(Unofficial) HTTP/1 and HTTP/2 WebSocket support for Mint 🌱
Mint.WebSocket works together with Mint.HTTP API. For example,
this snippet shows sending and receiving a text frame of "hello world" to a
WebSocket server which echos our frames:
# bootstrap
{:ok, conn} = Mint.HTTP.connect(:http, "echo", 9000)
{:ok, conn, ref} = Mint.WebSocket.upgrade(:ws, conn, "/", [])
http_get_message = receive(do: (message -> message))
{:ok, conn, [{:status, ^ref, status}, {:headers, ^ref, resp_headers}, {:done, ^ref}]} =
Mint.WebSocket.stream(conn, http_get_message)
{:ok, conn, websocket} = Mint.WebSocket.new(conn, ref, status, resp_headers)
# send the hello world frame
{:ok, websocket, data} = Mint.WebSocket.encode(websocket, {:text, "hello world"})
{:ok, conn} = Mint.WebSocket.stream_request_body(conn, ref, data)
# receive the hello world reply frame
hello_world_echo_message = receive(do: (message -> message))
{:ok, conn, [{:data, ^ref, data}]} = Mint.WebSocket.stream(conn, hello_world_echo_message)
{:ok, websocket, [{:text, "hello world"}]} = Mint.WebSocket.decode(websocket, data)Mint is a functional HTTP/1 and HTTP/2 client library written in Elixir.
Why does it matter that it's functional? Isn't Elixir functional?
Existing WebSocket implementations like
:gun /
:websocket_client /
Socket /
WebSockex work by spawning and
passing messages among processes. This is a very convenient interface in
Elixir and Erlang, but it does not allow the author much control over
the WebSocket connection.
Instead Mint.WebSocket is process-less: the entire HTTP and WebSocket
states are kept in immutable data structures. This enables authors of
WebSocket clients a more fine-grained control over the connections:
Mint.WebSocket does not prescribe a process archicture.
For more information, check out Mint#Usage.
This library aims to follow RFC6455 and RFC8441 as closely as possible and uses Autobahn|Testsuite to check conformance with every run of tests/CI. The auto-generated report produced by the Autobahn|Testsuite is uploaded on each push to main.
See the report here: https://mint-websocket.nyc3.digitaloceanspaces.com/autobahn/index.html
HTTP/2 WebSockets are not a built-in feature of HTTP/2. RFC8441 is an extension to the HTTP/2 protocol and server libraries are not obligated to implement it. In the current landscape, very few server libraries support the HTTP/2 extended CONNECT method which bootstraps WebSockets.
If Mint.WebSocket.upgrade/4 returns
{:error, conn, %Mint.WebSocketError{reason: :extended_connect_disabled}}Then the server does not support HTTP/2 WebSockets or does not have them enabled.
Interested in developing Mint.WebSocket? The docker-compose.yml sets up
an Elixir container, a simple websocket echo server, and the Autobahn|Testsuite
fuzzing server.
(host)$ docker-compose up -d
(host)$ docker-compose exec app bash
(app)$ mix deps.get
(app)$ mix test
(app)$ iex -S mix