Apache HTTP Server Version 2.5

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# API Changes in Apache HTTP Server 2.4 since 2.2

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`.

## Changed APIs ¶

### ap_expr (NEW!)

Introduces a new API to parse and evaluate boolean and algebraic expressions, including provision for a standard syntax and customized 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 literals.
- New function `ap_register_errorlog_handler` to register error log format string handlers.
- Arguments of `error_log` hook have changed. Declaration has moved to `http_core.h`.
- 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 `AP_AUTH_INTERNAL_PER_URI`
- 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`, `ap_hook_auth_checker`

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)

- 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 `get_name`
- CHANGED interfaces: `monitor` hook, `ap_reclaim_child_processes`, `ap_relieve_child_processes`

### 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 ¶

### Logging

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
APLOG_USE_MODULE(foo);
#endif`

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, `APLOG_MODULE_INDEX`.

`/* 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 behavior 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...

`ap_default_type()`
  This is no longer available; Content-Type must be configured explicitly or added by the application.
`ap_get_server_name()`
  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.
`ap_get_server_version()`
  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 `ap_get_server_banner()`.
`ap_graceful_stop_signalled()`
  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 `AP_MPMQ_MAX_DAEMON_USED`, `AP_MPMQ_GENERATION`, and `AP_MPMQ_MAX_THREADS`, respectively.
`ap_mpm_query()`
  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.
`ap_requires()`
  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.)
`ap_server_conf->process->pool` userdata
  Optional:
  - 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 `ap_retained_data_get()`.
`apr_global_mutex_create()`, `apr_proc_mutex_create()`
  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
`CORE_PRIVATE`
  This is now unnecessary and ignored.
`dav_new_error()` 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`, `DEFAULT_THREAD_LIMIT`, `DEFAULT_PIDLOG`, etc.
  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`.
`unixd_config`
  This has been renamed to ap_unixd_config.
`conn_rec->remote_ip` and `conn_rec->remote_addr`
  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 `request_rec->useragent_addr`.
  - 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`.

### If your module interfaces with this feature...

suEXEC
  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 available.

### Does your module...

Parse query args
  Consider if `ap_args_to_table()` would be helpful.
Parse form data...
  Use `ap_parse_form_data()`.
Check for request header fields `Content-Length` and `Transfer-Encoding` to see if a body was specified
  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, etc.
  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.