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20 <p class="apache">Apache HTTP Server Version 2.5</p>
21 <img alt="" src="../images/feather.png" /></div>
22 <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
24 <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>
26 <p><span>Available Languages: </span><a href="../en/developer/modguide.html" title="English"> en </a></p>
29 <p>This document explains how you can develop modules for the Apache HTTP
32 <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#introduction">Introduction</a></li>
33 <li><img alt="" src="../images/down.gif" /> <a href="#basics">Defining a module</a></li>
34 <li><img alt="" src="../images/down.gif" /> <a href="#hooking">Getting started: Hooking into the server</a></li>
35 <li><img alt="" src="../images/down.gif" /> <a href="#handling">Building a handler</a></li>
36 <li><img alt="" src="../images/down.gif" /> <a href="#configuration">Adding configuration options</a></li>
37 <li><img alt="" src="../images/down.gif" /> <a href="#context">Context aware configurations</a></li>
38 <li><img alt="" src="../images/down.gif" /> <a href="#summary">Summing up</a></li>
39 <li><img alt="" src="../images/down.gif" /> <a href="#snippets">Some useful snippets of code</a></li>
40 </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><li><a href="#comments_section">Comments</a></li></ul></div>
41 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
43 <h2><a name="introduction" id="introduction">Introduction</a></h2>
44 <h3><a name="what" id="what">What we will be discussing in this document</a></h3>
46 This document will discuss how you can create modules for the Apache
47 HTTP Server 2.4, by exploring an example module called
48 <code>mod_example</code>. In the first part of this document, the purpose
49 of this module will be to calculate and print out various digest values for
50 existing files on your web server, whenever we access the URL <code>
51 http://hostname/filename.sum</code>. For instance, if we want to know the
52 MD5 digest value of the file located at <code>
53 http://www.example.com/index.html</code>, we would visit <code>
54 http://www.example.com/index.html.sum</code>.
58 In the second part of this document, which deals with configuration
59 directive and context awareness, we will be looking at a module that simply
60 writes out its own configuration to the client.
64 <h3><a name="prerequisites" id="prerequisites">Prerequisites</a></h3>
66 First and foremost, you are expected to have a basic knowledge of how the C
67 programming language works. In most cases, we will try to be as pedagogical
68 as possible and link to documents describing the functions used in the
69 examples, but there are also many cases where it is necessary to either
70 just assume that "it works" or do some digging yourself into what the hows
71 and whys of various function calls.
74 Lastly, you will need to have a basic understanding of how modules are
75 loaded and configured in the Apache HTTP Server, as well as how to get the headers for
76 Apache if you do not have them already, as these are needed for compiling
80 <h3><a name="compiling" id="compiling">Compiling your module</a></h3>
82 To compile the source code we are building in this document, we will be
83 using <a href="../programs/apxs.html">APXS</a>. Assuming your source file
84 is called mod_example.c, compiling, installing and activating the module is
87 <div class="example"><pre>apxs -i -a -c mod_example.c</pre></div>
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">module AP_MODULE_DECLARE_DATA example_module =
102 STANDARD20_MODULE_STUFF,
103 create_dir_conf, /* Per-directory configuration handler */
104 merge_dir_conf, /* Merge handler for per-directory configurations */
105 create_svr_conf, /* Per-server configuration handler */
106 merge_svr_conf, /* Merge handler for per-server configurations */
107 directives, /* Any directives we may have for httpd */
108 register_hooks /* Our hook registering function */
114 This bit of code lets the server know that we have now registered a new module
115 in the system, and that its name is <code>example_module</code>. The name
116 of the module is used primarily for two things:<br />
119 <li>Letting the server know how to load the module using the LoadModule</li>
120 <li>Setting up a namespace for the module to use in configurations</li>
123 For now, we're only concerned with the first purpose of the module name,
124 which comes into play when we need to load the module:
126 <pre class="prettyprint lang-config">LoadModule example_module "modules/mod_example.so"</pre>
129 In essence, this tells the server to open up <code>mod_example.so</code> and look for a module
130 called <code>example_module</code>.
133 Within this name tag of ours is also a bunch of references to how we would
134 like to handle things: Which directives do we respond to in a configuration
135 file or .htaccess, how do we operate within specific contexts, and what
136 handlers are we interested in registering with the Apache HTTP service. We'll
137 return to all these elements later in this document.
139 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
140 <div class="section">
141 <h2><a name="hooking" id="hooking">Getting started: Hooking into the server</a></h2>
142 <h3><a name="hook_intro" id="hook_intro">An introduction to hooks</a></h3>
144 When handling requests in Apache HTTP Server 2.4, the first thing you will need to do is
145 create a hook into the request handling process. A hook is essentially a
146 message telling the server that you are willing to either serve or at least
147 take a glance at certain requests given by clients. All handlers, whether
148 it's mod_rewrite, mod_authn_*, mod_proxy and so on, are hooked into
149 specific parts of the request process. As you are probably aware, modules
150 serve different purposes; Some are authentication/authorization handlers,
151 others are file or script handlers while some third modules rewrite URIs or
152 proxies content. Furthermore, in the end, it is up to the user of the server
153 how and when each module will come into place. Thus, the server itself does not
154 presume to know which module is responsible for handling a specific
155 request, and will ask each module whether they have an interest in a given
156 request or not. It is then up to each module to either gently decline
157 serving a request, accept serving it or flat out deny the request from
158 being served, as authentication/authorization modules do: <br />
159 <img src="../images/build_a_mod_2.png" alt="Hook handling in httpd" /><br />
160 To make it a bit easier for handlers such as our mod_example to know
161 whether the client is requesting content we should handle or not, the server
162 has directives for hinting to modules whether their assistance is needed or
163 not. Two of these are <code class="directive"><a href="../mod/mod_mime.html#addhandler">AddHandler</a></code>
164 and <code class="directive"><a href="../mod/core.html#sethandler">SetHandler</a></code>. Let's take a look at
165 an example using <code class="directive"><a href="../mod/mod_mime.html#addhandler">AddHandler</a></code>. In
166 our example case, we want every request ending with .sum to be served by
167 <code>mod_example</code>, so we'll add a configuration directive that tells
168 the server to do just that:
170 <pre class="prettyprint lang-config">AddHandler example-handler ".sum"</pre>
173 What this tells the server is the following: <em>Whenever we receive a request
174 for a URI ending in .sum, we are to let all modules know that we are
175 looking for whoever goes by the name of "example-handler" </em>.
176 Thus, when a request is being served that ends in .sum, the server will let all
177 modules know, that this request should be served by "example-handler".
178 As you will see later, when we start building mod_example, we will
179 check for this handler tag relayed by <code>AddHandler</code> and reply to
180 the server based on the value of this tag.
183 <h3><a name="hook_declaration" id="hook_declaration">Hooking into httpd</a></h3>
185 To begin with, we only want to create a simple handler, that replies to the
186 client browser when a specific URL is requested, so we won't bother setting
187 up configuration handlers and directives just yet. Our initial module
188 definition will look like this:</p>
192 <pre class="prettyprint lang-c">module AP_MODULE_DECLARE_DATA example_module =
194 STANDARD20_MODULE_STUFF,
200 register_hooks /* Our hook registering function */
206 <p>This lets the server know that we are not interested in anything fancy, we
207 just want to hook onto the requests and possibly handle some of them. </p>
209 <p> The reference in our example declaration, <code>register_hooks</code>
210 is the name of a function we will create to manage how we hook onto the
211 request process. In this example module, the function has just one purpose;
212 To create a simple hook that gets called after all the rewrites, access
213 control etc has been handled. Thus, we will let the server know, that we want
214 to hook into its process as one of the last modules:
218 <pre class="prettyprint lang-c">static void register_hooks(apr_pool_t *pool)
220 /* Create a hook in the request handler, so we get called when a request arrives */
221 ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
227 The <code>example_handler</code> reference is the function that will handle
228 the request. We will discuss how to create a handler in the next chapter.
231 <h3><a name="hook_others" id="hook_others">Other useful hooks</a></h3>
233 Hooking into the request handling phase is but one of many hooks that you
234 can create. Some other ways of hooking are:
237 <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>
238 <li><code>ap_hook_pre_config</code>: Place a hook that executes before any configuration data has been read (very early hook)</li>
239 <li><code>ap_hook_post_config</code>: Place a hook that executes after configuration has been parsed, but before the server has forked</li>
240 <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>
241 <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>
242 <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>
246 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
247 <div class="section">
248 <h2><a name="handling" id="handling">Building a handler</a></h2>
250 A handler is essentially a function that receives a callback when a request
251 to the server is made. It is passed a record of the current request (how it was
252 made, which headers and requests were passed along, who's giving the
253 request and so on), and is put in charge of either telling the server that it's
254 not interested in the request or handle the request with the tools provided.
256 <h3><a name="simple_handler" id="simple_handler">A simple "Hello, world!"
258 <p>Let's start off by making a very simple request handler
259 that does the following:
262 <li>Check that this is a request that should be served by "example-handler"</li>
263 <li>Set the content type of our output to <code>text/html</code></li>
264 <li>Write "Hello, world!" back to the client browser</li>
265 <li>Let the server know that we took care of this request and everything went fine</li>
268 In C code, our example handler will now look like this:
272 <pre class="prettyprint lang-c">static int example_handler(request_rec *r)
274 /* First off, we need to check if this is a call for the "example-handler" handler.
275 * If it is, we accept it and do our things, if not, we simply return DECLINED,
276 * and the server will try somewhere else.
278 if (!r->handler || strcmp(r->handler, "example-handler")) return (DECLINED);
280 /* Now that we are handling this request, we'll write out "Hello, world!" to the client.
281 * To do so, we must first set the appropriate content type, followed by our output.
283 ap_set_content_type(r, "text/html");
284 ap_rprintf(r, "Hello, world!");
286 /* Lastly, we must tell the server that we took care of this request and everything went fine.
287 * We do so by simply returning the value OK to the server.
295 Now, we put all we have learned together and end up with a program that
297 <a href="http://people.apache.org/~humbedooh/mods/examples/mod_example_1.c">mod_example_1.c</a>
298 . The functions used in this example will be explained later in the section
299 <a href="#functions">"Some useful functions you should know"</a>.
302 <h3><a name="request_rec" id="request_rec">The request_rec structure</a></h3>
303 <p>The most essential part of any request is the <em>request record
304 </em>. In a call to a handler function, this is represented by the <code>
305 request_rec* </code> structure passed along with every call that is made.
306 This struct, typically just referred to as <code>r</code> in modules,
307 contains all the information you need for your module to fully process any
308 HTTP request and respond accordingly.</p> <p>Some key elements of the <code>
309 request_rec </code> structure are:
312 <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>
313 <li><code>r->method (char*):</code> Contains the HTTP method being used, f.x. GET or POST</li>
314 <li><code>r->filename (char*):</code> Contains the translated filename the client is requesting</li>
315 <li><code>r->args (char*):</code> Contains the query string of the request, if any</li>
316 <li><code>r->headers_in (apr_table_t*):</code> Contains all the headers sent by the client</li>
317 <li><code>r->connection (conn_rec*):</code> A record containing information about the current connection</li>
318 <li><code>r->user (char*):</code> If the URI requires authentication, this is set to the username provided</li>
319 <li><code>r->useragent_ip (char*):</code> The IP address of the client connecting to us</li>
320 <li><code>r->pool (apr_pool_t*)</code>: The memory pool of this request. We'll discuss this in the
321 "<a href="#memory">Memory management</a>" chapter.</li>
324 A complete list of all the values contained within the <code>request_rec</code> structure can be found in
325 the <a href="http://svn.apache.org/repos/asf/httpd/httpd/trunk/include/httpd.h"><code>httpd.h</code></a> header
326 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>.
331 Let's try out some of these variables in another example handler:<br />
335 <pre class="prettyprint lang-c">static int example_handler(request_rec *r)
337 /* Set the appropriate content type */
338 ap_set_content_type(r, "text/html");
340 /* Print out the IP address of the client connecting to us: */
341 ap_rprintf(r, "<h2>Hello, %s!</h2>", r->useragent_ip);
343 /* If we were reached through a GET or a POST request, be happy, else sad. */
344 if ( !strcmp(r->method, "POST") || !strcmp(r->method, "GET") ) {
345 ap_rputs("You used a GET or a POST method, that makes us happy!<br/>", r);
348 ap_rputs("You did not use POST or GET, that makes us sad :(<br/>", r);
351 /* Lastly, if there was a query string, let's print that too! */
353 ap_rprintf(r, "Your query string was: %s", r->args);
362 <h3><a name="return_value" id="return_value">Return values</a></h3>
364 Apache relies on return values from handlers to signify whether a request
365 was handled or not, and if so, whether the request went well or not. If a
366 module is not interested in handling a specific request, it should always
367 return the value <code>DECLINED</code>. If it is handling a request, it
368 should either return the generic value <code>OK</code>, or a specific HTTP
369 status code, for example:
373 <pre class="prettyprint lang-c">static int example_handler(request_rec *r)
375 /* Return 404: Not found */
376 return HTTP_NOT_FOUND;
382 Returning <code>OK</code> or a HTTP status code does not necessarily mean
383 that the request will end. The server may still have other handlers that are
384 interested in this request, for instance the logging modules which, upon a
385 successful request, will write down a summary of what was requested and how
386 it went. To do a full stop and prevent any further processing after your
387 module is done, you can return the value <code>DONE</code> to let the server
388 know that it should cease all activity on this request and carry on with
389 the next, without informing other handlers.
391 <strong>General response codes:</strong>
394 <li><code>DECLINED</code>: We are not handling this request</li>
395 <li><code>OK</code>: We handled this request and it went well</li>
396 <li><code>DONE</code>: We handled this request and the server should just close this thread without further processing</li>
399 <strong>HTTP specific return codes (excerpt):</strong>
402 <li><code>HTTP_OK (200)</code>: Request was okay</li>
403 <li><code>HTTP_MOVED_PERMANENTLY (301)</code>: The resource has moved to a new URL</li>
404 <li><code>HTTP_UNAUTHORIZED (401)</code>: Client is not authorized to visit this page</li>
405 <li><code>HTTP_FORBIDDEN (403)</code>: Permission denied</li>
406 <li><code>HTTP_NOT_FOUND (404)</code>: File not found</li>
407 <li><code>HTTP_INTERNAL_SERVER_ERROR (500)</code>: Internal server error (self explanatory)</li>
411 <h3><a name="functions" id="functions">Some useful functions you should know</a></h3>
415 <code>ap_rputs(const char *string, request_rec *r)</code>: <br />
416 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">
421 <pre class="prettyprint lang-c">ap_rputs("Hello, world!", r);</pre>
429 <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#ga5e91eb6ca777c9a427b2e82bf1eeb81d">ap_rprintf</a></code>: <br />
430 This function works just like <code>printf</code>, except it sends the result to the client.
434 <pre class="prettyprint lang-c">ap_rprintf(r, "Hello, %s!", r->useragent_ip);</pre>
441 <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#gaa2f8412c400197338ec509f4a45e4579">ap_set_content_type</a>(request_rec *r, const char *type)</code>: <br />
442 Sets the content type of the output you are sending.
446 <pre class="prettyprint lang-c">ap_set_content_type(r, "text/plain"); /* force a raw text output */</pre>
456 <h3><a name="memory" id="memory">Memory management</a></h3>
458 Managing your resources in Apache HTTP Server 2.4 is quite easy, thanks to the memory pool
459 system. In essence, each server, connection and request have their own
460 memory pool that gets cleaned up when its scope ends, e.g. when a request
461 is done or when a server process shuts down. All your module needs to do is
462 latch onto this memory pool, and you won't have to worry about having to
463 clean up after yourself - pretty neat, huh?
467 In our module, we will primarily be allocating memory for each request, so
468 it's appropriate to use the <code>r->pool</code>
469 reference when creating new objects. A few of the functions for allocating
470 memory within a pool are:
473 <li><code>void* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__pools.html#ga85f1e193c31d109affda72f9a92c6915">apr_palloc</a>(
474 apr_pool_t *p, apr_size_t size)</code>: Allocates <code>size</code> number of bytes in the pool for you</li>
475 <li><code>void* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__pools.html#gaf61c098ad258069d64cdf8c0a9369f9e">apr_pcalloc</a>(
476 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>
477 <li><code>char* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__strings.html#gabc79e99ff19abbd7cfd18308c5f85d47">apr_pstrdup</a>(
478 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>
479 <li><code>char* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__strings.html#ga3eca76b8d293c5c3f8021e45eda813d8">apr_psprintf</a>(
480 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>
483 <p>Let's put these functions into an example handler:</p>
487 <pre class="prettyprint lang-c">static int example_handler(request_rec *r)
489 const char *original = "You can't edit this!";
493 /* Allocate space for 10 integer values and set them all to zero. */
494 integers = apr_pcalloc(r->pool, sizeof(int)*10);
496 /* Create a copy of the 'original' variable that we can edit. */
497 copy = apr_pstrdup(r->pool, original);
504 This is all well and good for our module, which won't need any
505 pre-initialized variables or structures. However, if we wanted to
506 initialize something early on, before the requests come rolling in, we
507 could simply add a call to a function in our <code>register_hooks</code>
508 function to sort it out:
512 <pre class="prettyprint lang-c">static void register_hooks(apr_pool_t *pool)
514 /* Call a function that initializes some stuff */
515 example_init_function(pool);
516 /* Create a hook in the request handler, so we get called when a request arrives */
517 ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
523 In this pre-request initialization function we would not be using the
524 same pool as we did when allocating resources for request-based functions.
525 Instead, we would use the pool given to us by the server for allocating memory
526 on a per-process based level.
530 <h3><a name="parsing" id="parsing">Parsing request data</a></h3>
532 In our example module, we would like to add a feature, that checks which
533 type of digest, MD5 or SHA1 the client would like to see. This could be
534 solved by adding a query string to the request. A query string is typically
535 comprised of several keys and values put together in a string, for instance
536 <code>valueA=yes&valueB=no&valueC=maybe</code>. It is up to the
537 module itself to parse these and get the data it requires. In our example,
538 we'll be looking for a key called <code>digest</code>, and if set to <code>
539 md5</code>, we'll produce an MD5 digest, otherwise we'll produce a SHA1
543 Since the introduction of Apache HTTP Server 2.4, parsing request data from GET and
544 POST requests have never been easier. All we require to parse both GET and
545 POST data is four simple lines:
550 <pre class="prettyprint lang-c">
551 <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__apr__tables.html#gad7ea82d6608a4a633fc3775694ab71e4">apr_table_t</a> *GET; <em>
552 </em><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/structapr__array__header__t.html">apr_array_header_t</a>*POST;
555 <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__SCRIPT.html#gaed25877b529623a4d8f99f819ba1b7bd">
556 ap_args_to_table</a>(r, &GET); <em>
557 </em><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__DAEMON.html#ga9d426b6382b49754d4f87c55f65af202">
558 ap_parse_form_data</a>(r, NULL, &POST, -1, 8192);</pre>
563 In our specific example module, we're looking for the <code>digest</code>
564 value from the query string, which now resides inside a table called <code>
565 GET</code>. To extract this value, we need only perform a simple operation:
570 <pre class="prettyprint lang-c">/* Get the "digest" key from the query string, if any. */
571 const char *digestType = apr_table_get(GET, "digest");
573 /* If no key was returned, we will set a default value instead. */
574 if (!digestType) digestType = "sha1";</pre>
579 The structures used for the POST and GET data are not exactly the same, so
580 if we were to fetch a value from POST data instead of the query string, we
581 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.
585 <h3><a name="advanced_handler" id="advanced_handler">Making an advanced handler</a></h3>
587 Now that we have learned how to parse form data and manage our resources,
588 we can move on to creating an advanced version of our module, that spits
589 out the MD5 or SHA1 digest of files:
594 <pre class="prettyprint lang-c">static int example_handler(request_rec *r)
601 apr_size_t readBytes;
604 apr_array_header_t *POST;
605 const char *digestType;
608 /* Check that the "example-handler" handler is being called. */
609 if (!r->handler || strcmp(r->handler, "example-handler")) return (DECLINED);
611 /* Figure out which file is being requested by removing the .sum from it */
612 filename = apr_pstrdup(r->pool, r->filename);
613 filename[strlen(filename)-4] = 0; /* Cut off the last 4 characters. */
615 /* Figure out if the file we request a sum on exists and isn't a directory */
616 rc = apr_stat(&finfo, filename, APR_FINFO_MIN, r->pool);
617 if (rc == APR_SUCCESS) {
620 (finfo.filetype != APR_NOFILE)
621 && !(finfo.filetype & APR_DIR)
623 if (!exists) return HTTP_NOT_FOUND; /* Return a 404 if not found. */
625 /* If apr_stat failed, we're probably not allowed to check this file. */
626 else return HTTP_FORBIDDEN;
628 /* Parse the GET and, optionally, the POST data sent to us */
630 ap_args_to_table(r, &GET);
631 ap_parse_form_data(r, NULL, &POST, -1, 8192);
633 /* Set the appropriate content type */
634 ap_set_content_type(r, "text/html");
636 /* Print a title and some general information */
637 ap_rprintf(r, "<h2>Information on %s:</h2>", filename);
638 ap_rprintf(r, "<b>Size:</b> %u bytes<br/>", finfo.size);
640 /* Get the digest type the client wants to see */
641 digestType = apr_table_get(GET, "digest");
642 if (!digestType) digestType = "MD5";
645 rc = apr_file_open(&file, filename, APR_READ, APR_OS_DEFAULT, r->pool);
646 if (rc == APR_SUCCESS) {
648 /* Are we trying to calculate the MD5 or the SHA1 digest? */
649 if (!strcasecmp(digestType, "md5")) {
650 /* Calculate the MD5 sum of the file */
656 apr_md5_init(&md5);
658 while ( apr_file_read(file, buffer, &readBytes) == APR_SUCCESS ) {
659 apr_md5_update(&md5, buffer, readBytes);
661 apr_md5_final(digest.chr, &md5);
663 /* Print out the MD5 digest */
664 ap_rputs("<b>MD5: </b><code>", r);
665 for (n = 0; n < APR_MD5_DIGESTSIZE/4; n++) {
666 ap_rprintf(r, "%08x", digest.num[n]);
668 ap_rputs("</code>", r);
669 /* Print a link to the SHA1 version */
670 ap_rputs("<br/><a href='?digest=sha1'>View the SHA1 hash instead</a>", r);
673 /* Calculate the SHA1 sum of the file */
679 apr_sha1_init(&sha1);
681 while ( apr_file_read(file, buffer, &readBytes) == APR_SUCCESS ) {
682 apr_sha1_update(&sha1, buffer, readBytes);
684 apr_sha1_final(digest.chr, &sha1);
686 /* Print out the SHA1 digest */
687 ap_rputs("<b>SHA1: </b><code>", r);
688 for (n = 0; n < APR_SHA1_DIGESTSIZE/4; n++) {
689 ap_rprintf(r, "%08x", digest.num[n]);
691 ap_rputs("</code>", r);
693 /* Print a link to the MD5 version */
694 ap_rputs("<br/><a href='?digest=md5'>View the MD5 hash instead</a>", r);
696 apr_file_close(file);
699 /* Let the server know that we responded to this request. */
706 This version in its entirety can be found here:
707 <a href="http://people.apache.org/~humbedooh/mods/examples/mod_example_2.c">mod_example_2.c</a>.
711 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
712 <div class="section">
713 <h2><a name="configuration" id="configuration">Adding configuration options</a></h2>
715 In this next segment of this document, we will turn our eyes away from the
716 digest module and create a new example module, whose only function is to
717 write out its own configuration. The purpose of this is to examine how
718 the server works with configuration, and what happens when you start writing
719 advanced configurations
722 <h3><a name="config_intro" id="config_intro">An introduction to configuration
725 If you are reading this, then you probably already know
726 what a configuration directive is. Simply put, a directive is a way of
727 telling an individual module (or a set of modules) how to behave, such as
728 these directives control how <code>mod_rewrite</code> works:
730 <pre class="prettyprint lang-config">RewriteEngine On
731 RewriteCond "%{REQUEST_URI}" "^/foo/bar"
732 RewriteRule "^/foo/bar/(.*)$" "/foobar?page=$1"</pre>
735 Each of these configuration directives are handled by a separate function,
736 that parses the parameters given and sets up a configuration accordingly.
739 <h3><a name="config_simple" id="config_simple">Making an example configuration</a></h3>
740 <p>To begin with, we'll create a basic configuration in C-space:</p>
744 <pre class="prettyprint lang-c">typedef struct {
745 int enabled; /* Enable or disable our module */
746 const char *path; /* Some path to...something */
747 int typeOfAction; /* 1 means action A, 2 means action B and so on */
748 } example_config;</pre>
753 Now, let's put this into perspective by creating a very small module that
754 just prints out a hard-coded configuration. You'll notice that we use the
755 <code>register_hooks</code> function for initializing the configuration
756 values to their defaults:
760 <pre class="prettyprint lang-c">typedef struct {
761 int enabled; /* Enable or disable our module */
762 const char *path; /* Some path to...something */
763 int typeOfAction; /* 1 means action A, 2 means action B and so on */
766 static example_config config;
768 static int example_handler(request_rec *r)
770 if (!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);
771 ap_set_content_type(r, "text/plain");
772 ap_rprintf(r, "Enabled: %u\n", config.enabled);
773 ap_rprintf(r, "Path: %s\n", config.path);
774 ap_rprintf(r, "TypeOfAction: %x\n", config.typeOfAction);
778 static void register_hooks(apr_pool_t *pool)
781 config.path = "/foo/bar";
782 config.typeOfAction = 0x00;
783 ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
786 /* Define our module as an entity and assign a function for registering hooks */
788 module AP_MODULE_DECLARE_DATA example_module =
790 STANDARD20_MODULE_STUFF,
791 NULL, /* Per-directory configuration handler */
792 NULL, /* Merge handler for per-directory configurations */
793 NULL, /* Per-server configuration handler */
794 NULL, /* Merge handler for per-server configurations */
795 NULL, /* Any directives we may have for httpd */
796 register_hooks /* Our hook registering function */
802 So far so good. To access our new handler, we could add the following to
805 <pre class="prettyprint lang-config"><Location "/example">
806 SetHandler example-handler
807 </Location></pre>
810 When we visit, we'll see our current configuration being spit out by our
815 <h3><a name="register_directive" id="register_directive">Registering directives with the server</a></h3>
817 What if we want to change our configuration, not by hard-coding new values
818 into the module, but by using either the httpd.conf file or possibly a
819 .htaccess file? It's time to let the server know that we want this to be
820 possible. To do so, we must first change our <em>name tag</em> to include a
821 reference to the configuration directives we want to register with the server:
825 <pre class="prettyprint lang-c">module AP_MODULE_DECLARE_DATA example_module =
827 STANDARD20_MODULE_STUFF,
828 NULL, /* Per-directory configuration handler */
829 NULL, /* Merge handler for per-directory configurations */
830 NULL, /* Per-server configuration handler */
831 NULL, /* Merge handler for per-server configurations */
832 example_directives, /* Any directives we may have for httpd */
833 register_hooks /* Our hook registering function */
839 This will tell the server that we are now accepting directives from the
840 configuration files, and that the structure called <code>example_directives
841 </code> holds information on what our directives are and how they work.
842 Since we have three different variables in our module configuration, we
843 will add a structure with three directives and a NULL at the end:
847 <pre class="prettyprint lang-c">static const command_rec example_directives[] =
849 AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, RSRC_CONF, "Enable or disable mod_example"),
850 AP_INIT_TAKE1("examplePath", example_set_path, NULL, RSRC_CONF, "The path to whatever"),
851 AP_INIT_TAKE2("exampleAction", example_set_action, NULL, RSRC_CONF, "Special action value!"),
858 <img src="../images/build_a_mod_4.png" alt="Directives structure" /><br />
859 As you can see, each directive needs at least 5 parameters set:
862 <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.
863 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
864 for more macros).</li>
865 <li><code>exampleEnabled</code>: This is the name of our directive. More precisely, it is what the user must put in his/her
866 configuration in order to invoke a configuration change in our module.</li>
867 <li><code>example_set_enabled</code>: This is a reference to a C function that parses the directive and sets the configuration
868 accordingly. We will discuss how to make this in the following paragraph.</li>
869 <li><code>RSRC_CONF</code>: This tells the server where the directive is permitted. We'll go into details on this value in the
870 later chapters, but for now, <code>RSRC_CONF</code> means that the server will only accept these directives in a server context.</li>
871 <li><code>"Enable or disable...."</code>: This is simply a brief description of what the directive does.</li>
874 (<em>The "missing" parameter in our definition, which is usually set to
875 <code>NULL</code>, is an optional function that can be run after the
876 initial function to parse the arguments have been run. This is usually
877 omitted, as the function for verifying arguments might as well be used to
881 <h3><a name="directive_handler" id="directive_handler">The directive handler function</a></h3>
883 Now that we have told the server to expect some directives for our module, it's
884 time to make a few functions for handling these. What the server reads in the
885 configuration file(s) is text, and so naturally, what it passes along to
886 our directive handler is one or more strings, that we ourselves need to
887 recognize and act upon. You'll notice, that since we set our <code>
888 exampleAction</code> directive to accept two arguments, its C function also
889 has an additional parameter defined:</p>
892 <pre class="prettyprint lang-c">/* Handler for the "exampleEnabled" directive */
893 const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
895 if(!strcasecmp(arg, "on")) config.enabled = 1;
896 else config.enabled = 0;
900 /* Handler for the "examplePath" directive */
901 const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
907 /* Handler for the "exampleAction" directive */
908 /* Let's pretend this one takes one argument (file or db), and a second (deny or allow), */
909 /* and we store it in a bit-wise manner. */
910 const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
912 if(!strcasecmp(arg1, "file")) config.typeOfAction = 0x01;
913 else config.typeOfAction = 0x02;
915 if(!strcasecmp(arg2, "deny")) config.typeOfAction += 0x10;
916 else config.typeOfAction += 0x20;
924 <h3><a name="directive_complete" id="directive_complete">Putting it all together</a></h3>
926 Now that we have our directives set up, and handlers configured for them,
927 we can assemble our module into one big file:
931 <pre class="prettyprint lang-c">/* mod_example_config_simple.c: */
932 #include <stdio.h>
933 #include "apr_hash.h"
934 #include "ap_config.h"
935 #include "ap_provider.h"
937 #include "http_core.h"
938 #include "http_config.h"
939 #include "http_log.h"
940 #include "http_protocol.h"
941 #include "http_request.h"
944 ==============================================================================
945 Our configuration prototype and declaration:
946 ==============================================================================
949 int enabled; /* Enable or disable our module */
950 const char *path; /* Some path to...something */
951 int typeOfAction; /* 1 means action A, 2 means action B and so on */
954 static example_config config;
957 ==============================================================================
958 Our directive handlers:
959 ==============================================================================
961 /* Handler for the "exampleEnabled" directive */
962 const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
964 if(!strcasecmp(arg, "on")) config.enabled = 1;
965 else config.enabled = 0;
969 /* Handler for the "examplePath" directive */
970 const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
976 /* Handler for the "exampleAction" directive */
977 /* Let's pretend this one takes one argument (file or db), and a second (deny or allow), */
978 /* and we store it in a bit-wise manner. */
979 const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
981 if(!strcasecmp(arg1, "file")) config.typeOfAction = 0x01;
982 else config.typeOfAction = 0x02;
984 if(!strcasecmp(arg2, "deny")) config.typeOfAction += 0x10;
985 else config.typeOfAction += 0x20;
990 ==============================================================================
991 The directive structure for our name tag:
992 ==============================================================================
994 static const command_rec example_directives[] =
996 AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, RSRC_CONF, "Enable or disable mod_example"),
997 AP_INIT_TAKE1("examplePath", example_set_path, NULL, RSRC_CONF, "The path to whatever"),
998 AP_INIT_TAKE2("exampleAction", example_set_action, NULL, RSRC_CONF, "Special action value!"),
1002 ==============================================================================
1004 ==============================================================================
1006 static int example_handler(request_rec *r)
1008 if(!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);
1009 ap_set_content_type(r, "text/plain");
1010 ap_rprintf(r, "Enabled: %u\n", config.enabled);
1011 ap_rprintf(r, "Path: %s\n", config.path);
1012 ap_rprintf(r, "TypeOfAction: %x\n", config.typeOfAction);
1017 ==============================================================================
1018 The hook registration function (also initializes the default config values):
1019 ==============================================================================
1021 static void register_hooks(apr_pool_t *pool)
1024 config.path = "/foo/bar";
1025 config.typeOfAction = 3;
1026 ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
1029 ==============================================================================
1030 Our module name tag:
1031 ==============================================================================
1033 module AP_MODULE_DECLARE_DATA example_module =
1035 STANDARD20_MODULE_STUFF,
1036 NULL, /* Per-directory configuration handler */
1037 NULL, /* Merge handler for per-directory configurations */
1038 NULL, /* Per-server configuration handler */
1039 NULL, /* Merge handler for per-server configurations */
1040 example_directives, /* Any directives we may have for httpd */
1041 register_hooks /* Our hook registering function */
1048 In our httpd.conf file, we can now change the hard-coded configuration by
1051 <pre class="prettyprint lang-config">ExampleEnabled On
1052 ExamplePath "/usr/bin/foo"
1053 ExampleAction file allow</pre>
1056 And thus we apply the configuration, visit <code>/example</code> on our
1057 web site, and we see the configuration has adapted to what we wrote in our
1063 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
1064 <div class="section">
1065 <h2><a name="context" id="context">Context aware configurations</a></h2>
1066 <h3><a name="context_intro" id="context_intro">Introduction to context aware configurations</a></h3>
1068 In Apache HTTP Server 2.4, different URLs, virtual hosts, directories etc can have very
1069 different meanings to the user of the server, and thus different contexts
1070 within which modules must operate. For example, let's assume you have this
1071 configuration set up for mod_rewrite:
1073 <pre class="prettyprint lang-config"><Directory "/var/www">
1074 RewriteCond "%{HTTP_HOST}" "^example.com$"
1075 RewriteRule "(.*)" "http://www.example.com/$1"
1077 <Directory "/var/www/sub">
1078 RewriteRule "^foobar$" "index.php?foobar=true"
1079 </Directory></pre>
1082 In this example, you will have set up two different contexts for
1085 <li>Inside <code>/var/www</code>, all requests for <code>http://example.com</code> must go to <code>http://www.example.com</code></li>
1086 <li>Inside <code>/var/www/sub</code>, all requests for <code>foobar</code> must go to <code>index.php?foobar=true</code></li>
1089 If mod_rewrite (or the entire server for that matter) wasn't context aware, then
1090 these rewrite rules would just apply to every and any request made,
1091 regardless of where and how they were made, but since the module can pull
1092 the context specific configuration straight from the server, it does not need
1093 to know itself, which of the directives are valid in this context, since
1094 the server takes care of this.</p>
1097 So how does a module get the specific configuration for the server,
1098 directory or location in question? It does so by making one simple call:
1102 <pre class="prettyprint lang-c">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);</pre>
1107 That's it! Of course, a whole lot goes on behind the scenes, which we will
1108 discuss in this chapter, starting with how the server came to know what our
1109 configuration looks like, and how it came to be set up as it is in the
1114 <h3><a name="context_base" id="context_base">Our basic configuration setup</a></h3>
1115 <p>In this chapter, we will be working with a slightly modified version of
1116 our previous context structure. We will set a <code>context</code>
1117 variable that we can use to track which context configuration is being
1118 used by the server in various places:
1121 <pre class="prettyprint lang-c">typedef struct {
1126 } example_config;</pre>
1130 <p>Our handler for requests will also be modified, yet still very simple:</p>
1134 <pre class="prettyprint lang-c">static int example_handler(request_rec *r)
1136 if(!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);
1137 example_config *config = (example_config*) ap_get_module_config(r->per_dir_config, &example_module);
1138 ap_set_content_type(r, "text/plain");
1139 ap_rprintf("Enabled: %u\n", config->enabled);
1140 ap_rprintf("Path: %s\n", config->path);
1141 ap_rprintf("TypeOfAction: %x\n", config->typeOfAction);
1142 ap_rprintf("Context: %s\n", config->context);
1150 <h3><a name="context_which" id="context_which">Choosing a context</a></h3>
1152 Before we can start making our module context aware, we must first define,
1153 which contexts we will accept. As we saw in the previous chapter, defining
1154 a directive required five elements be set:</p>
1158 <pre class="prettyprint lang-c">AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, RSRC_CONF, "Enable or disable mod_example"),</pre>
1163 <p>The <code>RSRC_CONF</code> definition told the server that we would only allow
1164 this directive in a global server context, but since we are now trying out
1165 a context aware version of our module, we should set this to something
1166 more lenient, namely the value <code>ACCESS_CONF</code>, which lets us use
1167 the directive inside <Directory> and <Location> blocks. For more
1168 control over the placement of your directives, you can combine the following
1169 restrictions together to form a specific rule:
1172 <li><code>RSRC_CONF</code>: Allow in .conf files (not .htaccess) outside <Directory> or <Location></li>
1173 <li><code>ACCESS_CONF</code>: Allow in .conf files (not .htaccess) inside <Directory> or <Location></li>
1174 <li><code>OR_OPTIONS</code>: Allow in .conf files and .htaccess when <code>AllowOverride Options</code> is set</li>
1175 <li><code>OR_FILEINFO</code>: Allow in .conf files and .htaccess when <code>AllowOverride FileInfo</code> is set</li>
1176 <li><code>OR_AUTHCFG</code>: Allow in .conf files and .htaccess when <code>AllowOverride AuthConfig</code> is set</li>
1177 <li><code>OR_INDEXES</code>: Allow in .conf files and .htaccess when <code>AllowOverride Indexes</code> is set</li>
1178 <li><code>OR_ALL</code>: Allow anywhere in .conf files and .htaccess</li>
1182 <h3><a name="context_pool" id="context_pool">Using the server to allocate configuration slots</a></h3>
1183 <p> A much smarter way to manage your configurations is by letting the server
1184 help you create them. To do so, we must first start off by changing our
1185 <em>name tag</em> to let the server know, that it should assist us in creating
1186 and managing our configurations. Since we have chosen the per-directory
1187 (or per-location) context for our module configurations, we'll add a
1188 per-directory creator and merger function reference in our tag:</p>
1191 <pre class="prettyprint lang-c">module AP_MODULE_DECLARE_DATA example_module =
1193 STANDARD20_MODULE_STUFF,
1194 create_dir_conf, /* Per-directory configuration handler */
1195 merge_dir_conf, /* Merge handler for per-directory configurations */
1196 NULL, /* Per-server configuration handler */
1197 NULL, /* Merge handler for per-server configurations */
1198 directives, /* Any directives we may have for httpd */
1199 register_hooks /* Our hook registering function */
1208 <h3><a name="context_new" id="context_new">Creating new context configurations</a></h3>
1210 Now that we have told the server to help us create and manage configurations,
1211 our first step is to make a function for creating new, blank
1212 configurations. We do so by creating the function we just referenced in
1213 our name tag as the Per-directory configuration handler:</p>
1215 <pre class="prettyprint lang-c">void *create_dir_conf(apr_pool_t *pool, char *context) {
1216 context = context ? context : "(undefined context)";
1217 example_config *cfg = apr_pcalloc(pool, sizeof(example_config));
1219 /* Set some default values */
1220 strcpy(cfg->context, context);
1221 cfg->enabled = 0;
1222 cfg->path = "/foo/bar";
1223 cfg->typeOfAction = 0x11;
1233 <h3><a name="context_merge" id="context_merge">Merging configurations</a></h3>
1235 Our next step in creating a context aware configuration is merging
1236 configurations. This part of the process particularly applies to scenarios
1237 where you have a parent configuration and a child, such as the following:
1239 <pre class="prettyprint lang-config"><Directory "/var/www">
1241 ExamplePath "/foo/bar"
1242 ExampleAction file allow
1244 <Directory "/var/www/subdir">
1245 ExampleAction file deny
1246 </Directory></pre>
1249 In this example, it is natural to assume that the directory <code>
1250 /var/www/subdir</code> should inherit the values set for the <code>/var/www
1251 </code> directory, as we did not specify an <code>ExampleEnabled</code> nor
1252 an <code>ExamplePath</code> for this directory. The server does not presume to
1253 know if this is true, but cleverly does the following:
1256 <li>Creates a new configuration for <code>/var/www</code></li>
1257 <li>Sets the configuration values according to the directives given for <code>/var/www</code></li>
1258 <li>Creates a new configuration for <code>/var/www/subdir</code></li>
1259 <li>Sets the configuration values according to the directives given for <code>/var/www/subdir</code></li>
1260 <li><strong>Proposes a merge</strong> of the two configurations into a new configuration for <code>/var/www/subdir</code></li>
1263 This proposal is handled by the <code>merge_dir_conf</code> function we
1264 referenced in our name tag. The purpose of this function is to assess the
1265 two configurations and decide how they are to be merged:</p>
1269 <pre class="prettyprint lang-c">void *merge_dir_conf(apr_pool_t *pool, void *BASE, void *ADD) {
1270 example_config *base = (example_config *) BASE ; /* This is what was set in the parent context */
1271 example_config *add = (example_config *) ADD ; /* This is what is set in the new context */
1272 example_config *conf = (example_config *) create_dir_conf(pool, "Merged configuration"); /* This will be the merged configuration */
1274 /* Merge configurations */
1275 conf->enabled = ( add->enabled == 0 ) ? base->enabled : add->enabled ;
1276 conf->typeOfAction = add->typeOfAction ? add->typeOfAction : base->typeOfAction;
1277 strcpy(conf->path, strlen(add->path) ? add->path : base->path);
1287 <h3><a name="context_example" id="context_example">Trying out our new context aware configurations</a></h3>
1289 Now, let's try putting it all together to create a new module that is
1290 context aware. First off, we'll create a configuration that lets us test
1291 how the module works:
1293 <pre class="prettyprint lang-config"><Location "/a">
1294 SetHandler example-handler
1296 ExamplePath "/foo/bar"
1297 ExampleAction file allow
1300 <Location "/a/b">
1301 ExampleAction file deny
1305 <Location "/a/b/c">
1306 ExampleAction db deny
1307 ExamplePath "/foo/bar/baz"
1309 </Location></pre>
1312 Then we'll assemble our module code. Note, that since we are now using our
1313 name tag as reference when fetching configurations in our handler, I have
1314 added some prototypes to keep the compiler happy:
1318 <pre class="prettyprint lang-c">/*$6
1319 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1320 * mod_example_config.c
1321 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1325 #include <stdio.h>
1326 #include "apr_hash.h"
1327 #include "ap_config.h"
1328 #include "ap_provider.h"
1330 #include "http_core.h"
1331 #include "http_config.h"
1332 #include "http_log.h"
1333 #include "http_protocol.h"
1334 #include "http_request.h"
1337 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1338 Configuration structure
1339 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1351 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1353 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1356 static int example_handler(request_rec *r);
1357 const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg);
1358 const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg);
1359 const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2);
1360 void *create_dir_conf(apr_pool_t *pool, char *context);
1361 void *merge_dir_conf(apr_pool_t *pool, void *BASE, void *ADD);
1362 static void register_hooks(apr_pool_t *pool);
1365 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1366 Configuration directives
1367 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1370 static const command_rec directives[] =
1372 AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, ACCESS_CONF, "Enable or disable mod_example"),
1373 AP_INIT_TAKE1("examplePath", example_set_path, NULL, ACCESS_CONF, "The path to whatever"),
1374 AP_INIT_TAKE2("exampleAction", example_set_action, NULL, ACCESS_CONF, "Special action value!"),
1379 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1381 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1384 module AP_MODULE_DECLARE_DATA example_module =
1386 STANDARD20_MODULE_STUFF,
1387 create_dir_conf, /* Per-directory configuration handler */
1388 merge_dir_conf, /* Merge handler for per-directory configurations */
1389 NULL, /* Per-server configuration handler */
1390 NULL, /* Merge handler for per-server configurations */
1391 directives, /* Any directives we may have for httpd */
1392 register_hooks /* Our hook registering function */
1396 =======================================================================================================================
1397 Hook registration function
1398 =======================================================================================================================
1400 static void register_hooks(apr_pool_t *pool)
1402 ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
1406 =======================================================================================================================
1407 Our example web service handler
1408 =======================================================================================================================
1410 static int example_handler(request_rec *r)
1412 if(!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);
1414 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1415 example_config *config = (example_config *) ap_get_module_config(r->per_dir_config, &example_module);
1416 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1418 ap_set_content_type(r, "text/plain");
1419 ap_rprintf(r, "Enabled: %u\n", config->enabled);
1420 ap_rprintf(r, "Path: %s\n", config->path);
1421 ap_rprintf(r, "TypeOfAction: %x\n", config->typeOfAction);
1422 ap_rprintf(r, "Context: %s\n", config->context);
1427 =======================================================================================================================
1428 Handler for the "exampleEnabled" directive
1429 =======================================================================================================================
1431 const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
1433 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1434 example_config *conf = (example_config *) cfg;
1435 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1439 if(!strcasecmp(arg, "on"))
1440 conf->enabled = 1;
1442 conf->enabled = 0;
1449 =======================================================================================================================
1450 Handler for the "examplePath" directive
1451 =======================================================================================================================
1453 const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
1455 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1456 example_config *conf = (example_config *) cfg;
1457 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1461 strcpy(conf->path, arg);
1468 =======================================================================================================================
1469 Handler for the "exampleAction" directive ;
1470 Let's pretend this one takes one argument (file or db), and a second (deny or allow), ;
1471 and we store it in a bit-wise manner.
1472 =======================================================================================================================
1474 const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
1476 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1477 example_config *conf = (example_config *) cfg;
1478 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1483 if(!strcasecmp(arg1, "file"))
1484 conf->typeOfAction = 0x01;
1486 conf->typeOfAction = 0x02;
1487 if(!strcasecmp(arg2, "deny"))
1488 conf->typeOfAction += 0x10;
1490 conf->typeOfAction += 0x20;
1498 =======================================================================================================================
1499 Function for creating new configurations for per-directory contexts
1500 =======================================================================================================================
1502 void *create_dir_conf(apr_pool_t *pool, char *context)
1504 context = context ? context : "Newly created configuration";
1506 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1507 example_config *cfg = apr_pcalloc(pool, sizeof(example_config));
1508 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1513 /* Set some default values */
1514 strcpy(cfg->context, context);
1515 cfg->enabled = 0;
1516 memset(cfg->path, 0, 256);
1517 cfg->typeOfAction = 0x00;
1525 =======================================================================================================================
1526 Merging function for configurations
1527 =======================================================================================================================
1529 void *merge_dir_conf(apr_pool_t *pool, void *BASE, void *ADD)
1531 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1532 example_config *base = (example_config *) BASE;
1533 example_config *add = (example_config *) ADD;
1534 example_config *conf = (example_config *) create_dir_conf(pool, "Merged configuration");
1535 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1537 conf->enabled = (add->enabled == 0) ? base->enabled : add->enabled;
1538 conf->typeOfAction = add->typeOfAction ? add->typeOfAction : base->typeOfAction;
1539 strcpy(conf->path, strlen(add->path) ? add->path : base->path);
1549 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
1550 <div class="section">
1551 <h2><a name="summary" id="summary">Summing up</a></h2>
1553 We have now looked at how to create simple modules for Apache HTTP Server 2.4 and
1554 configuring them. What you do next is entirely up to you, but it is my
1555 hope that something valuable has come out of reading this documentation.
1556 If you have questions on how to further develop modules, you are welcome
1557 to join our <a href="http://httpd.apache.org/lists.html">mailing lists</a>
1558 or check out the rest of our documentation for further tips.
1560 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
1561 <div class="section">
1562 <h2><a name="snippets" id="snippets">Some useful snippets of code</a></h2>
1564 <h3><a name="get_post" id="get_post">Retrieve variables from POST form data</a></h3>
1568 <pre class="prettyprint lang-c">typedef struct {
1573 keyValuePair *readPost(request_rec *r) {
1574 apr_array_header_t *pairs = NULL;
1582 res = ap_parse_form_data(r, NULL, &pairs, -1, HUGE_STRING_LEN);
1583 if (res != OK || !pairs) return NULL; /* Return NULL if we failed or if there are is no POST data */
1584 kvp = apr_pcalloc(r->pool, sizeof(keyValuePair) * (pairs->nelts + 1));
1585 while (pairs && !apr_is_empty_array(pairs)) {
1586 ap_form_pair_t *pair = (ap_form_pair_t *) apr_array_pop(pairs);
1587 apr_brigade_length(pair->value, 1, &len);
1588 size = (apr_size_t) len;
1589 buffer = apr_palloc(r->pool, size + 1);
1590 apr_brigade_flatten(pair->value, buffer, &size);
1592 kvp[i].key = apr_pstrdup(r->pool, pair->name);
1593 kvp[i].value = buffer;
1599 static int example_handler(request_rec *r)
1601 /*~~~~~~~~~~~~~~~~~~~~~~*/
1602 keyValuePair *formData;
1603 /*~~~~~~~~~~~~~~~~~~~~~~*/
1605 formData = readPost(r);
1608 for (i = 0; &formData[i]; i++) {
1609 if (formData[i].key && formData[i].value) {
1610 ap_rprintf(r, "%s = %s\n", formData[i].key, formData[i].value);
1611 } else if (formData[i].key) {
1612 ap_rprintf(r, "%s\n", formData[i].key);
1613 } else if (formData[i].value) {
1614 ap_rprintf(r, "= %s\n", formData[i].value);
1628 <h3><a name="headers_out" id="headers_out">Printing out every HTTP header received</a></h3>
1632 <pre class="prettyprint lang-c">static int example_handler(request_rec *r)
1634 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1635 const apr_array_header_t *fields;
1637 apr_table_entry_t *e = 0;
1638 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1640 fields = apr_table_elts(r->headers_in);
1641 e = (apr_table_entry_t *) fields->elts;
1642 for(i = 0; i < fields->nelts; i++) {
1643 ap_rprintf(r, "%s: %s\n", e[i].key, e[i].val);
1653 <h3><a name="request_body" id="request_body">Reading the request body into memory</a></h3>
1657 <pre class="prettyprint lang-c">static int util_read(request_rec *r, const char **rbuf, apr_off_t *size)
1663 if((rc = ap_setup_client_block(r, REQUEST_CHUNKED_ERROR))) {
1667 if(ap_should_client_block(r)) {
1669 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1670 char argsbuffer[HUGE_STRING_LEN];
1671 apr_off_t rsize, len_read, rpos = 0;
1672 apr_off_t length = r->remaining;
1673 /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
1675 *rbuf = (const char *) apr_pcalloc(r->pool, (apr_size_t) (length + 1));
1677 while((len_read = ap_get_client_block(r, argsbuffer, sizeof(argsbuffer))) > 0) {
1678 if((rpos + len_read) > length) {
1679 rsize = length - rpos;
1685 memcpy((char *) *rbuf + rpos, argsbuffer, (size_t) rsize);
1692 static int example_handler(request_rec *r)
1694 /*~~~~~~~~~~~~~~~~*/
1697 /*~~~~~~~~~~~~~~~~*/
1699 if(util_read(r, &buffer, &size) == OK) {
1700 ap_rprintf(r, "We read a request body that was %" APR_OFF_T_FMT " bytes long", size);
1712 <div class="bottomlang">
1713 <p><span>Available Languages: </span><a href="../en/developer/modguide.html" title="English"> en </a></p>
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