NodeJS Express MySQL发布请求抛出“发送到客户端后无法设置标头”答案

【问题标题】：NodeJS Express MySQL post request throwing "Cannot set headers after they are sent to the client"NodeJS Express MySQL发布请求抛出“发送到客户端后无法设置标头”
【发布时间】：2018-07-29 03:48:17
【问题描述】：

我尝试通过 express post 请求发回一些 MySQL 结果，但无论我尝试什么，总是出现以下错误：

(node:3743) UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at validateHeader (_http_outgoing.js:503:11)
    at ServerResponse.setHeader (_http_outgoing.js:510:3)
    at ServerResponse.header (/home/dvs23/projects/Group/Visualizer/node_modules/express/lib/response.js:767:10)
    at ServerResponse.send (/home/dvs23/projects/Group/Visualizer/node_modules/express/lib/response.js:170:12)
    at ServerResponse.json (/home/dvs23/projects/Group/Visualizer/node_modules/express/lib/response.js:267:15)
    at ServerResponse.send (/home/dvs23/projects/Group/Visualizer/node_modules/express/lib/response.js:158:21)
    at /home/dvs23/projects/Group/Visualizer/index.js:193:11
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:160:7)
(node:3743) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:3743) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

代码的重要部分是：

app.post('/getNews', (req, res) => {
  var prom = new Promise(function(resolve, reject) {
      //create nodes for result
      con.connect(function() {
        console.log("Connected!");
        con.query("SELECT ID,length(Text) FROM news;", function(err, result, fields) {
          if (err) {
            console.log(err);
            reject(err);
            return;
          }

          var nodesArr = [];
          result.forEach((row) => {
            nodesArr.push({
              "id": row["ID"],
              "size": row["length(Text)"]
            });
          });

          con.query("SELECT * FROM newsSim;", function(err, result2, fields) {
            if (err){
              console.log(err);
              reject(err);
              return;
            }

            var linksArr = [];
            result2.forEach((row) => {
              linksArr.push({
                "source": row["TID1"],
                "target": row["TID2"],
                "value": row["SIM"]
              });
            });
            console.log({
              "nodes": nodesArr,
              "links": linksArr
            });
            resolve({
              "nodes": nodesArr,
              "links": linksArr
            });
          });
        });
      });
    })
    .then(function(result) {
      console.log(result);
      res.send(result); //send result to client
    }, function(err) {
      console.log("END"+err);
      res.send({
        "nodes": [],
        "links": []
      });
    });
});

App 是我的 express-app，请求来自静态 HTML 页面，该页面也由 NodeJS 服务器通过 jQuery 提供服务。
我已经使用了一个承诺，所以怎么可能 send 已经被调用了？同样没有承诺，只是嵌套查询，存在相同的错误（显然没有 UnhandledPromiseRejectionWarning 的东西）。

编辑：

嵌套的 MySQL 查询不是问题，即使以下内容也不起作用：

app.post('/getNews', (req, res) => {
  //var text = req.fields["text"];

  var prom = new Promise(function(resolve, reject) {
      //create nodes for result
      con.connect(function() {
        console.log("Connected!");
        con.query("SELECT ID,length(Text) FROM news;", function(err, result, fields) {
          if (err) {
            console.log(err);
            reject(err);
            return;
          }

          var nodesArr = [];
          result.forEach((row) => {
            nodesArr.push({
              "id": row["ID"],
              "size": row["length(Text)"]
            });
          });

          resolve(nodesArr);
          return;
        });
      });
    })
    .then(function(news) {
      console.log(news);
      //if (res.headersSent) return;
      res.send(news); //send result to client
    }, function(err) {
      console.log("END"+err);
      //if (res.headersSent) return;
      res.send({
        "nodes": [],
        "links": []
      });
    });
});

如果我使用 if(res.headersSent)，则根本不会将任何内容发送回我的站点，既不是空结果，也不是根据需要获取的真实结果 -> 我可以将其记录到控制台...

EDIT2：

app.post('/getNews', (req, res) => {
  //var text = req.fields["text"];
  req.connection.setTimeout(6000000, function () { 
    console.log("Timeout 2");
    res.status(500).end(); 
  });

  var prom = new Promise(function(resolve, reject) {
      //create nodes for result
      con.connect(function() {
        console.log("Connected!");
        con.query("SELECT ID,length(Text) FROM news;", function(err, result, fields) {
          if (err) {
            console.log(err);
            reject(err);
            return;
          }

          var nodesArr = [];
          result.forEach((row) => {
            nodesArr.push({
              "id": row["ID"],
              "size": row["length(Text)"]
            });
          });

          con.query("SELECT * FROM newsSim;", function(err2, result2, fields2) {
            if (err2){
              console.log(err2);
              reject(err2);
              return;
            }

            var linksArr = [];
            result2.forEach((row) => {
              linksArr.push({
                "source": row["TID1"],
                "target": row["TID2"],
                "value": row["SIM"]
              });
            });
            resolve({
              "nodes": nodesArr,
              "links": linksArr
            });
            return;
          });
        });
      });
    })
    .then(function(news) {
      //if (res.headersSent) return;
      res.send(news); //send result to client
      console.log(news);
    }, function(err) {
      console.log("END"+err);
      //if (res.headersSent) return;
      res.send({
        "nodes": [],
        "links": []
      });
    });
});

试图设置超时，但现在错误发生之前超时回调被调用...

(node:9926) UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at validateHeader (_http_outgoing.js:503:11)
    at ServerResponse.setHeader (_http_outgoing.js:510:3)
    at ServerResponse.header (/home/dvs23/projects/Group/Visualizer/node_modules/express/lib/response.js:767:10)
    at ServerResponse.send (/home/dvs23/projects/Group/Visualizer/node_modules/express/lib/response.js:170:12)
    at ServerResponse.json (/home/dvs23/projects/Group/Visualizer/node_modules/express/lib/response.js:267:15)
    at ServerResponse.send (/home/dvs23/projects/Group/Visualizer/node_modules/express/lib/response.js:158:21)
    at /home/dvs23/projects/Group/Visualizer/index.js:198:11
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:160:7)
(node:9926) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:9926) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
Timeout 2

【问题讨论】：

您还有其他处理程序来捕获发布操作吗？路径/getNews 可能被另一个处理程序捕获，该处理程序在此方法之前调用res.send。
还有另一个 post 处理程序，但它被分配到另一个路径 (/getAnalysis)...并且该路径仍然有效 :)
我唯一能想到的另一件事是这些查询很慢，并且在执行结束之前达到了“httpServer.timeout”。
我想我被误解了。在使用let server = app.listen(80) 或类似的东西创建服务器后，您应该检查server.timeout 的值。但我不认为这应该是一个问题，因为它的默认值为 2 分钟。我希望我能帮助你更多，但我看不出你描述的应用程序有什么问题。
查看您发布的完整代码，唯一可能造成一些问题的是app.use(express.static('static')); 行。我能给你的最后一个建议是尝试注释掉除你共享的第一段代码之外的所有内容，并检查问题是否仍然存在。

标签： mysql node.js express promise

【解决方案1】：

不要问我为什么，但它现在似乎工作了......可能按照 oniramarf 的建议设置特定的超时是关键。还加了

multipleStatements: true

到 mysql.createConnection(...) 并将静态内容移动到不同的路径：

app.use('/site', express.static('static'));

但这可能不是它现在起作用的原因:)

代码：

app.post('/getNews', (req, res) => {
  //var text = req.fields["text"];

  var prom = new Promise(function(resolve, reject) {
      //create nodes for result
      con.connect(function() {
        console.log("Connected!");
        con.query("SELECT ID,length(Text) from news;", function(err, result, fields) { //SELECT ID,length(Text) FROM news;
          if (err) {
            console.log(err);
            reject(err);
            return;
          }

          con.query("SELECT * FROM newsSim;", function(err2, result2, fields2) {
            if (err2) {
              console.log(err2);
              reject(err2);
              return;
            }

            var imporIDs = new Set();

            var linksArr = [];
            result2.forEach((row) => {
              if (row["SIM"] > 0.25) {
                imporIDs.add(row["TID1"]);
                imporIDs.add(row["TID2"]);
                linksArr.push({
                  "source": row["TID1"],
                  "target": row["TID2"],
                  "value": row["SIM"]
                });
              }
            });

            var nodesArr = [];
            result.forEach((row) => {
              if (imporIDs.has(row["ID"])){
                nodesArr.push({
                  "id": row["ID"],
                  "size": row["length(Text)"]
                });
              }
            });
            resolve({
              "nodes": nodesArr,
              "links": linksArr
            });
            return;
          });
        });
      });
    })
    .then(function(news) {
      //if (res.headersSent) return;
      res.send(news); //send result to client
      console.log(news);
    }, function(err) {
      console.log("END" + err);
      //if (res.headersSent) return;
      res.send({
        "nodes": [],
        "links": []
      });
    });
});

var server = http.createServer(app);

server.listen(8080, function() {
  console.log('localhost:8080!');
});
server.timeout = 120000;

编辑：
确实似乎是超时，经过一些更改后再次发生错误，所以我设置 server.timeout = 12000000 并且它再次工作:)

【讨论】：