<?xml version='1.0' encoding='UTF-8' ?>

<!DOCTYPE manualpage SYSTEM "/style/manualpage.dtd">

<?xml-stylesheet type="text/xsl" href="/style/manual.en.xsl"?>

<manualpage metafile="new_api_2_4.xml.meta">

<title>API Changes in Apache HTTP Server 2.4 since 2.2</title>

<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>

<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>

</summary>

<section id="api_changes">

<title>Changed APIs</title>

<section id="ap_expr">

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

<p>Introduces a new API to parse and evaluate boolean and algebraic

expressions, including provision for a standard syntax and

customised variants.</p>

</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>

</section>

<section id="ap_mpm">

<title>ap_mpm (changed)</title>

<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>

</section>

<section id="ap_regex">

<title>ap_regex (changed)</title>

<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

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

and to execute them against arbitrary strings. Support for regexp

backreference.</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>

</section>

<section id="ap_socache">

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

<p>API to manage a shared object cache.</p>

</section>

<section id="heartbeat">

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

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

</section>

<section id="ap_parse_htaccess">

<title>ap_parse_htaccess (changed)</title>

<p>The function signature for <code>ap_parse_htaccess</code> has been

changed. A <code>apr_table_t</code> of individual directives allowed

for override must now be passed (override remains).</p>

</section>

<section id="http_config">

<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

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>

</ul>

</section>

<section id="http_core">

<title>http_core (changed)</title>

<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>

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

connection. This should be used instead of accessing the core

connection config directly.</li>

</ul>

</section>

<section id="httpd">

<title>httpd (changed)</title>

<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>

<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>

</ul>

</section>

<section id="http_log">

<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 (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>

</section>

<section id="http_request">

<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>

</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>

</section>

<section id="mod_auth">

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

<p>Introduces the new provider framework for authn and authz</p>

</section>

<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>

</section>

<section id="mod_core">

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

<p>This introduces low-level APIs to send arbitrary headers,

and exposes functions to handle HTTP OPTIONS and TRACE.</p>

</section>

<section id="mod_cache_disk">

<title>mod_cache_disk (changed)</title>

<p>Changes the disk format of the disk cache to support atomic cache

updates without locking. The device/inode pair of the body file is

embedded in the header file, allowing confirmation that the header

and body belong to one another.</p>

</section>

<section id="mod_disk_cache">

<title>mod_disk_cache (renamed)</title>

<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>

</section>

<section id="mod_request">

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

<p>The API for <module>mod_request</module>, to make input data

available to multiple application/handler modules where required,

and to parse HTML form data.</p>

</section>

<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>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>

</section>

<section id="scoreboard">

<title>scoreboard (changed)</title>

<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>

</section>

<section id="util_cookies">

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

<p>Introduces a new API for managing HTTP Cookies.</p>

</section>

<section id="util_ldap">

<title>util_ldap (changed)</title>

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

</section>

<section id="util_mutex">

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

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

</section>

<section id="util_script">

<title>util_script (changed)</title>

<p>NEW: ap_args_to_table</p>

</section>

<section id="util_time">

<title>util_time (changed)</title>

<p>NEW: ap_recent_ctime_ex</p>

</section>

</section>

<section id="upgrading">

<title>Specific information on upgrading modules from 2.2</title>

<section id="upgrading_logging">

<title>Logging</title>

<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>

<example>

#include &lt;http_log.h&gt;<br/>

<br/>

#ifdef APLOG_USE_MODULE<br/>

APLOG_USE_MODULE(foo);<br/>

#endif

</example>

<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>

<example>

/* code for httpd 2.0/2.2 */<br />

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 />

</example>

<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>

<p>Modules sometimes add process id and/or thread id to their log

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>

</section>

<section id="upgrading_byfunction">

<title>If your module uses these existing APIs...</title>

<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

the <directive module="core">Mutex</directive> directive;

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>

<dt><code>mpm_default.h</code>, <code>DEFAULT_LOCKFILE</code>,

<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

available via <code>ap_config.h</code>.</dd>

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

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

</dl>

</section>

<section id="upgrading_byfeature">

<title>If your module interfaces with this feature...</title>

<dl>

<dt>suEXEC</dt>

<dd>Optional: If your module logs an error

when <code>ap_unixd_config.suexec_enabled</code> is 0,

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>

</section>

<section id="upgrading_newfeatures">

<title>Does your module...</title>

<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>

</section>

</section>

</manualpage>