Intrduction

Libwebsockets is a simple-to-use, MIT-license, pure C library providing client and server for http/1, http/2, websockets, MQTT and other protocols in a security-minded, lightweight, configurable, scalable and flexible way. It’s easy to build and cross-build via cmake and is suitable for tasks from embedded RTOS through mass cloud serving.

It supports a lot of lightweight ancilliary implementations for things like JSON, CBOR, JOSE, COSE, and supports OpenSSL and MbedTLS v2 and v3 out of the box for everything. It’s very gregarious when it comes to event loop sharing, supporting libuv, libevent, libev, sdevent, glib and uloop, as well as custom event libs.

100+ independent minimal examples for various scenarios, CC0-licensed (public domain) for cut-and-paste, allow you to get started quickly.

There are a lot of READMEs on a variety of topics.

We do a huge amount of CI testing per push, currently 582 builds on 30 platforms. You can see the lws CI rack and read about how lws-based Sai is used to coordinate all the testing.

Architecture

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Serialized Secure Streams

Secure Streams direct

Secure Streams APIs are also serializable, the exact same client code can fulfil the connection directly in the same process as you would expect, or forward the actions, metadata and payloads to an SS Proxy that owns the policy over a Unix Domain or TCP socket connection to be fulfilled centrally. This allows, eg, h2 streams from different processes sharing a single connection.

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The serialized SS can also travel over generic transports like UART, an example is provided implementing the Binance example on an RPi Pico with a UART transport to a UART transport SS proxy, where the pico itself has no network stack, tls, compression or wss stack, but can send and receive to and from the endpoint as if it did.

The optional lws_trasport_mux is used to interpose between the UART transport and the SSPC layer, allowing a single pipe to carry many separate SS connections.

The user SS code is identical however it is transported, muxed and fulfilled.

v4.3 is released

See the changelog

Lws work retrospective

The initial commit for lws will have been 11 years ago come Oct 28 2021, it’s been a lot of work. There are a total of 4.3K patches, touching 800KLOC cumulatively (this is not the size in the repo, but over the years, how many source lines were changed by patches).
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Gratifyingly, it turns out over the years, ~15% of that was contributed by 404 contributors: that’s not so bad. Thanks a lot to everyone who has provided patches.

Today at least tens of millions of devices and product features rely on lws to handle their communications including several from FAANG; Google now include lws as part of Android sources.