text: /* Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  /**
   * @file  http_protocol.h
   * @brief HTTP protocol handling
   *
   * @defgroup APACHE_CORE_PROTO HTTP Protocol Handling
   * @ingroup  APACHE_CORE
   * @{
   */
  
  #ifndef APACHE_HTTP_PROTOCOL_H
  #define APACHE_HTTP_PROTOCOL_H
  
  #include "httpd.h"
  #include "apr_portable.h"
  #include "apr_mmap.h"
  #include "apr_buckets.h"
  #include "util_filter.h"
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  /**
   * This hook allows modules to insert filters for the current error response
   * @param r the current request
   * @ingroup hooks
   */
  AP_DECLARE_HOOK(void,insert_error_filter,(request_rec *r))
  
  /** This is an optimization.  We keep a record of the filter_rec that
   * stores the old_write filter, so that we can avoid strcmp's later.
   */
  AP_DECLARE_DATA extern ap_filter_rec_t *ap_old_write_func;
  
  /*
   * Prototypes for routines which either talk directly back to the user,
   * or control the ones that eventually do.
   */
  
  /**
   * Read a request and fill in the fields.
   * @param c The current connection
   * @return The new request_rec
   */
  request_rec *ap_read_request(conn_rec *c);
  
  /**
   * Read the mime-encoded headers.
   * @param r The current request
   */
  AP_DECLARE(void) ap_get_mime_headers(request_rec *r);
  
  /**
   * Optimized version of ap_get_mime_headers() that requires a
   * temporary brigade to work with
   * @param r The current request
   * @param bb temp brigade
   */
  AP_DECLARE(void) ap_get_mime_headers_core(request_rec *r,
                                            apr_bucket_brigade *bb);
  
  /* Finish up stuff after a request */
  
  /**
   * Called at completion of sending the response.  It sends the terminating
   * protocol information.
   * @param r The current request
   */
  AP_DECLARE(void) ap_finalize_request_protocol(request_rec *r);
  
  /**
   * Send error back to client.
   * @param r The current request
   * @param recursive_error last arg indicates error status in case we get
   *      an error in the process of trying to deal with an ErrorDocument
   *      to handle some other error.  In that case, we print the default
   *      report for the first thing that went wrong, and more briefly report
   *      on the problem with the ErrorDocument.
   */
  AP_DECLARE(void) ap_send_error_response(request_rec *r, int recursive_error);
  
  /* Set last modified header line from the lastmod date of the associated file.
   * Also, set content length.
   *
   * May return an error status, typically HTTP_NOT_MODIFIED (that when the
   * permit_cache argument is set to one).
   */
  
  /**
   * Set the content length for this request
   * @param r The current request
   * @param length The new content length
   */
  AP_DECLARE(void) ap_set_content_length(request_rec *r, apr_off_t length);
  
  /**
   * Set the keepalive status for this request
   * @param r The current request
   * @return 1 if keepalive can be set, 0 otherwise
   */
  AP_DECLARE(int) ap_set_keepalive(request_rec *r);
  
  /**
   * Return the latest rational time from a request/mtime pair.  Mtime is
   * returned unless it's in the future, in which case we return the current time.
   * @param r The current request
   * @param mtime The last modified time
   * @return the latest rational time.
   */
  AP_DECLARE(apr_time_t) ap_rationalize_mtime(request_rec *r, apr_time_t mtime);
  
  /**
   * Build the content-type that should be sent to the client from the
   * content-type specified.  The following rules are followed:
   *    - if type is NULL or "", return NULL (do not set content-type).
   *    - if charset adding is disabled, stop processing and return type.
   *    - then, if there are no parameters on type, add the default charset
   *    - return type
   * @param r The current request
   * @param type The content type
   * @return The content-type
   */
  AP_DECLARE(const char *) ap_make_content_type(request_rec *r,
                                                const char *type);
  
  /**
   * Precompile metadata structures used by ap_make_content_type()
   * @param pool The pool to use for allocations
   */
  AP_DECLARE(void) ap_setup_make_content_type(apr_pool_t *pool);
  
  /**
   * Construct an entity tag from the resource information.  If it's a real
   * file, build in some of the file characteristics.
   * @param r The current request
   * @param force_weak Force the entity tag to be weak - it could be modified
   *                   again in as short an interval.
   * @return The entity tag
   */
  AP_DECLARE(char *) ap_make_etag(request_rec *r, int force_weak);
  
  /**
   * Set the E-tag outgoing header
   * @param r The current request
   */
  AP_DECLARE(void) ap_set_etag(request_rec *r);
  
  /**
   * Set the last modified time for the file being sent
   * @param r The current request
   */
  AP_DECLARE(void) ap_set_last_modified(request_rec *r);
  
  typedef enum {
      AP_CONDITION_NONE,
      AP_CONDITION_NOMATCH,
      AP_CONDITION_WEAK,
      AP_CONDITION_STRONG
  } ap_condition_e;
  
  /**
   * Tests conditional request rules for the If-Match header.
   * @param r The current request
   * @param headers The response headers to check against
   * @return AP_CONDITION_NONE if the header is missing, AP_CONDITION_NOMATCH
   *         if the header does not match, AP_CONDITION_STRONG for a strong
   *         match. Weak matches are not permitted for the If-Match header.
   */
  AP_DECLARE(ap_condition_e) ap_condition_if_match(request_rec *r,
          apr_table_t *headers);
  
  /**
   * Tests conditional request rules for the If-Unmodified-Since header.
   * @param r The current request
   * @param headers The response headers to check against
   * @return AP_CONDITION_NONE if the header is missing, AP_CONDITION_NOMATCH
   *         if the header does not match, AP_CONDITION_WEAK if a weak match
   *         was present and allowed by RFC2616, AP_CONDITION_STRONG for a
   *         strong match.
   */
  AP_DECLARE(ap_condition_e) ap_condition_if_unmodified_since(request_rec *r,
          apr_table_t *headers);
  
  /**
   * Tests conditional request rules for the If-None-Match header.
   * @param r The current request
   * @param headers The response headers to check against
   * @return AP_CONDITION_NONE if the header is missing, AP_CONDITION_NOMATCH
   *         if the header does not match, AP_CONDITION_WEAK if a weak match
   *         was present and allowed by RFC2616, AP_CONDITION_STRONG for a
   *         strong match.
   */
  AP_DECLARE(ap_condition_e) ap_condition_if_none_match(request_rec *r,
          apr_table_t *headers);
  
  /**
   * Tests conditional request rules for the If-Modified-Since header.
   * @param r The current request
   * @param headers The response headers to check against
   * @return AP_CONDITION_NONE if the header is missing, AP_CONDITION_NOMATCH
   *         if the header does not match, AP_CONDITION_WEAK if a weak match
   *         was present and allowed by RFC2616, AP_CONDITION_STRONG for a
   *         strong match.
   */
  AP_DECLARE(ap_condition_e) ap_condition_if_modified_since(request_rec *r,
          apr_table_t *headers);
  
  /**
   * Tests conditional request rules for the If-Range header.
   * @param r The current request
   * @param headers The response headers to check against
   * @return AP_CONDITION_NONE if either the If-Range or Range header is
   *         missing, AP_CONDITION_NOMATCH if the header does not match,
   *         AP_CONDITION_STRONG for a strong match. Weak matches are not
   *         permitted for the If-Range header.
   */
  AP_DECLARE(ap_condition_e) ap_condition_if_range(request_rec *r,
          apr_table_t *headers);
  
  /**
   * Implements condition GET rules for HTTP/1.1 specification.  This function
   * inspects the client headers and determines if the response fulfills
   * the requirements specified.
   * @param r The current request
   * @return OK if the response fulfills the condition GET rules, some
   *         other status code otherwise
   */
  AP_DECLARE(int) ap_meets_conditions(request_rec *r);
  
  /* Other ways to send stuff at the client.  All of these keep track
   * of bytes_sent automatically.  This indirection is intended to make
   * it a little more painless to slide things like HTTP-NG packetization
   * underneath the main body of the code later.  In the meantime, it lets
   * us centralize a bit of accounting (bytes_sent).
   *
   * These also return the number of bytes written by the call.
   * They should only be called with a timeout registered, for obvious reaasons.
   * (Ditto the send_header stuff).
   */
  
  /**
   * Send an entire file to the client, using sendfile if supported by the
   * current platform
   * @param fd The file to send.
   * @param r The current request
   * @param offset Offset into the file to start sending.
   * @param length Amount of data to send
   * @param nbytes Amount of data actually sent
   */
  AP_DECLARE(apr_status_t) ap_send_fd(apr_file_t *fd, request_rec *r, apr_off_t offset,
                                     apr_size_t length, apr_size_t *nbytes);
  
  #if APR_HAS_MMAP
  /**
   * Send an MMAP'ed file to the client
   * @param mm The MMAP'ed file to send
   * @param r The current request
   * @param offset The offset into the MMAP to start sending
   * @param length The amount of data to send
   * @return The number of bytes sent
   */
  AP_DECLARE(apr_size_t) ap_send_mmap(apr_mmap_t *mm,
                                      request_rec *r,
                                      apr_size_t offset,
                                      apr_size_t length);
  #endif
  
  
  /**
   * Register a new request method, and return the offset that will be
   * associated with that method.
   *
   * @param p        The pool to create registered method numbers from.
   * @param methname The name of the new method to register.
   * @return         An int value representing an offset into a bitmask.
   */
  AP_DECLARE(int) ap_method_register(apr_pool_t *p, const char *methname);
  
  /**
   * Initialize the method_registry and allocate memory for it.
   *
   * @param p Pool to allocate memory for the registry from.
   */
  AP_DECLARE(void) ap_method_registry_init(apr_pool_t *p);
  
  /**
   * This is a convenience macro to ease with checking a mask
   * against a method name.
   */
  #define AP_METHOD_CHECK_ALLOWED(mask, methname) \
      ((mask) & (AP_METHOD_BIT << ap_method_number_of((methname))))
  
  /**
   * Create a new method list with the specified number of preallocated
   * slots for extension methods.
   *
   * @param   p       Pointer to a pool in which the structure should be
   *                  allocated.
   * @param   nelts   Number of preallocated extension slots
   * @return  Pointer to the newly created structure.
   */
  AP_DECLARE(ap_method_list_t *) ap_make_method_list(apr_pool_t *p, int nelts);
  
  
  /**
   * Copy a method list
   *
   * @param   dest List to copy to
   * @param   src  List to copy from
   */
  AP_DECLARE(void) ap_copy_method_list(ap_method_list_t *dest,
                                       ap_method_list_t *src);
  
  /**
   * Search for an HTTP method name in an ap_method_list_t structure, and
   * return true if found.
   *
   * @param   method  String containing the name of the method to check.
   * @param   l       Pointer to a method list, such as r->allowed_methods.
   * @return  1 if method is in the list, otherwise 0
   */
  AP_DECLARE(int) ap_method_in_list(ap_method_list_t *l, const char *method);
  
  /**
   * Add an HTTP method name to an ap_method_list_t structure if it isn't
   * already listed.
   *
   * @param   method  String containing the name of the method to check.
   * @param   l       Pointer to a method list, such as r->allowed_methods.
   * @return  None.
   */
  AP_DECLARE(void) ap_method_list_add(ap_method_list_t *l, const char *method);
  
  /**
   * Remove an HTTP method name from an ap_method_list_t structure.
   *
   * @param   l       Pointer to a method list, such as r->allowed_methods.
   * @param   method  String containing the name of the method to remove.
   * @return  None.
   */
  AP_DECLARE(void) ap_method_list_remove(ap_method_list_t *l,
                                         const char *method);
  
  /**
   * Reset a method list to be completely empty.
   *
   * @param   l       Pointer to a method list, such as r->allowed_methods.
   * @return  None.
   */
  AP_DECLARE(void) ap_clear_method_list(ap_method_list_t *l);
  
  /**
   * Set the content type for this request (r->content_type).
   * @param r The current request
   * @param ct The new content type
   * @warning This function must be called to set r->content_type in order
   * for the AddOutputFilterByType directive to work correctly.
   */
  AP_DECLARE(void) ap_set_content_type(request_rec *r, const char *ct);
  
  /**
   * Set the Accept-Ranges header for this response
   * @param r The current request
   */
  AP_DECLARE(void) ap_set_accept_ranges(request_rec *r);
  
  
  /* Hmmm... could macrofy these for now, and maybe forever, though the
   * definitions of the macros would get a whole lot hairier.
   */
  
  /**
   * Output one character for this request
   * @param c the character to output
   * @param r the current request
   * @return The number of bytes sent
   */
  AP_DECLARE(int) ap_rputc(int c, request_rec *r);
  
  /**
   * Write a buffer for the current request
   * @param buf The buffer to write
   * @param nbyte The number of bytes to send from the buffer
   * @param r The current request
   * @return The number of bytes sent
   */
  AP_DECLARE(int) ap_rwrite(const void *buf, int nbyte, request_rec *r);
  
  /**
   * Output a string for the current request
   * @param str The string to output
   * @param r The current request
   * @return The number of bytes sent
   * @note ap_rputs may be implemented as macro or inline function
   */
  static APR_INLINE int ap_rputs(const char *str, request_rec *r)
  {
      return ap_rwrite(str, (int)strlen(str), r);
  }
  
  /**
   * Write an unspecified number of strings to the request
   * @param r The current request
   * @param ... The strings to write
   * @return The number of bytes sent
   */
  AP_DECLARE_NONSTD(int) ap_rvputs(request_rec *r,...)
                         AP_FN_ATTR_SENTINEL;
  
  /**
   * Output data to the client in a printf format
   * @param r The current request
   * @param fmt The format string
   * @param vlist The arguments to use to fill out the format string
   * @return The number of bytes sent
   */
  AP_DECLARE(int) ap_vrprintf(request_rec *r, const char *fmt, va_list vlist);
  
  /**
   * Output data to the client in a printf format
   * @param r The current request
   * @param fmt The format string
   * @param ... The arguments to use to fill out the format string
   * @return The number of bytes sent
   */
  AP_DECLARE_NONSTD(int) ap_rprintf(request_rec *r, const char *fmt,...)
                                  __attribute__((format(printf,2,3)));
  
  /**
   * Flush all of the data for the current request to the client
   * @param r The current request
   * @return 0 on success, -1 if an error occurred
   */
  AP_DECLARE(int) ap_rflush(request_rec *r);
  
  /**
   * Index used in custom_responses array for a specific error code
   * (only use outside protocol.c is in getting them configured).
   * @param status HTTP status code
   * @return The index of the response
   */
  AP_DECLARE(int) ap_index_of_response(int status);
  
  /**
   * Return the Status-Line for a given status code (excluding the
   * HTTP-Version field). If an invalid or unknown status code is
   * passed, "500 Internal Server Error" will be returned.
   * @param status The HTTP status code
   * @return The Status-Line
   */
  AP_DECLARE(const char *) ap_get_status_line(int status);
  
  /* Reading a block of data from the client connection (e.g., POST arg) */
  
  /**
   * Setup the client to allow Apache to read the request body.
   * @param r The current request
   * @param read_policy How the server should interpret a chunked
   *                    transfer-encoding.  One of: <pre>
   *    REQUEST_NO_BODY          Send 413 error if message has any body
   *    REQUEST_CHUNKED_ERROR    Send 411 error if body without Content-Length
   *    REQUEST_CHUNKED_DECHUNK  If chunked, remove the chunks for me.
   * </pre>
   * @return either OK or an error code
   */
  AP_DECLARE(int) ap_setup_client_block(request_rec *r, int read_policy);
  
  /**
   * Determine if the client has sent any data.  This also sends a
   * 100 Continue response to HTTP/1.1 clients, so modules should not be called
   * until the module is ready to read content.
   * @warning Never call this function more than once.
   * @param r The current request
   * @return 0 if there is no message to read, 1 otherwise
   */
  AP_DECLARE(int) ap_should_client_block(request_rec *r);
  
  /**
   * Call this in a loop.  It will put data into a buffer and return the length
   * of the input block
   * @param r The current request
   * @param buffer The buffer in which to store the data
   * @param bufsiz The size of the buffer
   * @return Number of bytes inserted into the buffer.  When done reading, 0
   *         if EOF, or -1 if there was an error
   */
  AP_DECLARE(long) ap_get_client_block(request_rec *r, char *buffer, apr_size_t bufsiz);
  
  /**
   * Map specific APR codes returned by the filter stack to HTTP error
   * codes, or the default status code provided. Use it as follows:
   *
   * return ap_map_http_request_error(rv, HTTP_BAD_REQUEST);
   *
   * If the filter has already handled the error, AP_FILTER_ERROR will
   * be returned, which is cleanly passed through.
   *
   * These mappings imply that the filter stack is reading from the
   * downstream client, the proxy will map these codes differently.
   * @param rv APR status code
   * @param status Default HTTP code should the APR code not be recognised
   * @return Mapped HTTP status code
   */
  AP_DECLARE(int) ap_map_http_request_error(apr_status_t rv, int status);
  
  /**
   * In HTTP/1.1, any method can have a body.  However, most GET handlers
   * wouldn't know what to do with a request body if they received one.
   * This helper routine tests for and reads any message body in the request,
   * simply discarding whatever it receives.  We need to do this because
   * failing to read the request body would cause it to be interpreted
   * as the next request on a persistent connection.
   * @param r The current request
   * @return error status if request is malformed, OK otherwise
   */
  AP_DECLARE(int) ap_discard_request_body(request_rec *r);
  
  /**
   * Setup the output headers so that the client knows how to authenticate
   * itself the next time, if an authentication request failed.
   * @param r The current request
   */
  AP_DECLARE(void) ap_note_auth_failure(request_rec *r);
  
  /**
   * @deprecated @see ap_note_auth_failure
   */
  AP_DECLARE(void) ap_note_basic_auth_failure(request_rec *r);
  
  /**
   * @deprecated @see ap_note_auth_failure
   */
  AP_DECLARE(void) ap_note_digest_auth_failure(request_rec *r);
  
  /**
   * This hook allows modules to add support for a specific auth type to
   * ap_note_auth_failure
   * @param r the current request
   * @param auth_type the configured auth_type
   * @return OK, DECLINED
   */
  AP_DECLARE_HOOK(int, note_auth_failure, (request_rec *r, const char *auth_type))
  
  /**
   * Get the password from the request headers
   * @param r The current request
   * @param pw The password as set in the headers
   * @return 0 (OK) if it set the 'pw' argument (and assured
   *         a correct value in r->user); otherwise it returns
   *         an error code, either HTTP_INTERNAL_SERVER_ERROR if things are
   *         really confused, HTTP_UNAUTHORIZED if no authentication at all
   *         seemed to be in use, or DECLINED if there was authentication but
   *         it wasn't Basic (in which case, the caller should presumably
   *         decline as well).
   */
  AP_DECLARE(int) ap_get_basic_auth_pw(request_rec *r, const char **pw);
  
  /**
   * parse_uri: break apart the uri
   * @warning Side Effects:
   *    @li sets r->args to rest after '?' (or NULL if no '?')
   *    @li sets r->uri to request uri (without r->args part)
   *    @li sets r->hostname (if not set already) from request (scheme://host:port)
   * @param r The current request
   * @param uri The uri to break apart
   */
  AP_CORE_DECLARE(void) ap_parse_uri(request_rec *r, const char *uri);
  
  /**
   * Get the next line of input for the request
   * @param s The buffer into which to read the line
   * @param n The size of the buffer
   * @param r The request
   * @param fold Whether to merge continuation lines
   * @return The length of the line, if successful
   *         n, if the line is too big to fit in the buffer
   *         -1 for miscellaneous errors
   */
  AP_DECLARE(int) ap_getline(char *s, int n, request_rec *r, int fold);
  
  /**
   * Get the next line of input for the request
   *
   * Note: on ASCII boxes, ap_rgetline is a macro which simply calls
   *       ap_rgetline_core to get the line of input.
   *
   *       on EBCDIC boxes, ap_rgetline is a wrapper function which
   *       translates ASCII protocol lines to the local EBCDIC code page
   *       after getting the line of input.
   *
   * @param s Pointer to the pointer to the buffer into which the line
   *          should be read; if *s==NULL, a buffer of the necessary size
   *          to hold the data will be allocated from the request pool
   * @param n The size of the buffer
   * @param read The length of the line.
   * @param r The request
   * @param fold Whether to merge continuation lines
   * @param bb Working brigade to use when reading buckets
   * @return APR_SUCCESS, if successful
   *         APR_ENOSPC, if the line is too big to fit in the buffer
   *         Other errors where appropriate
   */
  #if APR_CHARSET_EBCDIC
  AP_DECLARE(apr_status_t) ap_rgetline(char **s, apr_size_t n,
                                       apr_size_t *read,
                                       request_rec *r, int fold,
                                       apr_bucket_brigade *bb);
  #else /* ASCII box */
  #define ap_rgetline(s, n, read, r, fold, bb) \
          ap_rgetline_core((s), (n), (read), (r), (fold), (bb))
  #endif
  
  /** @see ap_rgetline */
  AP_DECLARE(apr_status_t) ap_rgetline_core(char **s, apr_size_t n,
                                            apr_size_t *read,
                                            request_rec *r, int fold,
                                            apr_bucket_brigade *bb);
  
  /**
   * Get the method number associated with the given string, assumed to
   * contain an HTTP method.  Returns M_INVALID if not recognized.
   * @param method A string containing a valid HTTP method
   * @return The method number
   */
  AP_DECLARE(int) ap_method_number_of(const char *method);
  
  /**
   * Get the method name associated with the given internal method
   * number.  Returns NULL if not recognized.
   * @param p A pool to use for temporary allocations.
   * @param methnum An integer value corresponding to an internal method number
   * @return The name corresponding to the method number
   */
  AP_DECLARE(const char *) ap_method_name_of(apr_pool_t *p, int methnum);
  
  
  /* Hooks */
  /*
   * pre_read_request --- run right before read_request_line(),
   *                  and not run during any subrequests.
   */
  /**
   * This hook allows modules to affect the request or connection immediately before
   * the request has been read, and before any other phases have been processes.
   * @param r The current request of the soon-to-be-read request
   * @param c The connection
   * @return None/void
   */
  AP_DECLARE_HOOK(void,pre_read_request,(request_rec *r, conn_rec *c))
  
  /*
   * post_read_request --- run right after read_request or internal_redirect,
   *                  and not run during any subrequests.
   */
  /**
   * This hook allows modules to affect the request immediately after the request
   * has been read, and before any other phases have been processes.  This allows
   * modules to make decisions based upon the input header fields
   * @param r The current request
   * @return OK or DECLINED
   */
  AP_DECLARE_HOOK(int,post_read_request,(request_rec *r))
  
  /**
   * This hook allows modules to perform any module-specific logging activities
   * over and above the normal server things.
   * @param r The current request
   * @return OK, DECLINED, or HTTP_...
   */
  AP_DECLARE_HOOK(int,log_transaction,(request_rec *r))
  
  /**
   * This hook allows modules to retrieve the http scheme for a request.  This
   * allows Apache modules to easily extend the schemes that Apache understands
   * @param r The current request
   * @return The http scheme from the request
   */
  AP_DECLARE_HOOK(const char *,http_scheme,(const request_rec *r))
  
  /**
   * Return the default port from the current request
   * @param r The current request
   * @return The current port
   */
  AP_DECLARE_HOOK(apr_port_t,default_port,(const request_rec *r))
  
  
  #define AP_PROTOCOL_HTTP1		"http/1.1"
  
  /**
   * Determine the list of protocols available for a connection/request. This may
   * be collected with or without any request sent, in which case the request is 
   * NULL. Or it may be triggered by the request received, e.g. through the 
   * "Upgrade" header.
   *
   * This hook will be run whenever protocols are being negotiated (ALPN as
   * one example). It may also be invoked at other times, e.g. when the server
   * wants to advertise protocols it is capable of switching to.
   * 
   * The identifiers for protocols are taken from the TLS extension type ALPN:
   * https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values.xml
   *
   * If no protocols are added to the proposals, the server not perform any
   * switch. If the protocol selected from the proposals is the protocol
   * already in place, also no protocol switch will be invoked.
   *
   * The client may already have announced the protocols it is willing to
   * accept. These will then be listed as offers. This parameter may also
   * be NULL, indicating that offers from the client are not known and
   * the hooks should propose all protocols that are valid for the
   * current connection/request.
   *
   * All hooks are run, unless one returns an error. Proposals may contain
   * duplicates. The order in which proposals are added is usually ignored.
   * 
   * @param c The current connection
   * @param r The current request or NULL
   * @param s The server/virtual host selected
   * @param offers A list of protocol identifiers offered by the client or
   *               NULL to indicated that the hooks are free to propose 
   * @param proposals The list of protocol identifiers proposed by the hooks
   * @return OK or DECLINED
   * @bug This API or implementation and order of operations should be considered
   * experimental and will continue to evolve in future 2.4 releases, with
   * a corresponding minor module magic number (MMN) bump to indicate the
   * API revision level.
   */
  AP_DECLARE_HOOK(int,protocol_propose,(conn_rec *c, request_rec *r,
                                        server_rec *s,
                                        const apr_array_header_t *offers,
                                        apr_array_header_t *proposals))
  
  /**
   * Perform a protocol switch on the connection. The exact requirements for
   * that depend on the protocol in place and the one switched to. The first 
   * protocol module to handle the switch is the last module run.
   * 
   * For a connection level switch (r == NULL), the handler must on return
   * leave the conn_rec in a state suitable for processing the switched
   * protocol, e.g. correct filters in place.
   *
   * For a request triggered switch (r != NULL), the protocol switch is done
   * before the response is sent out. When switching from "http/1.1" via Upgrade
   * header, the 101 intermediate response will have been sent. The
   * hook needs then to process the connection until it can be closed. Which
   * the server will enforce on hook return.
   * Any error the hook might encounter must already be sent by the hook itself
   * to the client in whatever form the new protocol requires.
   *
   * @param c The current connection
   * @param r The current request or NULL
   * @param s The server/virtual host selected
   * @param choices A list of protocol identifiers, normally the clients whishes
   * @param proposals the list of protocol identifiers proposed by the hooks
   * @return OK or DECLINED
   * @bug This API or implementation and order of operations should be considered
   * experimental and will continue to evolve in future 2.4 releases, with
   * a corresponding minor module magic number (MMN) bump to indicate the
   * API revision level.
   */
  AP_DECLARE_HOOK(int,protocol_switch,(conn_rec *c, request_rec *r,
                                       server_rec *s,
                                       const char *protocol))
  
  /**
   * Return the protocol used on the connection. Modules implementing
   * protocol switching must register here and return the correct protocol
   * identifier for connections they switched.
   *
   * To find out the protocol for the current connection, better call
   * @see ap_get_protocol which internally uses this hook.
   *
   * @param c The current connection
   * @return The identifier of the protocol in place or NULL
   * @bug This API or implementation and order of operations should be considered
   * experimental and will continue to evolve in future 2.4 releases, with
   * a corresponding minor module magic number (MMN) bump to indicate the
   * API revision level.
   */
  AP_DECLARE_HOOK(const char *,protocol_get,(const conn_rec *c))
  
  /**
   * Get the protocols that the connection and optional request may
   * upgrade to - besides the protocol currently active on the connection. These
   * values may be used to announce to a client what choices it has.
   *
   * If report_all == 0, only protocols more preferable than the one currently
   * being used, are reported. Otherwise, all available protocols beside the
   * current one are being reported.
   *
   * @param c The current connection
   * @param r The current request or NULL
   * @param s The server/virtual host selected or NULL
   * @param report_all include also protocols less preferred than the current one
   * @param pupgrades on return, possible protocols to upgrade to in descending order 
   *                 of preference. Maybe NULL if none are available.    
   * @bug This API or implementation and order of operations should be considered
   * experimental and will continue to evolve in future 2.4 releases, with
   * a corresponding minor module magic number (MMN) bump to indicate the
   * API revision level.
   */
  AP_DECLARE(apr_status_t) ap_get_protocol_upgrades(conn_rec *c, request_rec *r, 
                                                    server_rec *s, int report_all, 
                                                    const apr_array_header_t **pupgrades);
                                                    
  /**
   * Select a protocol for the given connection and optional request. Will return
   * the protocol identifier selected which may be the protocol already in place
   * on the connection. The selected protocol will be NULL if non of the given
   * choices could be agreed upon (e.g. no proposal as made).
   *
   * A special case is where the choices itself is NULL (instead of empty). In
   * this case there are no restrictions imposed on protocol selection.
   *
   * @param c The current connection
   * @param r The current request or NULL
   * @param s The server/virtual host selected
   * @param choices A list of protocol identifiers, normally the clients whishes
   * @return The selected protocol or NULL if no protocol could be agreed upon
   * @bug This API or implementation and order of operations should be considered
   * experimental and will continue to evolve in future 2.4 releases, with
   * a corresponding minor module magic number (MMN) bump to indicate the
   * API revision level.
   */
  AP_DECLARE(const char *) ap_select_protocol(conn_rec *c, request_rec *r, 
                                              server_rec *s,
                                              const apr_array_header_t *choices);
  
  /**
   * Perform the actual protocol switch. The protocol given must have been
   * selected before on the very same connection and request pair.
   *
   * @param c The current connection
   * @param r The current request or NULL
   * @param s The server/virtual host selected
   * @param protocol the protocol to switch to
   * @return APR_SUCCESS, if caller may continue processing as usual
   *         APR_EOF,     if caller needs to stop processing the connection
   *         APR_EINVAL,  if the protocol is already in place
   *         APR_NOTIMPL, if no module performed the switch
   *         Other errors where appropriate
   * @bug This API or implementation and order of operations should be considered
   * experimental and will continue to evolve in future 2.4 releases, with
   * a corresponding minor module magic number (MMN) bump to indicate the
   * API revision level.
   */
  AP_DECLARE(apr_status_t) ap_switch_protocol(conn_rec *c, request_rec *r, 
                                              server_rec *s,
                                              const char *protocol);
  
  /**
   * Call the protocol_get hook to determine the protocol currently in use
   * for the given connection.
   *
   * Unless another protocol has been switch to, will default to
   * @see AP_PROTOCOL_HTTP1 and modules implementing a  new protocol must
   * report a switched connection via the protocol_get hook.
   *
   * @param c The connection to determine the protocol for
   * @return the protocol in use, never NULL
   * @bug This API or implementation and order of operations should be considered
   * experimental and will continue to evolve in future 2.4 releases, with
   * a corresponding minor module magic number (MMN) bump to indicate the
   * API revision level.
   */
  AP_DECLARE(const char *) ap_get_protocol(conn_rec *c);
  
  /**
   * Check if the given protocol is an allowed choice on the given
   * combination of connection, request and server. 
   *
   * When server is NULL, it is taken from request_rec, unless
   * request_rec is NULL. Then it is taken from the connection base
   * server.
   *
   * @param c The current connection
   * @param r The current request or NULL
   * @param s The server/virtual host selected or NULL
   * @param protocol the protocol to switch to
   * @return != 0 iff protocol is allowed
   * @bug This API or implementation and order of operations should be considered
   * experimental and will continue to evolve in future 2.4 releases, with
   * a corresponding minor module magic number (MMN) bump to indicate the
   * API revision level.
   */
  AP_DECLARE(int) ap_is_allowed_protocol(conn_rec *c, request_rec *r,
                                         server_rec *s, const char *protocol);
  
  /** @see ap_bucket_type_error */
  typedef struct ap_bucket_error ap_bucket_error;
  
  /**
   * @struct ap_bucket_error
   * @brief  A bucket referring to an HTTP error
   *
   * This bucket can be passed down the filter stack to indicate that an
   * HTTP error occurred while running a filter.  In order for this bucket
   * to be used successfully, it MUST be sent as the first bucket in the
   * first brigade to be sent from a given filter.
   */
  struct ap_bucket_error {
      /** Number of buckets using this memory */
      apr_bucket_refcount refcount;
      /** The error code */
      int status;
      /** The error string */
      const char    *data;
  };
  
  /** @see ap_bucket_type_error */
  AP_DECLARE_DATA extern const apr_bucket_type_t ap_bucket_type_error;
  
  /**
   * Determine if a bucket is an error bucket
   * @param e The bucket to inspect
   * @return true or false
   */
  #define AP_BUCKET_IS_ERROR(e)         (e->type == &ap_bucket_type_error)
  
  /**
   * Make the bucket passed in an error bucket
   * @param b The bucket to make into an error bucket
   * @param error The HTTP error code to put in the bucket.
   * @param buf An optional error string to put in the bucket.
   * @param p A pool to allocate out of.
   * @return The new bucket, or NULL if allocation failed
   */
  AP_DECLARE(apr_bucket *) ap_bucket_error_make(apr_bucket *b, int error,
                  const char *buf, apr_pool_t *p);
  
  /**
   * Create a bucket referring to an HTTP error.
   * @param error The HTTP error code to put in the bucket.
   * @param buf An optional error string to put in the bucket.
   * @param p A pool to allocate the error string out of.
   * @param list The bucket allocator from which to allocate the bucket
   * @return The new bucket, or NULL if allocation failed
   */
  AP_DECLARE(apr_bucket *) ap_bucket_error_create(int error, const char *buf,
                                                  apr_pool_t *p,
                                                  apr_bucket_alloc_t *list);
  
  AP_DECLARE_NONSTD(apr_status_t) ap_byterange_filter(ap_filter_t *f, apr_bucket_brigade *b);
  AP_DECLARE_NONSTD(apr_status_t) ap_http_header_filter(ap_filter_t *f, apr_bucket_brigade *b);
  AP_DECLARE_NONSTD(apr_status_t) ap_content_length_filter(ap_filter_t *,
                                                                apr_bucket_brigade *);
  AP_DECLARE_NONSTD(apr_status_t) ap_old_write_filter(ap_filter_t *f, apr_bucket_brigade *b);
  
  /**
   * Sett up the protocol fields for subsidiary requests
   * @param rnew New Sub Request
   * @param r current request
   */
  AP_DECLARE(void) ap_set_sub_req_protocol(request_rec *rnew, const request_rec *r);
  
  /**
   * A wrapup function to keep the internal accounting straight.
   * Indicates that there is no more content coming.
   * @param sub_r Subrequest that is now compete
   */
  AP_DECLARE(void) ap_finalize_sub_req_protocol(request_rec *sub_r);
  
  /**
   * Send an interim (HTTP 1xx) response immediately.
   * @param r The request
   * @param send_headers Whether to send&clear headers in r->headers_out
   */
  AP_DECLARE(void) ap_send_interim_response(request_rec *r, int send_headers);
  
  #ifdef __cplusplus
  }
  #endif
  
  #endif  /* !APACHE_HTTP_PROTOCOL_H */
  /** @} */
  