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<title>API Changes in Apache HTTP Server 2.4 since 2.2 - Apache HTTP Server</title>
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<p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/directives.html">Directives</a> | <a href="/faq/">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p>
<p class="apache">Apache HTTP Server Version 2.3</p>
<div id="path">
<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.3</a></div><div id="page-content"><div id="preamble"><h1>API Changes in Apache HTTP Server 2.4 since 2.2</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="/en/developer/new_api_2_4.html" title="English"> en </a></p>
</div>
<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>
<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
(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
recompiling and may call for some attention, but most should not
require any substantial updating (although some may be able to
take advantage of API changes to offer significant improvements).</p>
<p>For the purpose of this document, the API is split according
to the public header files. These headers are themselves the
reference documentation, and can be used to generate a browsable
HTML reference with <code>make docs</code>.</p>
</div>
<div id="quickview"><ul id="toc"><li><img alt="" src="/images/down.gif" /> <a href="#api_changes">Changed APIs</a></li>
<li><img alt="" src="/images/down.gif" /> <a href="#upgrading">Specific information on upgrading modules from 2.2</a></li>
</ul></div>
<div class="section">
<h2><a name="api_changes" id="api_changes">Changed APIs</a></h2>
<h3><a name="ap_expr" id="ap_expr">ap_expr (NEW!)</a></h3>
<p>Introduces a new API to parse and evaluate boolean and algebraic
expressions, including provision for a standard syntax and
customised variants.</p>
<h3><a name="ap_listen" id="ap_listen">ap_listen (changed; back-compatible)</a></h3>
<p>Introduces new API to enable apache child processes to serve different purposes.</p>
<h3><a name="ap_mpm" id="ap_mpm">ap_mpm (changed)</a></h3>
<p><code>ap_mpm_run</code> is replaced by a new <code>mpm</code> hook.
Also <code>ap_graceful_stop_signalled</code> is lost, and
<code>ap_mpm_register_timed_callback</code> is new.</p>
<h3><a name="ap_regex" id="ap_regex">ap_regex (changed)</a></h3>
<p>In addition to the existing regexp wrapper, a new higher-level API
<code>ap_rxplus</code> is now provided. This provides the capability to
and to execute them against arbitrary strings. Support for regexp
backreference.</p>
<h3><a name="ap_slotmem" id="ap_slotmem">ap_slotmem (NEW!)</a></h3>
<p>Introduces an API for modules to allocate and manage memory slots
(normally) for shared memory.</p>
<h3><a name="ap_socache" id="ap_socache">ap_socache (NEW!)</a></h3>
<p>API to manage a shared object cache.</p>
<h3><a name="heartbeat" id="heartbeat">heartbeat (NEW!)</a></h3>
<p>common structures for heartbeat modules (should this be public API?)</p>
<h3><a name="http_config" id="http_config">http_config (changed)</a></h3>
<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
multi-file modules.</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>
</ul>
<h3><a name="http_core" id="http_core">http_core (changed)</a></h3>
<ul>
<li>REMOVED ap_default_type, ap_requires, 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
format string handlers.</li>
<li>New function ap_state_query 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>
</ul>
<h3><a name="httpd" id="httpd">httpd (changed)</a></h3>
<ul>
<li>Introduce per-directory, per-module loglevel</li>
<li>New loglevels APLOG_TRACEn</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>
</ul>
<h3><a name="http_log" id="http_log">http_log (changed)</a></h3>
<ul>
<li>Introduce per-directory, per-module loglevel</li>
<li>New loglevels APLOG_TRACEn</li>
<li>ap_log_*error become macro wrappers (fully back-compatible if
APLOG_MARK macro is used)</li>
<li>piped logging revamped</li>
<li>module_index added to error_log hook</li>
<li>new function: ap_log_command_line</li>
</ul>
<h3><a name="http_request" id="http_request">http_request (changed)</a></h3>
<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>
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>
</ul>
<p>When possible, registering all access control hooks (including
authentication and authorization hooks) using AP_AUTH_INTERNAL_PER_CONF
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
directives as the initial request (which is the common case), it can
avoid invoking the access control hooks another time.</p>
<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>
<h3><a name="mod_auth" id="mod_auth">mod_auth (NEW!)</a></h3>
<p>Introduces the new provider framework for authn and authz</p>
<h3><a name="mod_cache" id="mod_cache">mod_cache (changed)</a></h3>
<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>
<h3><a name="mod_core" id="mod_core">mod_core (NEW!)</a></h3>
<p>This introduces low-level APIs to send arbitrary headers,
and exposes functions to handle HTTP OPTIONS and TRACE.</p>
<h3><a name="mod_cache_disk" id="mod_cache_disk">mod_cache_disk (changed)</a></h3>
<p>Changes the disk format of the disk cache to support atomic cache
embedded in the header file, allowing confirmation that the header
and body belong to one another.</p>
<h3><a name="mod_disk_cache" id="mod_disk_cache">mod_disk_cache (renamed)</a></h3>
<p>The mod_disk_cache module has been renamed to mod_cache_disk in
order to be consistent with the naming of other modules within the
server.</p>
<h3><a name="mod_request" id="mod_request">mod_request (NEW!)</a></h3>
<p>The API for <code class="module"><a href="/mod/mod_request.html">mod_request</a></code>, to make input data
available to multiple application/handler modules where required,
and to parse HTML form data.</p>
<h3><a name="mpm_common" id="mpm_common">mpm_common (changed)</a></h3>
<ul>
<li>REMOVES: accept, lockfile, lock_mech, set_scoreboard (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>
</ul>
<h3><a name="scoreboard" id="scoreboard">scoreboard (changed)</a></h3>
<p>ap_get_scoreboard_worker is gratuitously made non-back-compatible
as an alternative version is introduced. Additional proxy_balancer
support. Child status stuff revamped.</p>
<h3><a name="util_cookies" id="util_cookies">util_cookies (NEW!)</a></h3>
<p>Introduces a new API for managing HTTP Cookies.</p>
<h3><a name="util_ldap" id="util_ldap">util_ldap (changed)</a></h3>
<p>I have yet to get a handle on this update.</p>
<h3><a name="util_mutex" id="util_mutex">util_mutex (NEW!)</a></h3>
<p>A wrapper for APR proc and global mutexes in httpd.</p>
<h3><a name="util_script" id="util_script">util_script (changed)</a></h3>
<p>NEW: ap_args_to_table</p>
<h3><a name="util_time" id="util_time">util_time (changed)</a></h3>
<p>NEW: ap_recent_ctime_ex</p>
<div class="section">
<h2><a name="upgrading" id="upgrading">Specific information on upgrading modules from 2.2</a></h2>
<h3><a name="upgrading_logging" id="upgrading_logging">Logging</a></h3>
<p>In order to take advantage of per-module loglevel configuration, any
source file that calls the <code>ap_log_*</code> functions should declare
which module it belongs to. If the module's module_struct is called
<code>foo_module</code>, the following code can be used to remain
backward compatible with HTTPD 2.0 and 2.2:</p>
<div class="example"><p><code>
#include <http_log.h><br />
<br />
#ifdef APLOG_USE_MODULE<br />
APLOG_USE_MODULE(foo);<br />
#endif
</code></p></div>
<p>Note: This is absolutely required for C++-language modules. It
can be skipped for C-language modules, though that breaks
module-specific log level support for files without it.</p>
<p>The number of parameters of the <code>ap_log_*</code> functions and the
definition of <code>APLOG_MARK</code> has changed. Normally, the change
is completely transparent. However, changes are required if a
module uses <code>APLOG_MARK</code> as a parameter to its own functions
or if a module calls <code>ap_log_*</code> without passing
<code>APLOG_MARK</code>. A module which uses wrappers
around <code>ap_log_*</code> typically uses both of these constructs.</p>
<p>The easiest way to change code which passes <code>APLOG_MARK</code> to
its own functions is to define and use a different macro that expands to
the parameters required by those functions, as <code>APLOG_MARK</code>
should only be used when calling <code>ap_log_*</code>
directly. In this way, the code will remain compatible with HTTPD 2.0
and 2.2.</p>
<p>Code which calls <code>ap_log_*</code> without passing
<code>APLOG_MARK</code> will necessarily differ between 2.4 and earlier
releases, as 2.4 requires a new third argument,
<code>APLOG_MODULE_INDEX</code>.</p>
<div class="example"><p><code>
ap_log_perror(file, line, APLOG_ERR, 0, p, "Failed to allocate dynamic lock structure");<br />
<br />
/* code for httpd 2.4 */<br />
ap_log_perror(file, line, APLOG_MODULE_INDEX, APLOG_ERR, 0, p, "Failed to allocate dynamic lock structure");<br />
<br />
</code></p></div>
<p>A <code>server_rec</code> pointer must be passed to
<code>ap_log_error()</code> when called after startup. This
was always appropriate, but there are even more limitations with
a <code>NULL</code> <code>server_rec</code> in 2.4 than in
previous releases. Beginning with 2.3.12, the global variable
<code>ap_server_conf</code> can always be used as
the <code>server_rec</code> parameter, as it will be
<code>NULL</code> only when it is valid to pass <code>NULL</code>
to <code>ap_log_error()</code>. <code>ap_server_conf</code>
should be used only when a more appropriate <code>server_rec</code>
is not available.</p>
<p>Consider the following changes to take advantage of the new
<code>APLOG_TRACE1..8</code> log levels:</p>
<ul>
<li>Check current use of <code>APLOG_DEBUG</code> and
consider if one of the <code>APLOG_TRACEn</code> levels is
more appropriate.</li>
<li>If your module currently has a mechanism for configuring
the amount of debug logging which is performed, consider
eliminating that mechanism and relying on the use of
different <code>APLOG_TRACEn</code> levels. If expensive
trace processing needs to be bypassed depending on the
configured log level, use the <code>APLOGtrace<em>n</em></code>
and <code>APLOGrtrace<em>n</em></code> macros to first check
if tracing is enabled.</li>
</ul>
messages. These ids are now logged by default, so it may not
be necessary for the module to log them explicitly. (Users may
remove them from the error log format, but they can be
instructed to add it back if necessary for problem diagnosis.)</p>
<h3><a name="upgrading_byfunction" id="upgrading_byfunction">If your module uses these existing APIs...</a></h3>
<dl>
<dt><code>ap_default_type()</code></dt>
<dd>This is no longer available; Content-Type must be configured
explicitly or added by the application.</dd>
<dt><code>ap_get_server_name()</code></dt>
<dd>If the returned server name is used in a URL,
use <code>ap_get_server_name_for_url()</code> instead. This new
function handles the odd case where the server name is an IPv6
literal address.</dd>
<dt><code>ap_get_server_version()</code></dt>
<dd>For logging purposes, where detailed information is
appropriate, use <code>ap_get_server_description()</code>.
When generating output, where the amount of information
should be configurable by ServerTokens, use
<code>ap_get_server_banner()</code>.</dd>
<dt><code>ap_graceful_stop_signalled()</code></dt>
<dd>Replace with a call
to <code>ap_mpm_query(AP_MPMQ_MPM_STATE)</code> and checking for
state <code>AP_MPMQ_STOPPING</code>.</dd>
<dt><code>ap_max_daemons_limit</code>, <code>ap_my_generation</code>,
and <code>ap_threads_per_child</code></dt>
<dd>Use <code>ap_mpm_query()</code> query codes
<code>AP_MPMQ_MAX_DAEMON_USED</code>, <code>AP_MPMQ_GENERATION</code>,
and <code>AP_MPMQ_MAX_THREADS</code>, respectively.</dd>
<dt><code>ap_mpm_query()</code></dt>
<dd>Ensure that it is not used until after the register-hooks
hook has completed. Otherwise, an MPM built as a DSO
would not have had a chance to enable support for this
function.</dd>
<dt><code>ap_server_conf->process->pool</code>
userdata</dt>
<dd>
Optional:
<ul>
<li>If your module uses this to determine which pass of the
startup hooks is being run,
use <code>ap_state_query(AP_SQ_MAIN_STATE)</code>.</li>
<li>If your module uses this to maintain data across the
unloading and reloading of your module, use
<code>ap_retained_data_create()</code> and
<code>ap_retained_data_get()</code>.</li>
</ul>
</dd>
<dt><code>apr_global_mutex_create()</code>,
<code>apr_proc_mutex_create()</code></dt>
<dd>Optional: See <code>ap_mutex_register()</code>,
<code>ap_global_mutex_create()</code>, and
<code>ap_proc_mutex_create()</code>; these allow your
mutexes to be configurable with
you can also remove any configuration mechanisms in your
module for such mutexes
</dd>
<dt><code>CORE_PRIVATE</code></dt>
<dd>This is now unnecessary and ignored.</dd>
<dt><code>dav_new_error()</code>
and <code>dav_new_error_tag()</code></dt>
<dd>Previously, these assumed that <code>errno</code> contained
information describing the failure. Now,
an <code>apr_status_t</code> parameter must be provided. Pass
0/APR_SUCCESS if there is no such error information, or a valid
<code>apr_status_t</code> value otherwise.</dd>
<code>DEFAULT_THREAD_LIMIT</code>, <code>DEFAULT_PIDLOG</code>,
etc.</dt>
<dd>The header file and most of the default configuration
values set in it are no longer visible to modules. (Most can
still be overridden at build time.) <code>DEFAULT_PIDLOG</code>
and <code>DEFAULT_REL_RUNTIMEDIR</code> are now universally
<dt><code>unixd_config</code></dt>
<dd>This has been renamed to ap_unixd_config.</dd>
</dl>
<h3><a name="upgrading_byfeature" id="upgrading_byfeature">If your module interfaces with this feature...</a></h3>
<dl>
<dt>suEXEC</dt>
<dd>Optional: If your module logs an error
also log the value of the new
field <code>suexec_disabled_reason</code>, which contains an
explanation of why it is not available.</dd>
<dt>Extended status data in the scoreboard</dt>
<dd>In previous releases, <code>ExtendedStatus</code> had to be
set to <code>On</code>, which in turn required that
mod_status was loaded. In 2.4, just
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>
<h3><a name="upgrading_newfeatures" id="upgrading_newfeatures">Does your module...</a></h3>
<dl>
<dt>Parse query args</dt>
<dd>Consider if <code>ap_args_to_table()</code> would be
helpful.</dd>
<dt>Parse form data...</dt>
<dd>Use <code>ap_parse_form_data()</code>.</dd>
<dt>Check for request header fields <code>Content-Length</code>
and <code>Transfer-Encoding</code> to see if a body was
specified</dt>
<dd>Use <code>ap_request_has_body()</code>.</dd>
<dt>Implement cleanups which clear pointer variables</dt>
<dd>Use <code>ap_pool_cleanup_set_null()</code>.</dd>
</dl>
</div></div>
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