
  
  //  *** EXPERIMENTAL -- DO NOT USE ***
  //
  // SealRecord encrypts the cleartext of |in| and scatters the resulting TLS
  // application data record between |out_prefix|, |out|, and |out_suffix|. It
  // returns true on success or false if an error occurred.
  //
  // The length of |out_prefix| must equal |SealRecordPrefixLen|. The length of
  // |out| must equal the length of |in|, which must not exceed
  // |SSL3_RT_MAX_PLAINTEXT_LENGTH|. The length of |out_suffix| must equal
  // |SealRecordSuffixLen|.
  //
  // If enabled, |SealRecord| may perform TLS 1.0 CBC 1/n-1 record splitting.
  // |SealRecordPrefixLen| accounts for the required overhead if that is the case.
  //
  // |out| may equal |in| to encrypt in-place but may not otherwise alias.
  // |out_prefix| and |out_suffix| may not alias anything.
  OPENSSL_EXPORT bool SealRecord(SSL *ssl, Span<uint8_t> out_prefix,
                                 Span<uint8_t> out, Span<uint8_t> out_suffix,
                                 Span<const uint8_t> in);
  
  
  // *** EXPERIMENTAL — DO NOT USE WITHOUT CHECKING ***
  //
  // Split handshakes.
  //
  // Split handshakes allows the handshake part of a TLS connection to be
  // performed in a different process (or on a different machine) than the data
  // exchange. This only applies to servers.
  //
  // In the first part of a split handshake, an |SSL| (where the |SSL_CTX| has
  // been configured with |SSL_CTX_set_handoff_mode|) is used normally. Once the
  // ClientHello message has been received, the handshake will stop and
  // |SSL_get_error| will indicate |SSL_ERROR_HANDOFF|. At this point (and only
  // at this point), |SSL_serialize_handoff| can be called to write the “handoff”
  // state of the connection.
  //
  // Elsewhere, a fresh |SSL| can be used with |SSL_apply_handoff| to continue
  // the connection. The connection from the client is fed into this |SSL| until
  // the handshake completes normally. At this point (and only at this point),
  // |SSL_serialize_handback| can be called to serialize the result of the
  // handshake.
  //
  // Back at the first location, a fresh |SSL| can be used with
  // |SSL_apply_handback|. Then the client's connection can be processed mostly
  // as normal.
  //
  // Lastly, when a connection is in the handoff state, whether or not
  // |SSL_serialize_handoff| is called, |SSL_decline_handoff| will move it back
  // into a normal state where the connection can procede without impact.
  //
  // WARNING: Currently only works with TLS 1.0–1.2.
  // WARNING: The serialisation formats are not yet stable: version skew may be
  //     fatal.
  // WARNING: The handback data contains sensitive key material and must be
  //     protected.
  // WARNING: Some calls on the final |SSL| will not work. Just as an example,
  //     calls like |SSL_get0_session_id_context| and |SSL_get_privatekey| won't
  //     work because the certificate used for handshaking isn't available.
  // WARNING: |SSL_apply_handoff| may trigger “msg” callback calls.
  
  OPENSSL_EXPORT void SSL_CTX_set_handoff_mode(SSL_CTX *ctx, bool on);
  OPENSSL_EXPORT bool SSL_serialize_handoff(const SSL *ssl, CBB *out);
  OPENSSL_EXPORT bool SSL_decline_handoff(SSL *ssl);
  OPENSSL_EXPORT bool SSL_apply_handoff(SSL *ssl, Span<const uint8_t> handoff);
  OPENSSL_EXPORT bool SSL_serialize_handback(const SSL *ssl, CBB *out);
  OPENSSL_EXPORT bool SSL_apply_handback(SSL *ssl, Span<const uint8_t> handback);
  
  }  // namespace bssl
  
  }  // extern C++
  
  #endif  // !defined(BORINGSSL_NO_CXX)
  
  #endif
  
  #define SSL_R_APP_DATA_IN_HANDSHAKE 100
  #define SSL_R_ATTEMPT_TO_REUSE_SESSION_IN_DIFFERENT_CONTEXT 101
  #define SSL_R_BAD_ALERT 102
  #define SSL_R_BAD_CHANGE_CIPHER_SPEC 103
  #define SSL_R_BAD_DATA_RETURNED_BY_CALLBACK 104
  #define SSL_R_BAD_DH_P_LENGTH 105
  #define SSL_R_BAD_DIGEST_LENGTH 106
  #define SSL_R_BAD_ECC_CERT 107
  #define SSL_R_BAD_ECPOINT 108
  #define SSL_R_BAD_HANDSHAKE_RECORD 109
  #define SSL_R_BAD_HELLO_REQUEST 110
  #define SSL_R_BAD_LENGTH 111
  #define SSL_R_BAD_PACKET_LENGTH 112
  #define SSL_R_BAD_RSA_ENCRYPT 113
  #define SSL_R_BAD_SIGNATURE 114
  #define SSL_R_BAD_SRTP_MKI_VALUE 115
  #define SSL_R_BAD_SRTP_PROTECTION_PROFILE_LIST 116
  #define SSL_R_BAD_SSL_FILETYPE 117
  #define SSL_R_BAD_WRITE_RETRY 118
  #define SSL_R_BIO_NOT_SET 119
  #define SSL_R_BN_LIB 120
  #define SSL_R_BUFFER_TOO_SMALL 121
  #define SSL_R_CA_DN_LENGTH_MISMATCH 122
  #define SSL_R_CA_DN_TOO_LONG 123
  #define SSL_R_CCS_RECEIVED_EARLY 124
  #define SSL_R_CERTIFICATE_VERIFY_FAILED 125
  #define SSL_R_CERT_CB_ERROR 126
  #define SSL_R_CERT_LENGTH_MISMATCH 127
  #define SSL_R_CHANNEL_ID_NOT_P256 128
  #define SSL_R_CHANNEL_ID_SIGNATURE_INVALID 129
  #define SSL_R_CIPHER_OR_HASH_UNAVAILABLE 130
  #define SSL_R_CLIENTHELLO_PARSE_FAILED 131
  #define SSL_R_CLIENTHELLO_TLSEXT 132
  #define SSL_R_CONNECTION_REJECTED 133
  #define SSL_R_CONNECTION_TYPE_NOT_SET 134
  #define SSL_R_CUSTOM_EXTENSION_ERROR 135
  #define SSL_R_DATA_LENGTH_TOO_LONG 136
  #define SSL_R_DECODE_ERROR 137
  #define SSL_R_DECRYPTION_FAILED 138
  #define SSL_R_DECRYPTION_FAILED_OR_BAD_RECORD_MAC 139
  #define SSL_R_DH_PUBLIC_VALUE_LENGTH_IS_WRONG 140
  #define SSL_R_DH_P_TOO_LONG 141
  #define SSL_R_DIGEST_CHECK_FAILED 142
  #define SSL_R_DTLS_MESSAGE_TOO_BIG 143
  #define SSL_R_ECC_CERT_NOT_FOR_SIGNING 144
  #define SSL_R_EMS_STATE_INCONSISTENT 145
  #define SSL_R_ENCRYPTED_LENGTH_TOO_LONG 146
  #define SSL_R_ERROR_ADDING_EXTENSION 147
  #define SSL_R_ERROR_IN_RECEIVED_CIPHER_LIST 148
  #define SSL_R_ERROR_PARSING_EXTENSION 149
  #define SSL_R_EXCESSIVE_MESSAGE_SIZE 150
  #define SSL_R_EXTRA_DATA_IN_MESSAGE 151
  #define SSL_R_FRAGMENT_MISMATCH 152
  #define SSL_R_GOT_NEXT_PROTO_WITHOUT_EXTENSION 153
  #define SSL_R_HANDSHAKE_FAILURE_ON_CLIENT_HELLO 154
  #define SSL_R_HTTPS_PROXY_REQUEST 155
  #define SSL_R_HTTP_REQUEST 156
  #define SSL_R_INAPPROPRIATE_FALLBACK 157
  #define SSL_R_INVALID_COMMAND 158
  #define SSL_R_INVALID_MESSAGE 159
  #define SSL_R_INVALID_SSL_SESSION 160
  #define SSL_R_INVALID_TICKET_KEYS_LENGTH 161
  #define SSL_R_LENGTH_MISMATCH 162
  #define SSL_R_MISSING_EXTENSION 164
  #define SSL_R_MISSING_RSA_CERTIFICATE 165
  #define SSL_R_MISSING_TMP_DH_KEY 166
  #define SSL_R_MISSING_TMP_ECDH_KEY 167
  #define SSL_R_MIXED_SPECIAL_OPERATOR_WITH_GROUPS 168
  #define SSL_R_MTU_TOO_SMALL 169
  #define SSL_R_NEGOTIATED_BOTH_NPN_AND_ALPN 170
  #define SSL_R_NESTED_GROUP 171
  #define SSL_R_NO_CERTIFICATES_RETURNED 172
  #define SSL_R_NO_CERTIFICATE_ASSIGNED 173
  #define SSL_R_NO_CERTIFICATE_SET 174
  #define SSL_R_NO_CIPHERS_AVAILABLE 175
  #define SSL_R_NO_CIPHERS_PASSED 176
  #define SSL_R_NO_CIPHER_MATCH 177
  #define SSL_R_NO_COMPRESSION_SPECIFIED 178
  #define SSL_R_NO_METHOD_SPECIFIED 179
  #define SSL_R_NO_P256_SUPPORT 180
  #define SSL_R_NO_PRIVATE_KEY_ASSIGNED 181
  #define SSL_R_NO_RENEGOTIATION 182
  #define SSL_R_NO_REQUIRED_DIGEST 183
  #define SSL_R_NO_SHARED_CIPHER 184
  #define SSL_R_NULL_SSL_CTX 185
  #define SSL_R_NULL_SSL_METHOD_PASSED 186
  #define SSL_R_OLD_SESSION_CIPHER_NOT_RETURNED 187
  #define SSL_R_OLD_SESSION_VERSION_NOT_RETURNED 188
  #define SSL_R_OUTPUT_ALIASES_INPUT 189
  #define SSL_R_PARSE_TLSEXT 190
  #define SSL_R_PATH_TOO_LONG 191
  #define SSL_R_PEER_DID_NOT_RETURN_A_CERTIFICATE 192
  #define SSL_R_PEER_ERROR_UNSUPPORTED_CERTIFICATE_TYPE 193
  #define SSL_R_PROTOCOL_IS_SHUTDOWN 194
  #define SSL_R_PSK_IDENTITY_NOT_FOUND 195
  #define SSL_R_PSK_NO_CLIENT_CB 196
  #define SSL_R_PSK_NO_SERVER_CB 197
  #define SSL_R_READ_TIMEOUT_EXPIRED 198
  #define SSL_R_RECORD_LENGTH_MISMATCH 199
  #define SSL_R_RECORD_TOO_LARGE 200
  #define SSL_R_RENEGOTIATION_ENCODING_ERR 201
  #define SSL_R_RENEGOTIATION_MISMATCH 202
  #define SSL_R_REQUIRED_CIPHER_MISSING 203
  #define SSL_R_RESUMED_EMS_SESSION_WITHOUT_EMS_EXTENSION 204
  #define SSL_R_RESUMED_NON_EMS_SESSION_WITH_EMS_EXTENSION 205
  #define SSL_R_SCSV_RECEIVED_WHEN_RENEGOTIATING 206
  #define SSL_R_SERVERHELLO_TLSEXT 207
  #define SSL_R_SESSION_ID_CONTEXT_UNINITIALIZED 208
  #define SSL_R_SESSION_MAY_NOT_BE_CREATED 209
  #define SSL_R_SIGNATURE_ALGORITHMS_EXTENSION_SENT_BY_SERVER 210
  #define SSL_R_SRTP_COULD_NOT_ALLOCATE_PROFILES 211
  #define SSL_R_SRTP_UNKNOWN_PROTECTION_PROFILE 212
  #define SSL_R_SSL3_EXT_INVALID_SERVERNAME 213
  #define SSL_R_SSL_CTX_HAS_NO_DEFAULT_SSL_VERSION 214
  #define SSL_R_SSL_HANDSHAKE_FAILURE 215
  #define SSL_R_SSL_SESSION_ID_CONTEXT_TOO_LONG 216
  #define SSL_R_TLS_PEER_DID_NOT_RESPOND_WITH_CERTIFICATE_LIST 217
  #define SSL_R_TLS_RSA_ENCRYPTED_VALUE_LENGTH_IS_WRONG 218
  #define SSL_R_TOO_MANY_EMPTY_FRAGMENTS 219
  #define SSL_R_TOO_MANY_WARNING_ALERTS 220
  #define SSL_R_UNABLE_TO_FIND_ECDH_PARAMETERS 221
  #define SSL_R_UNEXPECTED_EXTENSION 222
  #define SSL_R_UNEXPECTED_MESSAGE 223
  #define SSL_R_UNEXPECTED_OPERATOR_IN_GROUP 224
  #define SSL_R_UNEXPECTED_RECORD 225
  #define SSL_R_UNINITIALIZED 226
  #define SSL_R_UNKNOWN_ALERT_TYPE 227
  #define SSL_R_UNKNOWN_CERTIFICATE_TYPE 228
  #define SSL_R_UNKNOWN_CIPHER_RETURNED 229
  #define SSL_R_UNKNOWN_CIPHER_TYPE 230
  #define SSL_R_UNKNOWN_DIGEST 231
  #define SSL_R_UNKNOWN_KEY_EXCHANGE_TYPE 232
  #define SSL_R_UNKNOWN_PROTOCOL 233
  #define SSL_R_UNKNOWN_SSL_VERSION 234
  #define SSL_R_UNKNOWN_STATE 235
  #define SSL_R_UNSAFE_LEGACY_RENEGOTIATION_DISABLED 236
  #define SSL_R_UNSUPPORTED_CIPHER 237
  #define SSL_R_UNSUPPORTED_COMPRESSION_ALGORITHM 238
  #define SSL_R_UNSUPPORTED_ELLIPTIC_CURVE 239
  #define SSL_R_UNSUPPORTED_PROTOCOL 240
  #define SSL_R_WRONG_CERTIFICATE_TYPE 241
  #define SSL_R_WRONG_CIPHER_RETURNED 242
  #define SSL_R_WRONG_CURVE 243
  #define SSL_R_WRONG_MESSAGE_TYPE 244
  #define SSL_R_WRONG_SIGNATURE_TYPE 245
  #define SSL_R_WRONG_SSL_VERSION 246
  #define SSL_R_WRONG_VERSION_NUMBER 247
  #define SSL_R_X509_LIB 248
  #define SSL_R_X509_VERIFICATION_SETUP_PROBLEMS 249
  #define SSL_R_SHUTDOWN_WHILE_IN_INIT 250
  #define SSL_R_INVALID_OUTER_RECORD_TYPE 251
  #define SSL_R_UNSUPPORTED_PROTOCOL_FOR_CUSTOM_KEY 252
  #define SSL_R_NO_COMMON_SIGNATURE_ALGORITHMS 253
  #define SSL_R_DOWNGRADE_DETECTED 254
  #define SSL_R_BUFFERED_MESSAGES_ON_CIPHER_CHANGE 255
  #define SSL_R_INVALID_COMPRESSION_LIST 256
  #define SSL_R_DUPLICATE_EXTENSION 257
  #define SSL_R_MISSING_KEY_SHARE 258
  #define SSL_R_INVALID_ALPN_PROTOCOL 259
  #define SSL_R_TOO_MANY_KEY_UPDATES 260
  #define SSL_R_BLOCK_CIPHER_PAD_IS_WRONG 261
  #define SSL_R_NO_CIPHERS_SPECIFIED 262
  #define SSL_R_RENEGOTIATION_EMS_MISMATCH 263
  #define SSL_R_DUPLICATE_KEY_SHARE 264
  #define SSL_R_NO_GROUPS_SPECIFIED 265
  #define SSL_R_NO_SHARED_GROUP 266
  #define SSL_R_PRE_SHARED_KEY_MUST_BE_LAST 267
  #define SSL_R_OLD_SESSION_PRF_HASH_MISMATCH 268
  #define SSL_R_INVALID_SCT_LIST 269
  #define SSL_R_TOO_MUCH_SKIPPED_EARLY_DATA 270
  #define SSL_R_PSK_IDENTITY_BINDER_COUNT_MISMATCH 271
  #define SSL_R_CANNOT_PARSE_LEAF_CERT 272
  #define SSL_R_SERVER_CERT_CHANGED 273
  #define SSL_R_CERTIFICATE_AND_PRIVATE_KEY_MISMATCH 274
  #define SSL_R_CANNOT_HAVE_BOTH_PRIVKEY_AND_METHOD 275
  #define SSL_R_TICKET_ENCRYPTION_FAILED 276
  #define SSL_R_ALPN_MISMATCH_ON_EARLY_DATA 277
  #define SSL_R_WRONG_VERSION_ON_EARLY_DATA 278
  #define SSL_R_UNEXPECTED_EXTENSION_ON_EARLY_DATA 279
  #define SSL_R_NO_SUPPORTED_VERSIONS_ENABLED 280
  #define SSL_R_APPLICATION_DATA_INSTEAD_OF_HANDSHAKE 281
  #define SSL_R_EMPTY_HELLO_RETRY_REQUEST 282
  #define SSL_R_EARLY_DATA_NOT_IN_USE 283
  #define SSL_R_HANDSHAKE_NOT_COMPLETE 284
  #define SSL_R_NEGOTIATED_TB_WITHOUT_EMS_OR_RI 285
  #define SSL_R_SERVER_ECHOED_INVALID_SESSION_ID 286
  #define SSL_R_PRIVATE_KEY_OPERATION_FAILED 287
  #define SSL_R_SSLV3_ALERT_CLOSE_NOTIFY 1000
  #define SSL_R_SSLV3_ALERT_UNEXPECTED_MESSAGE 1010
  #define SSL_R_SSLV3_ALERT_BAD_RECORD_MAC 1020
  #define SSL_R_TLSV1_ALERT_DECRYPTION_FAILED 1021
  #define SSL_R_TLSV1_ALERT_RECORD_OVERFLOW 1022
  #define SSL_R_SSLV3_ALERT_DECOMPRESSION_FAILURE 1030
  #define SSL_R_SSLV3_ALERT_HANDSHAKE_FAILURE 1040
  #define SSL_R_SSLV3_ALERT_NO_CERTIFICATE 1041
  #define SSL_R_SSLV3_ALERT_BAD_CERTIFICATE 1042
  #define SSL_R_SSLV3_ALERT_UNSUPPORTED_CERTIFICATE 1043
  #define SSL_R_SSLV3_ALERT_CERTIFICATE_REVOKED 1044
  #define SSL_R_SSLV3_ALERT_CERTIFICATE_EXPIRED 1045
  #define SSL_R_SSLV3_ALERT_CERTIFICATE_UNKNOWN 1046
  #define SSL_R_SSLV3_ALERT_ILLEGAL_PARAMETER 1047
  #define SSL_R_TLSV1_ALERT_UNKNOWN_CA 1048
  #define SSL_R_TLSV1_ALERT_ACCESS_DENIED 1049
  #define SSL_R_TLSV1_ALERT_DECODE_ERROR 1050
  #define SSL_R_TLSV1_ALERT_DECRYPT_ERROR 1051
  #define SSL_R_TLSV1_ALERT_EXPORT_RESTRICTION 1060
  #define SSL_R_TLSV1_ALERT_PROTOCOL_VERSION 1070
  #define SSL_R_TLSV1_ALERT_INSUFFICIENT_SECURITY 1071
  #define SSL_R_TLSV1_ALERT_INTERNAL_ERROR 1080
  #define SSL_R_TLSV1_ALERT_INAPPROPRIATE_FALLBACK 1086
  #define SSL_R_TLSV1_ALERT_USER_CANCELLED 1090
  #define SSL_R_TLSV1_ALERT_NO_RENEGOTIATION 1100
  #define SSL_R_TLSV1_UNSUPPORTED_EXTENSION 1110
  #define SSL_R_TLSV1_CERTIFICATE_UNOBTAINABLE 1111
  #define SSL_R_TLSV1_UNRECOGNIZED_NAME 1112
  #define SSL_R_TLSV1_BAD_CERTIFICATE_STATUS_RESPONSE 1113
  #define SSL_R_TLSV1_BAD_CERTIFICATE_HASH_VALUE 1114
  #define SSL_R_TLSV1_UNKNOWN_PSK_IDENTITY 1115
  #define SSL_R_TLSV1_CERTIFICATE_REQUIRED 1116
  #define SSL_R_TOO_MUCH_READ_EARLY_DATA 1117
  
  #endif  // OPENSSL_HEADER_SSL_H
  