您正在查看: Apache 分类下的文章

Apache 2.0 Hook Functions - Apache 2.2 中文版参考手册

apache > HTTP Server > 文档 > 版本2.2 > 开发者文档
   致谢 | 译者声明 | 本篇译者:<虚位以待> | 本篇译稿完成时间:?年?月?日 | 获取最新版本
apache 2.0 Hook Functions
Warning

This document is still in development and may be partially out of date.

In general, a hook function is one that Apache will call at some point during the processing of a request. Modules can provide functions that are called, and specify when they get called in comparison to other modules.

Creating a hook function

In order to create a new hook, four things need to be done:

Declare the hook function

Use the AP_DECLARE_HOOK macro, which needs to be given the return type of the hook function, the name of the hook, and the arguments. For example, if the hook returns an int and takes a request_rec * and an int and is called do_something, then declare it like this:

AP_DECLARE_HOOK(int, do_something, (request_rec *r, int n))

This should go in a header which modules will include if they want to use the hook.

Create the hook structure

Each source file that exports a hook has a private structure which is used to record the module functions that use the hook. This is declared as follows:

APR_HOOK_STRUCT(

APR_HOOK_LINK(do_something)

...

)

Implement the hook caller

The source file that exports the hook has to implement a function that will call the hook. There are currently three possible ways to do this. In all cases, the calling function is called ap_run_hookname().

Void hooks

If the return value of a hook is void, then all the hooks are called, and the caller is implemented like this:

AP_IMPLEMENT_HOOK_VOID(do_something, (request_rec *r, int n), (r, n))

The second and third arguments are the dummy argument declaration and the dummy arguments as they will be used when calling the hook. In other words, this macro expands to something like this:

void ap_run_do_something(request_rec *r, int n)
{

...

do_something(r, n);

}

Hooks that return a value

If the hook returns a value, then it can either be run until the first hook that does something interesting, like so:

AP_IMPLEMENT_HOOK_RUN_FIRST(int, do_something, (request_rec *r, int n), (r, n), DECLINED)

The first hook that does not return DECLINED stops the loop and its return value is returned from the hook caller. Note that DECLINED is the tradition Apache hook return meaning "I didn't do anything", but it can be whatever suits you.

Alternatively, all hooks can be run until an error occurs. This boils down to permitting two return values, one of which means "I did something, and it was OK" and the other meaning "I did nothing". The first function that returns a value other than one of those two stops the loop, and its return is the return value. Declare these like so:

AP_IMPLEMENT_HOOK_RUN_ALL(int, do_something, (request_rec *r, int n), (r, n), OK, DECLINED)

Again, OK和DECLINED are the traditional values. You can use what you want.

Call the hook callers

At appropriate moments in the code, call the hook caller, like so:

int n, ret;
request_rec *r;

ret=ap_run_do_something(r, n);

Hooking the hook

A module that wants a hook to be called needs to do two things.

Implement the hook function

Include the appropriate header, and define a static function of the correct type:

static int my_something_doer(request_rec *r, int n)
{

...

return OK;

}

Add a hook registering function

During initialisation, Apache will call each modules hook registering function, which is included in the module structure:

static void my_register_hooks()
{

ap_hook_do_something(my_something_doer, NULL, NULL, APR_HOOK_MIDDLE);

}



mode MODULE_VAR_EXPORT my_module =

{

...

my_register_hooks/* register hooks */

};

Controlling hook calling order

In the example above, we didn't use the three arguments in the hook registration function that control calling order. There are two mechanisms for doing this. The first, rather crude, method, allows us to specify roughly where the hook is run relative to other modules. The final argument control this. There are three possible values: APR_HOOK_FIRST, APR_HOOK_MIDDLE和APR_HOOK_LAST.

All modules using any particular value may be run in any order relative to each other, but, of course, all modules using APR_HOOK_FIRST will be run before APR_HOOK_MIDDLE which are before APR_HOOK_LAST. Modules that don't care when they are run should use APR_HOOK_MIDDLE. (I spaced these out so people could do stuff like APR_HOOK_FIRST-2 to get in slightly earlier, but is this wise? - Ben)

Note that there are two more values, APR_HOOK_REALLY_FIRST和APR_HOOK_REALLY_LAST. These should only be used by the hook exporter.

The other method allows finer control. When a module knows that it must be run before (or after) some other modules, it can specify them by name. The second (third) argument is a NULL-terminated array of strings consisting of the names of modules that must be run before (after) the current module. For example, suppose we want "mod_xyz.c" and "mod_abc.c" to run before we do, then we'd hook as follows:

static void register_hooks()
{

static const char * const aszPre[] = { "mod_xyz.c", "mod_abc.c", NULL };



ap_hook_do_something(my_something_doer, aszPre, NULL, APR_HOOK_MIDDLE);

}

Note that the sort used to achieve this is stable, so ordering set by APR_HOOK_ORDER is preserved, as far as is possible.

Ben Laurie, 15th August 1999

Converting Modules from Apache 1.3 to Apache 2.0 - Apache 2.2 中文版参考手册

apache > HTTP Server > 文档 > 版本2.2 > 开发者文档
   致谢 | 译者声明 | 本篇译者:<虚位以待> | 本篇译稿完成时间:?年?月?日 | 获取最新版本
Converting Modules from apache 1.3 to Apache 2.0

This is a first attempt at writing the lessons I learned when trying to convert the mod_mmap_static module to Apache 2.0. It's by no means definitive and probably won't even be correct in some ways, but it's a start.

The easier changes ...

Cleanup Routines

These now need to be of type apr_status_t and return a value of that type. Normally the return value will be APR_SUCCESS unless there is some need to signal an error in the cleanup. Be aware that even though you signal an error not all code yet checks and acts upon the error.

Initialisation Routines

These should now be renamed to better signify where they sit in the overall process. So the name gets a small change from mmap_init to mmap_post_config. The arguments passed have undergone a radical change and now look like

  • apr_pool_t *p
  • apr_pool_t *plog
  • apr_pool_t *ptemp
  • server_rec *s

Data Types

A lot of the data types have been moved into the APR. This means that some have had a name change, such as the one shown above. The following is a brief list of some of the changes that you are likely to have to make.

  • pool becomes apr_pool_t
  • table becomes apr_table_t
The messier changes...

Register Hooks

The new architecture uses a series of hooks to provide for calling your functions. These you'll need to add to your module by way of a new function, static void register_hooks(void). The function is really reasonably straightforward once you understand what needs to be done. Each function that needs calling at some stage in the processing of a request needs to be registered, handlers do not. There are a number of phases where functions can be added, and for each you can specify with a high degree of control the relative order that the function will be called in.

This is the code that was added to mod_mmap_static:

static void register_hooks(void)
{
static const char * const aszPre[]={ "http_core.c",NULL };
ap_hook_post_config(mmap_post_config,NULL,NULL,HOOK_MIDDLE);
ap_hook_translate_name(mmap_static_xlat,aszPre,NULL,HOOK_LAST);
};

This registers 2 functions that need to be called, one in the post_config stage (virtually every module will need this one) and one for the translate_name phase. note that while there are different function names the format of each is identical. So what is the format?

ap_hook_phase_name(function_name, predecessors, successors, position);

There are 3 hook positions defined...

  • HOOK_FIRST
  • HOOK_MIDDLE
  • HOOK_LAST

To define the position you use the position and then modify it with the predecessors and successors. Each of the modifiers can be a list of functions that should be called, either before the function is run (predecessors) or after the function has run (successors).

In the mod_mmap_static case I didn't care about the post_config stage, but the mmap_static_xlat must be called after the core module had done it's name translation, hence the use of the aszPre to define a modifier to the position HOOK_LAST.

Module Definition

There are now a lot fewer stages to worry about when creating your module definition. The old defintion looked like

module MODULE_VAR_EXPORT module_name_module =
{
STANDARD_MODULE_STUFF,
/* initializer */
/* dir config creater */
/* dir merger --- default is to override */
/* server config */
/* merge server config */
/* command handlers */
/* handlers */
/* filename translation */
/* check_user_id */
/* check auth */
/* check access */
/* type_checker */
/* fixups */
/* logger */
/* header parser */
/* child_init */
/* child_exit */
/* post read-request */
};

The new structure is a great deal simpler...

module MODULE_VAR_EXPORT module_name_module =
{
STANDARD20_MODULE_STUFF,
/* create per-directory config structures */
/* merge per-directory config structures  */
/* create per-server config structures*/
/* merge per-server config structures*/
/* command handlers */
/* handlers */
/* register hooks */
};

Some of these read directly across, some don't. I'll try to summarise what should be done below.

The stages that read directly across :

/* dir config creater /
/
create per-directory config structures */

/* server config /
/
create per-server config structures */

/* dir merger /
/
merge per-directory config structures */

/* merge server config /
/
merge per-server config structures */

/* command table /
/
command apr_table_t */

/* handlers /
/
handlers */

The remainder of the old functions should be registered as hooks. There are the following hook stages defined so far...

ap_hook_post_config
this is where the old _init routines get
registered

ap_hook_http_method
retrieve the http method from a request. (legacy)

ap_hook_open_logs
open any specified logs

ap_hook_auth_checker
check if the resource requires authorization

ap_hook_access_checker
check for module-specific restrictions

ap_hook_check_user_id
check the user-id and password

ap_hook_default_port
retrieve the default port for the server

ap_hook_pre_connection
do any setup required just before processing, but after
accepting

ap_hook_process_connection
run the correct protocol

ap_hook_child_init
call as soon as the child is started

ap_hook_create_request
??

ap_hook_fixups
last chance to modify things before generating content

ap_hook_handler
generate the content

ap_hook_header_parser
lets modules look at the headers, not used by most modules, because
they use post_read_request for this

ap_hook_insert_filter
to insert filters into the filter chain

ap_hook_log_transaction
log information about the request

ap_hook_optional_fn_retrieve
retrieve any functions registered as optional

ap_hook_post_read_request
called after reading the request, before any other phase

ap_hook_quick_handler
called before any request processing, used by cache modules.

ap_hook_translate_name
translate the URI into a filename

ap_hook_type_checker
determine and/or set the doc type

mod_version - Apache 2.2 中文版参考手册

apache > HTTP Server > 文档 > 版本2.2 > 模块
   致谢 | 译者声明 | 本篇译者:<虚位以待> | 本篇译稿完成时间:?年?月?日 | 获取最新版本
apache模块 mod_version 说明状态模块名源文件兼容性
提供基于版本的配置段支持
扩展(E)
version_module
mod_version.c
仅在 Apache 2.0.56 及以后的版本中可用
概述

This module is designed for the use in test suites and large networks which have to deal with different httpd versions and different configurations. It provides a new container -- <IfVersion>, which allows a flexible version checking including numeric comparisons and regular expressions.

例子

<IfVersion 2.1.0>

current httpd version is exactly 2.1.0

</IfVersion>



<IfVersion >= 2.2>

use really new features :-)

</IfVersion>

See below for further possibilities.

<IfVersion> 指令 说明语法作用域覆盖项状态模块
contains version dependent configuration
<IfVersion [[!]operator] version> ... </IfVersion>
server config, virtual host, directory, .htaccess
All
扩展(E)
mod_version

<IfVersion> section encloses configuration directives which are executed only if the httpd version matches the desired criteria. For normal (numeric) comparisons the version argument has the format major[.minor[.patch]], e.g. 2.1.0或2.2. minor和patch are optional. If these numbers are omitted, they are assumed to be zero. The following numerical operators are possible:

operatordescription
=或==httpd version is equal
>httpd version is greater than
>=httpd version is greater or equal
<httpd version is less than
<=httpd version is less or equal
示例

<IfVersion >= 2.1>

this happens only in versions greater or

equal 2.1.0.

</IfVersion>

Besides the numerical comparison it is possible to match a regular expression against the httpd version. There are two ways to write it:

operatordescription
=或==version has the form /regex/
~version has the form regex
示例

<IfVersion = /^2.1.[01234]$/>

e.g. workaround for buggy versions

</IfVersion>

In order to reverse the meaning, all operators can be preceded by an exclamation mark (!):

<IfVersion !~ ^2.1.[01234]$>

not for those versions

</IfVersion>

If the operator is omitted, it is assumed to be =.

mod_vhost_alias - Apache 2.2 中文版参考手册

apache > HTTP Server > 文档 > 版本2.2 > 模块
   致谢 | 译者声明 | 本篇译者:金步国 | 本页最后更新:2006年1月29日 | 获取最新版本
apache模块 mod_vhost_alias 说明状态模块名源文件
提供大批量虚拟主机的动态配置支持
扩展(E)
vhost_alias_module
mod_vhost_alias.c
概述

本模块通过将HTTP请求中的IP地址和/或"Host:"头内容转换为所要提供服务的文件路径名来创建动态的虚拟主机配置。这样的做法,使得应用配置大量相似的虚拟主机变得更为容易。

注意

如果使用mod_alias或mod_userdir来将URI转换为文件名,那么mod_vhost_alias的设定将被覆盖。例如,下面的配置将始终把/cgi-bin/script.pl 映射为/usr/local/apache2/cgi-bin/script.pl 。

ScriptAlias /cgi-bin/ /usr/local/apache2/cgi-bin/
VirtualScriptAlias /never/found/%0/cgi-bin/

目录名称的转换

本模块中的所有指令都用于将字符串替换为路径名。被替换的字符串(以后称为"name")可以是服务器名(参见UseCanonicalName指令以了解决策方法)或者是"点数字"格式的虚拟主机IP地址。替换操作由printf格式修饰符控制,该修饰符有以下几种格式:

<table border="1" cellpadding="0" cellspacing="0" bordercolor="#AAAAAA">
%%插入一个百分号(%) %p插入虚拟主机的端口号 %N.M插入名称(或者名称的一部分)

N和M被用来指定name中的子字符串。N从name中用小数点分隔的某部分中选取,而M是从N选中的字符串中选取部分字符。M是可选的且默认为"0";小数点当且仅当M存在时才必须书写。替换操作如下:

0整个name
1第一部分
2第二部分
-1最后一部分
-2倒数第二部分
2+从第二部分开始到最后的所有部分
-2+倒数第二部分以及之前的各部分
1+和-1+等同于0

如果N或M大于部分的个数,则简单的用下划线来替换。

示例

对于一个简单的基于名称的虚拟主机,配置文件中可能会使用下面的指令:

UseCanonicalNameOff
VirtualDocumentRoot /usr/local/apache/vhosts/%0

那么对http://www.example.com/directory/file.html的请求将会返回文件/usr/local/apache/vhosts/www.example.com/directory/file.html

对于拥有大量虚拟主机的情况而言,减少vhosts目录大小的一个好办法就是重新组织。为此你可以使用下面的配置:

UseCanonicalNameOff
VirtualDocumentRoot /usr/local/apache/vhosts/%3+/%2.1/%2.2/%2.3/%2

那么对http://www.domain.example.com/directory/file.html的请求将会返回文件/usr/local/apache/vhosts/example.com/d/o/m/domain/directory/file.html

进一步的分割可以用name尾字符来索引(hashing),例如:

VirtualDocumentRoot /usr/local/apache/vhosts/%3+/%2.-1/%2.-2/%2.-3/%2

该例返回文件/usr/local/apache/vhosts/example.com/n/i/a/domain/directory/file.html

也可以这样使用:

VirtualDocumentRoot /usr/local/apache/vhosts/%3+/%2.1/%2.2/%2.3/%2.4+

该例返回文件/usr/local/apache/vhosts/example.com/d/o/m/ain/directory/file.html

对于基于IP地址的虚拟主机,可以这样配置:

UseCanonicalName DNS
VirtualDocumentRootIP /usr/local/apache/vhosts/%1/%2/%3/%4/docs
VirtualScriptAliasIP /usr/local/apache/vhosts/%1/%2/%3/%4/cgi-bin

对http://www.domain.example.com/directory/file.html的请求将会返回文件/usr/local/apache/vhosts/10/20/30/40/docs/directory/file.html ,这里假设www.domain.example.com的IP地址为10.20.30.40。对http://www.domain.example.com/cgi-bin/script.pl的请求将会执行程序/usr/local/apache/vhosts/10/20/30/40/cgi-bin/script.pl

如果你希望在VirtualDocumentRoot指令中包含点字符(.),但这又和%指令产生冲突,可以这样解决:

<div class="example"><p>

VirtualDocumentRoot /usr/local/apache/vhosts/%2.0.%3.0

对http://www.domain.example.com/directory/file.html的请求将会返回文件/usr/local/apache/vhosts/domain.example/directory/file.html

LogFormat指令的%V和%A在和本模块的协同中起了一定作用。

VirtualDocumentRoot 指令 说明语法默认值作用域状态模块
对于给定的基于名称的虚拟主机动态配置根文档目录
VirtualDocumentRoot interpolated-directory|none
VirtualDocumentRoot none
server config, virtual host
扩展(E)
mod_vhost_alias

VirtualDocumentRoot指令使Apache可以通过虚拟主机的域名找到相应的文档。扩展interpolated-directory所得到的目录将会作为虚拟主机的根目录,这和DocumentRoot指令的参数是一样的。如果interpolated-directory为none ,那么VirtualDocumentRoot将被关闭。该指令不能和VirtualDocumentRootIP指令在同一作用域中使用。

VirtualDocumentRootIP 指令 说明语法默认值作用域状态模块
对于给定的基于IP的虚拟主机动态配置根文档目录
VirtualDocumentRootIP interpolated-directory|none
VirtualDocumentRootIP none
server config, virtual host
扩展(E)
mod_vhost_alias

VirtualDocumentRootIP与VirtualDocumentRoot相似,只是替换操作时用的不是虚拟主机名称,而是IP地址。

VirtualScriptAlias 指令 说明语法默认值作用域状态模块
对于给定的基于名称的虚拟主机动态配置CGI目录
VirtualScriptAlias interpolated-directory|none
VirtualScriptAlias none
server config, virtual host
扩展(E)
mod_vhost_alias

VirtualScriptAlias指令使Apache确定何处存放的是CGI脚本,这和VirtualDocumentRoot的做法是一样的。它匹配请求中的以/cgi-bin/开始的URI,更像"ScriptAlias /cgi-bin/"的作用。

VirtualScriptAliasIP 指令 说明语法默认值作用域状态模块
对于给定的基于IP的虚拟主机动态配置CGI目录
VirtualScriptAliasIP interpolated-directory|none
VirtualScriptAliasIP none
server config, virtual host
扩展(E)
mod_vhost_alias

VirtualScriptAliasIP和VirtualScriptAlias相似,只是替换操作使用的不是虚拟主机名称,而是IP地址。

Apache 1.3 API 备忘录 - Apache 2.2 中文版参考手册

apache > HTTP Server > 文档 > 版本2.2 > 开发者文档
   致谢 | 译者声明 | 本篇译者:<虚位以待> | 本篇译稿完成时间:?年?月?日 | 获取最新版本
apache 1.3 API notes
Warning

This document has not been updated to take into account changes made in the 2.0 version of the Apache HTTP Server. Some of the information may still be relevant, but please use it with care.

These are some notes on the Apache API and the data structures you have to deal with, etc. They are not yet nearly complete, but hopefully, they will help you get your bearings. Keep in mind that the API is still subject to change as we gain experience with it. (See the TODO file for what might be coming). However, it will be easy to adapt modules to any changes that are made. (We have more modules to adapt than you do).

A few notes on general pedagogical style here. In the interest of conciseness, all structure declarations here are incomplete -- the real ones have more slots that I'm not telling you about. For the most part, these are reserved to one component of the server core or another, and should be altered by modules with caution. However, in some cases, they really are things I just haven't gotten around to yet. Welcome to the bleeding edge.

Finally, here's an outline, to give you some bare idea of what's coming up, and in what order:

  • Basic concepts.
    • Handlers, Modules, and Requests
    • A brief tour of a module
  • How handlers work
    • A brief tour of the request_rec
    • Where request_rec structures come from
    • Handling requests, declining, and returning error codes
    • Special considerations for response handlers
    • Special considerations for authentication handlers
    • Special considerations for logging handlers
  • Resource allocation and resource pools
  • Configuration, commands and the like
    • Per-directory configuration structures
    • Command handling
    • Side notes --- per-server configuration, virtual servers, etc.
Basic concepts

We begin with an overview of the basic concepts behind the API, and how they are manifested in the code.

Handlers, Modules, and Requests

Apache breaks down request handling into a series of steps, more or less the same way the Netscape server API does (although this API has a few more stages than NetSite does, as hooks for stuff I thought might be useful in the future). These are:

  • URI -> Filename translation
  • Auth ID checking [is the user who they say they are?]
  • Auth access checking [is the user authorized here?]
  • Access checking other than auth
  • Determining MIME type of the object requested
  • 'Fixups' -- there aren't any of these yet, but the phase is intended as a hook for possible extensions like SetEnv, which don't really fit well elsewhere.
  • Actually sending a response back to the client.
  • Logging the request

These phases are handled by looking at each of a succession of modules, looking to see if each of them has a handler for the phase, and attempting invoking it if so. The handler can typically do one of three things:

  • Handle the request, and indicate that it has done so by returning the magic constant OK.
  • Decline to handle the request, by returning the magic integer constant DECLINED. In this case, the server behaves in all respects as if the handler simply hadn't been there.
  • Signal an error, by returning one of the HTTP error codes. This terminates normal handling of the request, although an ErrorDocument may be invoked to try to mop up, and it will be logged in any case.

Most phases are terminated by the first module that handles them; however, for logging, 'fixups', and non-access authentication checking, all handlers always run (barring an error). Also, the response phase is unique in that modules may declare multiple handlers for it, via a dispatch table keyed on the MIME type of the requested object. Modules may declare a response-phase handler which can handle any request, by giving it the key */* (i.e., a wildcard MIME type specification). However, wildcard handlers are only invoked if the server has already tried and failed to find a more specific response handler for the MIME type of the requested object (either none existed, or they all declined).

The handlers themselves are functions of one argument (a request_rec structure. vide infra), which returns an integer, as above.

A brief tour of a module

At this point, we need to explain the structure of a module. Our candidate will be one of the messier ones, the CGI module -- this handles both CGI scripts and the ScriptAlias config file command. It's actually a great deal more complicated than most modules, but if we're going to have only one example, it might as well be the one with its fingers in every place.

Let's begin with handlers. In order to handle the CGI scripts, the module declares a response handler for them. Because of ScriptAlias, it also has handlers for the name translation phase (to recognize ScriptAliased URIs), the type-checking phase (any ScriptAliased request is typed as a CGI script).

The module needs to maintain some per (virtual) server information, namely, the ScriptAliases in effect; the module structure therefore contains pointers to a functions which builds these structures, and to another which combines two of them (in case the main server and a virtual server both have ScriptAliases declared).

Finally, this module contains code to handle the ScriptAlias command itself. This particular module only declares one command, but there could be more, so modules have command tables which declare their commands, and describe where they are permitted, and how they are to be invoked.

A final note on the declared types of the arguments of some of these commands: a pool is a pointer to a resource pool structure; these are used by the server to keep track of the memory which has been allocated, files opened, etc., either to service a particular request, or to handle the process of configuring itself. That way, when the request is over (or, for the configuration pool, when the server is restarting), the memory can be freed, and the files closed, en masse, without anyone having to write explicit code to track them all down and dispose of them. Also, a cmd_parms structure contains various information about the config file being read, and other status information, which is sometimes of use to the function which processes a config-file command (such as ScriptAlias). With no further ado, the module itself:

/* Declarations of handlers. */

int translate_scriptalias (request_rec *);
int type_scriptalias (request_rec *);
int cgi_handler (request_rec *);

/* Subsidiary dispatch table for response-phase
 * handlers, by MIME type */

handler_rec cgi_handlers[] = {

{ "application/x-httpd-cgi", cgi_handler },

{ NULL }

};



/* Declarations of routines to manipulate the

 * module's configuration info. Note that these are

 * returned, and passed in, as void 's; the server

 
core keeps track of them, but it doesn't, and can't,

 * know their internal structure.

 */



void *make_cgi_server_config (pool *);

void *merge_cgi_server_config (pool *, void *, void );



/
Declarations of routines to handle config-file commands */



extern char *script_alias(cmd_parms *, void *per_dir_config, char *fake,
char *real);



command_rec cgi_cmds[] = {

{ "ScriptAlias", script_alias, NULL, RSRC_CONF, TAKE2,

"a fakename and a realname"},

{ NULL }

};



module cgi_module = {

  STANDARD_MODULE_STUFF,
  NULL,/* initializer */
  NULL,/* dir config creator */
  NULL,/* dir merger */
  make_cgi_server_config,/* server config */
  merge_cgi_server_config,  /* merge server config */
  cgi_cmds,/* command table */
  cgi_handlers,/* handlers */
  translate_scriptalias,/* filename translation */
  NULL,/* check_user_id */
  NULL,/* check auth */
  NULL,/* check access */
  type_scriptalias,/* type_checker */
  NULL,/* fixups */
  NULL,/* logger */
  NULL/* header parser */
};
How handlers work

The sole argument to handlers is a request_rec structure. This structure describes a particular request which has been made to the server, on behalf of a client. In most cases, each connection to the client generates only one request_rec structure.

A brief tour of the request_rec

request_rec contains pointers to a resource pool which will be cleared when the server is finished handling the request; to structures containing per-server and per-connection information, and most importantly, information on the request itself.

The most important such information is a small set of character strings describing attributes of the object being requested, including its URI, filename, content-type and content-encoding (these being filled in by the translation and type-check handlers which handle the request, respectively).

Other commonly used data items are tables giving the MIME headers on the client's original request, MIME headers to be sent back with the response (which modules can add to at will), and environment variables for any subprocesses which are spawned off in the course of servicing the request. These tables are manipulated using the ap_table_get and ap_table_set routines.

Note that the Content-type header value cannot be set by module content-handlers using the ap_table_*() routines. Rather, it is set by pointing the content_type field in the request_rec structure to an appropriate string. 例如,

r->content_type = "text/html";

Finally, there are pointers to two data structures which, in turn, point to per-module configuration structures. Specifically, these hold pointers to the data structures which the module has built to describe the way it has been configured to operate in a given directory (via .htaccess files or <Directory> sections), for private data it has built in the course of servicing the request (so modules' handlers for one phase can pass 'notes' to their handlers for other phases). There is another such configuration vector in the server_rec data structure pointed to by the request_rec, which contains per (virtual) server configuration data.

Here is an abridged declaration, giving the fields most commonly used:

struct request_rec {

pool *pool;
conn_rec *connection;
server_rec *server;

/* What object is being requested */

char *uri;
char *filename;
char *path_info;

char *args;/* QUERY_ARGS, if any */
struct stat finfo;/* Set by server core;
* st_mode set to zero if no such file */

char *content_type;
char *content_encoding;

/* MIME header environments, in and out. Also,
 * an array containing environment variables to
 * be passed to subprocesses, so people can write
 * modules to add to that environment.
 *
 * The difference between headers_out and
 * err_headers_out is that the latter are printed
 * even on error, and persist across internal
 * redirects (so the headers printed for
 * ErrorDocument handlers will have them).
 */

table *headers_in;
table *headers_out;
table *err_headers_out;
table *subprocess_env;

/* Info about the request itself... */

int header_only;/* HEAD request, as opposed to GET */
char *protocol;/* Protocol, as given to us, or HTTP/0.9 */
char *method;/* GET, HEAD, POST, etc. */
int method_number;/* M_GET, M_POST, etc. */

/* Info for logging */

char *the_request;
int bytes_sent;

/* A flag which modules can set, to indicate that
 * the data being returned is volatile, and clients
 * should be told not to cache it.
 */

int no_cache;

/* Various other config info which may change
 * with .htaccess files
 * These are config vectors, with one void*
 * pointer for each module (the thing pointed
 * to being the module's business).
 */

void *per_dir_config;/* Options set in config files, etc. */
void *request_config;/* Notes on *this* request */


};

Where request_rec structures come from

Most request_rec structures are built by reading an HTTP request from a client, and filling in the fields. However, there are a few exceptions:

  • If the request is to an imagemap, a type map (i.e., a *.var file), or a CGI script which returned a local 'Location:', then the resource which the user requested is going to be ultimately located by some URI other than what the client originally supplied. In this case, the server does an internal redirect, constructing a new request_rec for the new URI, and processing it almost exactly as if the client had requested the new URI directly.
  • If some handler signaled an error, and an ErrorDocument is in scope, the same internal redirect machinery comes into play.
  • Finally, a handler occasionally needs to investigate 'what would happen if' some other request were run. For instance, the directory indexing module needs to know what MIME type would be assigned to a request for each directory entry, in order to figure out what icon to use.

    Such handlers can construct a sub-request, using the functions ap_sub_req_lookup_file, ap_sub_req_lookup_uri, and ap_sub_req_method_uri; these construct a new request_rec structure and processes it as you would expect, up to but not including the point of actually sending a response. (These functions skip over the access checks if the sub-request is for a file in the same directory as the original request).

    (Server-side includes work by building sub-requests and then actually invoking the response handler for them, via the function ap_run_sub_req).

Handling requests, declining, and returning
error codes

As discussed above, each handler, when invoked to handle a particular request_rec, has to return an int to indicate what happened. That can either be

  • OK -- the request was handled successfully. This may or may not terminate the phase.
  • DECLINED -- no erroneous condition exists, but the module declines to handle the phase; the server tries to find another.
  • an HTTP error code, which aborts handling of the request.

Note that if the error code returned is REDIRECT, then the module should put a Location in the request's headers_out, to indicate where the client should be redirected to.

Special considerations for response
handlers

Handlers for most phases do their work by simply setting a few fields in the request_rec structure (or, in the case of access checkers, simply by returning the correct error code). However, response handlers have to actually send a request back to the client.

They should begin by sending an HTTP response header, using the function ap_send_http_header. (You don't have to do anything special to skip sending the header for HTTP/0.9 requests; the function figures out on its own that it shouldn't do anything). If the request is marked header_only, that's all they should do; they should return after that, without attempting any further output.

Otherwise, they should produce a request body which responds to the client as appropriate. The primitives for this are ap_rputc and ap_rprintf, for internally generated output, and ap_send_fd, to copy the contents of some FILE * straight to the client.

At this point, you should more or less understand the following piece of code, which is the handler which handles GET requests which have no more specific handler; it also shows how conditional GETs can be handled, if it's desirable to do so in a particular response handler -- ap_set_last_modified checks against the If-modified-since value supplied by the client, if any, and returns an appropriate code (which will, if nonzero, be USE_LOCAL_COPY). No similar considerations apply for ap_set_content_length, but it returns an error code for symmetry.

int default_handler (request_rec *r)
{

int errstatus;

FILE *f;



if (r->method_number != M_GET) return DECLINED;

if (r->finfo.st_mode == 0) return NOT_FOUND;



if ((errstatus = ap_set_content_length (r, r->finfo.st_size))

    ||
(errstatus = ap_set_last_modified (r, r->finfo.st_mtime)))

return errstatus;



f = fopen (r->filename, "r");



if (f == NULL) {

log_reason("file permissions deny server access", r->filename, r);

return FORBIDDEN;

}



register_timeout ("send", r);

ap_send_http_header (r);



if (!r->header_only) send_fd (f, r);

ap_pfclose (r->pool, f);

return OK;

}

Finally, if all of this is too much of a challenge, there are a few ways out of it. First off, as shown above, a response handler which has not yet produced any output can simply return an error code, in which case the server will automatically produce an error response. Secondly, it can punt to some other handler by invoking ap_internal_redirect, which is how the internal redirection machinery discussed above is invoked. A response handler which has internally redirected should always return OK.

(Invoking ap_internal_redirect from handlers which are not response handlers will lead to serious confusion).

Special considerations for authentication
handlers

Stuff that should be discussed here in detail:

  • Authentication-phase handlers not invoked unless auth is configured for the directory.
  • Common auth configuration stored in the core per-dir configuration; it has accessors ap_auth_type, ap_auth_name, and ap_requires.
  • Common routines, to handle the protocol end of things, at least for HTTP basic authentication (ap_get_basic_auth_pw, which sets the connection->user structure field automatically, and ap_note_basic_auth_failure, which arranges for the proper WWW-Authenticate: header to be sent back).

Special considerations for logging
handlers

When a request has internally redirected, there is the question of what to log. Apache handles this by bundling the entire chain of redirects into a list of request_rec structures which are threaded through the r->prev and r->next pointers. The request_rec which is passed to the logging handlers in such cases is the one which was originally built for the initial request from the client; note that the bytes_sent field will only be correct in the last request in the chain (the one for which a response was actually sent).

Resource allocation and resource pools

One of the problems of writing and designing a server-pool server is that of preventing leakage, that is, allocating resources (memory, open files, etc.), without subsequently releasing them. The resource pool machinery is designed to make it easy to prevent this from happening, by allowing resource to be allocated in such a way that they are automatically released when the server is done with them.

The way this works is as follows: the memory which is allocated, file opened, etc., to deal with a particular request are tied to a resource pool which is allocated for the request. The pool is a data structure which itself tracks the resources in question.

When the request has been processed, the pool is cleared. At that point, all the memory associated with it is released for reuse, all files associated with it are closed, and any other clean-up functions which are associated with the pool are run. When this is over, we can be confident that all the resource tied to the pool have been released, and that none of them have leaked.

Server restarts, and allocation of memory and resources for per-server configuration, are handled in a similar way. There is a configuration pool, which keeps track of resources which were allocated while reading the server configuration files, and handling the commands therein (for instance, the memory that was allocated for per-server module configuration, log files and other files that were opened, and so forth). When the server restarts, and has to reread the configuration files, the configuration pool is cleared, and so the memory and file descriptors which were taken up by reading them the last time are made available for reuse.

It should be noted that use of the pool machinery isn't generally obligatory, except for situations like logging handlers, where you really need to register cleanups to make sure that the log file gets closed when the server restarts (this is most easily done by using the function ap_pfopen, which also arranges for the underlying file descriptor to be closed before any child processes, such as for CGI scripts, are execed), or in case you are using the timeout machinery (which isn't yet even documented here). However, there are two benefits to using it: resources allocated to a pool never leak (even if you allocate a scratch string, and just forget about it); also, for memory allocation, ap_palloc is generally faster than malloc.

We begin here by describing how memory is allocated to pools, and then discuss how other resources are tracked by the resource pool machinery.

Allocation of memory in pools

Memory is allocated to pools by calling the function ap_palloc, which takes two arguments, one being a pointer to a resource pool structure, and the other being the amount of memory to allocate (in chars). Within handlers for handling requests, the most common way of getting a resource pool structure is by looking at the pool slot of the relevant request_rec; hence the repeated appearance of the following idiom in module code:

int my_handler(request_rec *r)
{

struct my_structure *foo;

...



foo = (foo *)ap_palloc (r->pool, sizeof(my_structure));

}

Note that there is no ap_pfree -- ap_palloced memory is freed only when the associated resource pool is cleared. This means that ap_palloc does not have to do as much accounting as malloc(); all it does in the typical case is to round up the size, bump a pointer, and do a range check.

(It also raises the possibility that heavy use of ap_palloc could cause a server process to grow excessively large. There are two ways to deal with this, which are dealt with below; briefly, you can use malloc, and try to be sure that all of the memory gets explicitly freed, or you can allocate a sub-pool of the main pool, allocate your memory in the sub-pool, and clear it out periodically. The latter technique is discussed in the section on sub-pools below, and is used in the directory-indexing code, in order to avoid excessive storage allocation when listing directories with thousands of files).

Allocating initialized memory

There are functions which allocate initialized memory, and are frequently useful. The function ap_pcalloc has the same interface as ap_palloc, but clears out the memory it allocates before it returns it. The function ap_pstrdup takes a resource pool and a char * as arguments, and allocates memory for a copy of the string the pointer points to, returning a pointer to the copy. Finally ap_pstrcat is a varargs-style function, which takes a pointer to a resource pool, and at least two char * arguments, the last of which must be NULL. It allocates enough memory to fit copies of each of the strings, as a unit; for instance:

ap_pstrcat (r->pool, "foo", "/", "bar", NULL);

returns a pointer to 8 bytes worth of memory, initialized to "foo/bar".

Commonly-used pools in the Apache Web
server

A pool is really defined by its lifetime more than anything else. There are some static pools in http_main which are passed to various non-http_main functions as arguments at opportune times. Here they are:

permanent_pool
never passed to anything else, this is the ancestor of all pools

pconf

  • subpool of permanent_pool
  • created at the beginning of a config "cycle"; exists until the server is terminated or restarts; passed to all config-time routines, either via cmd->pool, or as the "pool *p" argument on those which don't take pools
  • passed to the module init() functions

ptemp

  • sorry I lie, this pool isn't called this currently in 1.3, I renamed it this in my pthreads development. I'm referring to the use of ptrans in the parent... contrast this with the later definition of ptrans in the child.
  • subpool of permanent_pool
  • created at the beginning of a config "cycle"; exists until the end of config parsing; passed to config-time routines via cmd->temp_pool. Somewhat of a "bastard child" because it isn't available everywhere. Used for temporary scratch space which may be needed by some config routines but which is deleted at the end of config.

pchild

  • subpool of permanent_pool
  • created when a child is spawned (or a thread is created); lives until that child (thread) is destroyed
  • passed to the module child_init functions
  • destruction happens right after the child_exit functions are called... (which may explain why I think child_exit is redundant and unneeded)

ptrans

  • should be a subpool of pchild, but currently is a subpool of permanent_pool, see above
  • cleared by the child before going into the accept() loop to receive a connection
  • used as connection->pool

r->pool

  • for the main request this is a subpool of connection->pool; for subrequests it is a subpool of the parent request's pool.
  • exists until the end of the request (i.e., ap_destroy_sub_req, or in child_main after process_request has finished)
  • note that r itself is allocated from r->pool; i.e., r->pool is first created and then r is the first thing palloc()d from it

For almost everything folks do, r->pool is the pool to use. But you can see how other lifetimes, such as pchild, are useful to some modules... such as modules that need to open a database connection once per child, and wish to clean it up when the child dies.

You can also see how some bugs have manifested themself, such as setting connection->user to a value from r->pool -- in this case connection exists for the lifetime of ptrans, which is longer than r->pool (especially if r->pool is a subrequest!). So the correct thing to do is to allocate from connection->pool.

And there was another interesting bug in mod_include / mod_cgi. You'll see in those that they do this test to decide if they should use r->pool or r->main->pool. In this case the resource that they are registering for cleanup is a child process. If it were registered in r->pool, then the code would wait() for the child when the subrequest finishes. With mod_include this could be any old #include, and the delay can be up to 3 seconds... and happened quite frequently. Instead the subprocess is registered in r->main->pool which causes it to be cleaned up when the entire request is done -- i.e., after the output has been sent to the client and logging has happened.

Tracking open files, etc.

As indicated above, resource pools are also used to track other sorts of resources besides memory. The most common are open files. The routine which is typically used for this is ap_pfopen, which takes a resource pool and two strings as arguments; the strings are the same as the typical arguments to fopen, 例如,

...
FILE *f = ap_pfopen (r->pool, r->filename, "r");

if (f == NULL) { ... } else { ... }

There is also a ap_popenf routine, which parallels the lower-level open system call. Both of these routines arrange for the file to be closed when the resource pool in question is cleared.

Unlike the case for memory, there are functions to close files allocated with ap_pfopen, and ap_popenf, namely ap_pfclose and ap_pclosef. (This is because, on many systems, the number of files which a single process can have open is quite limited). It is important to use these functions to close files allocated with ap_pfopen and ap_popenf, since to do otherwise could cause fatal errors on systems such as linux, which react badly if the same FILE* is closed more than once.

(Using the close functions is not mandatory, since the file will eventually be closed regardless, but you should consider it in cases where your module is opening, or could open, a lot of files).

Other sorts of resources -- cleanup functions

More text goes here. Describe the the cleanup primitives in terms of which the file stuff is implemented; also, spawn_process.

Pool cleanups live until clear_pool() is called: clear_pool(a) recursively calls destroy_pool() on all subpools of a; then calls all the cleanups for a; then releases all the memory for a. destroy_pool(a) calls clear_pool(a) and then releases the pool structure itself. i.e., clear_pool(a) doesn't delete a, it just frees up all the resources and you can start using it again immediately.

Fine control -- creating and dealing with sub-pools, with
a note on sub-requests

On rare occasions, too-free use of ap_palloc() and the associated primitives may result in undesirably profligate resource allocation. You can deal with such a case by creating a sub-pool, allocating within the sub-pool rather than the main pool, and clearing or destroying the sub-pool, which releases the resources which were associated with it. (This really is a rare situation; the only case in which it comes up in the standard module set is in case of listing directories, and then only with very large directories. Unnecessary use of the primitives discussed here can hair up your code quite a bit, with very little gain).

The primitive for creating a sub-pool is ap_make_sub_pool, which takes another pool (the parent pool) as an argument. When the main pool is cleared, the sub-pool will be destroyed. The sub-pool may also be cleared or destroyed at any time, by calling the functions ap_clear_pool and ap_destroy_pool, respectively. (The difference is that ap_clear_pool frees resources associated with the pool, while ap_destroy_pool also deallocates the pool itself. In the former case, you can allocate new resources within the pool, and clear it again, and so forth; in the latter case, it is simply gone).

One final note -- sub-requests have their own resource pools, which are sub-pools of the resource pool for the main request. The polite way to reclaim the resources associated with a sub request which you have allocated (using the ap_sub_req_... functions) is ap_destroy_sub_req, which frees the resource pool. Before calling this function, be sure to copy anything that you care about which might be allocated in the sub-request's resource pool into someplace a little less volatile (for instance, the filename in its request_rec structure).

(Again, under most circumstances, you shouldn't feel obliged to call this function; only 2K of memory or so are allocated for a typical sub request, and it will be freed anyway when the main request pool is cleared. It is only when you are allocating many, many sub-requests for a single main request that you should seriously consider the ap_destroy_... functions).

Configuration, commands and the like

One of the design goals for this server was to maintain external compatibility with the NCSA 1.3 server --- that is, to read the same configuration files, to process all the directives therein correctly, and in general to be a drop-in replacement for NCSA. On the other hand, another design goal was to move as much of the server's functionality into modules which have as little as possible to do with the monolithic server core. The only way to reconcile these goals is to move the handling of most commands from the central server into the modules.

However, just giving the modules command tables is not enough to divorce them completely from the server core. The server has to remember the commands in order to act on them later. That involves maintaining data which is private to the modules, and which can be either per-server, or per-directory. Most things are per-directory, including in particular access control and authorization information, but also information on how to determine file types from suffixes, which can be modified by AddType and DefaultType directives, and so forth. In general, the governing philosophy is that anything which can be made configurable by directory should be; per-server information is generally used in the standard set of modules for information like Aliases and Redirects which come into play before the request is tied to a particular place in the underlying file system.

Another requirement for emulating the NCSA server is being able to handle the per-directory configuration files, generally called .htaccess files, though even in the NCSA server they can contain directives which have nothing at all to do with access control. Accordingly, after URI -> filename translation, but before performing any other phase, the server walks down the directory hierarchy of the underlying filesystem, following the translated pathname, to read any .htaccess files which might be present. The information which is read in then has to be merged with the applicable information from the server's own config files (either from the <Directory> sections in access.conf, or from defaults in srm.conf, which actually behaves for most purposes almost exactly like <Directory />).

Finally, after having served a request which involved reading .htaccess files, we need to discard the storage allocated for handling them. That is solved the same way it is solved wherever else similar problems come up, by tying those structures to the per-transaction resource pool.

Per-directory configuration structures

Let's look out how all of this plays out in mod_mime.c, which defines the file typing handler which emulates the NCSA server's behavior of determining file types from suffixes. What we'll be looking at, here, is the code which implements the AddType and AddEncoding commands. These commands can appear in .htaccess files, so they must be handled in the module's private per-directory data, which in fact, consists of two separate tables for MIME types and encoding information, and is declared as follows:

typedef struct {
table *forced_types;/* Additional AddTyped stuff */
table *encoding_types;/* Added with AddEncoding... */
} mime_dir_config;

When the server is reading a configuration file, or <Directory> section, which includes one of the MIME module's commands, it needs to create a mime_dir_config structure, so those commands have something to act on. It does this by invoking the function it finds in the module's 'create per-dir config slot', with two arguments: the name of the directory to which this configuration information applies (or NULL for srm.conf), and a pointer to a resource pool in which the allocation should happen.

(If we are reading a .htaccess file, that resource pool is the per-request resource pool for the request; otherwise it is a resource pool which is used for configuration data, and cleared on restarts. Either way, it is important for the structure being created to vanish when the pool is cleared, by registering a cleanup on the pool if necessary).

For the MIME module, the per-dir config creation function just ap_pallocs the structure above, and a creates a couple of tables to fill it. That looks like this:

void *create_mime_dir_config (pool *p, char *dummy)
{

mime_dir_config *new =

(mime_dir_config *) ap_palloc (p, sizeof(mime_dir_config));



new->forced_types = ap_make_table (p, 4);

new->encoding_types = ap_make_table (p, 4);



return new;

}

Now, suppose we've just read in a .htaccess file. We already have the per-directory configuration structure for the next directory up in the hierarchy. If the .htaccess file we just read in didn't have any AddType or AddEncoding commands, its per-directory config structure for the MIME module is still valid, and we can just use it. Otherwise, we need to merge the two structures somehow.

To do that, the server invokes the module's per-directory config merge function, if one is present. That function takes three arguments: the two structures being merged, and a resource pool in which to allocate the result. For the MIME module, all that needs to be done is overlay the tables from the new per-directory config structure with those from the parent:

void *merge_mime_dir_configs (pool *p, void *parent_dirv, void *subdirv)
{

mime_dir_config *parent_dir = (mime_dir_config *)parent_dirv;

mime_dir_config *subdir = (mime_dir_config *)subdirv;

mime_dir_config *new =

(mime_dir_config *)ap_palloc (p, sizeof(mime_dir_config));



new->forced_types = ap_overlay_tables (p, subdir->forced_types,

parent_dir->forced_types);

new->encoding_types = ap_overlay_tables (p, subdir->encoding_types,

parent_dir->encoding_types);



return new;

}

As a note -- if there is no per-directory merge function present, the server will just use the subdirectory's configuration info, and ignore the parent's. For some modules, that works just fine (例如,for the includes module, whose per-directory configuration information consists solely of the state of the XBITHACK), and for those modules, you can just not declare one, and leave the corresponding structure slot in the module itself NULL.

Command handling

Now that we have these structures, we need to be able to figure out how to fill them. That involves processing the actual AddType and AddEncoding commands. To find commands, the server looks in the module's command table. That table contains information on how many arguments the commands take, and in what formats, where it is permitted, and so forth. That information is sufficient to allow the server to invoke most command-handling functions with pre-parsed arguments. Without further ado, let's look at the AddType command handler, which looks like this (the AddEncoding command looks basically the same, and won't be shown here):

char *add_type(cmd_parms *cmd, mime_dir_config *m, char *ct, char *ext)
{

if (*ext == '.') ++ext;

ap_table_set (m->forced_types, ext, ct);

return NULL;

}

This command handler is unusually simple. As you can see, it takes four arguments, two of which are pre-parsed arguments, the third being the per-directory configuration structure for the module in question, and the fourth being a pointer to a cmd_parms structure. That structure contains a bunch of arguments which are frequently of use to some, but not all, commands, including a resource pool (from which memory can be allocated, and to which cleanups should be tied), and the (virtual) server being configured, from which the module's per-server configuration data can be obtained if required.

Another way in which this particular command handler is unusually simple is that there are no error conditions which it can encounter. If there were, it could return an error message instead of NULL; this causes an error to be printed out on the server's stderr, followed by a quick exit, if it is in the main config files; for a .htaccess file, the syntax error is logged in the server error log (along with an indication of where it came from), and the request is bounced with a server error response (HTTP error status, code 500).

The MIME module's command table has entries for these commands, which look like this:

command_rec mime_cmds[] = {

{ "AddType", add_type, NULL, OR_FILEINFO, TAKE2,

"a mime type followed by a file extension" },

{ "AddEncoding", add_encoding, NULL, OR_FILEINFO, TAKE2,

"an encoding (例如,gzip), followed by a file extension" },

{ NULL }

};

The entries in these tables are:

  • The name of the command
  • The function which handles it
  • a (void *) pointer, which is passed in the cmd_parms structure to the command handler --- this is useful in case many similar commands are handled by the same function.
  • A bit mask indicating where the command may appear. There are mask bits corresponding to each AllowOverride option, and an additional mask bit, RSRC_CONF, indicating that the command may appear in the server's own config files, but not in any .htaccess file.
  • A flag indicating how many arguments the command handler wants pre-parsed, and how they should be passed in. TAKE2 indicates two pre-parsed arguments. Other options are TAKE1, which indicates one pre-parsed argument, FLAG, which indicates that the argument should be On or Off, and is passed in as a boolean flag, RAW_ARGS, which causes the server to give the command the raw, unparsed arguments (everything but the command name itself). There is also ITERATE, which means that the handler looks the same as TAKE1, but that if multiple arguments are present, it should be called multiple times, and finally ITERATE2, which indicates that the command handler looks like a TAKE2, but if more arguments are present, then it should be called multiple times, holding the first argument constant.
  • Finally, we have a string which describes the arguments that should be present. If the arguments in the actual config file are not as required, this string will be used to help give a more specific error message. (You can safely leave this NULL).

Finally, having set this all up, we have to use it. This is ultimately done in the module's handlers, specifically for its file-typing handler, which looks more or less like this; note that the per-directory configuration structure is extracted from the request_rec's per-directory configuration vector by using the ap_get_module_config function.

int find_ct(request_rec *r)
{

int i;

char *fn = ap_pstrdup (r->pool, r->filename);

mime_dir_config *conf = (mime_dir_config *)

ap_get_module_config(r->per_dir_config, &mime_module);

char *type;



if (S_ISDIR(r->finfo.st_mode)) {

r->content_type = DIR_MAGIC_TYPE;

return OK;

}



if((i=ap_rind(fn,'.')) < 0) return DECLINED;

++i;



if ((type = ap_table_get (conf->encoding_types, &fn[i])))

{

r->content_encoding = type;



/* go back to previous extension to try to use it as a type */

fn[i-1] = '\0';

if((i=ap_rind(fn,'.')) < 0) return OK;

++i;

}



if ((type = ap_table_get (conf->forced_types, &fn[i])))

{

r->content_type = type;

}



return OK;

}

Side notes -- per-server configuration,
virtual servers, etc.

The basic ideas behind per-server module configuration are basically the same as those for per-directory configuration; there is a creation function and a merge function, the latter being invoked where a virtual server has partially overridden the base server configuration, and a combined structure must be computed. (As with per-directory configuration, the default if no merge function is specified, and a module is configured in some virtual server, is that the base configuration is simply ignored).

The only substantial difference is that when a command needs to configure the per-server private module data, it needs to go to the cmd_parms data to get at it. Here's an example, from the alias module, which also indicates how a syntax error can be returned (note that the per-directory configuration argument to the command handler is declared as a dummy, since the module doesn't actually have per-directory config data):

char *add_redirect(cmd_parms *cmd, void *dummy, char *f, char *url)
{

server_rec *s = cmd->server;

alias_server_conf *conf = (alias_server_conf *)

ap_get_module_config(s->module_config,&alias_module);

alias_entry *new = ap_push_array (conf->redirects);



if (!ap_is_url (url)) return "Redirect to non-URL";



new->fake = f; new->real = url;

return NULL;

}