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| author |   hongbotian <hongbo.tianhongbo@huawei.com> | 2015-11-30 03:10:21 -0500 |
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| committer | hongbotian <hongbo.tianhongbo@huawei.com> | 2015-11-30 03:10:21 -0500 |
| commit | c0b7206652b2852bc574694e7ba07ba1c2acdc00 (patch) | |
| tree | 5cb95cb0e19e03610525903df46279df2c3b7eb1 /rubbos/app/httpd-2.0.64/docs/manual/developer/API.html.en | |
| parent | b6d3d6e668b793220f2d3af1bc3e828553dc3fe6 (diff) | |
delete app
Change-Id: Id4c572809969ebe89e946e88063eaed262cff3f2
Signed-off-by: hongbotian <hongbo.tianhongbo@huawei.com>
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diff --git a/rubbos/app/httpd-2.0.64/docs/manual/developer/API.html.en b/rubbos/app/httpd-2.0.64/docs/manual/developer/API.html.en deleted file mode 100644 index db62a134..00000000 --- a/rubbos/app/httpd-2.0.64/docs/manual/developer/API.html.en +++ /dev/null @@ -1,1223 +0,0 @@ -<?xml version="1.0" encoding="ISO-8859-1"?> -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> -<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!-- - XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX - This file is generated from xml source: DO NOT EDIT - XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX - --> -<title>Apache 1.3 API notes - Apache HTTP Server</title> -<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> -<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> -<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /> -<link href="../images/favicon.ico" rel="shortcut icon" /></head> -<body id="manual-page"><div id="page-header"> -<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p> -<p class="apache">Apache HTTP Server Version 2.0</p> -<img alt="" src="../images/feather.gif" /></div> -<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div> -<div id="path"> -<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">Developer Documentation</a></div><div id="page-content"><div id="preamble"><h1>Apache 1.3 API notes</h1> -<div class="toplang"> -<p><span>Available Languages: </span><a href="../en/developer/API.html" title="English"> en </a></p> -</div> - - <div class="warning"><h3>Warning</h3> - <p>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.</p> - </div> - - <p>These are some notes on the Apache API and the data structures you have - to deal with, <em>etc.</em> 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 <em>might</em> 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).</p> - - <p>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.</p> - - <p>Finally, here's an outline, to give you some bare idea of what's coming - up, and in what order:</p> - - <ul> - <li> - <a href="#basics">Basic concepts.</a> - - <ul> - <li><a href="#HMR">Handlers, Modules, and - Requests</a></li> - - <li><a href="#moduletour">A brief tour of a - module</a></li> - </ul> - </li> - - <li> - <a href="#handlers">How handlers work</a> - - <ul> - <li><a href="#req_tour">A brief tour of the - <code>request_rec</code></a></li> - - <li><a href="#req_orig">Where request_rec structures come - from</a></li> - - <li><a href="#req_return">Handling requests, declining, - and returning error codes</a></li> - - <li><a href="#resp_handlers">Special considerations for - response handlers</a></li> - - <li><a href="#auth_handlers">Special considerations for - authentication handlers</a></li> - - <li><a href="#log_handlers">Special considerations for - logging handlers</a></li> - </ul> - </li> - - <li><a href="#pools">Resource allocation and resource - pools</a></li> - - <li> - <a href="#config">Configuration, commands and the like</a> - - <ul> - <li><a href="#per-dir">Per-directory configuration - structures</a></li> - - <li><a href="#commands">Command handling</a></li> - - <li><a href="#servconf">Side notes --- per-server - configuration, virtual servers, <em>etc</em>.</a></li> - </ul> - </li> - </ul> -</div> -<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#basics">Basic concepts</a></li> -<li><img alt="" src="../images/down.gif" /> <a href="#handlers">How handlers work</a></li> -<li><img alt="" src="../images/down.gif" /> <a href="#pools">Resource allocation and resource pools</a></li> -<li><img alt="" src="../images/down.gif" /> <a href="#config">Configuration, commands and the like</a></li> -</ul></div> -<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> -<div class="section"> -<h2><a name="basics" id="basics">Basic concepts</a></h2> - <p>We begin with an overview of the basic concepts behind the API, and how - they are manifested in the code.</p> - - <h3><a name="HMR" id="HMR">Handlers, Modules, and Requests</a></h3> - <p>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:</p> - - <ul> - <li>URI -> Filename translation</li> - <li>Auth ID checking [is the user who they say they are?]</li> - <li>Auth access checking [is the user authorized <em>here</em>?]</li> - <li>Access checking other than auth</li> - <li>Determining MIME type of the object requested</li> - <li>`Fixups' -- there aren't any of these yet, but the phase is intended - as a hook for possible extensions like <code class="directive"><a href="../mod/mod_env.html#setenv">SetEnv</a></code>, which don't really fit well elsewhere.</li> - <li>Actually sending a response back to the client.</li> - <li>Logging the request</li> - </ul> - - <p>These phases are handled by looking at each of a succession of - <em>modules</em>, 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:</p> - - <ul> - <li><em>Handle</em> the request, and indicate that it has done so by - returning the magic constant <code>OK</code>.</li> - - <li><em>Decline</em> to handle the request, by returning the magic integer - constant <code>DECLINED</code>. In this case, the server behaves in all - respects as if the handler simply hadn't been there.</li> - - <li>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.</li> - </ul> - - <p>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 <em>any</em> request, - by giving it the key <code>*/*</code> (<em>i.e.</em>, 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).</p> - - <p>The handlers themselves are functions of one argument (a - <code>request_rec</code> structure. vide infra), which returns an integer, - as above.</p> - - - <h3><a name="moduletour" id="moduletour">A brief tour of a module</a></h3> - <p>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 <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code> 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.</p> - - <p>Let's begin with handlers. In order to handle the CGI scripts, the - module declares a response handler for them. Because of <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code>, it also has handlers for the - name translation phase (to recognize <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code>ed URIs), the type-checking phase (any - <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code>ed request is typed - as a CGI script).</p> - - <p>The module needs to maintain some per (virtual) server information, - namely, the <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code>es 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 <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code>es declared).</p> - - <p>Finally, this module contains code to handle the <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code> command itself. This particular - module only declares one command, but there could be more, so modules have - <em>command tables</em> which declare their commands, and describe where - they are permitted, and how they are to be invoked.</p> - - <p>A final note on the declared types of the arguments of some of these - commands: a <code>pool</code> is a pointer to a <em>resource pool</em> - structure; these are used by the server to keep track of the memory which - has been allocated, files opened, <em>etc.</em>, 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, - <em>en masse</em>, without anyone having to write explicit code to track - them all down and dispose of them. Also, a <code>cmd_parms</code> - 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 <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code>). With no further ado, the - module itself:</p> - - <div class="example"><p><code> - /* Declarations of handlers. */<br /> - <br /> - int translate_scriptalias (request_rec *);<br /> - int type_scriptalias (request_rec *);<br /> - int cgi_handler (request_rec *);<br /> - <br /> - /* Subsidiary dispatch table for response-phase <br /> - * handlers, by MIME type */<br /> - <br /> - handler_rec cgi_handlers[] = {<br /> - <span class="indent"> - { "application/x-httpd-cgi", cgi_handler },<br /> - { NULL }<br /> - </span> - };<br /> - <br /> - /* Declarations of routines to manipulate the <br /> - * module's configuration info. Note that these are<br /> - * returned, and passed in, as void *'s; the server<br /> - * core keeps track of them, but it doesn't, and can't,<br /> - * know their internal structure.<br /> - */<br /> - <br /> - void *make_cgi_server_config (pool *);<br /> - void *merge_cgi_server_config (pool *, void *, void *);<br /> - <br /> - /* Declarations of routines to handle config-file commands */<br /> - <br /> - extern char *script_alias(cmd_parms *, void *per_dir_config, char *fake, - char *real);<br /> - <br /> - command_rec cgi_cmds[] = {<br /> - <span class="indent"> - { "ScriptAlias", script_alias, NULL, RSRC_CONF, TAKE2,<br /> - <span class="indent">"a fakename and a realname"},<br /></span> - { NULL }<br /> - </span> - };<br /> - <br /> - module cgi_module = { -</code></p><pre> 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 */ -};</pre></div> - -</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> -<div class="section"> -<h2><a name="handlers" id="handlers">How handlers work</a></h2> - <p>The sole argument to handlers is a <code>request_rec</code> 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 <code>request_rec</code> structure.</p> - - <h3><a name="req_tour" id="req_tour">A brief tour of the request_rec</a></h3> - <p>The <code>request_rec</code> 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.</p> - - <p>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).</p> - - <p>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 <code>ap_table_get</code> - and <code>ap_table_set</code> routines.</p> - - <div class="note"> - <p>Note that the <code>Content-type</code> header value <em>cannot</em> - be set by module content-handlers using the <code>ap_table_*()</code> - routines. Rather, it is set by pointing the <code>content_type</code> - field in the <code>request_rec</code> structure to an appropriate - string. <em>e.g.</em>,</p> - <div class="example"><p><code> - r->content_type = "text/html"; - </code></p></div> - </div> - - <p>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 - <code>.htaccess</code> files or <code class="directive"><a href="../mod/core.html#directory"><Directory></a></code> 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 <code>server_rec</code> data structure pointed - to by the <code>request_rec</code>, which contains per (virtual) server - configuration data.</p> - - <p>Here is an abridged declaration, giving the fields most commonly - used:</p> - - <div class="example"><p><code> - struct request_rec {<br /> - <br /> - pool *pool;<br /> - conn_rec *connection;<br /> - server_rec *server;<br /> - <br /> - /* What object is being requested */<br /> - <br /> - char *uri;<br /> - char *filename;<br /> - char *path_info; -</code></p><pre>char *args; /* QUERY_ARGS, if any */ -struct stat finfo; /* Set by server core; - * st_mode set to zero if no such file */</pre><p><code> - char *content_type;<br /> - char *content_encoding;<br /> - <br /> - /* MIME header environments, in and out. Also, <br /> - * an array containing environment variables to<br /> - * be passed to subprocesses, so people can write<br /> - * modules to add to that environment.<br /> - *<br /> - * The difference between headers_out and <br /> - * err_headers_out is that the latter are printed <br /> - * even on error, and persist across internal<br /> - * redirects (so the headers printed for <br /> - * <code class="directive"><a href="../mod/core.html#errordocument">ErrorDocument</a></code> handlers will have - them).<br /> - */<br /> - <br /> - table *headers_in;<br /> - table *headers_out;<br /> - table *err_headers_out;<br /> - table *subprocess_env;<br /> - <br /> - /* Info about the request itself... */<br /> - <br /> -</code></p><pre>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, <em>etc.</em> */ -int method_number; /* M_GET, M_POST, <em>etc.</em> */ - -</pre><p><code> - /* Info for logging */<br /> - <br /> - char *the_request;<br /> - int bytes_sent;<br /> - <br /> - /* A flag which modules can set, to indicate that<br /> - * the data being returned is volatile, and clients<br /> - * should be told not to cache it.<br /> - */<br /> - <br /> - int no_cache;<br /> - <br /> - /* Various other config info which may change<br /> - * with .htaccess files<br /> - * These are config vectors, with one void*<br /> - * pointer for each module (the thing pointed<br /> - * to being the module's business).<br /> - */<br /> - <br /> -</code></p><pre>void *per_dir_config; /* Options set in config files, <em>etc.</em> */ -void *request_config; /* Notes on *this* request */ - -</pre><p><code> - }; - </code></p></div> - - - <h3><a name="req_orig" id="req_orig">Where request_rec structures come from</a></h3> - <p>Most <code>request_rec</code> structures are built by reading an HTTP - request from a client, and filling in the fields. However, there are a - few exceptions:</p> - - <ul> - <li>If the request is to an imagemap, a type map (<em>i.e.</em>, a - <code>*.var</code> 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 <em>internal redirect</em>, - constructing a new <code>request_rec</code> for the new URI, and - processing it almost exactly as if the client had requested the new URI - directly.</li> - - <li>If some handler signaled an error, and an <code>ErrorDocument</code> - is in scope, the same internal redirect machinery comes into play.</li> - - <li><p>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.</p> - - <p>Such handlers can construct a <em>sub-request</em>, using the - functions <code>ap_sub_req_lookup_file</code>, - <code>ap_sub_req_lookup_uri</code>, and <code>ap_sub_req_method_uri</code>; - these construct a new <code>request_rec</code> 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).</p> - - <p>(Server-side includes work by building sub-requests and then actually - invoking the response handler for them, via the function - <code>ap_run_sub_req</code>).</p> - </li> - </ul> - - - <h3><a name="req_return" id="req_return">Handling requests, declining, and returning - error codes</a></h3> - <p>As discussed above, each handler, when invoked to handle a particular - <code>request_rec</code>, has to return an <code>int</code> to indicate - what happened. That can either be</p> - - <ul> - <li><code>OK</code> -- the request was handled successfully. This may or - may not terminate the phase.</li> - - <li><code>DECLINED</code> -- no erroneous condition exists, but the module - declines to handle the phase; the server tries to find another.</li> - - <li>an HTTP error code, which aborts handling of the request.</li> - </ul> - - <p>Note that if the error code returned is <code>REDIRECT</code>, then - the module should put a <code>Location</code> in the request's - <code>headers_out</code>, to indicate where the client should be - redirected <em>to</em>.</p> - - - <h3><a name="resp_handlers" id="resp_handlers">Special considerations for response - handlers</a></h3> - <p>Handlers for most phases do their work by simply setting a few fields - in the <code>request_rec</code> 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.</p> - - <p>They should begin by sending an HTTP response header, using the - function <code>ap_send_http_header</code>. (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 <code>header_only</code>, that's all they should do; they should - return after that, without attempting any further output.</p> - - <p>Otherwise, they should produce a request body which responds to the - client as appropriate. The primitives for this are <code>ap_rputc</code> - and <code>ap_rprintf</code>, for internally generated output, and - <code>ap_send_fd</code>, to copy the contents of some <code>FILE *</code> - straight to the client.</p> - - <p>At this point, you should more or less understand the following piece - of code, which is the handler which handles <code>GET</code> requests - which have no more specific handler; it also shows how conditional - <code>GET</code>s can be handled, if it's desirable to do so in a - particular response handler -- <code>ap_set_last_modified</code> checks - against the <code>If-modified-since</code> 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 - <code>ap_set_content_length</code>, but it returns an error code for - symmetry.</p> - - <div class="example"><p><code> - int default_handler (request_rec *r)<br /> - {<br /> - <span class="indent"> - int errstatus;<br /> - FILE *f;<br /> - <br /> - if (r->method_number != M_GET) return DECLINED;<br /> - if (r->finfo.st_mode == 0) return NOT_FOUND;<br /> - <br /> - if ((errstatus = ap_set_content_length (r, r->finfo.st_size))<br /> - || - (errstatus = ap_set_last_modified (r, r->finfo.st_mtime)))<br /> - return errstatus;<br /> - <br /> - f = fopen (r->filename, "r");<br /> - <br /> - if (f == NULL) {<br /> - <span class="indent"> - log_reason("file permissions deny server access", r->filename, r);<br /> - return FORBIDDEN;<br /> - </span> - }<br /> - <br /> - register_timeout ("send", r);<br /> - ap_send_http_header (r);<br /> - <br /> - if (!r->header_only) send_fd (f, r);<br /> - ap_pfclose (r->pool, f);<br /> - return OK;<br /> - </span> - } - </code></p></div> - - <p>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 - <code>ap_internal_redirect</code>, which is how the internal redirection - machinery discussed above is invoked. A response handler which has - internally redirected should always return <code>OK</code>.</p> - - <p>(Invoking <code>ap_internal_redirect</code> from handlers which are - <em>not</em> response handlers will lead to serious confusion).</p> - - - <h3><a name="auth_handlers" id="auth_handlers">Special considerations for authentication - handlers</a></h3> - <p>Stuff that should be discussed here in detail:</p> - - <ul> - <li>Authentication-phase handlers not invoked unless auth is - configured for the directory.</li> - - <li>Common auth configuration stored in the core per-dir - configuration; it has accessors <code>ap_auth_type</code>, - <code>ap_auth_name</code>, and <code>ap_requires</code>.</li> - - <li>Common routines, to handle the protocol end of things, at - least for HTTP basic authentication - (<code>ap_get_basic_auth_pw</code>, which sets the - <code>connection->user</code> structure field - automatically, and <code>ap_note_basic_auth_failure</code>, - which arranges for the proper <code>WWW-Authenticate:</code> - header to be sent back).</li> - </ul> - - - <h3><a name="log_handlers" id="log_handlers">Special considerations for logging - handlers</a></h3> - <p>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 <code>request_rec</code> structures which are threaded - through the <code>r->prev</code> and <code>r->next</code> pointers. - The <code>request_rec</code> 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 <code>bytes_sent</code> field will only be - correct in the last request in the chain (the one for which a response was - actually sent).</p> - -</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> -<div class="section"> -<h2><a name="pools" id="pools">Resource allocation and resource pools</a></h2> - <p>One of the problems of writing and designing a server-pool server is - that of preventing leakage, that is, allocating resources (memory, open - files, <em>etc.</em>), 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 - <em>automatically</em> released when the server is done with them.</p> - - <p>The way this works is as follows: the memory which is allocated, file - opened, <em>etc.</em>, to deal with a particular request are tied to a - <em>resource pool</em> which is allocated for the request. The pool is a - data structure which itself tracks the resources in question.</p> - - <p>When the request has been processed, the pool is <em>cleared</em>. 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.</p> - - <p>Server restarts, and allocation of memory and resources for per-server - configuration, are handled in a similar way. There is a <em>configuration - pool</em>, 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.</p> - - <p>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 <code><a href="#pool-files">ap_pfopen</a></code>, which also arranges for the - underlying file descriptor to be closed before any child processes, such as - for CGI scripts, are <code>exec</code>ed), 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, <code>ap_palloc</code> is generally faster than - <code>malloc</code>.</p> - - <p>We begin here by describing how memory is allocated to pools, and then - discuss how other resources are tracked by the resource pool machinery.</p> - - <h3>Allocation of memory in pools</h3> - <p>Memory is allocated to pools by calling the function - <code>ap_palloc</code>, which takes two arguments, one being a pointer to - a resource pool structure, and the other being the amount of memory to - allocate (in <code>char</code>s). Within handlers for handling requests, - the most common way of getting a resource pool structure is by looking at - the <code>pool</code> slot of the relevant <code>request_rec</code>; hence - the repeated appearance of the following idiom in module code:</p> - - <div class="example"><p><code> - int my_handler(request_rec *r)<br /> - {<br /> - <span class="indent"> - struct my_structure *foo;<br /> - ...<br /> - <br /> - foo = (foo *)ap_palloc (r->pool, sizeof(my_structure));<br /> - </span> - } - </code></p></div> - - <p>Note that <em>there is no <code>ap_pfree</code></em> -- - <code>ap_palloc</code>ed memory is freed only when the associated resource - pool is cleared. This means that <code>ap_palloc</code> does not have to - do as much accounting as <code>malloc()</code>; all it does in the typical - case is to round up the size, bump a pointer, and do a range check.</p> - - <p>(It also raises the possibility that heavy use of - <code>ap_palloc</code> 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 <code>malloc</code>, and try to be sure that all of - the memory gets explicitly <code>free</code>d, 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).</p> - - - <h3>Allocating initialized memory</h3> - <p>There are functions which allocate initialized memory, and are - frequently useful. The function <code>ap_pcalloc</code> has the same - interface as <code>ap_palloc</code>, but clears out the memory it - allocates before it returns it. The function <code>ap_pstrdup</code> - takes a resource pool and a <code>char *</code> as arguments, and - allocates memory for a copy of the string the pointer points to, returning - a pointer to the copy. Finally <code>ap_pstrcat</code> is a varargs-style - function, which takes a pointer to a resource pool, and at least two - <code>char *</code> arguments, the last of which must be - <code>NULL</code>. It allocates enough memory to fit copies of each of - the strings, as a unit; for instance:</p> - - <div class="example"><p><code> - ap_pstrcat (r->pool, "foo", "/", "bar", NULL); - </code></p></div> - - <p>returns a pointer to 8 bytes worth of memory, initialized to - <code>"foo/bar"</code>.</p> - - - <h3><a name="pools-used" id="pools-used">Commonly-used pools in the Apache Web - server</a></h3> - <p>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:</p> - - <dl> - <dt><code>permanent_pool</code></dt> - <dd>never passed to anything else, this is the ancestor of all pools</dd> - - <dt><code>pconf</code></dt> - <dd> - <ul> - <li>subpool of permanent_pool</li> - - <li>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</li> - - <li>passed to the module init() functions</li> - </ul> - </dd> - - <dt><code>ptemp</code></dt> - <dd> - <ul> - <li>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.</li> - - <li>subpool of permanent_pool</li> - - <li>created at the beginning of a config "cycle"; exists - until the end of config parsing; passed to config-time - routines <em>via</em> 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.</li> - </ul> - </dd> - - <dt><code>pchild</code></dt> - <dd> - <ul> - <li>subpool of permanent_pool</li> - - <li>created when a child is spawned (or a thread is - created); lives until that child (thread) is - destroyed</li> - - <li>passed to the module child_init functions</li> - - <li>destruction happens right after the child_exit - functions are called... (which may explain why I think - child_exit is redundant and unneeded)</li> - </ul> - </dd> - - <dt><code>ptrans</code></dt> - <dd> - <ul> - <li>should be a subpool of pchild, but currently is a - subpool of permanent_pool, see above</li> - - <li>cleared by the child before going into the accept() - loop to receive a connection</li> - - <li>used as connection->pool</li> - </ul> - </dd> - - <dt><code>r->pool</code></dt> - <dd> - <ul> - <li>for the main request this is a subpool of - connection->pool; for subrequests it is a subpool of - the parent request's pool.</li> - - <li>exists until the end of the request (<em>i.e.</em>, - ap_destroy_sub_req, or in child_main after - process_request has finished)</li> - - <li>note that r itself is allocated from r->pool; - <em>i.e.</em>, r->pool is first created and then r is - the first thing palloc()d from it</li> - </ul> - </dd> - </dl> - - <p>For almost everything folks do, <code>r->pool</code> 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.</p> - - <p>You can also see how some bugs have manifested themself, such as - setting <code>connection->user</code> to a value from - <code>r->pool</code> -- in this case connection exists for the - lifetime of <code>ptrans</code>, which is longer than - <code>r->pool</code> (especially if <code>r->pool</code> is a - subrequest!). So the correct thing to do is to allocate from - <code>connection->pool</code>.</p> - - <p>And there was another interesting bug in <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> - / <code class="module"><a href="../mod/mod_cgi.html">mod_cgi</a></code>. You'll see in those that they do this test - to decide if they should use <code>r->pool</code> or - <code>r->main->pool</code>. In this case the resource that they are - registering for cleanup is a child process. If it were registered in - <code>r->pool</code>, then the code would <code>wait()</code> for the - child when the subrequest finishes. With <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> this - could be any old <code>#include</code>, and the delay can be up to 3 - seconds... and happened quite frequently. Instead the subprocess is - registered in <code>r->main->pool</code> which causes it to be - cleaned up when the entire request is done -- <em>i.e.</em>, after the - output has been sent to the client and logging has happened.</p> - - - <h3><a name="pool-files" id="pool-files">Tracking open files, etc.</a></h3> - <p>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 <code>ap_pfopen</code>, which takes a - resource pool and two strings as arguments; the strings are the same as - the typical arguments to <code>fopen</code>, <em>e.g.</em>,</p> - - <div class="example"><p><code> - ...<br /> - FILE *f = ap_pfopen (r->pool, r->filename, "r");<br /> - <br /> - if (f == NULL) { ... } else { ... }<br /> - </code></p></div> - - <p>There is also a <code>ap_popenf</code> routine, which parallels the - lower-level <code>open</code> system call. Both of these routines arrange - for the file to be closed when the resource pool in question is - cleared.</p> - - <p>Unlike the case for memory, there <em>are</em> functions to close files - allocated with <code>ap_pfopen</code>, and <code>ap_popenf</code>, namely - <code>ap_pfclose</code> and <code>ap_pclosef</code>. (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 <code>ap_pfopen</code> and <code>ap_popenf</code>, since to - do otherwise could cause fatal errors on systems such as Linux, which - react badly if the same <code>FILE*</code> is closed more than once.</p> - - <p>(Using the <code>close</code> 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).</p> - - - <h3>Other sorts of resources -- cleanup functions</h3> - <p>More text goes here. Describe the cleanup primitives in terms of - which the file stuff is implemented; also, <code>spawn_process</code>.</p> - - <p>Pool cleanups live until <code>clear_pool()</code> is called: - <code>clear_pool(a)</code> recursively calls <code>destroy_pool()</code> - on all subpools of <code>a</code>; then calls all the cleanups for - <code>a</code>; then releases all the memory for <code>a</code>. - <code>destroy_pool(a)</code> calls <code>clear_pool(a)</code> and then - releases the pool structure itself. <em>i.e.</em>, - <code>clear_pool(a)</code> doesn't delete <code>a</code>, it just frees - up all the resources and you can start using it again immediately.</p> - - - <h3>Fine control -- creating and dealing with sub-pools, with - a note on sub-requests</h3> - <p>On rare occasions, too-free use of <code>ap_palloc()</code> and the - associated primitives may result in undesirably profligate resource - allocation. You can deal with such a case by creating a <em>sub-pool</em>, - 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 <em>is</em> 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 <em>very</em> large directories. - Unnecessary use of the primitives discussed here can hair up your code - quite a bit, with very little gain).</p> - - <p>The primitive for creating a sub-pool is <code>ap_make_sub_pool</code>, - 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 - <code>ap_clear_pool</code> and <code>ap_destroy_pool</code>, respectively. - (The difference is that <code>ap_clear_pool</code> frees resources - associated with the pool, while <code>ap_destroy_pool</code> 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).</p> - - <p>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 <code>ap_sub_req_...</code> functions) is - <code>ap_destroy_sub_req</code>, 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 - <code>request_rec</code> structure).</p> - - <p>(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 - <code>ap_destroy_...</code> functions).</p> - -</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> -<div class="section"> -<h2><a name="config" id="config">Configuration, commands and the like</a></h2> - <p>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.</p> - - <p>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 - <code class="directive"><a href="../mod/mod_mime.html#addtype">AddType</a></code> and <code class="directive"><a href="../mod/core.html#defaulttype">DefaultType</a></code> directives, and so forth. In general, - the governing philosophy is that anything which <em>can</em> be made - configurable by directory should be; per-server information is generally - used in the standard set of modules for information like - <code class="directive"><a href="../mod/mod_alias.html#alias">Alias</a></code>es and <code class="directive"><a href="../mod/mod_alias.html#redirect">Redirect</a></code>s which come into play before the - request is tied to a particular place in the underlying file system.</p> - - <p>Another requirement for emulating the NCSA server is being able to handle - the per-directory configuration files, generally called - <code>.htaccess</code> 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 - <code>.htaccess</code> files which might be present. The information which - is read in then has to be <em>merged</em> with the applicable information - from the server's own config files (either from the <code class="directive"><a href="../mod/core.html#directory"><Directory></a></code> sections in - <code>access.conf</code>, or from defaults in <code>srm.conf</code>, which - actually behaves for most purposes almost exactly like <code><Directory - /></code>).</p> - - <p>Finally, after having served a request which involved reading - <code>.htaccess</code> 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.</p> - - <h3><a name="per-dir" id="per-dir">Per-directory configuration structures</a></h3> - <p>Let's look out how all of this plays out in <code>mod_mime.c</code>, - 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 <code class="directive"><a href="../mod/mod_mime.html#addtype">AddType</a></code> and <code class="directive"><a href="../mod/mod_mime.html#addencoding">AddEncoding</a></code> commands. These commands can appear in - <code>.htaccess</code> 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:</p> - - <div class="example"><pre>typedef struct { - table *forced_types; /* Additional AddTyped stuff */ - table *encoding_types; /* Added with AddEncoding... */ -} mime_dir_config;</pre></div> - - <p>When the server is reading a configuration file, or <code class="directive"><a href="../mod/core.html#directory"><Directory></a></code> section, which includes - one of the MIME module's commands, it needs to create a - <code>mime_dir_config</code> 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 - <code>NULL</code> for <code>srm.conf</code>), and a pointer to a - resource pool in which the allocation should happen.</p> - - <p>(If we are reading a <code>.htaccess</code> 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).</p> - - <p>For the MIME module, the per-dir config creation function just - <code>ap_palloc</code>s the structure above, and a creates a couple of - tables to fill it. That looks like this:</p> - - <div class="example"><p><code> - void *create_mime_dir_config (pool *p, char *dummy)<br /> - {<br /> - <span class="indent"> - mime_dir_config *new =<br /> - <span class="indent"> - (mime_dir_config *) ap_palloc (p, sizeof(mime_dir_config));<br /> - </span> - <br /> - new->forced_types = ap_make_table (p, 4);<br /> - new->encoding_types = ap_make_table (p, 4);<br /> - <br /> - return new;<br /> - </span> - } - </code></p></div> - - <p>Now, suppose we've just read in a <code>.htaccess</code> file. We - already have the per-directory configuration structure for the next - directory up in the hierarchy. If the <code>.htaccess</code> file we just - read in didn't have any <code class="directive"><a href="../mod/mod_mime.html#addtype">AddType</a></code> - or <code class="directive"><a href="../mod/mod_mime.html#addencoding">AddEncoding</a></code> 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.</p> - - <p>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:</p> - - <div class="example"><p><code> - void *merge_mime_dir_configs (pool *p, void *parent_dirv, void *subdirv)<br /> - {<br /> - <span class="indent"> - mime_dir_config *parent_dir = (mime_dir_config *)parent_dirv;<br /> - mime_dir_config *subdir = (mime_dir_config *)subdirv;<br /> - mime_dir_config *new =<br /> - <span class="indent"> - (mime_dir_config *)ap_palloc (p, sizeof(mime_dir_config));<br /> - </span> - <br /> - new->forced_types = ap_overlay_tables (p, subdir->forced_types,<br /> - <span class="indent"> - parent_dir->forced_types);<br /> - </span> - new->encoding_types = ap_overlay_tables (p, subdir->encoding_types,<br /> - <span class="indent"> - parent_dir->encoding_types);<br /> - </span> - <br /> - return new;<br /> - </span> - } - </code></p></div> - - <p>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 (<em>e.g.</em>, for - the includes module, whose per-directory configuration information - consists solely of the state of the <code>XBITHACK</code>), and for those - modules, you can just not declare one, and leave the corresponding - structure slot in the module itself <code>NULL</code>.</p> - - - <h3><a name="commands" id="commands">Command handling</a></h3> - <p>Now that we have these structures, we need to be able to figure out how - to fill them. That involves processing the actual <code class="directive"><a href="../mod/mod_mime.html#addtype">AddType</a></code> and <code class="directive"><a href="../mod/mod_mime.html#addencoding">AddEncoding</a></code> 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 <code class="directive"><a href="../mod/mod_mime.html#addtype">AddType</a></code> - command handler, which looks like this (the <code class="directive"><a href="../mod/mod_mime.html#addencoding">AddEncoding</a></code> command looks basically the same, and won't be - shown here):</p> - - <div class="example"><p><code> - char *add_type(cmd_parms *cmd, mime_dir_config *m, char *ct, char *ext)<br /> - {<br /> - <span class="indent"> - if (*ext == '.') ++ext;<br /> - ap_table_set (m->forced_types, ext, ct);<br /> - return NULL;<br /> - </span> - } - </code></p></div> - - <p>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 <code>cmd_parms</code> 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.</p> - - <p>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 <code>NULL</code>; - this causes an error to be printed out on the server's - <code>stderr</code>, followed by a quick exit, if it is in the main config - files; for a <code>.htaccess</code> 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).</p> - - <p>The MIME module's command table has entries for these commands, which - look like this:</p> - - <div class="example"><p><code> - command_rec mime_cmds[] = {<br /> - <span class="indent"> - { "AddType", add_type, NULL, OR_FILEINFO, TAKE2,<br /> - <span class="indent">"a mime type followed by a file extension" },<br /></span> - { "AddEncoding", add_encoding, NULL, OR_FILEINFO, TAKE2,<br /> - <span class="indent"> - "an encoding (<em>e.g.</em>, gzip), followed by a file extension" },<br /> - </span> - { NULL }<br /> - </span> - }; - </code></p></div> - - <p>The entries in these tables are:</p> - <ul> - <li>The name of the command</li> - <li>The function which handles it</li> - <li>a <code>(void *)</code> pointer, which is passed in the - <code>cmd_parms</code> structure to the command handler --- - this is useful in case many similar commands are handled by - the same function.</li> - - <li>A bit mask indicating where the command may appear. There - are mask bits corresponding to each - <code>AllowOverride</code> option, and an additional mask - bit, <code>RSRC_CONF</code>, indicating that the command may - appear in the server's own config files, but <em>not</em> in - any <code>.htaccess</code> file.</li> - - <li>A flag indicating how many arguments the command handler - wants pre-parsed, and how they should be passed in. - <code>TAKE2</code> indicates two pre-parsed arguments. Other - options are <code>TAKE1</code>, which indicates one - pre-parsed argument, <code>FLAG</code>, which indicates that - the argument should be <code>On</code> or <code>Off</code>, - and is passed in as a boolean flag, <code>RAW_ARGS</code>, - which causes the server to give the command the raw, unparsed - arguments (everything but the command name itself). There is - also <code>ITERATE</code>, which means that the handler looks - the same as <code>TAKE1</code>, but that if multiple - arguments are present, it should be called multiple times, - and finally <code>ITERATE2</code>, which indicates that the - command handler looks like a <code>TAKE2</code>, but if more - arguments are present, then it should be called multiple - times, holding the first argument constant.</li> - - <li>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 <code>NULL</code>).</li> - </ul> - - <p>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 <code>request_rec</code>'s - per-directory configuration vector by using the - <code>ap_get_module_config</code> function.</p> - - <div class="example"><p><code> - int find_ct(request_rec *r)<br /> - {<br /> - <span class="indent"> - int i;<br /> - char *fn = ap_pstrdup (r->pool, r->filename);<br /> - mime_dir_config *conf = (mime_dir_config *)<br /> - <span class="indent"> - ap_get_module_config(r->per_dir_config, &mime_module);<br /> - </span> - char *type;<br /> - <br /> - if (S_ISDIR(r->finfo.st_mode)) {<br /> - <span class="indent"> - r->content_type = DIR_MAGIC_TYPE;<br /> - return OK;<br /> - </span> - }<br /> - <br /> - if((i=ap_rind(fn,'.')) < 0) return DECLINED;<br /> - ++i;<br /> - <br /> - if ((type = ap_table_get (conf->encoding_types, &fn[i])))<br /> - {<br /> - <span class="indent"> - r->content_encoding = type;<br /> - <br /> - /* go back to previous extension to try to use it as a type */<br /> - fn[i-1] = '\0';<br /> - if((i=ap_rind(fn,'.')) < 0) return OK;<br /> - ++i;<br /> - </span> - }<br /> - <br /> - if ((type = ap_table_get (conf->forced_types, &fn[i])))<br /> - {<br /> - <span class="indent"> - r->content_type = type;<br /> - </span> - }<br /> - <br /> - return OK; - </span> - } - </code></p></div> - - - <h3><a name="servconf" id="servconf">Side notes -- per-server configuration, - virtual servers, <em>etc</em>.</a></h3> - <p>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).</p> - - <p>The only substantial difference is that when a command needs to - configure the per-server private module data, it needs to go to the - <code>cmd_parms</code> 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):</p> - - <div class="example"><p><code> - char *add_redirect(cmd_parms *cmd, void *dummy, char *f, char *url)<br /> - {<br /> - <span class="indent"> - server_rec *s = cmd->server;<br /> - alias_server_conf *conf = (alias_server_conf *)<br /> - <span class="indent"> - ap_get_module_config(s->module_config,&alias_module);<br /> - </span> - alias_entry *new = ap_push_array (conf->redirects);<br /> - <br /> - if (!ap_is_url (url)) return "Redirect to non-URL";<br /> - <br /> - new->fake = f; new->real = url;<br /> - return NULL;<br /> - </span> - } - </code></p></div> - -</div></div> -<div class="bottomlang"> -<p><span>Available Languages: </span><a href="../en/developer/API.html" title="English"> en </a></p> -</div><div id="footer"> -<p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p> -<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div> -</body></html>
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