mod_xsendfile

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.

Some applications require checking for special privileges.
Other have to lookup values first (e.g.. from a DB) in order to correctly process a download request.
Or store values (download-counters come into mind).
etc.

Benefits

Uses apache internals
Optimal delivery through sendfile and mmap (if available).
Sets correct cache headers such as Etag and If-Modified-Since as if the file was statically served.
Processes cache headers such as If-None-Match or If-Modified-Since.

Download

mod_xsendfile.c
Source tarball: mod_xsendfile-0.9.tar.gz
Win32 binary: mod_xsendfile-0.9.bin.zip

Installation

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

Configuration

Two flags, that all folks ;)

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.

XSendFileAllowAbove

Description	Allows or disallows sending files above Request path
Syntax	XSendFileAllowAbove on\|off
Default	XSendFileAllowAbove off
Context	server config, virtual host, directory, .htaccess

Setting XSendFileAllowAbove on will allow sending files not below the path of the Request (this refers to the request URI not the translated path).

Example

.htaccess

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

out.php

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

Limitations / Issues / Security considerations

The Content-Encoding header - if present - will be dropped, as the module cannot know if it was set by intention of the programmer or the handler. E.g. php with output compression enabled will set this header, but the replacement file send via mod_xsendfile is most likely not compressed.
The header key (X-SENDFILE) is not case-sensitive.
X-Sendfile will also send files that are otherwise protected (e.g. Deny from all). This includes .htaccess and such!
At least as long as one has regular file access permissions defined in the file system.
But, on the other hand, how is this different from the usual scripting?

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 such and obviously core.c.

License

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.