用 Go + WebSocket 快速实现一个 chat 服务

// HTML 操作 {js}
if (window["WebSocket"]) {
  conn = new WebSocket("ws://" + document.location.host + "/ws");
  conn.onclose = function (evt) {
    var item = document.createElement("div");
    item.innerHTML = "<b>Connection closed.</b>";
    appendLog(item);
  };
  ...
}
// 路由
engine.AddRoute(rest.Route{
  Method: http.MethodGet,
  Path:   "/ws",
  Handler: func(w http.ResponseWriter, r *http.Request) {
    internal.ServeWs(hub, w, r)
  },
})
// 接入逻辑
func ServeWs(hub *Hub, w http.ResponseWriter, r *http.Request) {
  // 将http请求升级为websocket
 conn, err := upgrader.Upgrade(w, r, nil)
 ...
  // 构建client：hub{engine}, con{websocker conn}, send{channel buff}
 client := &Client{
  hub:  hub,
  conn: conn,
  send: make(chan []byte, bufSize),
 }
 client.hub.register <- client
  // 开始客户端双工的通信，接收和写入数据
  go client.writePump()
 go client.readPump()
}

type Hub struct {
 clients map[*Client]bool  // 上线clients
 broadcast chan []byte    // 客户端发送的消息 ->广播给其他的客户端
 register chan *Client     // 注册channel，接收注册msg
 unregister chan *Client   // 下线channel
}
func (h *Hub) Run() {
 for {
  select {
    // 注册channel：存放到注册表中，数据流也就在这些client中发生
  case client := <-h.register:
   h.clients[client] = true
    // 下线channel：从注册表里面删除
  case client := <-h.unregister:
   if _, ok := h.clients[client]; ok {
    delete(h.clients, client)
    close(client.send)
   }
    // 广播消息：发送给注册表中的client中，send接收到并显示到client上
  case message := <-h.broadcast:
   for client := range h.clients {
    select {
    case client.send <- message:
    default:
     close(client.send)
     delete(h.clients, client)
    }
   }
  }
 }
}

func (c *Client) readPump() {
 ...
 for {
    // 1
  _, message, err := c.conn.ReadMessage()
  if err != nil {
   if websocket.IsUnexpectedCloseError(err, websocket.CloseGoingAway, websocket.CloseAbnormalClosure) {
    log.Printf("error: %v", err)
   }
   break
  }
  message = bytes.TrimSpace(bytes.Replace(message, newline, space, -1))
    // 2.
  c.hub.broadcast <- message
 }
}

func (c *Client) writePump() {
  // 写超时控制
 ticker := time.NewTicker(pingPeriod)
  ...
 for {
  select {
  case message, ok := <-c.send:
      // 当接收消息写入时，延长写超时时间。
   c.conn.SetWriteDeadline(time.Now().Add(writeWait))
   ...
   w, err := c.conn.NextWriter(websocket.TextMessage)
   ...
   w.Write(message)
   // 依次读取 send 中消息，并write
   n := len(c.send)
   for i := 0; i < n; i++ {
    w.Write(newline)
    w.Write(<-c.send)
   }
      ...
  case <-ticker.C:
   c.conn.SetWriteDeadline(time.Now().Add(writeWait))
   ...
  }
 }
}