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17 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
18 <p class="apache">Apache HTTP Server Version 2.5</p>
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22 <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 2.5</a> > <a href="./">Developer</a></div><div id="page-content"><div id="preamble"><h1>Developing modules for the Apache HTTP Server 2.4</h1>
24 <p><span>Available Languages: </span><a href="../en/developer/modguide.html" title="English"> en </a></p>
27 <p>This document explains how you can develop modules for the Apache HTTP
30 <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#introduction">Introduction</a></li>
31 <li><img alt="" src="../images/down.gif" /> <a href="#basics">Defining a module</a></li>
32 <li><img alt="" src="../images/down.gif" /> <a href="#hooking">Getting started: Hooking into the server</a></li>
33 <li><img alt="" src="../images/down.gif" /> <a href="#handling">Building a handler</a></li>
34 <li><img alt="" src="../images/down.gif" /> <a href="#configuration">Adding configuration options</a></li>
35 <li><img alt="" src="../images/down.gif" /> <a href="#context">Context aware configurations</a></li>
36 <li><img alt="" src="../images/down.gif" /> <a href="#summary">Summing up</a></li>
37 <li><img alt="" src="../images/down.gif" /> <a href="#snippets">Some useful snippets of code</a></li>
38 </ul><h3>See also</h3><ul class="seealso"><li><a href="request.html">Request Processing in Apache 2.4</a></li><li><a href="hooks.html">Apache 2.x Hook Functions</a></li></ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
39 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
41 <h2><a name="introduction" id="introduction">Introduction</a></h2>
42 <h3><a name="what" id="what">What we will be discussing in this document</a></h3>
44 This document will discuss how you can create modules for the Apache
45 HTTP Server 2.4, by exploring an example module called
46 <code>mod_example</code>. In the first part of this document, the purpose
47 of this module will be to calculate and print out various digest values for
48 existing files on your web server, whenever we access the URL <code>
49 http://hostname/filename.sum</code>. For instance, if we want to know the
50 MD5 digest value of the file located at <code>
51 http://www.example.com/index.html</code>, we would visit <code>
52 http://www.example.com/index.html.sum</code>.
56 In the second part of this document, which deals with configuration
57 directive and context awareness, we will be looking at a module that simply
58 write out its own configuration to the client.
62 <h3><a name="prerequisites" id="prerequisites">Prerequisites</a></h3>
64 First and foremost, you are expected to have a basic knowledge of how the C
65 programming language works. In most cases, we will try to be as pedagogical
66 as possible and link to documents describing the functions used in the
67 examples, but there are also many cases where it is necessary to either
68 just assume that "it works" or do some digging yourself into what the hows
69 and whys of various function calls.
72 Lastly, you will need to have a basic understanding of how modules are
73 loaded and configured in the Apache HTTP Server, as well as how to get the headers for
74 Apache if you do not have them already, as these are needed for compiling
78 <h3><a name="compiling" id="compiling">Compiling your module</a></h3>
80 To compile the source code we are building in this document, we will be
81 using <a href="../programs/apxs.html">APXS</a>. Assuming your source file
82 is called mod_example.c, compiling, installing and activating the module is
85 <div class="example"><pre>
86 apxs -i -a -c mod_example.c
90 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
92 <h2><a name="basics" id="basics">Defining a module</a></h2>
94 <img src="../images/build_a_mod_3.png" alt="Module name tags" /><br />
95 Every module starts with the same declaration, or name tag if you will,
96 that defines a module as <em>a separate entity within Apache</em>:</p>
100 <pre class="prettyprint lang-c">
101 module AP_MODULE_DECLARE_DATA example_module =
103 STANDARD20_MODULE_STUFF,
104 create_dir_conf, /* Per-directory configuration handler */
105 merge_dir_conf, /* Merge handler for per-directory configurations */
106 create_svr_conf, /* Per-server configuration handler */
107 merge_svr_conf, /* Merge handler for per-server configurations */
108 directives, /* Any directives we may have for httpd */
109 register_hooks /* Our hook registering function */
116 This bit of code lets the server know that we have now registered a new module
117 in the system, and that its name is <code>example_module</code>. The name
118 of the module is used primarily for two things:<br />
121 <li>Letting the server know how to load the module using the LoadModule</li>
122 <li>Setting up a namespace for the module to use in configurations</li>
125 For now, we're only concerned with the first purpose of the module name,
126 which comes into play when we need to load the module:
128 <pre class="prettyprint lang-config">
129 LoadModule example_module modules/mod_example.so
133 In essence, this tells the server to open up <code>mod_example.so</code> and look for a module
134 called <code>example_module</code>.
137 Within this name tag of ours is also a bunch of references to how we would
138 like to handle things: Which directives do we respond to in a configuration
139 file or .htaccess, how do we operate within specific contexts, and what
140 handlers are we interested in registering with the Apache HTTP service. We'll
141 return to all these elements later in this document.
143 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
144 <div class="section">
145 <h2><a name="hooking" id="hooking">Getting started: Hooking into the server</a></h2>
146 <h3><a name="hook_intro" id="hook_intro">An introduction to hooks</a></h3>
148 When handling requests in Apache HTTP Server 2.4, the first thing you will need to do is
149 create a hook into the request handling process. A hook is essentially a
150 message telling the server that you are willing to either serve or at least
151 take a glance at certain requests given by clients. All handlers, whether
152 it's mod_rewrite, mod_authn_*, mod_proxy and so on, are hooked into
153 specific parts of the request process. As you are probably aware, modules
154 serve different purposes; Some are authentication/authorization handlers,
155 others are file or script handlers while some third modules rewrite URIs or
156 proxies content. Furthermore, in the end, it is up to the user of the server
157 how and when each module will come into place. Thus, the server itself does not
158 presume to know which module is responsible for handling a specific
159 request, and will ask each module whether they have an interest in a given
160 request or not. It is then up to each module to either gently decline
161 serving a request, accept serving it or flat out deny the request from
162 being served, as authentication/authorization modules do: <br />
163 <img src="../images/build_a_mod_2.png" alt="Hook handling in httpd" /><br />
164 To make it a bit easier for handlers such as our mod_example to know
165 whether the client is requesting content we should handle or not, the server
166 has directives for hinting to modules whether their assistance is needed or
167 not. Two of these are <code class="directive"><a href="../mod/mod_mime.html#addhandler">AddHandler</a></code>
168 and <code class="directive"><a href="../mod/core.html#sethandler">SetHandler</a></code>. Let's take a look at
169 an example using <code class="directive"><a href="../mod/mod_mime.html#addhandler">AddHandler</a></code>. In
170 our example case, we want every request ending with .sum to be served by
171 <code>mod_example</code>, so we'll add a configuration directive that tells
172 the server to do just that:
174 <pre class="prettyprint lang-config">
175 AddHandler example-handler .sum
179 What this tells the server is the following: <em>Whenever we receive a request
180 for a URI ending in .sum, we are to let all modules know that we are
181 looking for whoever goes by the name of "example-handler" </em>.
182 Thus, when a request is being served that ends in .sum, the server will let all
183 modules know, that this request should be served by "example-handler
184 ". As you will see later, when we start building mod_example, we will
185 check for this handler tag relayed by <code>AddHandler</code> and reply to
186 the server based on the value of this tag.
189 <h3><a name="hook_declaration" id="hook_declaration">Hooking into httpd</a></h3>
191 To begin with, we only want to create a simple handler, that replies to the
192 client browser when a specific URL is requested, so we won't bother setting
193 up configuration handlers and directives just yet. Our initial module
194 definition will look like this:</p>
198 <pre class="prettyprint lang-c">
199 module AP_MODULE_DECLARE_DATA example_module =
201 STANDARD20_MODULE_STUFF,
207 register_hooks /* Our hook registering function */
214 <p>This lets the server know that we are not interesting in anything fancy, we
215 just want to hook onto the requests and possibly handle some of them. </p>
217 <p> The reference in our example declaration, <code>register_hooks</code>
218 is the name of a function we will create to manage how we hook onto the
219 request process. In this example module, the function has just one purpose;
220 To create a simple hook that gets called after all the rewrites, access
221 control etc has been handled. Thus, we will let the server know, that we want
222 to hook into its process as one of the last modules:
226 <pre class="prettyprint lang-c">
227 static void register_hooks(apr_pool_t *pool)
229 /* Create a hook in the request handler, so we get called when a request arrives */
230 ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
237 The <code>example_handler</code> reference is the function that will handle
238 the request. We will discuss how to create a handler in the next chapter.
241 <h3><a name="hook_others" id="hook_others">Other useful hooks</a></h3>
243 Hooking into the request handling phase is but one of many hooks that you
244 can create. Some other ways of hooking are:
247 <li><code>ap_hook_child_init</code>: Place a hook that executes when a child process is spawned (commonly used for initializing modules after the server has forked)</li>
248 <li><code>ap_hook_pre_config</code>: Place a hook that executes before any configuration data has been read (very early hook)</li>
249 <li><code>ap_hook_post_config</code>: Place a hook that executes after configuration has been parsed, but before the server has forked</li>
250 <li><code>ap_hook_translate_name</code>: Place a hook that executes when a URI needs to be translated into a filename on the server (think <code>mod_rewrite</code>)</li>
251 <li><code>ap_hook_quick_handler</code>: Similar to <code>ap_hook_handler</code>, except it is run before any other request hooks (translation, auth, fixups etc)</li>
252 <li><code>ap_hook_log_transaction</code>: Place a hook that executes when the server is about to add a log entry of the current request</li>
256 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
257 <div class="section">
258 <h2><a name="handling" id="handling">Building a handler</a></h2>
260 A handler is essentially a function that receives a callback when a request
261 to the server is made. It is passed a record of the current request (how it was
262 made, which headers and requests were passed along, who's giving the
263 request and so on), and is put in charge of either telling the server that it's
264 not interested in the request or handle the request with the tools provided.
266 <h3><a name="simple_handler" id="simple_handler">A simple "Hello, world!"
268 <p>Let's start off by making a very simple request handler
269 that does the following:
272 <li>Check that this is a request that should be served by "example-handler"</li>
273 <li>Set the content type of our output to <code>text/html</code></li>
274 <li>Write "Hello, world!" back to the client browser</li>
275 <li>Let the server know that we took care of this request and everything went fine</li>
278 In C code, our example handler will now look like this:
282 <pre class="prettyprint lang-c">
283 static int example_handler(request_rec *r)
285 /* First off, we need to check if this is a call for the "example-handler" handler.
286 * If it is, we accept it and do our things, if not, we simply return DECLINED,
287 * and the server will try somewhere else.
289 if (!r->handler || strcmp(r->handler, "example-handler")) return (DECLINED);
291 /* Now that we are handling this request, we'll write out "Hello, world!" to the client.
292 * To do so, we must first set the appropriate content type, followed by our output.
294 ap_set_content_type(r, "text/html");
295 ap_rprintf(r, "Hello, world!");
297 /* Lastly, we must tell the server that we took care of this request and everything went fine.
298 * We do so by simply returning the value OK to the server.
307 Now, we put all we have learned together and end up with a program that
309 <a href="http://people.apache.org/~humbedooh/mods/examples/mod_example_1.c">mod_example_1.c</a>
310 . The functions used in this example will be explained later in the section
311 <a href="#functions">"Some useful functions you should know"</a>.
314 <h3><a name="request_rec" id="request_rec">The request_rec structure</a></h3>
315 <p>The most essential part of any request is the <em>request record
316 </em>. In a call to a handler function, this is represented by the <code>
317 request_req* </code> structure passed along with every call that is made.
318 This struct, typically just refered to as <code>r</code> in modules,
319 contains all the information you need for your module to fully process any
320 HTTP request and respond accordingly.</p> <p>Some key elements of the <code>
321 request_req </code> structure are:
324 <li><code>r->handler (char*):</code> Contains the name of the handler the server is currently asking to do the handling of this request</li>
325 <li><code>r->method (char*):</code> Contains the HTTP method being used, f.x. GET or POST</li>
326 <li><code>r->filename (char*):</code> Contains the translated filename the client is requesting</li>
327 <li><code>r->args (char*):</code> Contains the query string of the request, if any</li>
328 <li><code>r->headers_in (apr_table_t*):</code> Contains all the headers sent by the client</li>
329 <li><code>r->connection (conn_rec*):</code> A record containing information about the current connection</li>
330 <li><code>r->user (char*):</code> If the URI requires authentication, this is set to the username provided</li>
331 <li><code>r->useragent_ip (char*):</code> The IP address of the client connecting to us</li>
332 <li><code>r->pool (apr_pool_t*)</code>: The memory pool of this request. We'll discuss this in the
333 "<a href="#memory">Memory management</a>" chapter.</li>
336 A complete list of all the values contained with in the <code>request_req</code> structure can be found in
337 the <a href="http://svn.apache.org/repos/asf/httpd/httpd/trunk/include/httpd.h"><code>httpd.h</code></a> header
338 file or at <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/structrequest__rec.html">http://ci.apache.org/projects/httpd/trunk/doxygen/structrequest__rec.html</a>.
343 Let's try out some of these variables in another example handler:<br />
347 <pre class="prettyprint lang-c">
348 static int example_handler(request_rec *r)
350 /* Set the appropriate content type */
351 ap_set_content_type(r, "text/html");
353 /* Print out the IP address of the client connecting to us: */
354 ap_rprintf(r, "<h2>Hello, %s!</h2>", r->useragent_ip);
356 /* If we were reached through a GET or a POST request, be happy, else sad. */
357 if ( !strcmp(r->method, "POST") || !strcmp(r->method, "GET") ) {
358 ap_rputs("You used a GET or a POST method, that makes us happy!<br/>", r);
361 ap_rputs("You did not use POST or GET, that makes us sad :(<br/>", r);
364 /* Lastly, if there was a query string, let's print that too! */
366 ap_rprintf(r, "Your query string was: %s", r->args);
376 <h3><a name="return_value" id="return_value">Return values</a></h3>
378 Apache relies on return values from handlers to signify whether a request
379 was handled or not, and if so, whether the request went well or not. If a
380 module is not interested in handling a specific request, it should always
381 return the value <code>DECLINED</code>. If it is handling a request, it
382 should either return the generic value <code>OK</code>, or a specific HTTP
383 status code, for example:
387 <pre class="prettyprint lang-c">
388 static int example_handler(request_rec *r)
390 /* Return 404: Not found */
391 return HTTP_NOT_FOUND;
398 Returning <code>OK</code> or a HTTP status code does not necessarily mean
399 that the request will end. The server may still have other handlers that are
400 interested in this request, for instance the logging modules which, upon a
401 successful request, will write down a summary of what was requested and how
402 it went. To do a full stop and prevent any further processing after your
403 module is done, you can return the value <code>DONE</code> to let the server
404 know that it should cease all activity on this request and carry on with
405 the next, without informing other handlers.
407 <strong>General response codes:</strong>
410 <li><code>DECLINED</code>: We are not handling this request</li>
411 <li><code>OK</code>: We handled this request and it went well</li>
412 <li><code>DONE</code>: We handled this request and the server should just close this thread without further processing</li>
415 <strong>HTTP specific return codes (excerpt):</strong>
418 <li><code>HTTP_OK (200)</code>: Request was okay</li>
419 <li><code>HTTP_MOVED_PERMANENTLY (301)</code>: The resource has moved to a new URL</li>
420 <li><code>HTTP_UNAUTHORIZED (401)</code>: Client is not authorized to visit this page</li>
421 <li><code>HTTP_FORBIDDEN (403)</code>: Permission denied</li>
422 <li><code>HTTP_NOT_FOUND (404)</code>: File not found</li>
423 <li><code>HTTP_INTERNAL_SERVER_ERROR (500)</code>: Internal server error (self explanatory)</li>
427 <h3><a name="functions" id="functions">Some useful functions you should know</a></h3>
431 <code>ap_rputs(const char *string, request_req *r)</code>: <br />
432 Sends a string of text to the client. This is a shorthand version of <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#gac827cd0537d2b6213a7c06d7c26cc36e">
437 <pre class="prettyprint lang-c">ap_rputs("Hello, world!", r);</pre>
445 <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#ga5e91eb6ca777c9a427b2e82bf1eeb81d">ap_rprintf</a></code>: <br />
446 This function works just like <code>printf</code>, except it sends the result to the client.
450 <pre class="prettyprint lang-c">ap_rprintf(r, "Hello, %s!", r->useragent_ip);</pre>
457 <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#gaa2f8412c400197338ec509f4a45e4579">ap_set_content_type</a>(request_req *r, const char *type)</code>: <br />
458 Sets the content type of the output you are sending.
462 <pre class="prettyprint lang-c">ap_set_content_type(r, "text/plain"); /* force a raw text output */</pre>
472 <h3><a name="memory" id="memory">Memory management</a></h3>
474 Managing your resources in Apache HTTP Server 2.4 is quite easy, thanks to the memory pool
475 system. In essence, each server, connection and request have their own
476 memory pool that gets cleaned up when its scope ends, e.g. when a request
477 is done or when a server process shuts down. All your module needs to do is
478 latch onto this memory pool, and you won't have to worry about having to
479 clean up after yourself - pretty neat, huh?
483 In our module, we will primarily be allocating memory for each request, so
484 it's appropriate to use the <code>r->pool</code>
485 reference when creating new objects. A few of the functions for allocating
486 memory within a pool are:
489 <li><code>void* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__pools.html#ga85f1e193c31d109affda72f9a92c6915">apr_palloc</a>(
490 apr_pool_t *p, apr_size_t size)</code>: Allocates <code>size</code> number of bytes in the pool for you</li>
491 <li><code>void* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__pools.html#gaf61c098ad258069d64cdf8c0a9369f9e">apr_pcalloc</a>(
492 apr_pool_t *p, apr_size_t size)</code>: Allocates <code>size</code> number of bytes in the pool for you and sets all bytes to 0</li>
493 <li><code>char* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__strings.html#gabc79e99ff19abbd7cfd18308c5f85d47">apr_pstrdup</a>(
494 apr_pool_t *p, const char *s)</code>: Creates a duplicate of the string <code>s</code>. This is useful for copying constant values so you can edit them</li>
495 <li><code>char* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__strings.html#ga3eca76b8d293c5c3f8021e45eda813d8">apr_psprintf</a>(
496 apr_pool_t *p, const char *fmt, ...)</code>: Similar to <code>sprintf</code>, except the server supplies you with an appropriately allocated target variable</li>
499 <p>Let's put these functions into an example handler:</p>
503 <pre class="prettyprint lang-c">
504 static int example_handler(request_rec *r)
506 const char* original = "You can't edit this!";
510 /* Allocate space for 10 integer values and set them all to zero. */
511 integers = apr_pcalloc(r->pool, sizeof(int)*10);
513 /* Create a copy of the 'original' variable that we can edit. */
514 copy = apr_pstrdup(r->pool, original);
522 This is all well and good for our module, which won't need any
523 pre-initialized variables or structures. However, if we wanted to
524 initialize something early on, before the requests come rolling in, we
525 could simply add a call to a function in our <code>register_hooks</code>
526 function to sort it out:
530 <pre class="prettyprint lang-c">
531 static void register_hooks(apr_pool_t *pool)
533 /* Call a function that initializes some stuff */
534 example_init_function(pool);
535 /* Create a hook in the request handler, so we get called when a request arrives */
536 ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
543 In this pre-request initialization function we would not be using the
544 same pool as we did when allocating resources for request-based functions.
545 Instead, we would use the pool given to us by the server for allocating memory
546 on a per-process based level.
550 <h3><a name="parsing" id="parsing">Parsing request data</a></h3>
552 In our example module, we would like to add a feature, that checks which
553 type of digest, MD5 or SHA1 the client would like to see. This could be
554 solved by adding a query string to the request. A query string is typically
555 comprised of several keys and values put together in a string, for instance
556 <code>valueA=yes&valueB=no&valueC=maybe</code>. It is up to the
557 module itself to parse these and get the data it requires. In our example,
558 we'll be looking for a key called <code>digest</code>, and if set to <code>
559 md5</code>, we'll produce an MD5 digest, otherwise we'll produce a SHA1
563 Since the introduction of Apache HTTP Server 2.4, parsing request data from GET and
564 POST requests have never been easier. All we require to parse both GET and
565 POST data is four simple lines:
570 <pre class="prettyprint lang-c">
571 <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__apr__tables.html#gad7ea82d6608a4a633fc3775694ab71e4">apr_table_t</a> *GET; <em>
572 </em><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/structapr__array__header__t.html">apr_array_header_t</a>*POST;
575 <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__SCRIPT.html#gaed25877b529623a4d8f99f819ba1b7bd">
576 ap_args_to_table</a>(r, &GET); <em>
577 </em><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__DAEMON.html#ga9d426b6382b49754d4f87c55f65af202">
578 ap_parse_form_data</a>(r, NULL, &POST, -1, 8192);
584 In our specific example module, we're looking for the <code>digest</code>
585 value from the query string, which now resides inside a table called <code>
586 GET</code>. To extract this value, we need only perform a simple operation:
591 <pre class="prettyprint lang-c">
592 /* Get the "digest" key from the query string, if any. */
593 const char *digestType = apr_table_get(GET, "digest");
595 /* If no key was returned, we will set a default value instead. */
596 if (!digestType) digestType = "sha1";
602 The structures used for the POST and GET data are not exactly the same, so
603 if we were to fetch a value from POST data instead of the query string, we
604 would have to resort to a few more lines, as outlined in <a href="#get_post">this example</a> in the last chapter of this document.
608 <h3><a name="advanced_handler" id="advanced_handler">Making an advanced handler</a></h3>
610 Now that we have learned how to parse form data and manage our resources,
611 we can move on to creating an advanced version of our module, that spits
612 out the MD5 or SHA1 digest of files:
617 <pre class="prettyprint lang-c">
618 static int example_handler(request_rec *r)
625 apr_size_t readBytes;
628 apr_array_header_t *POST;
629 const char *digestType;
632 /* Check that the "example-handler" handler is being called. */
633 if (!r->handler || strcmp(r->handler, "example-handler")) return (DECLINED);
635 /* Figure out which file is being requested by removing the .sum from it */
636 filename = apr_pstrdup(r->pool, r->filename);
637 filename[strlen(filename)-4] = 0; /* Cut off the last 4 characters. */
639 /* Figure out if the file we request a sum on exists and isn't a directory */
640 rc = apr_stat(&finfo, filename, APR_FINFO_MIN, r->pool);
641 if (rc == APR_SUCCESS) {
644 (finfo.filetype != APR_NOFILE)
645 && !(finfo.filetype & APR_DIR)
647 if (!exists) return HTTP_NOT_FOUND; /* Return a 404 if not found. */
649 /* If apr_stat failed, we're probably not allowed to check this file. */
650 else return HTTP_FORBIDDEN;
652 /* Parse the GET and, optionally, the POST data sent to us */
654 ap_args_to_table(r, &GET);
655 ap_parse_form_data(r, NULL, &POST, -1, 8192);
657 /* Set the appropriate content type */
658 ap_set_content_type(r, "text/html");
660 /* Print a title and some general information */
661 ap_rprintf(r, "<h2>Information on %s:</h2>", filename);
662 ap_rprintf(r, "<b>Size:</b> %u bytes<br/>", finfo.size);
664 /* Get the digest type the client wants to see */
665 digestType = apr_table_get(GET, "digest");
666 if (!digestType) digestType = "MD5";
669 rc = apr_file_open(&file, filename, APR_READ, APR_OS_DEFAULT, r->pool);
670 if (rc == APR_SUCCESS) {
672 /* Are we trying to calculate the MD5 or the SHA1 digest? */
673 if (!strcasecmp(digestType, "md5")) {
674 /* Calculate the MD5 sum of the file */
680 apr_md5_init(&md5);
682 while ( apr_file_read(file, buffer, &readBytes) == APR_SUCCESS ) {
683 apr_md5_update(&md5, buffer, readBytes);
685 apr_md5_final(digest.chr, &md5);
687 /* Print out the MD5 digest */
688 ap_rputs("<b>MD5: </b><code>", r);
689 for (n = 0; n < APR_MD5_DIGESTSIZE/4; n++) {
690 ap_rprintf(r, "%08x", digest.num[n]);
692 ap_rputs("</code>", r);
693 /* Print a link to the SHA1 version */
694 ap_rputs("<br/><a href='?digest=sha1'>View the SHA1 hash instead</a>", r);
697 /* Calculate the SHA1 sum of the file */
703 apr_sha1_init(&sha1);
705 while ( apr_file_read(file, buffer, &readBytes) == APR_SUCCESS ) {
706 apr_sha1_update(&sha1, buffer, readBytes);
708 apr_sha1_final(digest.chr, &sha1);
710 /* Print out the SHA1 digest */
711 ap_rputs("<b>SHA1: </b><code>", r);
712 for (n = 0; n < APR_SHA1_DIGESTSIZE/4; n++) {
713 ap_rprintf(r, "%08x", digest.num[n]);
715 ap_rputs("</code>", r);
717 /* Print a link to the MD5 version */
718 ap_rputs("<br/><a href='?digest=md5'>View the MD5 hash instead</a>", r);
720 apr_file_close(file);
723 /* Let the server know that we responded to this request. */
731 This version in its entirity can be found here:
732 <a href="http://people.apache.org/~humbedooh/mods/examples/mod_example_2.c">mod_example_2.c</a>.
736 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
737 <div class="section">
738 <h2><a name="configuration" id="configuration">Adding configuration options</a></h2>
740 In this next segment of this document, we will turn our eyes away from the
741 digest module and create a new example module, whose only function is to
742 write out its own configuration. The purpose of this is to examine how
743 the server works with configuration, and what happens when you start writing
744 advanced configurations
747 <h3><a name="config_intro" id="config_intro">An introduction to configuration
750 If you are reading this, then you probably already know
751 what a configuration directive is. Simply put, a directive is a way of
752 telling an individual module (or a set of modules) how to behave, such as
753 these directives control how <code>mod_rewrite</code> works:
755 <pre class="prettyprint lang-config">
757 RewriteCond %{REQUEST_URI} ^/foo/bar
758 RewriteRule ^/foo/bar/(.*)$ /foobar?page=$1
762 Each of these configuration directives are handled by a separate function,
763 that parses the parameters given and sets up a configuration accordingly.
766 <h3><a name="config_simple" id="config_simple">Making an example configuration</a></h3>
767 <p>To begin with, we'll create a basic configuration in C-space:</p>
771 <pre class="prettyprint lang-c">
773 int enabled; /* Enable or disable our module */
774 const char *path; /* Some path to...something */
775 int typeOfAction; /* 1 means action A, 2 means action B and so on */
782 Now, let's put this into perspective by creating a very small module that
783 just prints out a hard-coded configuration. You'll notice that we use the
784 <code>register_hooks</code> function for initializing the configuration
785 values to their defaults:
789 <pre class="prettyprint lang-c">
791 int enabled; /* Enable or disable our module */
792 const char *path; /* Some path to...something */
793 int typeOfAction; /* 1 means action A, 2 means action B and so on */
796 static example_config config;
798 static int example_handler(request_rec *r)
800 if (!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);
801 ap_set_content_type(r, "text/plain");
802 ap_rprintf(r, "Enabled: %u\n", config.enabled);
803 ap_rprintf(r, "Path: %s\n", config.path);
804 ap_rprintf(r, "TypeOfAction: %x\n", config.typeOfAction);
808 static void register_hooks(apr_pool_t *pool)
811 config.path = "/foo/bar";
812 config.typeOfAction = 0x00;
813 ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
816 /* Define our module as an entity and assign a function for registering hooks */
818 module AP_MODULE_DECLARE_DATA example_module =
820 STANDARD20_MODULE_STUFF,
821 NULL, /* Per-directory configuration handler */
822 NULL, /* Merge handler for per-directory configurations */
823 NULL, /* Per-server configuration handler */
824 NULL, /* Merge handler for per-server configurations */
825 NULL, /* Any directives we may have for httpd */
826 register_hooks /* Our hook registering function */
833 So far so good. To access our new handler, we could add the following to
836 <pre class="prettyprint lang-config">
837 <Location /example>
838 SetHandler example-handler
843 When we visit, we'll see our current configuration being spit out by our
848 <h3><a name="register_directive" id="register_directive">Registering directives with the server</a></h3>
850 What if we want to change our configuration, not by hard-coding new values
851 into the module, but by using either the httpd.conf file or possibly a
852 .htaccess file? It's time to let the server know that we want this to be
853 possible. To do so, we must first change our <em>name tag</em> to include a
854 reference to the configuration directives we want to register with the server:
858 <pre class="prettyprint lang-c">
859 module AP_MODULE_DECLARE_DATA example_module =
861 STANDARD20_MODULE_STUFF,
862 NULL, /* Per-directory configuration handler */
863 NULL, /* Merge handler for per-directory configurations */
864 NULL, /* Per-server configuration handler */
865 NULL, /* Merge handler for per-server configurations */
866 example_directives, /* Any directives we may have for httpd */
867 register_hooks /* Our hook registering function */
874 This will tell the server that we are now accepting directives from the
875 configuration files, and that the structure called <code>example_directives
876 </code> holds information on what our directives are and how they work.
877 Since we have three different variables in our module configuration, we
878 will add a structure with three directives and a NULL at the end:
882 <pre class="prettyprint lang-c">
883 static const command_rec example_directives[] =
885 AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, RSRC_CONF, "Enable or disable mod_example"),
886 AP_INIT_TAKE1("examplePath", example_set_path, NULL, RSRC_CONF, "The path to whatever"),
887 AP_INIT_TAKE2("exampleAction", example_set_action, NULL, RSRC_CONF, "Special action value!"),
895 <img src="../images/build_a_mod_4.png" alt="Directives structure" /><br />
896 As you can see, each directive needs at least 5 parameters set:
899 <li><code><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#ga07c7d22ae17805e61204463326cf9c34">AP_INIT_TAKE1</a></code>: This is a macro that tells the server that this directive takes one and only one argument.
900 If we required two arguments, we could use the macro <code><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#gafaec43534fcf200f37d9fecbf9247c21">AP_INIT_TAKE2</a></code> and so on (refer to httpd_conf.h
901 for more macros).</li>
902 <li><code>exampleEnabled</code>: This is the name of our directive. More precisely, it is what the user must put in his/her
903 configuration in order to invoke a configuration change in our module.</li>
904 <li><code>example_set_enabled</code>: This is a reference to a C function that parses the directive and sets the configuration
905 accordingly. We will discuss how to make this in the following paragraph.</li>
906 <li><code>RSRC_CONF</code>: This tells the server where the directive is permitted. We'll go into details on this value in the
907 later chapters, but for now, <code>RSRC_CONF</code> means that the server will only accept these directives in a server context.</li>
908 <li><code>"Enable or disable...."</code>: This is simply a brief description of what the directive does.</li>
911 (<em>The "missing" parameter in our definition, which is usually set to
912 <code>NULL</code>, is an optional function that can be run after the
913 initial function to parse the arguments have been run. This is usually
914 omitted, as the function for verifying arguments might as well be used to
918 <h3><a name="directive_handler" id="directive_handler">The directive handler function</a></h3>
920 Now that we've told the server to expect some directives for our module, it's
921 time to make a few functions for handling these. What the server reads in the
922 configuration file(s) is text, and so naturally, what it passes along to
923 our directive handler is one or more strings, that we ourselves need to
924 recognize and act upon. You'll notice, that since we set our <code>
925 exampleAction</code> directive to accept two arguments, its C function also
926 has an additional parameter defined:</p>
929 <pre class="prettyprint lang-c">
930 /* Handler for the "exambleEnabled" directive */
931 const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
933 if(!strcasecmp(arg, "on")) config.enabled = 1;
934 else config.enabled = 0;
938 /* Handler for the "examplePath" directive */
939 const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
945 /* Handler for the "exampleAction" directive */
946 /* Let's pretend this one takes one argument (file or db), and a second (deny or allow), */
947 /* and we store it in a bit-wise manner. */
948 const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char* arg2)
950 if(!strcasecmp(arg1, "file")) config.typeOfAction = 0x01;
951 else config.typeOfAction = 0x02;
953 if(!strcasecmp(arg2, "deny")) config.typeOfAction += 0x10;
954 else config.typeOfAction += 0x20;
963 <h3><a name="directive_complete" id="directive_complete">Putting it all together</a></h3>
965 Now that we have our directives set up, and handlers configured for them,
966 we can assemble our module into one big file:
970 <pre class="prettyprint lang-c">
971 /* mod_example_config_simple.c: */
972 #include <stdio.h>
973 #include "apr_hash.h"
974 #include "ap_config.h"
975 #include "ap_provider.h"
977 #include "http_core.h"
978 #include "http_config.h"
979 #include "http_log.h"
980 #include "http_protocol.h"
981 #include "http_request.h"
984 ==============================================================================
985 Our configuration prototype and declaration:
986 ==============================================================================
989 int enabled; /* Enable or disable our module */
990 const char *path; /* Some path to...something */
991 int typeOfAction; /* 1 means action A, 2 means action B and so on */
994 static example_config config;
997 ==============================================================================
998 Our directive handlers:
999 ==============================================================================
1001 /* Handler for the "exambleEnabled" directive */
1002 const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
1004 if(!strcasecmp(arg, "on")) config.enabled = 1;
1005 else config.enabled = 0;
1009 /* Handler for the "examplePath" directive */
1010 const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
1016 /* Handler for the "exampleAction" directive */
1017 /* Let's pretend this one takes one argument (file or db), and a second (deny or allow), */
1018 /* and we store it in a bit-wise manner. */
1019 const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char* arg2)
1021 if(!strcasecmp(arg1, "file")) config.typeOfAction = 0x01;
1022 else config.typeOfAction = 0x02;
1024 if(!strcasecmp(arg2, "deny")) config.typeOfAction += 0x10;
1025 else config.typeOfAction += 0x20;
1030 ==============================================================================
1031 The directive structure for our name tag:
1032 ==============================================================================
1034 static const command_rec example_directives[] =
1036 AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, RSRC_CONF, "Enable or disable mod_example"),
1037 AP_INIT_TAKE1("examplePath", example_set_path, NULL, RSRC_CONF, "The path to whatever"),
1038 AP_INIT_TAKE2("exampleAction", example_set_action, NULL, RSRC_CONF, "Special action value!"),
1042 ==============================================================================
1044 ==============================================================================
1046 static int example_handler(request_rec *r)
1048 if(!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);
1049 ap_set_content_type(r, "text/plain");
1050 ap_rprintf(r, "Enabled: %u\n", config.enabled);
1051 ap_rprintf(r, "Path: %s\n", config.path);
1052 ap_rprintf(r, "TypeOfAction: %x\n", config.typeOfAction);
1057 ==============================================================================
1058 The hook registration function (also initializes the default config values):
1059 ==============================================================================
1061 static void register_hooks(apr_pool_t *pool)
1064 config.path = "/foo/bar";
1065 config.typeOfAction = 3;
1066 ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
1069 ==============================================================================
1070 Our module name tag:
1071 ==============================================================================
1073 module AP_MODULE_DECLARE_DATA example_module =
1075 STANDARD20_MODULE_STUFF,
1076 NULL, /* Per-directory configuration handler */
1077 NULL, /* Merge handler for per-directory configurations */
1078 NULL, /* Per-server configuration handler */
1079 NULL, /* Merge handler for per-server configurations */
1080 example_directives, /* Any directives we may have for httpd */
1081 register_hooks /* Our hook registering function */
1089 In our httpd.conf file, we can now change the hard-coded configuration by
1092 <pre class="prettyprint lang-config">
1094 ExamplePath "/usr/bin/foo"
1095 ExampleAction file allow
1099 And thus we apply the configuration, visit <code>/example</code> on our
1100 web site, and we see the configuration has adapted to what we wrote in our
1106 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
1107 <div class="section">
1108 <h2><a name="context" id="context">Context aware configurations</a></h2>
1109 <h3><a name="context_intro" id="context_intro">Introduction to context aware configurations</a></h3>
1111 In Apache HTTP Server 2.4, different URLs, virtual hosts, directories etc can have very
1112 different meanings to the user of the server, and thus different contexts
1113 within which modules must operate. For example, let's assume you have this
1114 configuration set up for mod_rewrite:
1116 <pre class="prettyprint lang-config">
1117 <Directory "/var/www">
1118 RewriteCond %{HTTP_HOST} ^example.com$
1119 RewriteRule (.*) http://www.example.com/$1
1121 <Directory "/var/www/sub">
1122 RewriteRule ^foobar$ index.php?foobar=true
1127 In this example, you will have set up two different contexts for
1130 <li>Inside <code>/var/www</code>, all requests for <code>http://example.com</code> must go to <code>http://www.example.com</code></li>
1131 <li>Inside <code>/var/www/sub</code>, all requests for <code>foobar</code> must go to <code>index.php?foobar=true</code></li>
1134 If mod_rewrite (or the entire server for that matter) wasn't context aware, then
1135 these rewrite rules would just apply to every and any request made,
1136 regardless of where and how they were made, but since the module can pull
1137 the context specific configuration straight from the server, it does not need
1138 to know itself, which of the directives are valid in this context, since
1139 the server takes care of this.</p>
1142 So how does a module get the specific configuration for the server,
1143 directory or location in question? It does so by making one simple call:
1147 <pre class="prettyprint lang-c">
1148 example_config *config = (example_config*) <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#ga1093a5908a384eacc929b028c79f2a02">ap_get_module_config</a>(r->per_dir_config, &example_module);
1154 That's it! Of course, a whole lot goes on behind the scenes, which we will
1155 discuss in this chapter, starting with how the server came to know what our
1156 configuration looks like, and how it came to be set up as it is in the
1161 <h3><a name="context_base" id="context_base">Our basic configuration setup</a></h3>
1162 <p>In this chapter, we will be working with a slightly modified version of
1163 our previous context structure. We will set a <code>context</code>
1164 variable that we can use to track which context configuration is being
1165 used by the server in various places:
1168 <pre class="prettyprint lang-c">
1179 <p>Our handler for requests will also be modified, yet still very simple:</p>
1183 <pre class="prettyprint lang-c">
1184 static int example_handler(request_rec *r)
1186 if(!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);
1187 example_config *config = (example_config*) ap_get_module_config(r->per_dir_config, &example_module);
1188 ap_set_content_type(r, "text/plain");
1189 ap_rprintf("Enabled: %u\n", config->enabled);
1190 ap_rprintf("Path: %s\n", config->path);
1191 ap_rprintf("TypeOfAction: %x\n", config->typeOfAction);
1192 ap_rprintf("Context: %s\n", config->context);
1201 <h3><a name="context_which" id="context_which">Choosing a context</a></h3>
1203 Before we can start making our module context aware, we must first define,
1204 which contexts we will accept. As we saw in the previous chapter, defining
1205 a directive required five elements be set:</p>
1209 <pre class="prettyprint lang-c">
1210 AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, RSRC_CONF, "Enable or disable mod_example"),
1216 <p>The <code>RSRC_CONF</code> definition told the server that we would only allow
1217 this directive in a global server context, but since we are now trying out
1218 a context aware version of our module, we should set this to something
1219 more lenient, namely the value <code>ACCESS_CONF</code>, which lets us use
1220 the directive inside <Directory> and <Location> blocks.
1224 <h3><a name="context_pool" id="context_pool">Using the server to allocate configuration slots</a></h3>
1225 <p> A much smarter way to manage your configurations is by letting the server
1226 help you create them. To do so, we must first start off by changing our
1227 <em>name tag</em> to let the server know, that it should assist us in creating
1228 and managing our configurations. Since we have chosen the per-directory
1229 (or per-location) context for our module configurations, we'll add a
1230 per-directory creator and merger function reference in our tag:</p>
1233 <pre class="prettyprint lang-c">
1234 module AP_MODULE_DECLARE_DATA example_module =
1236 STANDARD20_MODULE_STUFF,
1237 create_dir_conf, /* Per-directory configuration handler */
1238 merge_dir_conf, /* Merge handler for per-directory configurations */
1239 NULL, /* Per-server configuration handler */
1240 NULL, /* Merge handler for per-server configurations */
1241 directives, /* Any directives we may have for httpd */
1242 register_hooks /* Our hook registering function */
1252 <h3><a name="context_new" id="context_new">Creating new context configurations</a></h3>
1254 Now that we have told the server to help us create and manage configurations,
1255 our first step is to make a function for creating new, blank
1256 configurations. We do so by creating the function we just referenced in
1257 our name tag as the Per-directory configuration handler:</p>
1259 <pre class="prettyprint lang-c">
1260 void* example_create_dir_conf(apr_pool_t* pool, char* context) {
1261 context = context ? context : "(undefined context)";
1262 example_config *cfg = apr_pcalloc(pool, sizeof(example_config));
1264 /* Set some default values */
1265 strcpy(cfg->context, x);
1266 cfg->enabled = 0;
1267 cfg->path = "/foo/bar";
1268 cfg->typeOfAction = 0x11;
1279 <h3><a name="context_merge" id="context_merge">Merging configurations</a></h3>
1281 Our next step in creating a context aware configuration is merging
1282 configurations. This part of the process particularly apply to scenarios
1283 where you have a parent configuration and a child, such as the following:
1285 <pre class="prettyprint lang-config">
1286 <Directory "/var/www">
1288 ExamplePath /foo/bar
1289 ExampleAction file allow
1291 <Directory "/var/www/subdir">
1292 ExampleAction file deny
1297 In this example, it is natural to assume that the directory <code>
1298 /var/www/subdir</code> should inherit the value set for the <code>/var/www
1299 </code> directory, as we did not specify a <code>ExampleEnable</code> nor
1300 an <code>ExamplePath</code> for this directory. The server does not presume to
1301 know if this is true, but cleverly does the following:
1304 <li>Creates a new configuration for <code>/var/www</code></li>
1305 <li>Sets the configuration values according to the directives given for <code>/var/www</code></li>
1306 <li>Creates a new configuration for <code>/var/www/subdir</code></li>
1307 <li>Sets the configuration values according to the directives given for <code>/var/www/subdir</code></li>
1308 <li><strong>Proposes a merge</strong> of the two configurations into a new configuration for <code>/var/www/subdir</code></li>
1311 This proposal is handled by the <code>merge_dir_conf</code> function we
1312 referenced in our name tag. The purpose of this function is to assess the
1313 two configurations and decide how they are to be merged:</p>
1317 <pre class="prettyprint lang-c">
1318 void* merge_dir_conf(apr_pool_t* pool, void* BASE, void* ADD) {
1319 example_config* base = (example_config *) BASE ; /* This is what was set in the parent context */
1320 example_config* add = (example_config *) ADD ; /* This is what is set in the new context */
1321 example_config* conf = (example_config *) create_dir_conf(pool, "Merged configuration"); /* This will be the merged configuration */
1323 /* Merge configurations */
1324 conf->enabled = ( add->enabled == 0 ) ? base->enabled : add->enabled ;
1325 conf->typeOfAction = add->typeOfAction ? add->typeOfAction : base->typeOfAction;
1326 strcpy(conf->path, strlen(add->path) ? add->path : base->path);
1337 <h3><a name="context_example" id="context_example">Trying out our new context aware configurations</a></h3>
1339 Now, let's try putting it all together to create a new module that is
1340 context aware. First off, we'll create a configuration that lets us test
1341 how the module works:
1343 <pre class="prettyprint lang-config">
1344 <Location "/a">
1345 SetHandler example-handler
1347 ExamplePath "/foo/bar"
1348 ExampleAction file allow
1351 <Location "/a/b">
1352 ExampleAction file deny
1356 <Location "/a/b/c">
1357 ExampleAction db deny
1358 ExamplePath "/foo/bar/baz"
1364 Then we'll assemble our module code. Note, that since we are now using our
1365 name tag as reference when fetching configurations in our handler, I have
1366 added some prototypes to keep the compiler happy:
1370 <pre class="prettyprint lang-c">
1372 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1373 * mod_example_config.c
1374 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1378 #include <stdio.h>
1379 #include "apr_hash.h"
1380 #include "ap_config.h"
1381 #include "ap_provider.h"
1383 #include "http_core.h"
1384 #include "http_config.h"
1385 #include "http_log.h"
1386 #include "http_protocol.h"
1387 #include "http_request.h"
1390 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1391 Configuration structure
1392 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1404 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1406 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1409 static int example_handler(request_rec *r);
1410 const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg);
1411 const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg);
1412 const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2);
1413 void *create_dir_conf(apr_pool_t *pool, char *context);
1414 void *merge_dir_conf(apr_pool_t *pool, void *BASE, void *ADD);
1415 static void register_hooks(apr_pool_t *pool);
1418 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1419 Configuration directives
1420 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1423 static const command_rec directives[] =
1425 AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, ACCESS_CONF, "Enable or disable mod_example"),
1426 AP_INIT_TAKE1("examplePath", example_set_path, NULL, ACCESS_CONF, "The path to whatever"),
1427 AP_INIT_TAKE2("exampleAction", example_set_action, NULL, ACCESS_CONF, "Special action value!"),
1432 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1434 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1437 module AP_MODULE_DECLARE_DATA example_module =
1439 STANDARD20_MODULE_STUFF,
1440 create_dir_conf, /* Per-directory configuration handler */
1441 merge_dir_conf, /* Merge handler for per-directory configurations */
1442 NULL, /* Per-server configuration handler */
1443 NULL, /* Merge handler for per-server configurations */
1444 directives, /* Any directives we may have for httpd */
1445 register_hooks /* Our hook registering function */
1449 =======================================================================================================================
1450 Hook registration function
1451 =======================================================================================================================
1453 static void register_hooks(apr_pool_t *pool)
1455 ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
1459 =======================================================================================================================
1460 Our example web service handler
1461 =======================================================================================================================
1463 static int example_handler(request_rec *r)
1465 if(!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);
1467 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1468 example_config *config = (example_config *) ap_get_module_config(r->per_dir_config, &example_module);
1469 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1471 ap_set_content_type(r, "text/plain");
1472 ap_rprintf(r, "Enabled: %u\n", config->enabled);
1473 ap_rprintf(r, "Path: %s\n", config->path);
1474 ap_rprintf(r, "TypeOfAction: %x\n", config->typeOfAction);
1475 ap_rprintf(r, "Context: %s\n", config->context);
1480 =======================================================================================================================
1481 Handler for the "exambleEnabled" directive
1482 =======================================================================================================================
1484 const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
1486 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1487 example_config *conf = (example_config *) cfg;
1488 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1492 if(!strcasecmp(arg, "on"))
1493 conf->enabled = 1;
1495 conf->enabled = 0;
1502 =======================================================================================================================
1503 Handler for the "examplePath" directive
1504 =======================================================================================================================
1506 const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
1508 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1509 example_config *conf = (example_config *) cfg;
1510 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1514 strcpy(conf->path, arg);
1521 =======================================================================================================================
1522 Handler for the "exampleAction" directive ;
1523 Let's pretend this one takes one argument (file or db), and a second (deny or allow), ;
1524 and we store it in a bit-wise manner.
1525 =======================================================================================================================
1527 const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
1529 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1530 example_config *conf = (example_config *) cfg;
1531 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1536 if(!strcasecmp(arg1, "file"))
1537 conf->typeOfAction = 0x01;
1539 conf->typeOfAction = 0x02;
1540 if(!strcasecmp(arg2, "deny"))
1541 conf->typeOfAction += 0x10;
1543 conf->typeOfAction += 0x20;
1551 =======================================================================================================================
1552 Function for creating new configurations for per-directory contexts
1553 =======================================================================================================================
1555 void *create_dir_conf(apr_pool_t *pool, char *context)
1557 context = context ? context : "Newly created configuration";
1559 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1560 example_config *cfg = apr_pcalloc(pool, sizeof(example_config));
1561 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1566 /* Set some default values */
1567 strcpy(cfg->context, context);
1568 cfg->enabled = 0;
1569 memset(cfg->path, 0, 256);
1570 cfg->typeOfAction = 0x00;
1578 =======================================================================================================================
1579 Merging function for configurations
1580 =======================================================================================================================
1582 void *merge_dir_conf(apr_pool_t *pool, void *BASE, void *ADD)
1584 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1585 example_config *base = (example_config *) BASE;
1586 example_config *add = (example_config *) ADD;
1587 example_config *conf = (example_config *) create_dir_conf(pool, "Merged configuration");
1588 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1590 conf->enabled = (add->enabled == 0) ? base->enabled : add->enabled;
1591 conf->typeOfAction = add->typeOfAction ? add->typeOfAction : base->typeOfAction;
1592 strcpy(conf->path, strlen(add->path) ? add->path : base->path);
1603 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
1604 <div class="section">
1605 <h2><a name="summary" id="summary">Summing up</a></h2>
1607 We have now looked at how to create simple modules for Apache HTTP Server 2.4 and
1608 configuring them. What you do next is entirely up to you, but it is my
1609 hope that something valuable has come out of reading this documentation.
1610 If you have questions on how to further develop modules, you are welcome
1611 to join our <a href="http://httpd.apache.org/lists.html">mailing lists</a>
1612 or check out the rest of our documentation for further tips.
1614 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
1615 <div class="section">
1616 <h2><a name="snippets" id="snippets">Some useful snippets of code</a></h2>
1618 <h3><a name="get_post" id="get_post">Retrieve variables from POST form data</a></h3>
1622 <pre class="prettyprint lang-c">
1628 keyValuePair* readPost(request_req* r) {
1629 apr_array_header_t *pairs = NULL;
1637 res = ap_parse_form_data(r, NULL, &pairs, -1, HUGE_STRING_LEN);
1638 if (res != OK || !pairs) return NULL; /* Return NULL if we failed or if there are is no POST data */
1639 kvp = apr_pcalloc(r->pool, sizeof(keyValuePair) * (pairs->nelts + 1));
1640 while (pairs && !apr_is_empty_array(pairs)) {
1642 ap_form_pair_t *pair = (ap_form_pair_t *) apr_array_pop(pairs);
1643 apr_brigade_length(pair->value, 1, &len);
1644 size = (apr_size_t) len;
1645 buffer = apr_palloc(r->pool, size + 1);
1646 apr_brigade_flatten(pair->value, buffer, &size);
1648 kvp[i]->key = apr_pstrdup(r->pool, pair->name);
1649 kvp[i]->value = buffer;
1654 static int example_handler(request_req *r)
1656 /*~~~~~~~~~~~~~~~~~~~~~~*/
1658 keyValuePair* formData;
1659 /*~~~~~~~~~~~~~~~~~~~~~~*/
1661 formData = readPost();
1664 for (i = 0; formData[i]; i++) {
1665 ap_rprintf(r, "%s = %s\n", formData[i]->key, formData[i]->value);
1677 <h3><a name="headers_out" id="headers_out">Printing out every HTTP header received</a></h3>
1681 <pre class="prettyprint lang-c">
1682 static int example_handler(request_req *r)
1684 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1685 const apr_array_header_t *fields;
1687 apr_table_entry_t *e = 0;
1688 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1690 fields = apr_table_elts(r->headers_in);
1691 e = (apr_table_entry_t *) fields->elts;
1692 for(i = 0; i < fields->nelts; i++) {
1693 ap_rprintf(r, "<b>%s</b>: %s<br/>", e[i].key, e[i].val);
1704 <h3><a name="request_body" id="request_body">Reading the request body into memory</a></h3>
1708 <pre class="prettyprint lang-c">
1709 static int util_read(request_rec *r, const char **rbuf, apr_off_t *size)
1715 if((rc = ap_setup_client_block(r, REQUEST_CHUNKED_ERROR))) {
1719 if(ap_should_client_block(r)) {
1721 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1722 char argsbuffer[HUGE_STRING_LEN];
1723 apr_off_t rsize, len_read, rpos = 0;
1724 apr_off_t length = r->remaining;
1725 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1727 *rbuf = (const char *) apr_pcalloc(r->pool, (apr_size_t) (length + 1));
1729 while((len_read = ap_get_client_block(r, argsbuffer, sizeof(argsbuffer))) > 0) {
1730 if((rpos + len_read) > length) {
1731 rsize = length - rpos;
1737 memcpy((char *) *rbuf + rpos, argsbuffer, (size_t) rsize);
1744 static int example_handler(request_req* r)
1746 /*~~~~~~~~~~~~~~~~*/
1749 /*~~~~~~~~~~~~~~~~*/
1751 if(util_read(r, &data, &size) == OK) {
1752 ap_rprintf("We read a request body that was %u bytes long", size);
1765 <div class="bottomlang">
1766 <p><span>Available Languages: </span><a href="../en/developer/modguide.html" title="English"> en </a></p>
1767 </div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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