Lwan is a lightweight asynchronous multi-threaded event-based web server.
Lwan was until recently just a personal research effort that focused mostly on building a solid infrastructure for a lightweight and speedy web server.
With its low disk and memory footprints, it’s suitable to be used from embedded devices to robust servers. Both static and dynamic content can be served, as it can also be used as a library. Dynamic content can be generated by code written in either C or Lua.
Its simple architecture and tiny source code guarantees the entire code base can be easily grokked.
This is free and open source software.
Features include:
- Low memory footprint (~500KiB for 10k idle connections).
- Small disk footprint: x86-64 executable has 198KiB (~86KiB if packed with UPX).
- Minimal memory allocations & copies.
- Minimal system calls.
- Hand-written HTTP request parser.
- Static file serving uses the most efficient way according to file size/;
- No copies between kernel and userland for files larger than 16KiB.
- Smaller files are sent using scatter-gather I/O.
- Header overhead is considered before considering deflate, zstd, or Brotli compression.
- Precompressed files are sent if the client asks for gzip compression.
- Mostly wait-free multi-threaded design:
- One thread accepts connections, one I/O thread per logical CPU handles them.
- One coroutines per connection makes asynchronous I/O a breeze in C.
- Supports Linux, OpenBSD, FreeBSD and macOS.
- Purpose-built I/O loop with async/await and timer support.
- Efficient, Guava-inspired loading cache. Used for:
- Directory listing.
- File information (size, last modified date, MIME type, etc).
- Compressed file contents.
- Compiled Lua scripts.
- Request rewriting support based on Lua pattern matching syntax:
- Lua scripts can be executed to control the rewriting behavior as well.
- Diminutive codebase with roughly 20000 lines of GNU11 code.
- Efficient Mustache templating engine:
- Used internally for directory listing & error messages (can be loaded from a file).
- Available for user-built handlers.
- Easy to use API to create web applications or extend the web server:
- Example: Freegeoip reimplementation, which performs better than the Go version and is roughly the same amount of lines of code. The live version has been up for years, and serves millions of requests per day, with a RSS of roughtly 5MiB.
- Handlers can be written in C and Lua.
- Supports rebimboca da parafuseta.
- No-nonsense configuration file syntax.
- Supports a subset of HTTP/1.0 and HTTP/1.1:
- Support for keep-alive connections.
- Support for pipelined requests.
- WebSockets.
- FastCGI.
- PROXY protocol support.
- Useful for TLS terminators such as Hitch.
- TLSv1.2 support with AES encryption offload (kTLS on Linux), with TLSv1.3 in the works.
systemd socket activation. - Named socket support for both TLS and non-TLS listeners.
- IPv6 ready.
- A continuous integration systems helps keep the house in order:
- Buildbots checks every commit (instance).
- Code is statically analyzed by Clang Static Analyzer.
- Debug & Release builds are tested and built.
- Workers build Lwan on various different platforms:
- Arch Linux (x86-64), always up-to-date.
- Debian GNU/Linux (aarch64).
- FreeBSD 10 and 11
- OpenBSD 6.6 (x86-64).
- macOS High Sierra (x86-64).
- Test suite written in Python tests the server as a black box.
- Test suite is executed with both Undefined Behavior and Address sanitizers on Linux and OpenBSD.
- Request parser continuously fuzzed with oss-fuzz.
Website: lwan.ws
Support: GitHub Code Repository
Developer: L. Pereira
License: GNU General Public License v2.0
Lwan is written in C. Learn C with our recommended free books and free tutorials.
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