http - websocket 消息总是会一次全部到达吗？

Question

这个 websockets 教程 https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API/Writing_WebSocket_client_applications有这个例子:

exampleSocket.onmessage = function(event) {
  var f = document.getElementById("chatbox").contentDocument;
  var text = "";
  var msg = JSON.parse(event.data);
  var time = new Date(msg.date);
  var timeStr = time.toLocaleTimeString();

  switch(msg.type) {
    case "id":
      clientID = msg.id;
      setUsername();
      break;
    case "username":
      text = "<b>User <em>" + msg.name + "</em> signed in at " + timeStr + "</b><br>";
      break;
    case "message":
      text = "(" + timeStr + ") <b>" + msg.name + "</b>: " + msg.text + "<br>";
      break;
    case "rejectusername":
      text = "<b>Your username has been set to <em>" + msg.name + "</em> because the name you chose is in use.</b><br>"
      break;
    case "userlist":
      var ul = "";
      for (i=0; i < msg.users.length; i++) {
        ul += msg.users[i] + "<br>";
      }
      document.getElementById("userlistbox").innerHTML = ul;
      break;
  }

  if (text.length) {
    f.write(text);
    document.getElementById("chatbox").contentWindow.scrollByPages(1);
  }
};

它解析从 websockets 服务器接收到的消息。但是，我可以相信由 websocket 服务器发送的 json 总是会立即到达客户端吗？如果它部分到达怎么办？解析它会破坏它。
即使对于非常大的 json 消息，我也可以做出这个假设吗？
我问是因为在 TCP 流上，这是不可能的。消息可能部分到达。
如果无法一次完全接收消息，我怎么知道何时解析 JSON？

Answer 1

是的，每条消息都是作为一个整体接收的。来自 RFC 6455:
1.2.协议(protocol)概述

After a successful handshake, clients and servers transfer data back and forth in conceptual units referred to in this specification as "messages". On the wire, a message is composed of one or more frames. The WebSocket message does not necessarily correspond to a particular network layer framing, as a fragmented message may be coalesced or split by an intermediary.

6.2.接收数据

If the frame comprises an unfragmented message (Section 5.4), it is said that A WebSocket Message Has Been Received with type /type/ and data /data/. If the frame is part of a fragmented message, the "Application data" of the subsequent data frames is concatenated to form the /data/. When the last fragment is received as indicated by the FIN bit (frame-fin), it is said that A WebSocket Message Has Been Received with data /data/ (comprised of the concatenation of the "Application data" of the fragments) and type /type/ (noted from the first frame of the fragmented message). Subsequent data frames MUST be interpreted as belonging to a new WebSocket message.

https://www.rfc-editor.org/rfc/rfc6455
混淆可能来自术语“套接字”，它是一个低级的原始操作系统 channel ，它以 block 的形式产生数据。但是，WebSocket 是更高级别的协议(protocol)。