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Subject svn commit: r1180925 - /httpd/httpd/trunk/docs/manual/rewrite/tech.xml
Date Mon, 10 Oct 2011 12:46:21 GMT
Author: rbowen
Date: Mon Oct 10 12:46:21 2011
New Revision: 1180925

Rewrites the 'API Phases' section to give a brief intro to what an API
Phase is, and how mod_rewrite handles rewrite rules in two different
phases. Removes some of the condescending tone. References


Modified: httpd/httpd/trunk/docs/manual/rewrite/tech.xml
--- httpd/httpd/trunk/docs/manual/rewrite/tech.xml (original)
+++ httpd/httpd/trunk/docs/manual/rewrite/tech.xml Mon Oct 10 12:46:21 2011
@@ -39,81 +39,81 @@ and URL matching.</p>
 <seealso><a href="advanced.html">Advanced techniques</a></seealso>
 <seealso><a href="avoid.html">When not to use mod_rewrite</a></seealso>
-<section id="Internal"><title>Internal Processing</title>
-      <p>The internal processing of this module is very complex but
-      needs to be explained once even to the average user to avoid
-      common mistakes and to let you exploit its full
-      functionality.</p>
 <section id="InternalAPI"><title>API Phases</title>
-      <p>First you have to understand that when Apache processes a
-      HTTP request it does this in phases. A hook for each of these
-      phases is provided by the Apache API. Mod_rewrite uses two of
-      these hooks: the URL-to-filename translation hook which is
-      used after the HTTP request has been read but before any
-      authorization starts and the Fixup hook which is triggered
-      after the authorization phases and after the per-directory
-      config files (<code>.htaccess</code>) have been read, but
-      before the content handler is activated.</p>
-      <p>So, after a request comes in and Apache has determined the
-      corresponding server (or virtual server) the rewriting engine
-      starts processing of all mod_rewrite directives from the
-      per-server configuration in the URL-to-filename phase. A few
-      steps later when the final data directories are found, the
-      per-directory configuration directives of mod_rewrite are
-      triggered in the Fixup phase. In both situations mod_rewrite
-      rewrites URLs either to new URLs or to filenames, although
-      there is no obvious distinction between them. This is a usage
-      of the API which was not intended to be this way when the API
-      was designed, but as of Apache 1.x this is the only way
-      mod_rewrite can operate. To make this point more clear
-      remember the following two points:</p>
-      <ol>
-        <li>Although mod_rewrite rewrites URLs to URLs, URLs to
-        filenames and even filenames to filenames, the API
-        currently provides only a URL-to-filename hook. In Apache
-        2.0 the two missing hooks will be added to make the
-        processing more clear. But this point has no drawbacks for
-        the user, it is just a fact which should be remembered:
-        Apache does more in the URL-to-filename hook than the API
-        intends for it.</li>
-        <li>
-          Unbelievably mod_rewrite provides URL manipulations in
-          per-directory context, <em>i.e.</em>, within
-          <code>.htaccess</code> files, although these are reached
-          a very long time after the URLs have been translated to
-          filenames. It has to be this way because
-          <code>.htaccess</code> files live in the filesystem, so
-          processing has already reached this stage. In other
-          words: According to the API phases at this time it is too
-          late for any URL manipulations. To overcome this chicken
-          and egg problem mod_rewrite uses a trick: When you
-          manipulate a URL/filename in per-directory context
-          mod_rewrite first rewrites the filename back to its
-          corresponding URL (which is usually impossible, but see
-          the <code>RewriteBase</code> directive below for the
-          trick to achieve this) and then initiates a new internal
-          sub-request with the new URL. This restarts processing of
-          the API phases.
-          <p>Again mod_rewrite tries hard to make this complicated
-          step totally transparent to the user, but you should
-          remember here: While URL manipulations in per-server
-          context are really fast and efficient, per-directory
-          rewrites are slow and inefficient due to this chicken and
-          egg problem. But on the other hand this is the only way
-          mod_rewrite can provide (locally restricted) URL
-          manipulations to the average user.</p>
-        </li>
-      </ol>
+    <p>The Apache HTTP Server handles requests in several phases. At
+    each of these phases, one or more modules may be called upon to
+    handle that portion of the request lifecycle. Phases include things
+    like URL-to-filename translation, authentication, authorization,
+    content, and logging. (These is not an exhaustive list.)</p>
+    <p>mod_rewrite acts in two of these phases (or "hooks", as they are
+    sometimes called) to influence how URLs may be rewritten.</p>
+    <p>First, it uses the URL-to-filename translation hook, which occurs
+    after the HTTP request has been read, but before any authorization
+    starts. Secondly, it uses the Fixup hook, which is after the
+    authorizatin phases, and after per-directory configuration files
+    (<code>.htaccess</code> files) have been read, but before the
+    content handler is called.</p>
+    <p>So, after a request comes in and a corresponding server or
+    virtual host has been determined, the rewriting engine starts
+    processing any <code>mod_rewrite</code> directives appearing in the
+    per-server configuration. (ie, in the main server configuration file
+    and <directive module="core" type="section">Virtualhost</directive>
+    sections.) This happens in the URL-to-filename phase.</p>
+    <p>A few steps later, when the finaly data directories are found,
+    the per-directory configuration directives (<code>.htaccess</code>
+    files and <directive module="core"
+    type="section">Directory</directive> blocks) are applied. This
+    happens in the Fixup phase.</p>
+    <p>In each of these cases, mod_rewrite rewrites the
+    <code>REQUEST_URI</code> either to a new URI, or to a filename.</p>
+    <p>In per-directory context (ie, within <code>.htaccess</code> files
+    and <code>Directory</code> blocks), these rules are being applied
+    after a URI has already been translated to a filename. Because of
+    this, mod_rewrite temporarily translates the filename back into a URI,
+    by stripping off directory paty before appling the rules. (See the
+    <directive module="mod_rewrite">RewriteBase</directive> directive to
+    see how you can further manipulate how this is handled.) Then, a new
+    internal subrequest is issued with the new URI. This restarts
+    processing of the API phases.</p>
+    <p>Because of this further manipulation of the URI in per-directory
+    context, you'll need to take care to craft your rewrite rules
+    differently in that context. In particular, remember that the
+    leading directory path will be stripped off of the URI that your
+    rewrite rules will see. Consider the examples below for further
+    clarification.</p>
+    <table border="1">
+        <tr>
+            <th>Location of rule</th>
+            <th>Rule</th>
+        </tr>
+        <tr>
+            <td>VirtualHost section</td>
+            <td>RewriteRule ^/images/(.+)\.jpg /images/$1.gif</td>
+        </tr>
+        <tr>
+            <td>.htaccess file in document root</td>
+            <td>RewriteRule ^images/(.+)\.jpg images/$1.gif</td>
+        </tr>
+        <tr>
+            <td>.htaccess file in images directory</td>
+            <td>RewriteRule ^(.+)\.jpg $1.gif</td>
+        </tr>
+    </table>
-      <p>Don't forget these two points!</p>
 <section id="InternalRuleset"><title>Ruleset Processing</title>

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