API Changes in Apache HTTP Server 2.4 since 2.2 - Apache HTTP Server Version 2.4

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Apache HTTP Server Version 2.4

Apache > HTTP Server > Documentation > Version 2.4API 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 
     description for the 2.4 release provides more information about API

  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.

 Changed APIs
 Specific information on upgrading modules from 2.2
See alsoComments

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)
      Introduces per-module, per-directory loglevels, including macro wrappers.
      New AP_DECLARE_MODULE macro to declare all modules.
      New APLOG_USE_MODULE macro necessary for per-module loglevels in
          multi-file modules.
      New API to retain data across module unload/load
      New check_config hook
      New ap_process_fnmatch_configs() function to process wildcards
      Change ap_configfile_t, ap_cfg_getline(), 
          ap_cfg_getc() to return error codes, and add 
          ap_pcfg_strerror() for retrieving an error description. 
      Any config directive permitted in ACCESS_CONF context must now
          correctly handle being called from an .htaccess file via the new
          AllowOverrideList directive.
          ap_check_cmd_context() accepts a new flag NOT_IN_HTACCESS to detect
          this case.

  http_core (changed)
      REMOVED ap_default_type, ap_requires, all 
          2.2 authnz API
      Introduces Optional Functions for logio and authnz
      New function ap_get_server_name_for_url to support IPv6
      New function ap_register_errorlog_handler to register error log
          format string handlers.
      Arguments of error_log hook have changed. Declaration has moved to
      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.
      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.

  httpd (changed)
      Introduce per-directory, per-module loglevel
      New loglevels APLOG_TRACEn
      Introduce errorlog ids for requests and connections
      Support for mod_request kept_body
      Support buffering filter data for async requests
      New CONN_STATE values
      Function changes: ap_escape_html updated; 
          ap_unescape_all, ap_escape_path_segment_buffer
      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.
      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.

  http_log (changed)
      Introduce per-directory, per-module loglevel
      New loglevels APLOG_TRACEn
      ap_log_*error become macro wrappers (backwards-compatible if
          APLOG_MARK macro is used, except that is no longer possible to
          use #ifdef inside the argument list)
      piped logging revamped
      module_index added to error_log hook
      new function: ap_log_command_line

  http_request (changed)
      New auth_internal API and auth_provider API
      New EOR bucket type
      New function ap_process_async_request
      New flags AP_AUTH_INTERNAL_PER_CONF and 
      New access_checker_ex hook to apply additional access control 
          and/or bypass authentication.
      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
      DEPRECATED direct use of ap_hook_access_checker, 
          access_checker_ex, ap_hook_check_user_id, 
    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 

  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

  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

  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)
      REMOVES: accept, lockfile, lock_mech,
          set_scoreboard (locking uses the new ap_mutex API)
      NEW API to drop privileges (delegates this platform-dependent
          function to modules)
      NEW Hooks: mpm_query, timed_callback, and 
      CHANGED interfaces: monitor hook,

  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>
        #ifdef APLOG_USE_MODULE
    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 transparent. However, changes are required if a
       module uses APLOG_MARK as a parameter to its own functions
       or if a module calls ap_log_* without passing
       APLOG_MARK.  A module which uses wrappers
       around ap_log_* typically uses both of these constructs.

    The easiest way to change code which passes APLOG_MARK to
       its own functions is to define and use a different macro that expands to
       the parameters required by those functions, as APLOG_MARK
       should only be used when calling ap_log_*
       directly.  In this way, the code will remain compatible with HTTPD 2.0
       and 2.2.

    Code which calls ap_log_* without passing
       APLOG_MARK will necessarily differ between 2.4 and earlier
       releases, as 2.4 requires a new third argument,

       /* code for httpd 2.0/2.2 */
       ap_log_perror(file, line, APLOG_ERR, 0, p, "Failed to allocate dynamic lock structure");
       /* code for httpd 2.4 */
       ap_log_perror(file, line, APLOG_MODULE_INDEX, APLOG_ERR, 0, p, "Failed to allocate dynamic lock structure");

    ap_log_*error are now implemented as macros. This means
       that it is no longer possible to use #ifdef inside the
       argument list of ap_log_*error, as this would cause
       undefined behavor according to C99.

    A server_rec pointer must be passed to
       ap_log_error() when called after startup.  This
       was always appropriate, but there are even more limitations with
       a NULL server_rec in 2.4 than in
       previous releases.  Beginning with 2.3.12, the global variable
       ap_server_conf can always be used as
       the server_rec parameter, as it will be
       NULL only when it is valid to pass NULL
       to ap_log_error().  ap_server_conf
       should be used only when a more appropriate server_rec
       is not available.

    Consider the following changes to take advantage of the new
       APLOG_TRACE1..8 log levels:
         Check current use of APLOG_DEBUG and
         consider if one of the APLOG_TRACEn levels is
         more appropriate.
         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 APLOG_TRACEn levels.  If expensive
         trace processing needs to be bypassed depending on the
         configured log level, use the APLOGtracen
         and APLOGrtracen macros to first check
         if tracing is enabled.

    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.)

  If your module uses these existing APIs...

      This is no longer available; Content-Type must be configured
          explicitly or added by the application.

      If the returned server name is used in a URL,
      use ap_get_server_name_for_url() instead.  This new
      function handles the odd case where the server name is an IPv6
      literal address.

      For logging purposes, where detailed information is
          appropriate, use ap_get_server_description().
          When generating output, where the amount of information
          should be configurable by ServerTokens, use

      Replace with a call
      to ap_mpm_query(AP_MPMQ_MPM_STATE) and checking for
      state AP_MPMQ_STOPPING.

      ap_max_daemons_limit, ap_my_generation,
          and ap_threads_per_child
      Use ap_mpm_query() query codes
          and AP_MPMQ_MAX_THREADS, respectively.

      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

      The core server now provides better infrastructure for handling
          Require configuration.
          Register an auth provider function for each supported entity using
          ap_register_auth_provider().  The function will be
          called as necessary during Require
          processing.  (Consult bundled modules for detailed examples.)

          If your module uses this to determine which pass of the
	  startup hooks is being run,
	  use ap_state_query(AP_SQ_MAIN_STATE).
          If your module uses this to maintain data across the
          unloading and reloading of your module, use
          ap_retained_data_create() and

      Optional: See ap_mutex_register(),
          ap_global_mutex_create(), and
          ap_proc_mutex_create(); these allow your
          mutexes to be configurable with
          the Mutex directive;
          you can also remove any configuration mechanisms in your
          module for such mutexes

      This is now unnecessary and ignored.

      and dav_new_error_tag()
      Previously, these assumed that errno contained
      information describing the failure.  Now,
      an apr_status_t parameter must be provided.  Pass
      0/APR_SUCCESS if there is no such error information, or a valid
      apr_status_t value otherwise.

      mpm_default.h, DEFAULT_LOCKFILE,
      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.)  DEFAULT_PIDLOG
      and DEFAULT_REL_RUNTIMEDIR are now universally
      available via ap_config.h.

      This has been renamed to ap_unixd_config.

      This has been renamed to ap_unixd_setup_child(), but most callers
          should call the added ap_run_drop_privileges() hook.

      conn_rec->remote_ip and 
      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:
        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
        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 

  If your module interfaces with this feature...
      Optional: If your module logs an error
          when ap_unixd_config.suexec_enabled is 0,
          also log the value of the new
          field suexec_disabled_reason, which contains an
          explanation of why it is not available.

      Extended status data in the scoreboard
      In previous releases, ExtendedStatus had to be
          set to On, which in turn required that
          mod_status was loaded.  In 2.4, just
          set ap_extended_status to 1 in a
          pre-config hook and the extended status data will be

  Does your module...
    Parse query args
    Consider if ap_args_to_table() would be

    Parse form data...
    Use ap_parse_form_data().

    Check for request header fields Content-Length
    and Transfer-Encoding to see if a body was
    Use ap_request_has_body().

    Implement cleanups which clear pointer variables
    Use ap_pool_cleanup_set_null().

    Create run-time files such as shared memory files, pid files,
    Use ap_runtime_dir_relative() so that the global
    configuration for the location of such files, either by the
    DEFAULT_REL_RUNTIMEDIR compile setting or the
    DefaultRuntimeDir directive,
    will be respected.  Apache httpd 2.4.2 and above.


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