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Websockets in Elixir with Cowboy and Plug
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defmodule MyApp do | |
use Application | |
def start(_type, _args) do | |
import Supervisor.Spec, warn: false | |
children = [ | |
Plug.Adapters.Cowboy.child_spec(:http, MyApp.Router, [], [ | |
dispatch: dispatch | |
]) | |
] | |
opts = [strategy: :one_for_one, name: Navis.Supervisor] | |
Supervisor.start_link(children, opts) | |
end | |
defp dispatch do | |
[ | |
{:_, [ | |
{"/ws", MyApp.SocketHandler, []}, | |
{:_, Plug.Adapters.Cowboy.Handler, {MyApp.Router, []}} | |
]} | |
] | |
end | |
end |
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defmodule MyApp.Router do | |
use Plug.Router | |
plug :match | |
plug :dispatch | |
match _ do | |
send_resp(conn, 200, "Hello from plug") | |
end | |
end |
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defmodule MyApp.SocketHandler | |
@behaviour :cowboy_websocket_handler | |
def init(_, _req, _opts) do | |
{:upgrade, :protocol, :cowboy_websocket} | |
end | |
@timeout 60000 # terminate if no activity for one minute | |
#Called on websocket connection initialization. | |
def websocket_init(_type, req, _opts) do | |
state = %{} | |
{:ok, req, state, @timeout} | |
end | |
# Handle 'ping' messages from the browser - reply | |
def websocket_handle({:text, "ping"}, req, state) do | |
{:reply, {:text, "pong"}, req, state} | |
end | |
# Handle other messages from the browser - don't reply | |
def websocket_handle({:text, message}, req, state) do | |
IO.puts(message) | |
{:ok, req, state} | |
end | |
# Format and forward elixir messages to client | |
def websocket_info(message, req, state) do | |
{:reply, {:text, message}, req, state} | |
end | |
# No matter why we terminate, remove all of this pids subscriptions | |
def websocket_terminate(_reason, _req, _state) do | |
:ok | |
end | |
end |
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I created a library to make the
Cowboy
andPlug.Router
integration much easier.https://github.com/kevinlang/plug_socket
Essentially: