Phoenix framework events error

chat.js

$(function () {
  var $messages = $("#messages");
  var $messageInput = $("#message-input");

  var socket = new Phoenix.Socket("/ws");
  socket.join("rooms", "public", {}, function (channel) {
    channel.on("new:message", function (message) {
      console.log(message);
      $messages.append("<li>" + message.content + "</li>");
    });

    channel.on("error", function(error) {
      console.log("Error :( Reason: " + error.reason);
    });

    $messageInput.off("keypress").on("keypress", function (e) {
      if (e.keyCode === 13) {
        console.log("SEND: " + $messageInput.val());
        channel.send("new:message", {
          content: $messageInput.val()
        });
        $messageInput.val("");
      }
    });
  });
});

elixir.ex

defmodule Chatdown.Router do
  use Phoenix.Router
  use Phoenix.Router.Socket, mount: "/ws"
  
  channel "rooms", Chatdown.Rooms
  
  # ..
end

# web/channels/rooms_channel.ex
defmodule Chatdown.Rooms do
  use Phoenix.Channel

  def join(socket, "public", message) do
    IO.puts "JOIN #{socket.channel}:#{socket.topic}"
    {:ok, socket}
  end

  def event(socket, "new:message", %{ message: message }) do
    IO.puts "new:message"
    broadcast socket, "new:message", %{ content: message["content"] }
    socket
  end
end

error

10:19:10.232 [error] #PID<0.248.0> running Chatdown.Endpoint terminated
Server: localhost:4000 (http)
Request: GET /ws
** (exit) an exception was raised:
    ** (ErlangError) erlang error: [reason: :function_clause, mfa: {Phoenix.Endpoint.CowboyHandler, :websocket_handle, 3}, stacktrace: [{Chatdown.Rooms, :event, [%Phoenix.Socket{assigns: %{}, authorized: true, channel: "rooms", conn: nil, pid: #PID<0.248.0>, router: Chatdown.Router, topic: "public"}, "new:message", %{"content" => "Hey!"}], [file: 'web/channels/rooms_channel.ex', line: 9]}, {Phoenix.Channel.Transport, :dispatch, 4, [file: 'lib/phoenix/channel/transport.ex', line: 102]}, {Phoenix.Channel.Transport, :dispatch, 4, [file: 'lib/phoenix/channel/transport.ex', line: 67]}, {Phoenix.Transports.WebSocket, :ws_handle, 2, [file: 'lib/phoenix/transports/websocket.ex', line: 45]}, {Phoenix.Endpoint.CowboyHandler, :websocket_handle, 3, [file: 'lib/phoenix/endpoint/cowboy_handler.ex', line: 65]}, {:cowboy_websocket, :handler_call, 7, [file: 'src/cowboy_websocket.erl', line: 588]}, {Phoenix.Endpoint.CowboyHandler, :upgrade, 4, [file: 'lib/phoenix/endpoint/cowboy_handler.ex', line: 17]}, {:cowboy_protocol, :execute, 4, [file: 'src/cowboy_protocol.erl', line: 435]}], msg: {:text, "{\"channel\":\"rooms\",\"topic\":\"public\",\"event\":\"new:message\",\"message\":{\"content\":\"Hey!\"}}"}, req: [socket: #Port<0.5912>, transport: :ranch_tcp, connection: :keepalive, pid: #PID<0.248.0>, method: "GET", version: :"HTTP/1.1", peer: {{127, 0, 0, 1}, 61714}, host: "localhost", host_info: :undefined, port: 4000, path: "/ws", path_info: :undefined, qs: "", qs_vals: :undefined, bindings: [], headers: [{"upgrade", "websocket"}, {"connection", "Upgrade"}, {"host", "localhost:4000"}, {"origin", "http://localhost:4000"}, {"cookie", "__utma=111872281.1407948937.1388959466.1388959466.1388959466.1; _ga=GA1.1.1407948937.1388959466; _chatdown_key=bHpabmpUS2xmT04vZXJUQXU0TVB1clN4Y21aeGQ0YjlONFJBNkF2RVBhWT0tLXl2YStxZW4zNXFTVUFMNUo1NDVHdmc9PQ==--KwQmg7LtqKlJrFdnOEWM2l8OEEo=; cart=3; remember_token=M8x9Q33aZwDC7L_mQLf5eQ"}, {"pragma", "no-cache"}, {"cache-control", "no-cache"}, {"sec-websocket-key", "T7151EulXBMhcgUv7YKh2Q=="}, {"sec-websocket-version", "13"}, {"sec-websocket-extensions", "x-webkit-deflate-frame"}, {"user-agent", "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_1) AppleWebKit/600.2.5 (KHTML, like Gecko) Version/8.0.2 Safari/600.2.5"}], p_headers: [{"sec-websocket-extensions", [{"x-webkit-deflate-frame", []}]}, {"upgrade", ["websocket"]}, {"connection", ["upgrade"]}], cookies: :undefined, meta: [websocket_version: 13, websocket_compress: false], body_state: :waiting, buffer: "", multipart: :undefined, resp_compress: false, resp_state: :done, resp_headers: [], resp_body: "", onresponse: :undefined], state: {Phoenix.Transports.WebSocket, %{router: Chatdown.Router, serializer: Phoenix.Transports.JSONSerializer, sockets: #HashDict<[{{"rooms", "public"}, %Phoenix.Socket{assigns: %{}, authorized: true, channel: "rooms", conn: nil, pid: #PID<0.248.0>, router: Chatdown.Router, topic: "public"}}]>}}]
        (phoenix) lib/phoenix/endpoint/cowboy_handler.ex:17: Phoenix.Endpoint.CowboyHandler.upgrade/4
        (cowboy) src/cowboy_protocol.erl:435: :cowboy_protocol.execute/4

So thanks to Jose Valim on irc I figured out that I needed:

  def event(socket, "new:message", %{ "content" => content }) do
    IO.puts "new:message"
    broadcast socket, "new:message", %{ "content" => content }
    socket
  end

Or, alternatively:

  def event(socket, "new:message", message) do
    broadcast socket, "new:message", %{ "content" => message["content"] }
    socket
  end