Skip to content

canonical websocket library


Notifications You must be signed in to change notification settings



Repository files navigation

Travis Build Status Appveyor Build status Coverity Scan Build Status CII Best Practices Codacy Badge


Libwebsockets is a simple-to-use, pure C library providing client and server for http/1, http/2, websockets 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.

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



New features on master

  • LWS_WITH_NETWORK cmake option (default on) allows one-step removal of vhost, wsi, roles, event loop and all network-related code from the build. This enables use-cases where you actually need unrelated features like JOSE or FTS compactly. lws_context still exists and if tls is enabled, the tls-related code is still built so the crypto is available, just nothing related to network.

  • New Crypto-agile APIs + JOSE / JWS / JWE / JWK support... apis work exactly the same with OpenSSL or mbedTLS tls library backends, and allow key cycling and crypto algorithm changes while allowing for grace periods


  • CMake config simplification for crypto: -DLWS_WITH_GENCRYPTO=1 for all generic cipher and hash apis built (which work the same on mbedtls and OpenSSL transparently), and -DLWS_WITH_JOSE=1 for all JOSE, JWK, JWS and JWE support built (which use gencrypto and so also work the same regardless of tls library backend).

  • x.509 - new generic x509 api allows PEM-based certificate and key trust relationship verification, and conversion between x.509 keys and JWK. Works for EC and RSA keys, and on mbedtls and OpenSSl the same.

    x.509 api, x.509 minimal example

  • JWE - JWE (RFC7516) Algorithms with CI tests:

Key Encryption Payload authentication + crypt Enc + Dec Support
RSAES-PKCS1-v1.5 2048b & 4096b AES_128_CBC_HMAC_SHA_256 Enc + Dec
RSAES-PKCS1-v1.5 2048b AES_192_CBC_HMAC_SHA_384 Enc + Dec
RSAES-PKCS1-v1.5 2048b AES_256_CBC_HMAC_SHA_512 Enc + Dec
AES128KW, AES192KW, AES256KW AES_128_CBC_HMAC_SHA_256 Enc + Dec
AES128KW, AES192KW, AES256KW AES_192_CBC_HMAC_SHA_384 Enc + Dec
AES128KW, AES192KW, AES256KW AES_256_CBC_HMAC_SHA_512 Enc + Dec
ECDH-ES (P-256/384/521 key) AES_128/192/256_GCM Enc + Dec
ECDH-ES+A128/192/256KW (P-256/384/521 key) AES_128/192/256_GCM Enc + Dec

All tests pass on both OpenSSL and mbedTLS backends, using keys generated on both OpenSSL and mbedTLS in the tests.

A minimal example tool shows how to encrypt and decrypt compact JWE objects from the commandline for all supported algorithms.

jwe api, jwe unit tests, jwe minimal example

  • lws-genec ECDSA - JWS-compatible ECDSA is supported on both OpenSSL and mbedtls.

  • JWS - JWS (RFC7515) is now supported for none, HS256/384/512, RS256/384/512, and ES256/384/512, on both OpenSSL and mbedtls. There's a minimal example tool that signs and verifies compact representation JWS from stdin. jws api, jws unit tests, jws minimal example

  • JWK - JWK (RFC7517) now supports oct, RSA and EC keys including JSON key arrays on both OpenSSL and mbedtls. A minimal example tool shows how to create new JSON JWK keys to specified parameters from the commandline for all supported ciphers.

    jwk minimal example

  • lws-genrsa OAEP + PSS support - in addition to PKCS#1 1.5 padding, OAEP and PSS are now supported on both mbedtls and openssl backends.

  • lws-genaes Generic AES crypto - thin api layer works identically with both mbedtls and openssl backends. Supports CBC, CFB128, CFB8, CTR, ECB, OFB, XTS and GCM variants. Unit tests in CI. genaes api, api test, CMake config: -DLWS_WITH_GENCRYPTO=1

  • http fallback support - you can specify a role and protocol to apply if non-http or non-tls packets arrive at an http(s) listen port. For example, you can specify that the new raw proxy role + protocol should be used, to proxy your sshd port over :443 or :80. Without affecting normal http(s) serving on those ports but allowing, eg, ssh -p 443 http fallback docs

  • raw tcp proxy role and protocol - adding raw tcp proxying is now trivial using the built-in lws implementation. You can control the onward connection using a pvo in the format "" raw proxy minimal example, raw proxy docs, Cmake config: -DLWS_ROLE_RAW_PROXY=1 -DLWS_WITH_PLUGINS=1

  • deaddrop HTML file upload protocol - protocol and minimal example for file upload and sharing using drag and drop and a file picker. Integrated with basic auth, uploaded files marked with upload user, and files owned by the authenticated user may be deleted via the UI. Supports multiple simultaneous uploads both by drag-and-drop and from the file picker. deaddrop minimal example

  • basic auth for ws(s) - You can apply basic auth credential requirement to ws connections same as on mounts now. Just add a pvo "basic-auth" with the value being the credentials file path when enabling the ws protocol for the vhost.

v3.1 released: new features in v3.1

  • lws threadpool - lightweight pool of pthreads integrated to lws wsi, with all synchronization to event loop handled internally, queue for excess tasks threadpool docs, threadpool minimal example, Cmake config: -DLWS_WITH_THREADPOOL=1

  • libdbus support integrated on lws event loop lws dbus docs, lws dbus client minimal examples, lws dbus server minimal examples, Cmake config: -DLWS_ROLE_DBUS=1

  • lws allocated chunks (lwsac) - helpers for optimized mass allocation of small objects inside a few larger malloc chunks... if you need to allocate a lot of inter-related structs for a limited time, this removes per-struct allocation library overhead completely and removes the need for any destruction handling lwsac docs, lwsac minimal example, Cmake Config: -DLWS_WITH_LWSAC=1

  • lws tokenizer - helper api for robustly tokenizing your own strings without allocating or adding complexity. Configurable by flags for common delimiter sets and comma-separated-lists in the tokenizer. Detects and reports syntax errors. lws_tokenize docs, lws_tokenize minimal example / api test

  • lws full-text search - optimized trie generation, serialization, autocomplete suggestion generation and instant global search support extensible to huge corpuses of UTF-8 text while remaining super lightweight on resources. full-text search docs, full-text search minimal example / api test, demo, demo sources, Cmake config: -DLWS_WITH_FTS=1 -DLWS_WITH_LWSAC=1

  • gzip + brotli http server-side compression - h1 and h2 detection of client support for server compression, and auto-application to files with mimetypes "text/*", "application/javascript" and "image/svg.xml". Cmake config: -DLWS_WITH_HTTP_STREAM_COMPRESSION=1 for gzip, optionally also give -DLWS_WITH_HTTP_BROTLI=1 for preferred br brotli compression

  • managed disk cache - API for managing a directory containing cached files with hashed names, and automatic deletion of LRU files once the cache is above a given limit. lws diskcache docs, Cmake config: -DLWS_WITH_DISKCACHE=1

  • http reverse proxy - lws mounts support proxying h1 or h2 requests to a local or remote IP, or unix domain socket over h1. This allows microservice type architectures where parts of the common URL space are actually handled by external processes which may be remote or on the same machine. lws gitohashi serving is handled this way. unix domain sockets reverse proxy docs, CMake config: -DLWS_WITH_HTTP_PROXY=1 and -DLWS_UNIX_SOCK=1 for Unix Domain Sockets

  • update minimal examples for strict Content Security Policy the minimal examples now show the best practices around Content Security Policy and disabling inline Javascript. Updated examples that are served with the recommended security restrictions show a new "Strict Content Security Policy" graphic. Read how to upgrade your applications to use a strict CSP.

  • release policy docs - unsure what branch, version or tag to use, or how to follow master cleanly? Read the release policy docs which explain how and why lws is developed, released and maintained.

v3.0.1 released

See the git log for the list of fixes.

v3.0.0 released

See the changelog for info

Major CI improvements for QA

The Travis build of lws done on every commit now runs:

Tests Count Explanation
Build / Linux / gcc 16 -Wall -Werror cmake config variants
Build / Mac / Clang 16 -Wall -Werror cmake config variants
Build / Windows / MSVC 7 default
Selftests openssl:43, mbedtls:43 minimal examples built and run against each other and remote server 225 Correctness, robustness and security tests for http parser
Autobahn Server 480 Testing lws ws client, including permessage-deflate
Autobahn Client 480 Testing lws ws server, including permaessage-deflate
h2spec openssl:146, mbedtls:146 Http/2 server compliance suite (in strict mode)
h2load openssl:6, mbedtls:6 Http/2 server load tool (checks 10K / 100K in h1 and h2, at 1, 10, 100 concurrency)
h2load SMP 6 Http/2 and http/1.1 server load checks on SMP server build

The over 1,500 tests run on every commit take 1hr 15 of compute time to complete. If any problems are found, it breaks the travis build, generating an email.

Codacy also checks every patch and the information used to keep lws at zero issues.

Current master is checked by Coverity at least daily and kept at zero issues.

Current master passes all the tests and these new CI arrangements will help keep it that way.

Lws has the first official ws-over-h2 server support


There's a new RFC that enables multiplexing ws connections over an http/2 link. Compared to making individual tcp and tls connections for each ws link back to the same server, this makes your site start up radically faster, and since all the connections are in one tls tunnel, with considerable memory reduction serverside.

To enable it on master you just need -DLWS_WITH_HTTP2=1 at cmake. No changes to existing code are necessary for either http/2 (if you use the official header creation apis if you return your own headers, as shown in the test apps for several versions) or to take advantage of ws-over-h2. When built with http/2 support, it automatically falls back to http/1 and traditional ws upgrade if that's all the client can handle.

Currently only Chrome Canary v67 supports this ws-over-h2 encapsulation (chrome must be started with --enable-websocket-over-http2 switch to enable it currently), and patches exist for Firefox. Authors of both browser implementations tested against the lws server implementation.

New "minimal examples"

These are like the test apps, but focus on doing one thing, the best way, with the minimum amount of code. For example the minimal-http-server serves the cwd on http/1 or http/2 in 50 LOC. Same thing with tls is just three more lines.

They build standalone, so it's easier to copy them directly to start your own project; they are CC0 licensed (public domain) to facilitate that.

Windows binary builds

32- and 64-bit Windows binary builds are available via Appveyor. Visit lws on Appveyor, click on a build, the ARTIFACTS, and unzip the zip file at C:\Program Files (x86)/libwebsockets.


This is the libwebsockets C library for lightweight websocket clients and servers. For support, visit

and consider joining the project mailing list at

You can get the latest version of the library from git:

Doxygen API docs for master:


canonical websocket library









  • C 84.2%
  • CMake 5.6%
  • JavaScript 4.7%
  • Makefile 1.3%
  • Shell 1.1%
  • HTML 1.1%
  • Other 2.0%