节点：将标头发送到客户端后无法设置标头

Question

我对以下错误做了一些研究：

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

我理解这个想法以及导致它的原因，但我不确定如何为我的控制器代码修复它：

exports.isServerOnline = (req, res, next) => {
    const sock = new net.Socket();
    sock.setTimeout(2500);
    sock.on('connect', function () {
        sock.destroy();
        return res.json({
            "server": "online"
        });
    }).on('error', function (e) {
        return res.json({
            "server": "offline"
        });
    }).on('timeout', function (e) {
        return res.json({
            "server": "offline"
        });
    }).connect(LS_PORT, LS_HOST);
}

我正在使用套接字来检查远程主机是启动还是关闭。这是我的客户端代码（Vue.js）：

created() {
    this.getServerStatus();
  },

  methods: {
    getServerStatus() {
      axios
        .get(`${process.env.VUE_APP_BACKEND_URL}/server/status`)
        .then(response => {
          if (response.data.server === "online") {
            // no interesting code here
          } else {
            // no interesting code here
          }
          /* eslint-disable no-console */
        })
        .catch(error => {
          console.log(error);
        });
    }
  }

完整的错误堆栈跟踪：

2020-07-02T07:40:47.743193+00:00 app[web.1]: _http_outgoing.js:518
2020-07-02T07:40:47.743201+00:00 app[web.1]: throw new ERR_HTTP_HEADERS_SENT('set');
2020-07-02T07:40:47.743202+00:00 app[web.1]: ^
2020-07-02T07:40:47.743202+00:00 app[web.1]:
2020-07-02T07:40:47.743204+00:00 app[web.1]: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
2020-07-02T07:40:47.743205+00:00 app[web.1]: at ServerResponse.setHeader (_http_outgoing.js:518:11)
2020-07-02T07:40:47.743206+00:00 app[web.1]: at ServerResponse.header (/app/node_modules/express/lib/response.js:771:10)
2020-07-02T07:40:47.743206+00:00 app[web.1]: at ServerResponse.json (/app/node_modules/express/lib/response.js:264:10)
2020-07-02T07:40:47.743206+00:00 app[web.1]: at Socket.<anonymous> (/app/src/controllers/status.js:15:20)
2020-07-02T07:40:47.743207+00:00 app[web.1]: at Socket.emit (events.js:315:20)
2020-07-02T07:40:47.743207+00:00 app[web.1]: at emitErrorNT (internal/streams/destroy.js:92:8)
2020-07-02T07:40:47.743208+00:00 app[web.1]: at emitErrorAndCloseNT (internal/streams/destroy.js:60:3)
2020-07-02T07:40:47.743208+00:00 app[web.1]: at processTicksAndRejections (internal/process/task_queues.js:84:21) {
2020-07-02T07:40:47.743209+00:00 app[web.1]: code: 'ERR_HTTP_HEADERS_SENT'
2020-07-02T07:40:47.743209+00:00 app[web.1]: }

如果有人能指出我正确的方向，我将不胜感激。

Answer 1

我不认为这种方法是正确的伙伴。您正在尝试在 http 端点内创建一个套接字，但这是行不通的。这是我发现的使用 NodeJS Socket 演示的要点。

https://gist.github.com/tedmiston/5935757

我会推荐使用 Socket.io 之类的东西。他们有大量的文档可以起步。