Open Source C WebSocket Libraries

Mongoose is a networking library for C/C++. It implements event-driven non-blocking APIs for TCP, UDP, HTTP, WebSocket, MQTT. It is designed for connecting devices and bringing them online. On the market since 2004, used by vast number of open source and commercial products - it even runs on the International Space Station! Mongoose makes embedded network programming fast, robust, and easy. Cross-platform, works on Linux/UNIX, MacOS, Windows, Android, FreeRTOS, etc. Supported embedded architectures: ESP32, NRF52, STM32, NXP, and more. Built-in protocols: plain TCP/UDP, HTTP, MQTT, Websocket. SSL/TLS support: mbedTLS, OpenSSL or custom (via API). Used to solve a wide range of business needs, like implementing Web UI interface on devices, RESTful API services, telemetry data exchange, remote control for a product, remote software updates, remote monitoring, and others.

WIC is a C99 implementation of rfc6455 websockets designed for embedded applications. WIC decouples the websocket protocol from the transport layer. This makes it possible to use WIC over any transport layer assuming that you are prepared to do the integration work.

Like libevent, libev, and libuv, libhv provides event loop with non-blocking IO and timer, but simpler api and richer protocols. Cross-platform (Linux, Windows, MacOS, BSD, Solaris, Android, iOS) High-performance EventLoop (IO, timer, idle, custom) TCP/UDP client/server/proxy. TCP supports heartbeat, reconnect, upstream, MultiThread-safe write and close, etc. Built-in common unpacking modes (FixedLength, Delimiter, LengthField) RUDP support: WITH_KCP. SSL/TLS support: (via WITH_OPENSSL or WITH_GNUTLS or WITH_MBEDTLS) HTTP client/server (support https http1/x http2 grpc). HTTP supports static service, indexof service, proxy service, sync/async API handler. HTTP supports RESTful, router, middleware, keep-alive, chunked, SSE, etc. WebSocket client/server.

A Lightweight and fully asynchronous WebSocket client library based on libev for Embedded Linux. And provide Lua-binding. libev tries to follow the UNIX toolbox philosophy of doing one thing only, as good as possible.

facil.io is an evented Network library written in C. facil.io provides high performance TCP/IP network services by using an evented design that was tested to provide an easy solution to the C10K problem. facil.io includes a mini-framework for Web Applications, with a fast HTTP / WebSocket server, integrated Pub/Sub, optional Redis connectivity, easy JSON handling, Mustache template rendering and more nifty tidbits. facil.io powers the HTTP/Websockets Ruby Iodine server and it can easily power your application as well. facil.io is easy to code with and aims at minimizing the developer's learning curve. In addition to detailed documentation and examples, the API is unified in style and the same types and API used for HTTP requests is used for JSON and Mustache rendering - so there's less to learn. facil.io should work on Linux / BSD / macOS (and possibly CYGWIN) and is continuously tested on both Linux and macOS.

Wslay is a WebSocket library written in C. It implements the protocol version 13 described in RFC 6455. This library offers 2 levels of API: event-based API and frame-based low-level API. For event-based API, it is suitable for non-blocking reactor pattern style. You can set callbacks in various events. For frame-based API, you can send WebSocket frame directly. Wslay only supports data transfer part of WebSocket protocol and does not perform opening handshake in HTTP. Wslay does not perform any I/O operations for its own. Instead, it offers callbacks for them. This makes Wslay independent on any I/O frameworks, SSL, sockets, etc. This makes Wslay protable across various platforms and the application authors can choose freely I/O frameworks.