lwan Web Server

Lwan is a high-performance & scalable web server for glibc/Linux platforms.

In development for almost 3 years, Lwan was until now a personal research effort that focused mostly on building a solid infrastructure for a lightweight and speedy web server:

• Low memory footprint (~500KiB for 10k idle connections)
• Minimal memory allocations & copies
• Minimal system calls
• Hand-crafted HTTP request parser
• Files are served using the most efficient way according to their size
  • No copies between kernel and userland for files larger than 16KiB
  • Smaller files are sent using vectored I/O of memory-mapped buffers
  • Header overhead is considered before compressing small files
• Mostly wait-free multi-threaded design
• Diminute code base with roughly 7200 lines of C code

It is now transitioning into a fully working, capable HTTP server. It is not, however, as feature-packed as other popular web servers. But it is free software, so scratching your own itches and making Lwan hum the way you want it to is possible.

Features include:

• Mustache templating engine
  • Used for directory listing & error messages
  • Available for user-built handlers
• Easy to use API to create web applications or extend the web server
• Supports rebimboca da parafuseta
• Test suite written in Python tests the server as a black box
• No-nonsense configuration file syntax
• Supports a subset of HTTP/1.0 and HTTP/1.1
• systemd socket activation
• IPv6 ready

The web site has more details.

Performance

It can achieve good performance, yielding about 320000 requests/second on a Core i7 laptop for requests without disk access.

When disk I/O is required, for files up to 16KiB, it yields about 290000 requests/second; for larger files, this drops to 185000 requests/second, which isn't too shabby either.

These results, of course, with keep-alive connections, and with weighttp running on the same machine (and thus using resources that could be used for the webserver itself).

Without keep-alive, these numbers drop around 6-fold.

Portability

Although it uses epoll and the Linux variant of sendfile(), it is fairly portable to other event-based pollers, like kqueue. An old version of lwan has been successfully ported to FreeBSD. Eventually, some event library such as libev or libevent will be used to aid in portability.

Building

Lwan uses CMake for its build system. To build it, create a build directory, issue cmake $LWAN_SOURCE_TREE, and then make, as usual.

The CMake script should look for libraries like TCMalloc, jemalloc, and Valgrind, and enable/link as appropriate.

Passing -DCMAKE_BUILD_TYPE=Release will enable some compiler optimizations, like LTO and tune the code for current architecture. Passing -DCMAKE_BUILD_TYPE=Debug will generate code suitable to be used under a debugger like gdb and force debug messages to be printed to the terminal.

Running

Set up the server by editing the provided lwan.conf; the format is very simple and should be self-explanatory.

Configuration files are loaded from the current directory. If no changes are made to this file, running lwan will serve static files located on ./wwwroot directory, and also provide a Hello, World! handler (which serves as an example of how to use its internal APIs). Lwan will listen on port 8080 on all interfaces.

Build status

Release	Debug	Static Analysis	Unit Tests
Waterfall	Waterfall	Waterfall - Reports	Waterfall