mod_xsendfile for Apache2/Apache2.2

Overview

mod_xsendfile is a small Apache2 module that processes X-SENDFILE headers registered by the original output handler.

If it encounters the presence of such header it will discard all output and send the file specified by that header instead using Apache internals including all optimizations like caching-headers and sendfile or mmap if configured.

It is useful for processing script-output of e.g. php, perl or any cgi.

Useful?

Yep, it is useful.

Benefits

Download

Installation

  1. Grab the source.
  2. Compile and install
    apxs -cia mod_xsendfile.c
  3. Restart apache
  4. That's all.

Configuration

XSendFile

Description Enables or disables header processing
Syntax XSendFile on|off
Default XSendFile off
Context server config, virtual host, directory, .htaccess

Setting XSendFile on will enable processing.

The file specified in X-SENDFILE header will be sent instead of the handler output.

If the response lacks the X-SENDFILE header nothing is done.

XSendFileIgnoreEtag

Description Ignore script provided Etag headers
Syntax XSendFileIgnoreEtag on|off
Default XSendFileIgnoreEtag off
Context server config, virtual host, directory, .htaccess

Setting XSendFileIgnoreEtag on will ignore all ETag headers the original output handler may have set.
This is helpful for applications that will generate such headers even for empty content.

XSendFileIgnoreLastModified

Description Ignore script provided LastModified headers
Syntax XSendFileIgnoreLastModified on|off
Default XSendFileIgnoreLastModified off
Context server config, virtual host, directory, .htaccess

Setting XSendFileIgnoreLastModified on will ignore all Last-Modified headers the original output handler may have set.
This is helpful for applications that will generate such headers even for empty content.

XSendFilePath

Description White-list more paths
Syntax XSendFilePath absolute path
Default None
Context server config, virtual host, directory

XSendFilePath allow you to add additional paths to some kind of white list. All files within these paths are allowed to get served through mod_xsendfile.

Provide an absolute path as Parameter to this directive.

You may provide more than one path.

Remarks - Relative paths

The current working directory (if it can be determined) will be always checked first.

If you provide relative paths via the X-SendFile header, then all whitelist items will be checked until a seamingly valid combination is found, i.e. the result is within the bounds of the whitelist item; it isn't checked at this point if the path in question actually exists.
Considering you whitelisted /tmp/pool and /tmp/pool2 and your script working directory is /var/www.

X-SendFile: file

  1. /var/www/file - Within bounds of /var/www, OK

X-SendFile: ../pool2/file

  1. /var/www/../pool2/file = /var/pool2/file - Not within bounds of /var/www
  2. /tmp/pool/../pool2/file = /tmp/pool2/file - Not within bounds of /tmp/pool
  3. /tmp/pool2/../pool2/file = /tmp/pool2/file - Within bounds of /tmp/pool2, OK

You still can only access paths that are whitelisted. However you have might expect a different behavior here, hence the documentation.

Remarks - Inheritance

The white list "inherits" entries from higher level configuration.

XSendFilePath /tmp
<VirtualHost *>
	ServerName someserver
	XSendFilePath /home/userxyz
</VirtualHost>
<VirtualHost *>
	ServerName anotherserver
	XSendFilePath /var/www/somesite/
	<Directory /var/www/somesite/fastcgis>
		XSendFilePath /var/www/shared
	</Directory>
</VirtualHost>

Above example will give:

*) Scripts, in this context, mean the actual script-starters. E.g. PHP as a handler will use the .php itself, while in CGI mode refers to the starter.

Windows users should take care to include the drive letter to those paths as well. Tests show that it has to be in upper-case.

Example

.htaccess

<Files out.php>
	XSendFile on
</Files>

out.php

<?php
...
if ($user->isLoggedIn())
{
    header("X-Sendfile: $path_to_somefile");
    header("Content-Type: application/octet-stream");
    header("Content-Disposition: attachment; filename=\"$somefile\"");
    exit;
}
?>
<h1>Permission denied</h1>
<p>Login first!</p>

Limitations / Issues / Security considerations

Credits

The idea comes from lighttpd - A fast web server with minimal memory footprint.

The module itself was inspired by many other Apache2 modules such as mod_rewrite, mod_headers and obviously core.c.

License

Copyright 2006-2010 by Nils Maier

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.

You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

See the License for the specific language governing permissions and limitations under the License.

Changes

Version 0.12

Version 0.11.1

Version 0.11

Version 0.10

Version 0.9

Version 0.8