sockets 和 channels 是Phoenix中用来实现实时效果的两大工具。

Sockets

socket是用来连接客户端与服务器的，它使用endpoint来声明：

defmodule GenPoker.Endpoint do  use Phoenix.Endpoint, otp_app: :gen_poker  socket "/socket", GenPoker.PlayerSocketend

Channels

客户端只有加入了channel之后才能发送消息。

defmodule GenPoker.PlayerSocket do  use Phoenix.Socket  channel "tables:*", GenPoker.TableChannelend

创建socket

defmodule GenPoker.PlayerSocket do  use Phoenix.Socket  transport :websocket, Phoenix.Transports.WebSocket  def connect(%{"playerId" => player_id}, socket) do    {:ok, assign(socket, :player_id, player_id)}  end  def id(socket) do     "players_socket:#{socket.assigns.player_id}"  endend

注册进程

defmodule Poker.Table do  use GenServer  def start_link(table_name, sup, storage, num_seats) do    GenServer.start_link(      __MODULE__,       [table_name, sup, storage, num_seats],       name: via_tuple(table_name)    )  end  defp via_tuple(table) do     {:via, :gproc, {:n, :l, {:table, table}}}  end  def whereis(table) do    :gproc.whereis_name({:n, :l, {:table, table}})  endend

我们使用了gproc库来注册进程，这样就可以使用一个term而不仅仅是atom作为名字。让我们来定义Channel：

module GenPoker.TableChannel do  use GenPoker.Web, :channel  alias Poker.Table  def join("tables:" <> table, _payload, socket) do    {:ok, assign(socket, :table, table)}  end  def handle_in(command, payload, socket)     when command in ~w(sit leave buy_in cash_out deal)   do    table = Table.whereis(socket.assigns.table)    arguments = [table, socket.assigns.player_id] ++ payload    result = apply(Table, String.to_atom(command), arguments)    if result == :ok do      broadcast! socket, "update", Table.get_state(table)    end    {:reply, result, socket}  endend

对于客户端的join请求，我们有不同的回复。在JavaScript中可以这样写：

channel.push("message", arguments)  .receive("ok", (msg) => console.log("Got OK!"))  .receive("error", (msg) => console.log("Oops!"))

发送初始的state

def join("tables:" <> table, _payload, socket) do  state = table |> Table.whereis |> Table.get_state  push socket, "update", state  {:ok, assign(socket, :table, table)}end

使用handle_info

def join("tables:" <> table, _payload, socket) do  send self, :after_join  {:ok, assign(socket, :table, table)}enddef handle_info(:after_join, socket) do  state = socket.assigns.table |> Table.whereis |> Table.get_state  push socket, "update", state  {:noreply, socket}enddef handle_info(_, socket) do  {:noreply, socket}end

拦截消息

def handle_out("update", state, socket) do  push socket, "update", hide_other_hands(state, socket)  {:noreply, socket}enddefp hide_other_hands(state, socket) do  player_id = socket.assigns.player_id  hide_hand_if_current_player = fn    %{id: ^player_id} = player -> player    player -> Map.delete(player, :hand)  end  update_in(state.players, fn players ->    Enum.map(players, hide_hand_if_current_player)  end)end