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| author | Daniel Gruno <humbedooh@apache.org> | 2012-04-10 15:11:20 +0000 |
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| committer | Daniel Gruno <humbedooh@apache.org> | 2012-04-10 15:11:20 +0000 |
| commit | 8a25bd19af45808ce9af9328ef6acd096536ee41 (patch) | |
| tree | 96a7994e97023c9e4ee394d06cde16237bfb5d56 /docs/manual/developer/modguide.xml | |
| parent | f92ed744cb7bb09f4e29343b5750381d3abaa489 (diff) | |
| download | httpd-8a25bd19af45808ce9af9328ef6acd096536ee41.tar.gz | |
Remove some commas
Wrap lines to 80 character limit where applicable
Fix broken links to the C examples
git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1311777 13f79535-47bb-0310-9956-ffa450edef68
Diffstat (limited to 'docs/manual/developer/modguide.xml')
| -rw-r--r-- | docs/manual/developer/modguide.xml | 475 |
1 files changed, 277 insertions, 198 deletions
diff --git a/docs/manual/developer/modguide.xml b/docs/manual/developer/modguide.xml index 75dec5b9b4..7d1f3596df 100644 --- a/docs/manual/developer/modguide.xml +++ b/docs/manual/developer/modguide.xml @@ -26,7 +26,8 @@ <title>Developing modules for the Apache HTTP Server 2.4</title> <summary> -<p>This document explains how you can develop modules for the Apache HTTP Server 2.4</p> +<p>This document explains how you can develop modules for the Apache HTTP +Server 2.4</p> </summary> <seealso><a href="request.html">Request Processing in Apache 2.4</a></seealso> @@ -35,33 +36,44 @@ <section id="introduction"><title>Introduction</title> <section id="what"><title>What we will be discussing in this document</title> <p> -This document will discuss how you can easily create modules for the Apache HTTP Server 2.4 ("Apache"), -by exploring an example module called <code>mod_example</code>. In the first part of this document, the purpose of this -module will be to calculate and print out various digest values for existing files on your web server, whenever we -access the URL <code>http://hostname/filename.sum</code>. For instance, if we want to know the MD5 digest value of the file -located at <code>http://www.example.com/index.html</code>, we would visit <code>http://www.example.com/index.html.sum</code>. +This document will discuss how you can easily create modules for the Apache +HTTP Server 2.4 ("Apache"), by exploring an example module called +<code>mod_example</code>. In the first part of this document, the purpose +of this module will be to calculate and print out various digest values for +existing files on your web server, whenever we access the URL <code> +http://hostname/filename.sum</code>. For instance, if we want to know the +MD5 digest value of the file located at <code> +http://www.example.com/index.html</code>, we would visit <code> +http://www.example.com/index.html.sum</code>. </p> <p> -In the second part of this document, which deals with configuration directive and context awareness, we will be looking at -a module that simply write out its own configuration to the client. +In the second part of this document, which deals with configuration +directive and context awareness, we will be looking at a module that simply +write out its own configuration to the client. </p> </section> <section id="prerequisites"><title>Prerequisites</title> <p> -First and foremost, you are expected to have a basic knowledge of how the C programming language works. In most cases, -we will try to be as pedagogical as possible and link to documents describing the functions used in the examples, -but there are also many cases where it is necessary to either just assume that "it works" or do some digging youself -into what the hows and whys of various function calls. +First and foremost, you are expected to have a basic knowledge of how the C +programming language works. In most cases, we will try to be as pedagogical +as possible and link to documents describing the functions used in the +examples, but there are also many cases where it is necessary to either +just assume that "it works" or do some digging youself into what the hows +and whys of various function calls. </p> <p> -Lastly, you will need to have a basic understanding of how modules are loaded and configured in Apache, as well as -how to get the headers for Apache if you do not have them already, as these are needed for compiling new modules. +Lastly, you will need to have a basic understanding of how modules are +loaded and configured in Apache, as well as how to get the headers for +Apache if you do not have them already, as these are needed for compiling +new modules. </p> </section> <section id="compiling"><title>Compiling your module</title> <p> -To compile the source code we are building in this document, we will be using <a href="../programs/apxs.html">APXS</a>. -Assuming your source file is called mod_example.c, compiling, installing and activating the module is as simple as: +To compile the source code we are building in this document, we will be +using <a href="../programs/apxs.html">APXS</a>. Assuming your source file +is called mod_example.c, compiling, installing and activating the module is +as simple as: <example><pre> apxs -i -a -c mod_example.c </pre></example> @@ -71,7 +83,8 @@ apxs -i -a -c mod_example.c <section id="basics"><title>Defining a module</title> <img src="../images/build_a_mod_3.png"/><br/> -<p>Every module starts with the same declaration, or name tag if you will, that defines a module as <em>a separate entity within Apache</em>: +<p>Every module starts with the same declaration, or name tag if you will, +that defines a module as <em>a separate entity within Apache</em>: <!-- BEGIN EXAMPLE CODE --> @@ -90,9 +103,9 @@ module AP_MODULE_DECLARE_DATA example_module <code style='color:#806030; '>=</ <!-- END EXAMPLE CODE --> -This bit of code lets Apache know that we have now registered a new module in the system, -and that its name is <code>example_module</code>. The name of the module is used primarilly -for two things:<br/> +This bit of code lets Apache know that we have now registered a new module +in the system, and that its name is <code>example_module</code>. The name +of the module is used primarilly for two things:<br/> <ul> <li>Letting Apache know how to load the module using the LoadModule</li> <li>Setting up a namespace for the module to use in configurations</li> @@ -104,51 +117,60 @@ In essence, this tells Apache to open up <code>mod_example.so</code> and look fo called <code>example_module</code>. </p> <p> -Within this name tag of ours is also a bunch of references to how we would like to handle things: -Which directives do we respond to in a configuration file or .htaccess, how do we operate -within specific contexts, and what handlers are we interested in registering with the Apache -service. We'll return to all these elements later in this document. +Within this name tag of ours is also a bunch of references to how we would +like to handle things: Which directives do we respond to in a configuration +file or .htaccess, how do we operate within specific contexts, and what +handlers are we interested in registering with the Apache service. We'll +return to all these elements later in this document. </p> </section> <section id="hooking"><title>Getting started: Hooking into Apache</title> <section id="hook_intro"><title>An introduction to hooks</title> <p> -When handling requests in Apache, the first thing you will need to do is create a hook into -the request handling process. A hook is essentially a message telling Apache that you are -willing to either serve or at least take a glance at certain requests given by clients. All -handlers, whether it's mod_rewrite, mod_authn_*, mod_proxy and so on, are hooked into specific -parts of the request process. As you are probably aware, modules serve different purposes; Some -are authentication/authorization handlers, others are file or script handlers while some third -modules rewrite URIs or proxies content. Furthermore, in the end, it is up to the user of Apache -how and when each module will come into place. Thus, Apache itself does not presume to know -which module is responsible for handling a specific request, and will ask each module whether -they have an interest in a given request or not. It is then up to each module to either gently -decline serving a request, accept serving it or flat out deny the request from being served, -as authentication/authorization modules do: <br/> +When handling requests in Apache, the first thing you will need to do is +create a hook into the request handling process. A hook is essentially a +message telling Apache that you are willing to either serve or at least +take a glance at certain requests given by clients. All handlers, whether +it's mod_rewrite, mod_authn_*, mod_proxy and so on, are hooked into +specific parts of the request process. As you are probably aware, modules +serve different purposes; Some are authentication/authorization handlers, +others are file or script handlers while some third modules rewrite URIs or +proxies content. Furthermore, in the end, it is up to the user of Apache +how and when each module will come into place. Thus, Apache itself does not +presume to know which module is responsible for handling a specific +request, and will ask each module whether they have an interest in a given +request or not. It is then up to each module to either gently decline +serving a request, accept serving it or flat out deny the request from +being served, as authentication/authorization modules do: <br/> <img src="../images/build_a_mod_2.png" /><br/> -To make it a bit easier for handlers such as our mod_example to know whether the client is -requesting content we should handle or not, Apache has directives for hinting to modules whether -their assistance is needed or not. Two of these are <directive -module="mod_mime">AddHandler</directive> and <directive module="core">SetHandler</directive>. -Let's take a look at an example using <directive module="mod_mime">AddHandler</directive>. -In our example case, we want every request ending with .sum to be served by <code>mod_example</code>, -so we'll add a configuration directive that tells Apache to do just that: +To make it a bit easier for handlers such as our mod_example to know +whether the client is requesting content we should handle or not, Apache +has directives for hinting to modules whether their assistance is needed or +not. Two of these are <directive module="mod_mime">AddHandler</directive> +and <directive module="core">SetHandler</directive>. Let's take a look at +an example using <directive module="mod_mime">AddHandler</directive>. In +our example case, we want every request ending with .sum to be served by +<code>mod_example</code>, so we'll add a configuration directive that tells +Apache to do just that: <example><pre> AddHandler example-handler .sum </pre></example> -What this tells Apache is the following: <em>Whenever we receive a request for a URI ending in .sum, -we are to let all modules know that we are looking for whoever goes by the name of "example-handler" -</em>. Thus, when a request is being served that ends in .sum, Apache will let all modules know, that -this request should be served by "example-handler". As you will see later, when we start -building mod_example, we will check for this handler tag relayed by <code>AddHandler</code> and -reply to Apache based on the value of this tag. +What this tells Apache is the following: <em>Whenever we receive a request +for a URI ending in .sum, we are to let all modules know that we are +looking for whoever goes by the name of "example-handler" </em>. +Thus, when a request is being served that ends in .sum, Apache will let all +modules know, that this request should be served by "example-handler +". As you will see later, when we start building mod_example, we will +check for this handler tag relayed by <code>AddHandler</code> and reply to +Apache based on the value of this tag. </p> </section> <section id="hook_declaration"><title>Hooking into httpd</title> <p> -To begin with, we only want to create a simple handler, that replies to the client browser -when a specific URL is requested, so we won't bother setting up configuration handlers and -directives just yet. Our initial module definition will look like this:<br/> +To begin with, we only want to create a simple handler, that replies to the +client browser when a specific URL is requested, so we won't bother setting +up configuration handlers and directives just yet. Our initial module +definition will look like this:<br/> <!-- BEGIN EXAMPLE CODE --> @@ -167,15 +189,14 @@ module AP_MODULE_DECLARE_DATA example_module = <!-- END EXAMPLE CODE --> -This lets Apache know that we are not interesting in anything fancy, we just want to hook onto -the requests and possibly handle some of them. -</p> -<p> -The reference in our example declaration, <code>register_hooks</code> is the name of a function -we will create to manage how we hook onto the request process. In this example module, the function -has just one purpose; To create a simple hook that gets called after all the rewrites, access -control etc has been handled. Thus, we will let Apache know, that we want to hook into its process -as one of the last modules: +This lets Apache know that we are not interesting in anything fancy, we +just want to hook onto the requests and possibly handle some of them. </p> +<p> The reference in our example declaration, <code>register_hooks</code> +is the name of a function we will create to manage how we hook onto the +request process. In this example module, the function has just one purpose; +To create a simple hook that gets called after all the rewrites, access +control etc has been handled. Thus, we will let Apache know, that we want +to hook into its process as one of the last modules: <!-- BEGIN EXAMPLE CODE --> @@ -189,13 +210,14 @@ as one of the last modules: <!-- END EXAMPLE CODE --> -The <code>example_handler</code> reference is the function that will handle the request. We will -discuss how to create a handler in the next chapter. +The <code>example_handler</code> reference is the function that will handle +the request. We will discuss how to create a handler in the next chapter. </p> </section> <section id="hook_others"><title>Other useful hooks</title> <p> -Hooking into the request handling phase is but one of many hooks that you can create. Some other ways of hooking are: +Hooking into the request handling phase is but one of many hooks that you +can create. Some other ways of hooking are: <ul> <li><code>ap_hook_child_init</code>: Place a hook that executes when a child process is spawned (commonly used for initializing modules after Apache has forked)</li> <li><code>ap_hook_pre_config</code>: Place a hook that executes before any configuration data has been read (very early hook)</li> @@ -208,13 +230,15 @@ Hooking into the request handling phase is but one of many hooks that you can cr <section id="handling"><title>Building a handler</title> <p> -A handler is essentially a function that receives a callback when a request to Apache is made. -It is passed a record of the current request (how it was made, which headers and requests were -passed along, who's giving the request and so on), and is put in charge of either telling -Apache that it's not interested in the request or handle the request with the tools provided. +A handler is essentially a function that receives a callback when a request +to Apache is made. It is passed a record of the current request (how it was +made, which headers and requests were passed along, who's giving the +request and so on), and is put in charge of either telling Apache that it's +not interested in the request or handle the request with the tools provided. </p> -<section id="simple_handler"><title>A simple "Hello, world!" handler</title> -Let's start off by making a very simple request handler that does the following: <br/> +<section id="simple_handler"><title>A simple "Hello, world!" +handler</title> Let's start off by making a very simple request handler +that does the following: <br/> <ol> <li>Check that this is a request that should be served by "example-handler"</li> <li>Set the content type of our output to <code>text/html</code></li> @@ -249,16 +273,19 @@ In C code, our example handler will now look like this:<br/> <!-- END EXAMPLE CODE --> -Now, we put all we have learned together and end up with a program that looks like <a href="mod_example_1.c"> -mod_example_1.c</a>. The functions used in this example will be explained later in the section -<a href="#functions">"Some useful functions you should know"</a>. -</section> -<section id="request_rec"><title>The request_rec structure</title> -<p>The most essential part of any request is the <em>request record</em>. In a call to a handler function, this -is represented by the <code>request_req*</code> structure passed along with every call that is made. This -struct, typically just refered to as <code>r</code> in modules, contains all the information you need for -your module to fully process any HTTP request and respond accordingly.</p> -<p>Some key elements of the <code>request_req</code> structure are: +Now, we put all we have learned together and end up with a program that +looks like +<a href="http://people.apache.org/~humbedooh/mods/examples/mod_example_1.c">mod_example_1.c</a> +. The functions used in this example will be explained later in the section +<a href= "#functions">"Some useful functions you should know"</a> +. </section> <section id="request_rec"><title>The request_rec structure +</title> <p>The most essential part of any request is the <em>request record +</em>. In a call to a handler function, this is represented by the <code> +request_req* </code> structure passed along with every call that is made. +This struct, typically just refered to as <code>r</code> in modules, +contains all the information you need for your module to fully process any +HTTP request and respond accordingly.</p> <p>Some key elements of the <code> +request_req </code> structure are: <ul> <li><code><code style='color:#008833'>r->handler</code> (char*)</code>: Contains the name of the handler Apache is currently asking to do the handling of this request</li> <li><code><code style='color:#008833'>r->method</code> (char*)</code>: Contains the HTTP method being used, f.x. GET or POST</li> @@ -311,11 +338,12 @@ Let's try out some of these variables in another example handler:<br/> <section id="return_value"><title>Return values</title> <p> -Apache relies on return values from handlers to signify whether a request was handled or not, -and if so, whether the request went well or not. If a module is not interested in handling -a specific request, it should always return the value <code>DECLINED</code>. If it is handling -a request, it should either return the generic value <code>OK</code>, or a specific HTTP status -code, for example: +Apache relies on return values from handlers to signify whether a request +was handled or not, and if so, whether the request went well or not. If a +module is not interested in handling a specific request, it should always +return the value <code>DECLINED</code>. If it is handling a request, it +should either return the generic value <code>OK</code>, or a specific HTTP +status code, for example: <!-- BEGIN EXAMPLE CODE --> @@ -329,12 +357,14 @@ code, for example: <!-- END EXAMPLE CODE --> -Returning <code>OK</code> or a HTTP status code does not necessarilly mean that the request will end. Apache -may still have other handlers that are interested in this request, for instance the logging modules -which, upon a successful request, will write down a summary of what was requested and how it went. -To do a full stop and prevent any further processing after your module is done, you can return the -value <code>DONE</code> to let Apache know that it should cease all activity on this request and -carry on with the next, without informing other handlers. +Returning <code>OK</code> or a HTTP status code does not necessarilly mean +that the request will end. Apache may still have other handlers that are +interested in this request, for instance the logging modules which, upon a +successful request, will write down a summary of what was requested and how +it went. To do a full stop and prevent any further processing after your +module is done, you can return the value <code>DONE</code> to let Apache +know that it should cease all activity on this request and carry on with +the next, without informing other handlers. <br/> <strong>General response codes:</strong> <ul> @@ -399,16 +429,19 @@ carry on with the next, without informing other handlers. <section id="memory"><title>Memory management</title> <p> -Managing your resources in Apache is quite easy, thanks to the memory pool system. In essence, -each server, connection and request have their own memory pool that gets cleaned up when its -scope ends, e.g. when a request is done or when a server process shuts down. All your module -needs to do is latch onto this memory pool, and you won't have to worry about having to clean -up after yourself - pretty neat, huh?</p> +Managing your resources in Apache is quite easy, thanks to the memory pool +system. In essence, each server, connection and request have their own +memory pool that gets cleaned up when its scope ends, e.g. when a request +is done or when a server process shuts down. All your module needs to do is +latch onto this memory pool, and you won't have to worry about having to +clean up after yourself - pretty neat, huh? +</p> <p> -In our module, we will primarilly be allocating memory for each request, so it's appropriate to -use the <code><code style='color:#008833'>r->pool</code></code> reference when creating new objects. A few of the functions for -allocating memory within a pool are: +In our module, we will primarilly be allocating memory for each request, so +it's appropriate to use the <code style='color:#008833'>r->pool</code> +reference when creating new objects. A few of the functions for allocating +memory within a pool are: <ul> <li><code>void* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__pools.html#ga85f1e193c31d109affda72f9a92c6915">apr_palloc</a>( apr_pool_t *p, apr_size_t size)</code>: Allocates <code>size</code> number of bytes in the pool for you</li> @@ -438,9 +471,11 @@ Let's put these functions into an example handler:<br/> </pre> <!-- END EXAMPLE CODE --> -This is all well and good for our module, which won't need any pre-initialized variables or structures. -However, if we wanted to initialize something early on, before the requests come rolling in, we could -simply add a call to a function in our <code>register_hooks</code> function to sort it out: +This is all well and good for our module, which won't need any +pre-initialized variables or structures. However, if we wanted to +initialize something early on, before the requests come rolling in, we +could simply add a call to a function in our <code>register_hooks</code> +function to sort it out: <!-- BEGIN EXAMPLE CODE --> <pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'> @@ -454,25 +489,30 @@ simply add a call to a function in our <code>register_hooks</code> function to s </pre> <!-- END EXAMPLE CODE --> -In this, pre-request initialization function, we would not be using the same pool as we did when -allocating resources for request-based functions. Instead, we would use the pool given to us by -Apache for allocating memory on a per-process based level. +In this pre-request initialization function we would not be using the +same pool as we did when allocating resources for request-based functions. +Instead, we would use the pool given to us by Apache for allocating memory +on a per-process based level. </p> </section> <section id="parsing"><title>Parsing request data</title> <p> -In our example module, we would like to add a feature, that checks which type of digest, MD5 or SHA1 -the client would like to see. This could be solved by adding a query string to the request. A query -string is typically comprised of several keys and values put together in a string, for instance -<code>valueA=yes&valueB=no&valueC=maybe</code>. It is up to the module itself to parse these -and get the data it requires. In our example, we'll be looking for a key called <code>digest</code>, -and if set to <code>md5</code>, we'll produce an MD5 digest, otherwise we'll produce a SHA1 digest. +In our example module, we would like to add a feature, that checks which +type of digest, MD5 or SHA1 the client would like to see. This could be +solved by adding a query string to the request. A query string is typically +comprised of several keys and values put together in a string, for instance +<code>valueA=yes&valueB=no&valueC=maybe</code>. It is up to the +module itself to parse these and get the data it requires. In our example, +we'll be looking for a key called <code>digest</code>, and if set to <code> +md5</code>, we'll produce an MD5 digest, otherwise we'll produce a SHA1 +digest. </p> <p> -Since the introduction of Apache 2.4, parsing request data from GET and POST requests have never -been easier. All we require to parse both GET and POST data is four simple lines: +Since the introduction of Apache 2.4, parsing request data from GET and +POST requests have never been easier. All we require to parse both GET and +POST data is four simple lines: <!-- BEGIN EXAMPLE CODE --> @@ -486,9 +526,10 @@ been easier. All we require to parse both GET and POST data is four simple lines <!-- END EXAMPLE CODE --> -In our specific example module, we're looking for the <code>digest</code> value from the query string, -which now resides inside a table called <code>GET</code>. To extract this value, we need only perform -a simple operation:<br/> +In our specific example module, we're looking for the <code>digest</code> +value from the query string, which now resides inside a table called <code> +GET</code>. To extract this value, we need only perform a simple operation: +<br/> <!-- BEGIN EXAMPLE CODE --> @@ -503,15 +544,17 @@ a simple operation:<br/> <!-- END EXAMPLE CODE --> -The structures used for the POST and GET data are not exactly the same, so if we were to fetch a value from -POST data instead of the query string, we 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. +The structures used for the POST and GET data are not exactly the same, so +if we were to fetch a value from POST data instead of the query string, we +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. </p> </section> <section id="advanced_handler"><title>Making an advanced handler</title> -Now that we have learned how to parse form data and manage our resources, we can move on to creating an advanced -version of our module, that spits out the MD5 or SHA1 digest of files:<br/> +Now that we have learned how to parse form data and manage our resources, +we can move on to creating an advanced version of our module, that spits +out the MD5 or SHA1 digest of files:<br/> <!-- BEGIN EXAMPLE CODE --> @@ -631,29 +674,33 @@ version of our module, that spits out the MD5 or SHA1 digest of files:<br/> <!-- END EXAMPLE CODE --> -This version in its entirity can be found here: <a href="mod_example_2.c">mod_example_2.c</a>. +This version in its entirity can be found here: +<a href="http://people.apache.org/~humbedooh/mods/examples/mod_example_2.c">mod_example_2.c</a>. </section> </section> <section id="configuration"><title>Adding configuration options</title> <p> -In this next segment of this document, we will turn our eyes away from the digest module and create a new -example module, whose only function is to write out its own configuration. The purpose of this is to -examine how Apache works with configuration, and what happens when you start writing advanced configurations +In this next segment of this document, we will turn our eyes away from the +digest module and create a new example module, whose only function is to +write out its own configuration. The purpose of this is to examine how +Apache works with configuration, and what happens when you start writing +advanced configurations for your modules. </p> -<section id="config_intro"><title>An introduction to configuration directives</title> -If you are reading this, then you probably already know what a configuration directive is. Simply put, -a directive is a way of telling an individual module (or a set of modules) how to behave, such as these -directives control how <code>mod_rewrite</code> works: +<section id="config_intro"><title>An introduction to configuration +directives</title> If you are reading this, then you probably already know +what a configuration directive is. Simply put, a directive is a way of +telling an individual module (or a set of modules) how to behave, such as +these directives control how <code>mod_rewrite</code> works: <example><pre> RewriteEngine On RewriteCond %{REQUEST_URI} ^/foo/bar RewriteRule ^/foo/bar/(.*)$ /foobar?page=$1 </pre></example> -Each of these configuration directives are handled by a separate function, that parses the parameters given -and sets up a configuration accordingly. +Each of these configuration directives are handled by a separate function, +that parses the parameters given and sets up a configuration accordingly. </section> <section id="config_simple"><title>Making an example configuration</title> To begin with, we'll create a basic configuration in C-space: @@ -670,9 +717,10 @@ To begin with, we'll create a basic configuration in C-space: <!-- END EXAMPLE CODE --> -Now, let's put this into perspective by creating a very small module that just prints out a hard-coded -configuration. You'll notice that we use the <code>register_hooks</code> function for initializing the -configuration values to their defaults: +Now, let's put this into perspective by creating a very small module that +just prints out a hard-coded configuration. You'll notice that we use the +<code>register_hooks</code> function for initializing the configuration +values to their defaults: <!-- BEGIN EXAMPLE CODE --> @@ -719,20 +767,23 @@ module AP_MODULE_DECLARE_DATA example_module <code style='color:#806030; '>=</ <!-- END EXAMPLE CODE --> -So far so good. To access our new handler, we could add the following to our configuration: +So far so good. To access our new handler, we could add the following to +our configuration: <example><pre> <Location /example> SetHandler example-handler </Location> </pre></example> -When we visit, we'll see our current configuration being spit out by our module. +When we visit, we'll see our current configuration being spit out by our +module. </section> <section id="register_directive"><title>Registering directives with Apache</title> -What if we want to change our configuration, not by hard-coding new values into the module, -but by using either the httpd.conf file or possibly a .htaccess file? It's time to let Apache -know that we want this to be possible. To do so, we must first change our <em>name tag</em> -to include a reference to the configuration directives we want to register with Apache: +What if we want to change our configuration, not by hard-coding new values +into the module, but by using either the httpd.conf file or possibly a +.htaccess file? It's time to let Apache know that we want this to be +possible. To do so, we must first change our <em>name tag</em> to include a +reference to the configuration directives we want to register with Apache: <!-- BEGIN EXAMPLE CODE --> @@ -751,10 +802,11 @@ module AP_MODULE_DECLARE_DATA example_module = <!-- END EXAMPLE CODE --> -This will tell Apache that we are now accepting directives from the configuration files, and that the -structure called <code>example_directives</code> holds information on what our directives are and how -they work. Since we have three different variables in our module configuration, we will add a structure -with three directives and a NULL at the end: +This will tell Apache that we are now accepting directives from the +configuration files, and that the structure called <code>example_directives +</code> holds information on what our directives are and how they work. +Since we have three different variables in our module configuration, we +will add a structure with three directives and a NULL at the end: <!-- BEGIN EXAMPLE CODE --> @@ -785,18 +837,22 @@ accordingly. We will discuss how to make this in the following paragraph.</li> later chapters, but for now, <code>RSRC_CONF</code> means that Apache will only accept these directives in a server context.</li> <li><code>"Enable or disable...."</code>: This is simply a brief description of what the directive does.</li> </ol> -(<em>The "missing" parameter in our definition, which is usually set to <code>NULL</code>, is an optional function that can be -run after the initial function to parse the arguments have been run. This is usually omitted, as the function for verifying -arguments might as well be used to set them.</em>) +(<em>The "missing" parameter in our definition, which is usually set to +<code>NULL</code>, is an optional function that can be run after the +initial function to parse the arguments have been run. This is usually +omitted, as the function for verifying arguments might as well be used to +set them.</em>) </p> </section> <section id="directive_handler"><title>The directive handler function</title> <p> -Now that we've told Apache to expect some directives for our module, it's time to make a few functions for handling these. What -Apache reads in the configuration file(s) is text, and so naturally, what it passes along to our directive handler is one or -more strings, that we ourselves need to recognize and act upon. You'll notice, that since we set our <code>exampleAction</code> -directive to accept two arguments, its C function also has an additional parameter defined:<br/> - +Now that we've told Apache to expect some directives for our module, it's +time to make a few functions for handling these. What Apache reads in the +configuration file(s) is text, and so naturally, what it passes along to +our directive handler is one or more strings, that we ourselves need to +recognize and act upon. You'll notice, that since we set our <code> +exampleAction</code> directive to accept two arguments, its C function also +has an additional parameter defined:<br/> <!-- BEGIN EXAMPLE CODE --> <pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'> @@ -835,8 +891,8 @@ directive to accept two arguments, its C function also has an additional paramet </section> <section id="directive_complete"><title>Putting it all together</title> <p> -Now that we have our directives set up, and handlers configured for them, we can assemble our module -into one big file: +Now that we have our directives set up, and handlers configured for them, +we can assemble our module into one big file: <!-- BEGIN EXAMPLE CODE --> @@ -959,14 +1015,16 @@ module AP_MODULE_DECLARE_DATA example_module <code style='color:#806030; '>=</ </p> <p> -In our httpd.conf file, we can now change the hard-coded configuration by adding a few lines: +In our httpd.conf file, we can now change the hard-coded configuration by +adding a few lines: <example><pre> ExampleEnabled On ExamplePath "/usr/bin/foo" ExampleAction file allow </pre></example> -And thus we apply the configuration, visit <code>/example</code> on our web site, and we see the configuration has -adapted to what we wrote in our configuration file. +And thus we apply the configuration, visit <code>/example</code> on our +web site, and we see the configuration has adapted to what we wrote in our +configuration file. </p> </section> @@ -976,9 +1034,10 @@ adapted to what we wrote in our configuration file. <section id="context"><title>Context aware configurations</title> <section id="context_intro"><title>Introduction to context aware configurations</title> <p> -In Apache, different URLs, virtual hosts, directories etc can have very different meanings -to the user of Apache, and thus different contexts within which modules must operate. For example, -let's assume you have this configuration set up for mod_rewrite: +In Apache, different URLs, virtual hosts, directories etc can have very +different meanings to the user of Apache, and thus different contexts +within which modules must operate. For example, let's assume you have this +configuration set up for mod_rewrite: <example><pre> <Directory "/var/www"> RewriteCond %{HTTP_HOST} ^example.com$ @@ -988,17 +1047,22 @@ let's assume you have this configuration set up for mod_rewrite: RewriteRule ^foobar$ index.php?foobar=true </Directory> </pre></example> -In this example, you will have set up two different contexts for mod_rewrite: +In this example, you will have set up two different contexts for +mod_rewrite: <ol> <li>Inside <code>/var/www</code>, all requests for <code>http://example.com</code> must go to <code>http://www.example.com</code></li> <li>Inside <code>/var/www/sub</code>, all requests for <code>foobar</code> must go to <code>index.php?foobar=true</code></li> </ol> -If mod_rewrite (or Apache for that matter) wasn't context aware, then these rewrite rules would just apply to every and any request made, -regardless of where and how they were made, but since the module can pull the context specific configuration straight from Apache, it -does not need to know itself, which of the directives are valid in this context, since Apache takes care of this.</p> +If mod_rewrite (or Apache for that matter) wasn't context aware, then +these rewrite rules would just apply to every and any request made, +regardless of where and how they were made, but since the module can pull +the context specific configuration straight from Apache, it does not need +to know itself, which of the directives are valid in this context, since +Apache takes care of this.</p> <p> -So how does a module get the specific configuration for the server, directory or location in question? It does so by making one simple call: +So how does a module get the specific configuration for the server, +directory or location in question? It does so by making one simple call: <!-- BEGIN EXAMPLE CODE --> @@ -1008,15 +1072,18 @@ So how does a module get the specific configuration for the server, directory or 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>(<code style='color:#008833'>r->per_dir_config</code>, &example_module); </pre> -That's it! Of course, a whole lot goes on behind the scenes, which we will discuss in this chapter, starting with how -Apache came to know what our configuration looks like, and how it came to be set up as it is in the specific context. +That's it! Of course, a whole lot goes on behind the scenes, which we will +discuss in this chapter, starting with how Apache came to know what our +configuration looks like, and how it came to be set up as it is in the +specific context. </p> </section> <section id="context_base"><title>Our basic configuration setup</title> -<p>In this chapter, we will be working with a slightly modified version of our previous -context structure. We will set a <code>context</code> variable that we can use to track -which context configuration is being used by Apache in various places: +<p>In this chapter, we will be working with a slightly modified version of +our previous context structure. We will set a <code>context</code> +variable that we can use to track which context configuration is being +used by Apache in various places: <!-- BEGIN EXAMPLE CODE --> @@ -1059,8 +1126,9 @@ which context configuration is being used by Apache in various places: <section id="context_which"><title>Choosing a context</title> <p> -Before we can start making our module context aware, we must first define, which contexts we will accept. -As we saw in the previous chapter, defining a directive required five elements be set: +Before we can start making our module context aware, we must first define, +which contexts we will accept. As we saw in the previous chapter, defining +a directive required five elements be set: <!-- BEGIN EXAMPLE CODE --> @@ -1070,18 +1138,21 @@ As we saw in the previous chapter, defining a directive required five elements b <!-- END EXAMPLE CODE --> -The <code>RSRC_CONF</code> definition told Apache that we would only allow this directive in a global server context, but -since we are now trying out a context aware version of our module, we should set this to something more lenient, namely -the value <code>ACCESS_CONF</code>, which lets us use the directive inside <Directory> and <Location> blocks. +The <code>RSRC_CONF</code> definition told Apache that we would only allow +this directive in a global server context, but since we are now trying out +a context aware version of our module, we should set this to something +more lenient, namely the value <code>ACCESS_CONF</code>, which lets us use +the directive inside <Directory> and <Location> blocks. </p> </section> <section id="context_pool"><title>Using Apache to allocate configuration slots</title> -<p> A much smarter way to manage your configurations is by letting Apache help you create them. -To do so, we must first start off by chancing our <em>name tag</em> to let Apache know, that -it should assist us in creating and managing our configurations. Since we have chosen the per-directory -(or per-location) context for our module configurations, we'll add a per-directory creator and merger -function reference in our tag: +<p> A much smarter way to manage your configurations is by letting Apache +help you create them. To do so, we must first start off by chancing our +<em>name tag</em> to let Apache know, that it should assist us in creating +and managing our configurations. Since we have chosen the per-directory +(or per-location) context for our module configurations, we'll add a +per-directory creator and merger function reference in our tag: <!-- BEGIN EXAMPLE CODE --> <pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'> @@ -1107,9 +1178,10 @@ module AP_MODULE_DECLARE_DATA example_module <code style='color:#806030; '>=</ <section id="context_which"><title>Creating new context configurations</title> <p> -Now that we have told Apache to help us create and manage configurations, our first step is to -make a function for creating new, blank configurations. We do so by creating the function we just -referenced in our name tag as the Per-directory configuration handler: +Now that we have told Apache to help us create and manage configurations, +our first step is to make a function for creating new, blank +configurations. We do so by creating the function we just referenced in +our name tag as the Per-directory configuration handler: <!-- BEGIN EXAMPLE CODE --> <pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'> <code style='color:#400000; font-weight:bold; '>void</code><code style='color:#806030; '>*</code> example_create_dir_conf<code style='color:#806030; '>(</code>apr_pool_t<code style='color:#806030; '>*</code> pool<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>char</code><code style='color:#806030; '>*</code> context<code style='color:#806030; '>)</code> <code style='color:#806030; '>{</code> @@ -1133,8 +1205,9 @@ referenced in our name tag as the Per-directory configuration handler: <section id="context_which"><title>Merging configurations</title> <p> -Our next step in creating a context aware configuration is merging configurations. This part of the process -particularly apply to scenarios where you have a parent configuration and a child, such as the following: +Our next step in creating a context aware configuration is merging +configurations. This part of the process particularly apply to scenarios +where you have a parent configuration and a child, such as the following: <example><pre> <Directory "/var/www"> ExampleEnable On @@ -1145,10 +1218,11 @@ particularly apply to scenarios where you have a parent configuration and a chil ExampleAction file deny </Directory> </pre></example> -In this example, it is natural to assume that the directory <code>/var/www/subdir</code> should inherit the -value set for the <code>/var/www</code> directory, as we did not specify a <code>ExampleEnable</code> nor an -<code>ExamplePath</code> for this directory. Apache does not presume to know if this is true, but cleverly -does the following: +In this example, it is natural to assume that the directory <code> +/var/www/subdir</code> should inherit the value set for the <code>/var/www +</code> directory, as we did not specify a <code>ExampleEnable</code> nor +an <code>ExamplePath</code> for this directory. Apache does not presume to +know if this is true, but cleverly does the following: <ol> <li>Creates a new configuration for <code>/var/www</code></li> <li>Sets the configuration values according to the directives given for <code>/var/www</code></li> @@ -1156,8 +1230,9 @@ does the following: <li>Sets the configuration values according to the directives given for <code>/var/www/subdir</code></li> <li><strong>Proposes a merge</strong> of the two configurations into a new configuration for <code>/var/www/subdir</code></li> </ol> -This proposal is handled by the <code>merge_dir_conf</code> function we referenced in our name tag. The purpose of -this function is to assess the two configurations and decide how they are to be merged: +This proposal is handled by the <code>merge_dir_conf</code> function we +referenced in our name tag. The purpose of this function is to assess the +two configurations and decide how they are to be merged: <!-- BEGIN EXAMPLE CODE --> @@ -1181,8 +1256,9 @@ this function is to assess the two configurations and decide how they are to be <section id="context_which"><title>Trying out our new context aware configurations</title> <p> -Now, let's try putting it all together to create a new module that it context aware. First off, we'll -create a configuration that lets us test how the module works: +Now, let's try putting it all together to create a new module that it +context aware. First off, we'll create a configuration that lets us test +how the module works: <example><pre> <Location "/a"> SetHandler example-handler @@ -1202,8 +1278,9 @@ create a configuration that lets us test how the module works: ExampleEnabled on </Location> </pre></example> -Then we'll assemble our module code. Note, that since we are now using our name tag as reference when fetching -configurations in our handler, I have added some prototypes to keep the compiler happy: +Then we'll assemble our module code. Note, that since we are now using our +name tag as reference when fetching configurations in our handler, I have +added some prototypes to keep the compiler happy: </p> <!-- BEGIN EXAMPLE CODE --> @@ -1443,9 +1520,11 @@ module AP_MODULE_DECLARE_DATA example_module <code style='color:#806030; '>=< <section id="summary"><title>Summing up</title> <p> -We have now looked at how to create simple modules for Apache and configuring them. What you do next is entirely up -to you, but it is my hope that something valuable has come out of reading this documentation. If you have questions -on how to further develop modules, you are welcome to join our <a href="http://httpd.apache.org/lists.html">mailing lists</a> +We have now looked at how to create simple modules for Apache and +configuring them. What you do next is entirely up to you, but it is my +hope that something valuable has come out of reading this documentation. +If you have questions on how to further develop modules, you are welcome +to join our <a href="http://httpd.apache.org/lists.html">mailing lists</a> or check out the rest of our documentation for further tips. </p> </section> |
