ashttpd - async sendfile http daemon

Copyright (c) 2010 Gianni Tedesco

INTRODUCTION

ashttpd was intended as a test rig for kernel asynchronous sendfile support. It is (yet another) simple http daemon for serving up static content. The main aims are simplicity and efficiency. It differs from other http daemons in that the backing store is not the VFS but a proprietary database. The benefits of this approach are performance - when the cache is warm, an open() syscall has a noticable performance impact. This also allows for atomic replacements of entire webroots as well as accurate precalculation of MIME types via libmagic and the reliable use of strong cache validators (ETags).

BUILDING

This might need a few tweaks to build on a non-linux platform but it should be doable. All the platform specific stuff has POSIX fallbacks but they've not been tested.

The main linux specific bits are just performance enhancements: accept4(), fallocate(), epoll, (no kqueue module for example, but it can fallback to poll or be written by a suitably motivated individual).

The libaio library is required for io_async, there's no POSIX AIO support at the moment because there's no way to integrate its mainloop with poll.

Also libmagic is needed for mkroot to determine the mime types of files.

RUNNING

To build a webroot run mkroot, for example:

$ ./mkroot /var/www www.webroot

Then the server is run with: $ ./httpd path-to-vhosts-dir

The dir is scanned for webroots, the filename will be the vhost name. You will probably want to store the webroots in one dir, and symlink them in to the vhosts dir like this:

$ ln -sf /path/to/www.webroot ./vhosts/www.example.com

Or to replace the default webroot:

$ ln -sf /path/to/defaultpages.webroot ./vhosts/__default__

Note that these webroot updates do not require the server to be restarted. You can dynamically add and remove websites and/or atomically replace webroots on the fly.

I/O Models

The httpd binary takes one (optional) commandline argument which selects the I/O model to be used:

• sync - traditional synchronous IO
• sendfile - recommended
• async - kernel AIO, will only be really async if kernel is patched
• async-sendfile - kernel AIO sendfile, requires patch to kernel and libaio
• dio - O_DIRECT kernel AIO (broken right now)

For example:

$ ./httpd ./vhosts sync

If you like and use this software then press to donate towards its development progress and email me to say what features you would like added.

TODO

The next steps in development are:

• multi-process support (ie. for multi-core)
• dynamic content via fcgi and uwsgi
• 'mount points' in webroots
• support for methods other than GET
• support for long HTTP responses (ie. those longer than a single buffer)
• niceties such as custom error pages, directory indexing
• gzip transfer encoding
• support more HTTP such as range queries, expires, chunked, etc