text: /*
   * DTLS implementation written by Nagendra Modadugu
   * (nagendra@cs.stanford.edu) for the OpenSSL project 2005. 
   */
  /* ====================================================================
   * Copyright (c) 1998-2005 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 (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.] */
  
  #include <openssl/ssl.h>
  
  #include <assert.h>
  #include <limits.h>
  #include <string.h>
  
  #include <openssl/buf.h>
  #include <openssl/err.h>
  #include <openssl/evp.h>
  #include <openssl/mem.h>
  #include <openssl/rand.h>
  #include <openssl/type_check.h>
  
  #include "../crypto/internal.h"
  #include "internal.h"
  
  
  /* TODO(davidben): 28 comes from the size of IP + UDP header. Is this reasonable
   * for these values? Notably, why is kMinMTU a function of the transport
   * protocol's overhead rather than, say, what's needed to hold a minimally-sized
   * handshake fragment plus protocol overhead. */
  
  /* kMinMTU is the minimum acceptable MTU value. */
  static const unsigned int kMinMTU = 256 - 28;
  
  /* kDefaultMTU is the default MTU value to use if neither the user nor
   * the underlying BIO supplies one. */
  static const unsigned int kDefaultMTU = 1500 - 28;
  
  
  /* Receiving handshake messages. */
  
  static void dtls1_hm_fragment_free(hm_fragment *frag) {
    if (frag == NULL) {
      return;
    }
    OPENSSL_free(frag->data);
    OPENSSL_free(frag->reassembly);
    OPENSSL_free(frag);
  }
  
  static hm_fragment *dtls1_hm_fragment_new(const struct hm_header_st *msg_hdr) {
    hm_fragment *frag = OPENSSL_malloc(sizeof(hm_fragment));
    if (frag == NULL) {
      OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
      return NULL;
    }
    OPENSSL_memset(frag, 0, sizeof(hm_fragment));
    frag->type = msg_hdr->type;
    frag->seq = msg_hdr->seq;
    frag->msg_len = msg_hdr->msg_len;
  
    /* Allocate space for the reassembled message and fill in the header. */
    frag->data = OPENSSL_malloc(DTLS1_HM_HEADER_LENGTH + msg_hdr->msg_len);
    if (frag->data == NULL) {
      OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
      goto err;
    }
  
    CBB cbb;
    if (!CBB_init_fixed(&cbb, frag->data, DTLS1_HM_HEADER_LENGTH) ||
        !CBB_add_u8(&cbb, msg_hdr->type) ||
        !CBB_add_u24(&cbb, msg_hdr->msg_len) ||
        !CBB_add_u16(&cbb, msg_hdr->seq) ||
        !CBB_add_u24(&cbb, 0 /* frag_off */) ||
        !CBB_add_u24(&cbb, msg_hdr->msg_len) ||
        !CBB_finish(&cbb, NULL, NULL)) {
      CBB_cleanup(&cbb);
      OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
      goto err;
    }
  
    /* If the handshake message is empty, |frag->reassembly| is NULL. */
    if (msg_hdr->msg_len > 0) {
      /* Initialize reassembly bitmask. */
      if (msg_hdr->msg_len + 7 < msg_hdr->msg_len) {
        OPENSSL_PUT_ERROR(SSL, ERR_R_OVERFLOW);
        goto err;
      }
      size_t bitmask_len = (msg_hdr->msg_len + 7) / 8;
      frag->reassembly = OPENSSL_malloc(bitmask_len);
      if (frag->reassembly == NULL) {
        OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
        goto err;
      }
      OPENSSL_memset(frag->reassembly, 0, bitmask_len);
    }
  
    return frag;
  
  err:
    dtls1_hm_fragment_free(frag);
    return NULL;
  }
  
  /* bit_range returns a |uint8_t| with bits |start|, inclusive, to |end|,
   * exclusive, set. */
  static uint8_t bit_range(size_t start, size_t end) {
    return (uint8_t)(~((1u << start) - 1) & ((1u << end) - 1));
  }
  
  /* dtls1_hm_fragment_mark marks bytes |start|, inclusive, to |end|, exclusive,
   * as received in |frag|. If |frag| becomes complete, it clears
   * |frag->reassembly|. The range must be within the bounds of |frag|'s message
   * and |frag->reassembly| must not be NULL. */
  static void dtls1_hm_fragment_mark(hm_fragment *frag, size_t start,
                                     size_t end) {
    size_t msg_len = frag->msg_len;
  
    if (frag->reassembly == NULL || start > end || end > msg_len) {
      assert(0);
      return;
    }
    /* A zero-length message will never have a pending reassembly. */
    assert(msg_len > 0);
  
    if ((start >> 3) == (end >> 3)) {
      frag->reassembly[start >> 3] |= bit_range(start & 7, end & 7);
    } else {
      frag->reassembly[start >> 3] |= bit_range(start & 7, 8);
      for (size_t i = (start >> 3) + 1; i < (end >> 3); i++) {
        frag->reassembly[i] = 0xff;
      }
      if ((end & 7) != 0) {
        frag->reassembly[end >> 3] |= bit_range(0, end & 7);
      }
    }
  
    /* Check if the fragment is complete. */
    for (size_t i = 0; i < (msg_len >> 3); i++) {
      if (frag->reassembly[i] != 0xff) {
        return;
      }
    }
    if ((msg_len & 7) != 0 &&
        frag->reassembly[msg_len >> 3] != bit_range(0, msg_len & 7)) {
      return;
    }
  
    OPENSSL_free(frag->reassembly);
    frag->reassembly = NULL;
  }
  
  /* dtls1_is_current_message_complete returns one if the current handshake
   * message is complete and zero otherwise. */
  static int dtls1_is_current_message_complete(const SSL *ssl) {
    hm_fragment *frag = ssl->d1->incoming_messages[ssl->d1->handshake_read_seq %
                                                   SSL_MAX_HANDSHAKE_FLIGHT];
    return frag != NULL && frag->reassembly == NULL;
  }
  
  /* dtls1_get_incoming_message returns the incoming message corresponding to
   * |msg_hdr|. If none exists, it creates a new one and inserts it in the
   * queue. Otherwise, it checks |msg_hdr| is consistent with the existing one. It
   * returns NULL on failure. The caller does not take ownership of the result. */
  static hm_fragment *dtls1_get_incoming_message(
      SSL *ssl, const struct hm_header_st *msg_hdr) {
    if (msg_hdr->seq < ssl->d1->handshake_read_seq ||
        msg_hdr->seq - ssl->d1->handshake_read_seq >= SSL_MAX_HANDSHAKE_FLIGHT) {
      return NULL;
    }
  
    size_t idx = msg_hdr->seq % SSL_MAX_HANDSHAKE_FLIGHT;
    hm_fragment *frag = ssl->d1->incoming_messages[idx];
    if (frag != NULL) {
      assert(frag->seq == msg_hdr->seq);
      /* The new fragment must be compatible with the previous fragments from this
       * message. */
      if (frag->type != msg_hdr->type ||
          frag->msg_len != msg_hdr->msg_len) {
        OPENSSL_PUT_ERROR(SSL, SSL_R_FRAGMENT_MISMATCH);
        ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
        return NULL;
      }
      return frag;
    }
  
    /* This is the first fragment from this message. */
    frag = dtls1_hm_fragment_new(msg_hdr);
    if (frag == NULL) {
      return NULL;
    }
    ssl->d1->incoming_messages[idx] = frag;
    return frag;
  }
  
  /* dtls1_process_handshake_record reads a handshake record and processes it. It
   * returns one if the record was successfully processed and 0 or -1 on error. */
  static int dtls1_process_handshake_record(SSL *ssl) {
    SSL3_RECORD *rr = &ssl->s3->rrec;
  
  start:
    if (rr->length == 0) {
      int ret = dtls1_get_record(ssl);
      if (ret <= 0) {
        return ret;
      }
    }
  
    /* Cross-epoch records are discarded, but we may receive out-of-order
     * application data between ChangeCipherSpec and Finished or a
     * ChangeCipherSpec before the appropriate point in the handshake. Those must
     * be silently discarded.
     *
     * However, only allow the out-of-order records in the correct epoch.
     * Application data must come in the encrypted epoch, and ChangeCipherSpec in
     * the unencrypted epoch (we never renegotiate). Other cases fall through and
     * fail with a fatal error. */
    if ((rr->type == SSL3_RT_APPLICATION_DATA &&
         ssl->s3->aead_read_ctx != NULL) ||
        (rr->type == SSL3_RT_CHANGE_CIPHER_SPEC &&
         ssl->s3->aead_read_ctx == NULL)) {
      rr->length = 0;
      goto start;
    }
  
    if (rr->type != SSL3_RT_HANDSHAKE) {
      ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_UNEXPECTED_MESSAGE);
      OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_RECORD);
      return -1;
    }
  
    CBS cbs;
    CBS_init(&cbs, rr->data, rr->length);
  
    while (CBS_len(&cbs) > 0) {
      /* Read a handshake fragment. */
      struct hm_header_st msg_hdr;
      CBS body;
      if (!dtls1_parse_fragment(&cbs, &msg_hdr, &body)) {
        OPENSSL_PUT_ERROR(SSL, SSL_R_BAD_HANDSHAKE_RECORD);
        ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
        return -1;
      }
  
      const size_t frag_off = msg_hdr.frag_off;
      const size_t frag_len = msg_hdr.frag_len;
      const size_t msg_len = msg_hdr.msg_len;
      if (frag_off > msg_len || frag_off + frag_len < frag_off ||
          frag_off + frag_len > msg_len ||
          msg_len > ssl_max_handshake_message_len(ssl)) {
        OPENSSL_PUT_ERROR(SSL, SSL_R_EXCESSIVE_MESSAGE_SIZE);
        ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
        return -1;
      }
  
      /* The encrypted epoch in DTLS has only one handshake message. */
      if (ssl->d1->r_epoch == 1 && msg_hdr.seq != ssl->d1->handshake_read_seq) {
        OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_RECORD);
        ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_UNEXPECTED_MESSAGE);
        return -1;
      }
  
      if (msg_hdr.seq < ssl->d1->handshake_read_seq ||
          msg_hdr.seq >
              (unsigned)ssl->d1->handshake_read_seq + SSL_MAX_HANDSHAKE_FLIGHT) {
        /* Ignore fragments from the past, or ones too far in the future. */
        continue;
      }
  
      hm_fragment *frag = dtls1_get_incoming_message(ssl, &msg_hdr);
      if (frag == NULL) {
        return -1;
      }
      assert(frag->msg_len == msg_len);
  
      if (frag->reassembly == NULL) {
        /* The message is already assembled. */
        continue;
      }
      assert(msg_len > 0);
  
      /* Copy the body into the fragment. */
      OPENSSL_memcpy(frag->data + DTLS1_HM_HEADER_LENGTH + frag_off,
                     CBS_data(&body), CBS_len(&body));
      dtls1_hm_fragment_mark(frag, frag_off, frag_off + frag_len);
    }
  
    rr->length = 0;
    ssl_read_buffer_discard(ssl);
    return 1;
  }
  
  int dtls1_get_message(SSL *ssl) {
    if (ssl->s3->tmp.reuse_message) {
      /* There must be a current message. */
      assert(ssl->init_msg != NULL);
      ssl->s3->tmp.reuse_message = 0;
    } else {
      dtls1_release_current_message(ssl, 0 /* don't free buffer */);
    }
  
    /* Process handshake records until the current message is ready. */
    while (!dtls1_is_current_message_complete(ssl)) {
      int ret = dtls1_process_handshake_record(ssl);
      if (ret <= 0) {
        return ret;
      }
    }
  
    hm_fragment *frag = ssl->d1->incoming_messages[ssl->d1->handshake_read_seq %
                                                   SSL_MAX_HANDSHAKE_FLIGHT];
    assert(frag != NULL);
    assert(frag->reassembly == NULL);
    assert(ssl->d1->handshake_read_seq == frag->seq);
  
    /* TODO(davidben): This function has a lot of implicit outputs. Simplify the
     * |ssl_get_message| API. */
    ssl->s3->tmp.message_type = frag->type;
    ssl->init_msg = frag->data + DTLS1_HM_HEADER_LENGTH;
    ssl->init_num = frag->msg_len;
  
    ssl_do_msg_callback(ssl, 0 /* read */, SSL3_RT_HANDSHAKE, frag->data,
                        ssl->init_num + DTLS1_HM_HEADER_LENGTH);
    return 1;
  }
  
  void dtls1_get_current_message(const SSL *ssl, CBS *out) {
    assert(dtls1_is_current_message_complete(ssl));
  
    hm_fragment *frag = ssl->d1->incoming_messages[ssl->d1->handshake_read_seq %
                                                   SSL_MAX_HANDSHAKE_FLIGHT];
    CBS_init(out, frag->data, DTLS1_HM_HEADER_LENGTH + frag->msg_len);
  }
  
  void dtls1_release_current_message(SSL *ssl, int free_buffer) {
    if (ssl->init_msg == NULL) {
      return;
    }
  
    assert(dtls1_is_current_message_complete(ssl));
    size_t index = ssl->d1->handshake_read_seq % SSL_MAX_HANDSHAKE_FLIGHT;
    dtls1_hm_fragment_free(ssl->d1->incoming_messages[index]);
    ssl->d1->incoming_messages[index] = NULL;
    ssl->d1->handshake_read_seq++;
  
    ssl->init_msg = NULL;
    ssl->init_num = 0;
  }
  
  void dtls_clear_incoming_messages(SSL *ssl) {
    for (size_t i = 0; i < SSL_MAX_HANDSHAKE_FLIGHT; i++) {
      dtls1_hm_fragment_free(ssl->d1->incoming_messages[i]);
      ssl->d1->incoming_messages[i] = NULL;
    }
  }
  
  int dtls_has_incoming_messages(const SSL *ssl) {
    size_t current = ssl->d1->handshake_read_seq % SSL_MAX_HANDSHAKE_FLIGHT;
    for (size_t i = 0; i < SSL_MAX_HANDSHAKE_FLIGHT; i++) {
      /* Skip the current message. */
      if (ssl->init_msg != NULL && i == current) {
        assert(dtls1_is_current_message_complete(ssl));
        continue;
      }
      if (ssl->d1->incoming_messages[i] != NULL) {
        return 1;
      }
    }
    return 0;
  }
  
  int dtls1_parse_fragment(CBS *cbs, struct hm_header_st *out_hdr,
                           CBS *out_body) {
    OPENSSL_memset(out_hdr, 0x00, sizeof(struct hm_header_st));
  
    if (!CBS_get_u8(cbs, &out_hdr->type) ||
        !CBS_get_u24(cbs, &out_hdr->msg_len) ||
        !CBS_get_u16(cbs, &out_hdr->seq) ||
        !CBS_get_u24(cbs, &out_hdr->frag_off) ||
        !CBS_get_u24(cbs, &out_hdr->frag_len) ||
        !CBS_get_bytes(cbs, out_body, out_hdr->frag_len)) {
      return 0;
    }
  
    return 1;
  }
  
  
  /* Sending handshake messages. */
  
  void dtls_clear_outgoing_messages(SSL *ssl) {
    for (size_t i = 0; i < ssl->d1->outgoing_messages_len; i++) {
      OPENSSL_free(ssl->d1->outgoing_messages[i].data);
      ssl->d1->outgoing_messages[i].data = NULL;
    }
    ssl->d1->outgoing_messages_len = 0;
    ssl->d1->outgoing_written = 0;
    ssl->d1->outgoing_offset = 0;
  }
  
  int dtls1_init_message(SSL *ssl, CBB *cbb, CBB *body, uint8_t type) {
    /* Pick a modest size hint to save most of the |realloc| calls. */
    if (!CBB_init(cbb, 64) ||
        !CBB_add_u8(cbb, type) ||
        !CBB_add_u24(cbb, 0 /* length (filled in later) */) ||
        !CBB_add_u16(cbb, ssl->d1->handshake_write_seq) ||
        !CBB_add_u24(cbb, 0 /* offset */) ||
        !CBB_add_u24_length_prefixed(cbb, body)) {
      return 0;
    }
  
    return 1;
  }
  
  int dtls1_finish_message(SSL *ssl, CBB *cbb, uint8_t **out_msg,
                           size_t *out_len) {
    *out_msg = NULL;
    if (!CBB_finish(cbb, out_msg, out_len) ||
        *out_len < DTLS1_HM_HEADER_LENGTH) {
      OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
      OPENSSL_free(*out_msg);
      return 0;
    }
  
    /* Fix up the header. Copy the fragment length into the total message
     * length. */
    OPENSSL_memcpy(*out_msg + 1, *out_msg + DTLS1_HM_HEADER_LENGTH - 3, 3);
    return 1;
  }
  
  /* add_outgoing adds a new handshake message or ChangeCipherSpec to the current
   * outgoing flight. It returns one on success and zero on error. In both cases,
   * it takes ownership of |data| and releases it with |OPENSSL_free| when
   * done. */
  static int add_outgoing(SSL *ssl, int is_ccs, uint8_t *data, size_t len) {
    OPENSSL_COMPILE_ASSERT(SSL_MAX_HANDSHAKE_FLIGHT <
                               (1 << 8 * sizeof(ssl->d1->outgoing_messages_len)),
                           outgoing_messages_len_is_too_small);
    if (ssl->d1->outgoing_messages_len >= SSL_MAX_HANDSHAKE_FLIGHT) {
      assert(0);
      OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
      OPENSSL_free(data);
      return 0;
    }
  
    if (!is_ccs) {
      /* TODO(svaldez): Move this up a layer to fix abstraction for SSL_TRANSCRIPT
       * on hs. */
      if (ssl->s3->hs != NULL &&
          !SSL_TRANSCRIPT_update(&ssl->s3->hs->transcript, data, len)) {
        OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
        OPENSSL_free(data);
        return 0;
      }
      ssl->d1->handshake_write_seq++;
    }
  
    DTLS_OUTGOING_MESSAGE *msg =
        &ssl->d1->outgoing_messages[ssl->d1->outgoing_messages_len];
    msg->data = data;
    msg->len = len;
    msg->epoch = ssl->d1->w_epoch;
    msg->is_ccs = is_ccs;
  
    ssl->d1->outgoing_messages_len++;
    return 1;
  }
  
  int dtls1_add_message(SSL *ssl, uint8_t *data, size_t len) {
    return add_outgoing(ssl, 0 /* handshake */, data, len);
  }
  
  int dtls1_add_change_cipher_spec(SSL *ssl) {
    return add_outgoing(ssl, 1 /* ChangeCipherSpec */, NULL, 0);
  }
  
  int dtls1_add_alert(SSL *ssl, uint8_t level, uint8_t desc) {
    /* The |add_alert| path is only used for warning alerts for now, which DTLS
     * never sends. This will be implemented later once closure alerts are
     * converted. */
    assert(0);
    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
    return 0;
  }
  
  /* dtls1_update_mtu updates the current MTU from the BIO, ensuring it is above
   * the minimum. */
  static void dtls1_update_mtu(SSL *ssl) {
    /* TODO(davidben): No consumer implements |BIO_CTRL_DGRAM_SET_MTU| and the
     * only |BIO_CTRL_DGRAM_QUERY_MTU| implementation could use
     * |SSL_set_mtu|. Does this need to be so complex?  */
    if (ssl->d1->mtu < dtls1_min_mtu() &&
        !(SSL_get_options(ssl) & SSL_OP_NO_QUERY_MTU)) {
      long mtu = BIO_ctrl(ssl->wbio, BIO_CTRL_DGRAM_QUERY_MTU, 0, NULL);
      if (mtu >= 0 && mtu <= (1 << 30) && (unsigned)mtu >= dtls1_min_mtu()) {
        ssl->d1->mtu = (unsigned)mtu;
      } else {
        ssl->d1->mtu = kDefaultMTU;
        BIO_ctrl(ssl->wbio, BIO_CTRL_DGRAM_SET_MTU, ssl->d1->mtu, NULL);
      }
    }
  
    /* The MTU should be above the minimum now. */
    assert(ssl->d1->mtu >= dtls1_min_mtu());
  }
  
  enum seal_result_t {
    seal_error,
    seal_no_progress,
    seal_partial,
    seal_success,
  };
  
  /* seal_next_message seals |msg|, which must be the next message, to |out|. If
   * progress was made, it returns |seal_partial| or |seal_success| and sets
   * |*out_len| to the number of bytes written. */
  static enum seal_result_t seal_next_message(SSL *ssl, uint8_t *out,
                                              size_t *out_len, size_t max_out,
                                              const DTLS_OUTGOING_MESSAGE *msg) {
    assert(ssl->d1->outgoing_written < ssl->d1->outgoing_messages_len);
    assert(msg == &ssl->d1->outgoing_messages[ssl->d1->outgoing_written]);
  
    /* DTLS renegotiation is unsupported, so only epochs 0 (NULL cipher) and 1
     * (negotiated cipher) exist. */
    assert(ssl->d1->w_epoch == 0 || ssl->d1->w_epoch == 1);
    assert(msg->epoch <= ssl->d1->w_epoch);
    enum dtls1_use_epoch_t use_epoch = dtls1_use_current_epoch;
    if (ssl->d1->w_epoch == 1 && msg->epoch == 0) {
      use_epoch = dtls1_use_previous_epoch;
    }
    size_t overhead = dtls_max_seal_overhead(ssl, use_epoch);
    size_t prefix = dtls_seal_prefix_len(ssl, use_epoch);
  
    if (msg->is_ccs) {
      /* Check there is room for the ChangeCipherSpec. */
      static const uint8_t kChangeCipherSpec[1] = {SSL3_MT_CCS};
      if (max_out < sizeof(kChangeCipherSpec) + overhead) {
        return seal_no_progress;
      }
  
      if (!dtls_seal_record(ssl, out, out_len, max_out,
                            SSL3_RT_CHANGE_CIPHER_SPEC, kChangeCipherSpec,
                            sizeof(kChangeCipherSpec), use_epoch)) {
        return seal_error;
      }
  
      ssl_do_msg_callback(ssl, 1 /* write */, SSL3_RT_CHANGE_CIPHER_SPEC,
                          kChangeCipherSpec, sizeof(kChangeCipherSpec));
      return seal_success;
    }
  
    /* DTLS messages are serialized as a single fragment in |msg|. */
    CBS cbs, body;
    struct hm_header_st hdr;
    CBS_init(&cbs, msg->data, msg->len);
    if (!dtls1_parse_fragment(&cbs, &hdr, &body) ||
        hdr.frag_off != 0 ||
        hdr.frag_len != CBS_len(&body) ||
        hdr.msg_len != CBS_len(&body) ||
        !CBS_skip(&body, ssl->d1->outgoing_offset) ||
        CBS_len(&cbs) != 0) {
      OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
      return seal_error;
    }
  
    /* Determine how much progress can be made. */
    if (max_out < DTLS1_HM_HEADER_LENGTH + 1 + overhead || max_out < prefix) {
      return seal_no_progress;
    }
    size_t todo = CBS_len(&body);
    if (todo > max_out - DTLS1_HM_HEADER_LENGTH - overhead) {
      todo = max_out - DTLS1_HM_HEADER_LENGTH - overhead;
    }
  
    /* Assemble a fragment, to be sealed in-place. */
    CBB cbb;
    uint8_t *frag = out + prefix;
    size_t max_frag = max_out - prefix, frag_len;
    if (!CBB_init_fixed(&cbb, frag, max_frag) ||
        !CBB_add_u8(&cbb, hdr.type) ||
        !CBB_add_u24(&cbb, hdr.msg_len) ||
        !CBB_add_u16(&cbb, hdr.seq) ||
        !CBB_add_u24(&cbb, ssl->d1->outgoing_offset) ||
        !CBB_add_u24(&cbb, todo) ||
        !CBB_add_bytes(&cbb, CBS_data(&body), todo) ||
        !CBB_finish(&cbb, NULL, &frag_len)) {
      CBB_cleanup(&cbb);
      OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
      return seal_error;
    }
  
    ssl_do_msg_callback(ssl, 1 /* write */, SSL3_RT_HANDSHAKE, frag, frag_len);
  
    if (!dtls_seal_record(ssl, out, out_len, max_out, SSL3_RT_HANDSHAKE,
                          out + prefix, frag_len, use_epoch)) {
      return seal_error;
    }
  
    if (todo == CBS_len(&body)) {
      /* The next message is complete. */
      ssl->d1->outgoing_offset = 0;
      return seal_success;
    }
  
    ssl->d1->outgoing_offset += todo;
    return seal_partial;
  }
  
  /* seal_next_packet writes as much of the next flight as possible to |out| and
   * advances |ssl->d1->outgoing_written| and |ssl->d1->outgoing_offset| as
   * appropriate. */
  static int seal_next_packet(SSL *ssl, uint8_t *out, size_t *out_len,
                              size_t max_out) {
    int made_progress = 0;
    size_t total = 0;
    assert(ssl->d1->outgoing_written < ssl->d1->outgoing_messages_len);
    for (; ssl->d1->outgoing_written < ssl->d1->outgoing_messages_len;
         ssl->d1->outgoing_written++) {
      const DTLS_OUTGOING_MESSAGE *msg =
          &ssl->d1->outgoing_messages[ssl->d1->outgoing_written];
      size_t len;
      enum seal_result_t ret = seal_next_message(ssl, out, &len, max_out, msg);
      switch (ret) {
        case seal_error:
          return 0;
  
        case seal_no_progress:
          goto packet_full;
  
        case seal_partial:
        case seal_success:
          out += len;
          max_out -= len;
          total += len;
          made_progress = 1;
  
          if (ret == seal_partial) {
            goto packet_full;
          }
          break;
      }
    }
  
  packet_full:
    /* The MTU was too small to make any progress. */
    if (!made_progress) {
      OPENSSL_PUT_ERROR(SSL, SSL_R_MTU_TOO_SMALL);
      return 0;
    }
  
    *out_len = total;
    return 1;
  }
  
  int dtls1_flush_flight(SSL *ssl) {
    dtls1_update_mtu(ssl);
  
    int ret = -1;
    uint8_t *packet = OPENSSL_malloc(ssl->d1->mtu);
    if (packet == NULL) {
      OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
      goto err;
    }
  
    while (ssl->d1->outgoing_written < ssl->d1->outgoing_messages_len) {
      uint8_t old_written = ssl->d1->outgoing_written;
      uint32_t old_offset = ssl->d1->outgoing_offset;
  
      size_t packet_len;
      if (!seal_next_packet(ssl, packet, &packet_len, ssl->d1->mtu)) {
        goto err;
      }
  
      int bio_ret = BIO_write(ssl->wbio, packet, packet_len);
      if (bio_ret <= 0) {
        /* Retry this packet the next time around. */
        ssl->d1->outgoing_written = old_written;
        ssl->d1->outgoing_offset = old_offset;
        ssl->rwstate = SSL_WRITING;
        ret = bio_ret;
        goto err;
      }
    }
  
    if (BIO_flush(ssl->wbio) <= 0) {
      ssl->rwstate = SSL_WRITING;
      goto err;
    }
  
    ret = 1;
  
  err:
    OPENSSL_free(packet);
    return ret;
  }
  
  int dtls1_retransmit_outgoing_messages(SSL *ssl) {
    /* Rewind to the start of the flight and write it again.
     *
     * TODO(davidben): This does not allow retransmits to be resumed on
     * non-blocking write. */
    ssl->d1->outgoing_written = 0;
    ssl->d1->outgoing_offset = 0;
  
    return dtls1_flush_flight(ssl);
  }
  
  unsigned int dtls1_min_mtu(void) {
    return kMinMTU;
  }
  