Apache > HTTP Server > Documentation > Version 2.4

API Changes in Apache HTTP Server 2.4 since 2.2

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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. As of the first GA release of the 2.4 branch API compatibility is preserved for the life of the 2.4 branch. (The VERSIONING description for the 2.4 release provides more information about API compatibility.)

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 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 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).

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 make docs.

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Changed APIs

ap_expr (NEW!)

Introduces a new API to parse and evaluate boolean and algebraic expressions, including provision for a standard syntax and customised variants.

ap_listen (changed; backwards-compatible)

Introduces a new API to enable httpd child processes to serve different purposes.

ap_mpm (changed)

ap_mpm_run is replaced by a new mpm hook. Also ap_graceful_stop_signalled is lost, and ap_mpm_register_timed_callback is new.

ap_regex (changed)

In addition to the existing regexp wrapper, a new higher-level API ap_rxplus is now provided. This provides the capability to compile Perl-style expressions like s/regexp/replacement/flags and to execute them against arbitrary strings. Support for regexp backreferences is also added.

ap_slotmem (NEW!)

Introduces an API for modules to allocate and manage memory slots, most commonly for shared memory.

ap_socache (NEW!)

API to manage a shared object cache.

heartbeat (NEW!)

common structures for heartbeat modules

ap_parse_htaccess (changed)

The function signature for ap_parse_htaccess has been changed. A apr_table_t of individual directives allowed for override must now be passed (override remains).

http_config (changed)

http_core (changed)

httpd (changed)

http_log (changed)

http_request (changed)

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.

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.

mod_auth (NEW!)

Introduces the new provider framework for authn and authz

mod_cache (changed)

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. All private structures and functions were removed.

mod_core (NEW!)

This introduces low-level APIs to send arbitrary headers, and exposes functions to handle HTTP OPTIONS and TRACE.

mod_cache_disk (changed)

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.

mod_disk_cache (renamed)

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.

mod_request (NEW!)

The API for mod_request, to make input data available to multiple application/handler modules where required, and to parse HTML form data.

mpm_common (changed)

scoreboard (changed)

ap_get_scoreboard_worker is made non-backwards-compatible as an alternative version is introduced. Additional proxy_balancer support. Child status stuff revamped.

util_cookies (NEW!)

Introduces a new API for managing HTTP Cookies.

util_ldap (changed)

no description available

util_mutex (NEW!)

A wrapper for APR proc and global mutexes in httpd, providing common configuration for the underlying mechanism and location of lock files.

util_script (changed)

NEW: ap_args_to_table

util_time (changed)

NEW: ap_recent_ctime_ex


Specific information on upgrading modules from 2.2


In order to take advantage of per-module loglevel configuration, any source file that calls the ap_log_* functions should declare which module it belongs to. If the module's module_struct is called foo_module, the following code can be used to remain backward compatible with HTTPD 2.0 and 2.2:

#include <http_log.h>


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.

The number of parameters of the ap_log_* functions and the definition of APLOG_MARK has changed. Normally, the change is completely