apply insufficient TLC, making some improvements to wording

<summary>

  <p>This document describes changes to the Apache HTTPD API from

     version 2.2 to 2.4, that may be of interest to module/application

     developers and core hacks.  At the time of writing, the 2.4 API

     is not finalised, and this document may serve to highlight

     points that call for further review.</p>

     developers and core hacks.  As of the first GA release of the

     2.4 branch API compatibility is preserved for the life of the

     2.4 branch.  (The 

     <a href="http://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x/VERSIONING">VERSIONING</a>

     description for the 2.4 release provides more information about API

     compatibility.)</p>

  <p>API changes fall into two categories: APIs that are altogether new,

     and existing APIs that are expanded or changed.  The latter are

     further divided into those where all changes are back-compatible

     further divided into those where all changes are backwards-compatible

     (so existing modules can ignore them), and those that might

     require attention by maintainers.  As with the transition from

     HTTPD 2.0 to 2.2, existing modules and applications will require

  </section>

  <section id="ap_listen">

    <title>ap_listen (changed; back-compatible)</title>

    <p>Introduces new API to enable apache child processes to serve different purposes.</p>

    <title>ap_listen (changed; backwards-compatible)</title>

    <p>Introduces a new API to enable httpd child processes to serve

       different purposes.</p>

  </section>

  <section id="ap_mpm">

  <code>ap_rxplus</code> is now provided.  This provides the capability to

  compile Perl-style expressions like <code>s/regexp/replacement/flags</code>

  and to execute them against arbitrary strings. Support for regexp

  backreference.</p>

  backreferences is also added.</p>

  </section>

  <section id="ap_slotmem">

    <title>ap_slotmem (NEW!)</title>

    <p>Introduces an API for modules to allocate and manage memory slots

    (normally) for shared memory.</p>

    <p>Introduces an API for modules to allocate and manage memory slots,

    most commonly for shared memory.</p>

  </section>

  <section id="ap_socache">

  <section id="heartbeat">

    <title>heartbeat (NEW!)</title>

    <p>common structures for heartbeat modules (should this be public API?)</p>

    <p>common structures for heartbeat modules</p>

  </section>

  <section id="ap_parse_htaccess">

    <title>http_config (changed)</title>

    <ul>

      <li>Introduces per-module, per-directory loglevels, including macro wrappers.</li>

      <li>New AP_DECLARE_MODULE macro to declare all modules.</li>

      <li>New APLOG_USE_MODULE macro necessary for per-module loglevels in

      <li>New <code>AP_DECLARE_MODULE</code> macro to declare all modules.</li>

      <li>New <code>APLOG_USE_MODULE</code> macro necessary for per-module loglevels in

          multi-file modules.</li>

      <li>New API to retain data across module unload/load</li>

      <li>New check_config hook</li>

      <li>New ap_process_fnmatch_configs() to process wildcards</li>

      <li>Change ap_configfile_t, ap_cfg_getline(), ap_cfg_getc() to return error

          code, new ap_pcfg_strerror().</li>

      <li>New <code>check_config</code> hook</li>

      <li>New <code>ap_process_fnmatch_configs()</code> function to process wildcards</li>

      <li>Change <code>ap_configfile_t</code>, <code>ap_cfg_getline()</code>, 

          <code>ap_cfg_getc()</code> to return error codes, and add 

          <code>ap_pcfg_strerror()</code> for retrieving an error description.</li> 

      <li>Any config directive permitted in ACCESS_CONF context must now

          correctly handle being called from an .htaccess file via the new

          <directive module="core">AllowOverrideList</directive> directive.

  <section id="http_core">

    <title>http_core (changed)</title>

    <ul>

      <li>REMOVED ap_default_type, ap_requires, all 2.2 authnz API</li>

      <li>REMOVED <code>ap_default_type</code>, <code>ap_requires</code>, all 

          2.2 authnz API</li>

      <li>Introduces Optional Functions for logio and authnz</li>

      <li>New function ap_get_server_name_for_url to support ipv6 literals.</li>

      <li>New function ap_register_errorlog_handler to register errorlog

      <li>New function <code>ap_get_server_name_for_url</code> to support IPv6

          literals.</li>

      <li>New function <code>ap_register_errorlog_handler</code> to register error log

          format string handlers.</li>

      <li>Arguments of error_log hook have changed. Declaration has moved to

      <li>Arguments of <code>error_log</code> hook have changed. Declaration has moved to

          <code>http_core.h</code>.</li>

      <li>New function ap_state_query to determine if the server is in the

      <li>New function <code>ap_state_query</code> to determine if the server is in the

          initial configuration preflight phase or not. This is both easier to

          use and more correct than the old method of creating a pool userdata

          entry in the process pool.</li>

      <li>New function ap_get_conn_socket to get the socket descriptor for a

      <li>New function <code>ap_get_conn_socket</code> to get the socket descriptor for a

          connection. This should be used instead of accessing the core

          connection config directly.</li>

    </ul>

    <title>httpd (changed)</title>

    <ul>

      <li>Introduce per-directory, per-module loglevel</li>

      <li>New loglevels APLOG_TRACEn</li>

      <li>New loglevels <code>APLOG_TRACEn</code></li>

      <li>Introduce errorlog ids for requests and connections</li>

      <li>Support for mod_request kept_body</li>

      <li>Support buffering filter data for async requests</li>

      <li>New CONN_STATE values</li>

      <li>Function changes: ap_escape_html updated; ap_unescape_all,

          ap_escape_path_segment_buffer</li>

      <li>Modules that load other modules later than the EXEC_ON_READ config

          reading stage need to call ap_reserve_module_slots() or

          ap_reserve_module_slots_directive() in their pre_config hook.</li>

      <li>The useragent IP address per request can now be specified

          independently of the client IP address of the connection for

          the benefit of load balancers</li>

      <li>New <code>CONN_STATE</code> values</li>

      <li>Function changes: <code>ap_escape_html</code> updated; 

          <code>ap_unescape_all</code>, <code>ap_escape_path_segment_buffer</code></li>

      <li>Modules that load other modules later than the <code>EXEC_ON_READ</code> config

          reading stage need to call <code>ap_reserve_module_slots()</code> or

          <code>ap_reserve_module_slots_directive()</code> in their 

          <code>pre_config hook</code>.</li>

      <li>The useragent IP address per request can now be tracked

          independently of the client IP address of the connection, for

          support of deployments with load balancers.</li>

    </ul>

  </section>

    <title>http_log (changed)</title>

    <ul>

      <li>Introduce per-directory, per-module loglevel</li>

      <li>New loglevels APLOG_TRACEn</li>

      <li>ap_log_*error become macro wrappers (back-compatible if

          APLOG_MARK macro is used, except that is no longer possible to

          use #ifdef inside the argument list)</li>

      <li>New loglevels <code>APLOG_TRACEn</code></li>

      <li><code>ap_log_*error</code> become macro wrappers (backwards-compatible if

          <code>APLOG_MARK</code> macro is used, except that is no longer possible to

          use <code>#ifdef</code> inside the argument list)</li>

      <li>piped logging revamped</li>

      <li>module_index added to error_log hook</li>

      <li>new function: ap_log_command_line</li>

      <li><code>module_index</code> added to error_log hook</li>

      <li>new function: <code>ap_log_command_line</code></li>

    </ul>

  </section>

    <title>http_request (changed)</title>

    <ul>

      <li>New auth_internal API and auth_provider API</li>

      <li>New EOR bucket type</li>

      <li>New function ap_process_async_request</li>

      <li>New flags AP_AUTH_INTERNAL_PER_CONF and AP_AUTH_INTERNAL_PER_URI</li>

      <li>New access_checker_ex hook to apply additional access control and/or

          bypass authentication.</li>

      <li>New functions ap_hook_check_access_ex, ap_hook_check_access,

          ap_hook_check_authn, ap_hook_check_authz which accept

          AP_AUTH_INTERNAL_PER_* flags</li>

      <li>DEPRECATED direct use of ap_hook_access_checker, access_checker_ex,

          ap_hook_check_user_id, ap_hook_auth_checker</li>

      <li>New <code>EOR</code> bucket type</li>

      <li>New function <code>ap_process_async_request</code></li>

      <li>New flags <code>AP_AUTH_INTERNAL_PER_CONF</code> and 

          <code>AP_AUTH_INTERNAL_PER_URI</code></li>

      <li>New <code>access_checker_ex</code> hook to apply additional access control 

          and/or bypass authentication.</li>

      <li>New functions <code>ap_hook_check_access_ex</code>, 

          <code>ap_hook_check_access</code>, <code>ap_hook_check_authn</code>, 

          <code>ap_hook_check_authz</code> which accept 

          <code>AP_AUTH_INTERNAL_PER_*</code> flags</li>

      <li>DEPRECATED direct use of <code>ap_hook_access_checker</code>, 

          <code>access_checker_ex</code>, <code>ap_hook_check_user_id</code>, 

          <code>ap_hook_auth_checker</code></li>

    </ul>

    <p>When possible, registering all access control hooks (including

       authentication and authorization hooks) using AP_AUTH_INTERNAL_PER_CONF

       authentication and authorization hooks) using <code>AP_AUTH_INTERNAL_PER_CONF</code>

       is recommended.  If all modules' access control hooks are registered

       with this flag, then whenever the server handles an internal

       sub-request that matches the same set of access control configuration

    <p>If your module requires the old behavior and must perform access

       control checks on every sub-request with a different URI from the

       initial request, even if that URI matches the same set of access

       control configuration directives, then use AP_AUTH_INTERNAL_PER_URI.</p>

       control configuration directives, then use 

       <code>AP_AUTH_INTERNAL_PER_URI</code>.</p>

  </section>

  <section id="mod_auth">

  <section id="mod_cache">

    <title>mod_cache (changed)</title>

    <p>Introduces a commit_entity() function to the cache provider interface,

    allowing atomic writes to cache. Add a cache_status() hook to report

    the cache decision. Remove all private structures and functions from the

    public mod_cache.h header file.</p>

    <p>Introduces a <code>commit_entity()</code> function to the cache provider 

    interface, allowing atomic writes to cache. Add a <code>cache_status()</code>

    hook to report the cache decision. All private structures and functions were

    removed.</p>

  </section>

  <section id="mod_core">

  <section id="mpm_common">

    <title>mpm_common (changed)</title>

    <ul>

      <li>REMOVES: accept, lockfile, lock_mech, set_scoreboard (locking uses the new ap_mutex API)</li>

      <li>REMOVES: <code>accept</code>, <code>lockfile</code>, <code>lock_mech</code>,

          <code>set_scoreboard</code> (locking uses the new ap_mutex API)</li>

      <li>NEW API to drop privileges (delegates this platform-dependent

          function to modules)</li>

      <li>NEW Hooks: mpm_query, timed_callback, and get_name</li>

      <li>CHANGED interfaces: monitor hook,

      ap_reclaim_child_processes, ap_relieve_child_processes</li>

      <li>NEW Hooks: <code>mpm_query</code>, <code>timed_callback</code>, and 

          <code>get_name</code></li>

      <li>CHANGED interfaces: <code>monitor</code> hook,

          <code>ap_reclaim_child_processes</code>, 

          <code>ap_relieve_child_processes</code></li>

    </ul>

  </section>

  <section id="scoreboard">

    <title>scoreboard (changed)</title>

    <p>ap_get_scoreboard_worker is gratuitously made non-back-compatible

    <p><code>ap_get_scoreboard_worker</code> is made non-backwards-compatible

    as an alternative version is introduced.  Additional proxy_balancer

    support.  Child status stuff revamped.</p>

  </section>

  <section id="util_ldap">

    <title>util_ldap (changed)</title>

    <p>I have yet to get a handle on this update.</p>

    <p><em>no description available</em></p>

  </section>

  <section id="util_mutex">

    <title>util_mutex (NEW!)</title>

    <p>A wrapper for APR proc and global mutexes in httpd.</p>

    <p>A wrapper for APR proc and global mutexes in httpd, providing

       common configuration for the underlying mechanism and location

       of lock files.</p>

  </section>

  <section id="util_script">

    <title>util_script (changed)</title>

    <p>NEW: ap_args_to_table</p>

    <p>NEW: <code>ap_args_to_table</code></p>

  </section>

  <section id="util_time">

    <title>util_time (changed)</title>

    <p>NEW: ap_recent_ctime_ex</p>

    <p>NEW: <code>ap_recent_ctime_ex</code></p>

  </section>

</section>

      <dt><code>unixd_config</code></dt>

      <dd>This has been renamed to ap_unixd_config.</dd>

      <dt><code>conn_rec->remote_ip and conn_rec->remote_addr</code></dt>

      <dd>In order to distinguish between the client IP address of the

      connection, and the useragent IP address of the request potentially

      overridden by a load balancer or proxy, the above variables have

      been renamed. If a module makes reference to either of the above

      variables, they need to be replaced with one of the following two

      options as appropriate for the module:

      <dt><code>conn_rec->remote_ip</code> and 

          <code>conn_rec->remote_addr</code></dt>

      <dd>These fields have been renamed in order to distinguish between 

      the client IP address of the connection and the useragent IP address

      of the request (potentially overridden by a load balancer or proxy).

      References to either of these fields must be updated with one of the

      following options, as appropriate for the module:

      <ul>

        <li>When you require the IP address of the user agent, which

        might be connected directly to the server, or might optionally be

        separated from the server by a transparent load balancer or

        proxy, use request_rec->useragent_ip and

        request_rec->useragent_addr.</li>

        proxy, use <code>request_rec->useragent_ip</code> and

        <code>request_rec->useragent_addr</code>.</li>

        <li>When you require the IP address of the client that is

        connected directly to the server, which might be the useragent or

        might be the load balancer or proxy itself, use

        conn_rec->client_ip and conn_rec->client_addr.</li>

        <code>conn_rec->client_ip</code> and 

        <code>conn_rec->client_addr</code>.</li>

      </ul>

      </dd>

    </dl>

          set <code>ap_extended_status</code> to <code>1</code> in a

          pre-config hook and the extended status data will be

          available.</dd>

    </dl>

  </section>