调研目的

• 在异常情况下，网络断开对WebSocket的影响

测试代码

• 测试代码没有心跳机制
• 心跳机制并不包含在WebSocket协议内部

var ws = new WebSocket('wss://echo.websocket.org/')

ws.onopen =function(e){

    console.log('onopen')
}

ws.onerror = function (e) {
  console.log('onerror: ' + e.code)
  console.log(e)
}

ws.onclose = function (e) {
  console.log('onclose: ' + e.code)
  console.log(e)
}

场景1: 断网后，是否会立即触发onerror, 或者onclose事件？

答案：不会立即触发

测试代码中没有心跳机制，断网后，并不会立即触发onerror或者onclose的回调函数。

个人测试的情况

场景2: 断网后，使用send()发送数据，回触发事件吗？

为什么无法准确拿到断开原因？

WebSocket关闭事件中有三个属性

• code 断开原因码
• reason 具体原因
• wasClean 是否是正常断开

官方文档上，code字段有很多个值。但是大多数情况下，要么拿到的值是undefined, 要么是1006，基本上没有其他情况。

这并不是浏览器的bug, 这是浏览器故意这样做的。在w3c的官方文档上给出的原因其实是处于安全的考虑。

试想一下，如果把断开原因给出的非常具体。那么一个恶意的js脚本就有可能做端口扫描或则恶意的注入。

User agents must not convey any failure information to scripts in a way that would allow a script to distinguish the following situations:

A server whose host name could not be resolved.

A server to which packets could not successfully be routed.

A server that refused the connection on the specified port.

A server that failed to correctly perform a TLS handshake (e.g., the server certificate can’t be verified).

A server that did not complete the opening handshake (e.g. because it was not a WebSocket server).

A WebSocket server that sent a correct opening handshake, but that specified options that caused the client to drop the connection (e.g. the server specified a subprotocol that the client did not offer).

A WebSocket server that abruptly closed the connection after successfully completing the opening handshake.

In all of these cases, the the WebSocket connection close code would be 1006, as required by the WebSocket Protocol specification. [WSP]

Allowing a script to distinguish these cases would allow a script to probe the user’s local network in preparation for an attack. https://www.w3.org/TR/websockets/%23concept-websocket-close-fail