mirror of
https://github.com/apache/httpd.git
synced 2025-06-01 23:21:45 +03:00
64670c57ff
phase runs in 2.0 (compared with 1.3.) git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@91111 13f79535-47bb-0310-9956-ffa450edef68
218 lines
8.9 KiB
HTML
218 lines
8.9 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
|
|
<HTML>
|
|
<HEAD>
|
|
<TITLE>Request Processing in Apache 2.0</TITLE>
|
|
</HEAD>
|
|
|
|
<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
|
|
<BODY
|
|
BGCOLOR="#FFFFFF"
|
|
TEXT="#000000"
|
|
LINK="#0000FF"
|
|
VLINK="#000080"
|
|
ALINK="#FF0000"
|
|
>
|
|
|
|
<!--#include virtual="header.html" -->
|
|
|
|
<h1>Request Processing in Apache 2.0</h1>
|
|
|
|
<p>Warning - this is a first (fast) draft that needs further revision!</p>
|
|
|
|
<p>Several changes in Apache 2.0 affect the internal request processing
|
|
mechanics. Module authors need to be aware of these changes so they
|
|
may take advantage of the optimizations and security enhancements.</p>
|
|
|
|
<p>The first major change is to the subrequest and redirect mechanisms.
|
|
There were a number of different code paths in Apache 1.3 to attempt
|
|
to optimize subrequest or redirect behavior. As patches were introduced
|
|
to 2.0, these optimizations (and the server behavior) were quickly broken
|
|
due to this duplication of code. All duplicate code has been folded
|
|
back into <code>ap_process_internal_request()</code> to prevent the
|
|
code from falling out of sync again.</p>
|
|
|
|
<p>This means that much of the existing code was 'unoptimized'. It is
|
|
the Apache HTTP Project's first goal to create a robust and correct
|
|
implementation of the HTTP server RFC. Additional goals include
|
|
security, scalability and optimization. New methods were sought to
|
|
optimize the server (beyond the performance of Apache 1.3) without
|
|
introducing fragile or insecure code.</p>
|
|
|
|
<h2>The Request Processing Cycle</h2>
|
|
|
|
<p>All requests pass through <code>ap_process_request_internal()</code>
|
|
in request.c, including subrequests and redirects. If a module doesn't
|
|
pass generated requests through this code, the author is cautioned that
|
|
the module may be broken by future changes to request processing.</p>
|
|
|
|
<p>To streamline requests, the module author can take advantage of the
|
|
hooks offered to drop out of the request cycle early, or to bypass
|
|
core Apache hooks which are irrelevant (and costly in terms of CPU.)</p>
|
|
|
|
<h2>The Request Parsing Phase</h3>
|
|
|
|
<h3>Unescapes the URL</h3>
|
|
|
|
<p>The request's parsed_uri path is unescaped, once and only once, at the
|
|
beginning of internal request processing.</p>
|
|
|
|
<p>This step is bypassed if the proxyreq flag is set, or the parsed_uri.path
|
|
element is unset. The module has no further control of this one-time
|
|
unescape operation, either failing to unescape or multiply unescaping
|
|
the URL leads to security reprecussions.</p>
|
|
|
|
<h3>Strips Parent and This Elements from the URI</h3>
|
|
|
|
<p>All <code>/../</code> and <code>/./</code> elements are removed by
|
|
<code>ap_getparents()</code>. This helps to ensure the path is (nearly)
|
|
absolute before the request processing continues.</p>
|
|
|
|
<p>This step cannot be bypassed.</p>
|
|
|
|
<h3>Initial URI Location Walk</h3>
|
|
|
|
<p>Every request is subject to an <code>ap_location_walk()</code> call.
|
|
This ensures that <Location > sections are consistently enforced for
|
|
all requests. If the request is an internal redirect or a sub-request,
|
|
it may borrow some or all of the processing from the previous or parent
|
|
request's ap_location_walk, so this step is generally very efficient
|
|
after processing the main request.</p>
|
|
|
|
<h3>Hook: translate_name</h3>
|
|
|
|
<p>Modules can determine the file name, or alter the given URI in this step.
|
|
For example, mod_vhost_alias will translate the URI's path into the
|
|
configured virtual host, mod_alias will translate the path to an alias
|
|
path, and if the request falls back on the core, the DocumentRoot is
|
|
prepended to the request resource.
|
|
|
|
<p>If all modules DECLINE this phase, an error 500 is returned to the browser,
|
|
and a "couldn't translate name" error is logged automatically.</p>
|
|
|
|
<h3>Hook: map_to_storage</h3>
|
|
|
|
<p>After the file or correct URI was determined, the appropriate per-dir
|
|
configurations are merged together. For example, mod_proxy compares
|
|
and merges the appropriate <Proxy > sections. If the URI is nothing
|
|
more than a local (non-proxy) TRACE request, the core handles the
|
|
request and returns DONE. If no module answers this hook with OK or
|
|
DONE, the core will run the request filename against the <Directory >
|
|
and <Files > sections. If the request 'filename' isn't an absolute,
|
|
legal filename, a note is set for later termination.</p>
|
|
|
|
<h3>Initial URI Location Walk</h3>
|
|
|
|
<p>Every request is hardened by a second <code>ap_location_walk()</code>
|
|
call. This reassures that a translated request is still subjected to
|
|
the configured <Location > sections. The request again borrows
|
|
some or all of the processing from it's previous location_walk above,
|
|
so this step is almost always very efficient unless the translated URI
|
|
mapped to a substantially different path or Virtual Host.</p>
|
|
|
|
<h3>Hook: header_parser</h3>
|
|
|
|
<p>The main request then parses the client's headers. This prepares
|
|
the remaining request processing steps to better serve the client's
|
|
request.</p>
|
|
|
|
<h2>The Security Phase</h3>
|
|
|
|
<p>Needs Documentation. Code is;</p>
|
|
<pre>
|
|
switch (ap_satisfies(r)) {
|
|
case SATISFY_ALL:
|
|
case SATISFY_NOSPEC:
|
|
if ((access_status = ap_run_access_checker(r)) != 0) {
|
|
return decl_die(access_status, "check access", r);
|
|
}
|
|
if (ap_some_auth_required(r)) {
|
|
if (((access_status = ap_run_check_user_id(r)) != 0) || !ap_auth_type(r)) {
|
|
return decl_die(access_status, ap_auth_type(r)
|
|
? "check user. No user file?"
|
|
: "perform authentication. AuthType not set!", r);
|
|
}
|
|
if (((access_status = ap_run_auth_checker(r)) != 0) || !ap_auth_type(r)) {
|
|
return decl_die(access_status, ap_auth_type(r)
|
|
? "check access. No groups file?"
|
|
: "perform authentication. AuthType not set!", r);
|
|
}
|
|
}
|
|
break;
|
|
case SATISFY_ANY:
|
|
if (((access_status = ap_run_access_checker(r)) != 0) || !ap_auth_type(r)) {
|
|
if (!ap_some_auth_required(r)) {
|
|
return decl_die(access_status, ap_auth_type(r)
|
|
? "check access"
|
|
: "perform authentication. AuthType not set!", r);
|
|
}
|
|
if (((access_status = ap_run_check_user_id(r)) != 0) || !ap_auth_type(r)) {
|
|
return decl_die(access_status, ap_auth_type(r)
|
|
? "check user. No user file?"
|
|
: "perform authentication. AuthType not set!", r);
|
|
}
|
|
if (((access_status = ap_run_auth_checker(r)) != 0) || !ap_auth_type(r)) {
|
|
return decl_die(access_status, ap_auth_type(r)
|
|
? "check access. No groups file?"
|
|
: "perform authentication. AuthType not set!", r);
|
|
}
|
|
}
|
|
break;
|
|
}
|
|
</pre>
|
|
<h2>The Preparation Phase</h2>
|
|
|
|
<h3>Hook: type_checker</h3>
|
|
|
|
<p>The modules have an opportunity to test the URI or filename against
|
|
the target resource, and set mime information for the request. Both
|
|
mod_mime and mod_mime_magic use this phase to compare the file name
|
|
or contents against the administrator's configuration and set the
|
|
content type, language, character set and request handler. Some
|
|
modules may set up their filters or other request handling parameters
|
|
at this time.</p>
|
|
|
|
<p>If all modules DECLINE this phase, an error 500 is returned to the browser,
|
|
and a "couldn't find types" error is logged automatically.</p>
|
|
|
|
<h3>Hook: fixups</h3>
|
|
|
|
<p>Many modules are 'trounced' by some phase above. The fixups phase is
|
|
used by modules to 'reassert' their ownership or force the request's
|
|
fields to their appropriate values. It isn't always the cleanest
|
|
mechanism, but occasionally it's the only option.</p>
|
|
|
|
<h3>Hook: insert_filter</h3>
|
|
|
|
<p>Modules that transform the content in some way can insert their values
|
|
and override existing filters, such that if the user configured a more
|
|
advanced filter out-of-order, then the module can move it's order as
|
|
need be.
|
|
|
|
<h2>The Handler Phase</h2>
|
|
|
|
<p>This phase is <strong><em>not</em></strong> part of the processing in
|
|
<code>ap_process_request_internal()</code>. Many modules prepare one
|
|
or more subrequests prior to creating any content at all. After the
|
|
core, or a module calls <code>ap_process_request_internal()</code> it
|
|
then calls <code>ap_invoke_handler()</code> to generate the request.</p>
|
|
|
|
<h3>Hook: handler</h3>
|
|
|
|
<p>The module finally has a chance to serve the request in it's handler
|
|
hook. Note that not every prepared request is sent to the handler
|
|
hook. Many modules, such as mod_autoindex, will create subrequests
|
|
for a given URI, and then never serve the subrequest, but simply
|
|
lists it for the user. Remember not to put required teardown from
|
|
the hooks above into this module, but register pool cleanups against
|
|
the request pool to free resources as required.</p>
|
|
|
|
<!--#include virtual="footer.html" -->
|
|
|
|
</body>
|
|
</html>
|
|
|
|
|
|
|
|
|
|
|