HTTP POST 请求错误“错误：发送后无法设置标头。”

Question

我的代码的特定部分遇到了问题。我设法将它隔离到这一块。这是一个 POST 请求，如果一切成功，它会发回 paymentSuccess : true 对象。然后前端会将用户重定向到/confirmation URL。

但是，POST请求一完成，就会出现如下错误：Error: Can't set headers after they are sent.

目前停留在可能导致问题的原因上，并查看了其他问题。我没有看到任何干扰，希望有人可以提供一些见解。

下面是我的代码，有点长，我知道：

// POST Registration Database Queries
router.post('/checkout', function(req, res, next) {

   // Constants for use in queries
   var dateRegistered = new Date();
   var userIDs = [];
   var billingID;

   // Register athletes if they don't already exist
   pool.getConnection(function(err, connection){
      connection.beginTransaction(function(err) {
         if (err) {
            throw err;
         }

         // Check to if users are already registered and register them in the database if not
         _.each(req.body.users, function(val, key){
            var existsQuery = 'SELECT `userId`, `firstName`, `lastName`, `email`, `dateRegistered` from Database.Users WHERE firstName = ? AND lastName = ? AND email = ?';
            // Check to see if the user is already in the database
            connection.query(existsQuery, [val.firstName, val.lastName, val.email], function(err, result){
               if (err) {
                  return connection.rollback(function() {
                     console.log(err);
                     res.send({ registerSuccess: false });
                  });
               } else if(_.isEmpty(result)){ // If the user doesn't exist
                  var registerQuery = 'INSERT INTO Database.Users (`firstName`, `lastName`, `email`, `dateRegistered`) VALUE ( ?, ?, ?, ?)';
                  connection.query(registerQuery, [val.firstName, val.lastName, val.email, dateRegistered], function(err, result){
                     if (err) {
                        return connection.rollback(function() {
                           console.log(err);
                           res.send({ registerSuccess: false });
                        });
                     } else {
                        console.log(result);
                        connection.commit(function(err) {
                           if (err) {
                              return connection.rollback(function() {
                                 console.log(err);
                                 res.send({ registerSuccess: false });
                              });
                           } else {
                              console.log("User registered successfully!");
                              userIDs.push(result.insertId);
                              res.send({ registerSuccess: true });
                           }
                        });
                     }
                  });
               } else { // If the user already exists
                  console.log("User already exists!");
                  userIDs.push(result[0].userId);
                  res.send({ registerSuccess: true });
               }
            });
         });

      });
   });

   // Register billing user into the database if they don't already exist
   pool.getConnection(function(err, connection){
      connection.beginTransaction(function(err) {
         if (err) {
            throw err;
         }

         // Confirm if payment is successful before continuing
         gateway.transaction.sale({
            amount: req.body.payment.totalCost,
            paymentMethodNonce: req.body.paymentData.paymentNonce,
            customer: {
               firstName: req.body.billing.firstName,
               lastName: req.body.billing.lastName,
               // company: "Braintree",
               phone: req.body.billing.phoneNumber,
               // fax: "312-555-12346",
               // website: "http://www.example.com",
               email: req.body.billing.email
            },
            billing: {
               firstName: req.body.billing.firstName,
               lastName: req.body.billing.lastName,
               // company: "Braintree",
               streetAddress: req.body.billing.address,
               // extendedAddress: "Suite 403",
               locality: req.body.billing.city,
               region: req.body.billing.province,
               postalCode: req.body.billing.postalCode,
               countryCodeAlpha2: "CA"
            },
            options: {
               submitForSettlement: true
            },
         }, function(err, result) {
            var paymentResult = result;
            if (result.success == true) {
               // If the payment is successful, make the queries for the entries
               var existsQuery = 'SELECT `userId`, `firstName`, `lastName`, `email`, `dateRegistered` from Database.Users WHERE firstName = ? AND lastName = ? AND email = ?';
               // Check to see if the user is already in the database
               connection.query(existsQuery, [req.body.billing.firstName, req.body.billing.lastName, req.body.billing.email], function(err, result){
                  if (err) {
                     return connection.rollback(function() {
                        console.log(err);
                        res.send({ paymentSuccess : false });
                     });
                  } else if(_.isEmpty(result)){ // If the user doesn't already exist
                     console.log("Billing user does not exist!");
                     sql = 'INSERT INTO Database.Users (`firstName`, `lastName`, `email`, `address`, `cellNumber`, `city`, `phoneNumber`, `postalCode`, `province`, `dateRegistered`) VALUE ( ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)';
                     data = [req.body.billing.firstName, req.body.billing.lastName, req.body.billing.email, req.body.billing.address, req.body.billing.cellNumber, req.body.billing.city, req.body.billing.phoneNumber, req.body.billing.postalCode, req.body.billing.province, dateRegistered];
                  } else { // If the user already exists
                     console.log("Billing user already exists!");
                     billingID = result[0].userId;
                     sql = 'UPDATE Database.Users SET `address` = ?, `cellNumber` = ?, `city` = ?, `phoneNumber` = ?, `postalCode` = ?, `province` = ? WHERE userID = ?';
                     data = [req.body.billing.address, req.body.billing.cellNumber, req.body.billing.city, req.body.billing.phoneNumber, req.body.billing.postalCode, req.body.billing.province, billingID];
                  }
                  // Add or update the billing user
                  connection.query(sql, data, function(err, result){
                     if (err) {
                        return connection.rollback(function() {
                           console.log(err);
                           res.send({ paymentSuccess : false });
                        });
                     } else {
                        // Insert transaction into the database
                        var fees = (paymentResult.transaction.amount * .029) + 0.3;
                        var timeStamp = new Date();
                        var rawResponse = JSON.stringify(paymentResult.transaction);
                        var transactionID = paymentResult.transaction.id;
                        var totalCost = paymentResult.transaction.amount;
                        var transaction = [billingID, paymentResult.transaction.id, paymentResult.transaction.merchantAccountId, paymentResult.transaction.amount, fees, paymentResult.transaction.currencyIsoCode, paymentResult.transaction.paymentInstrumentType, timeStamp, 0, 0, rawResponse];
                        connection.query('INSERT INTO Database.Transactions (userID, braintreeTransactionID, braintreeMerchantAccount, amount, fees, currency, paymentInstrumentType, timeStamp, processed, refunded, rawResponse) VALUE (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)', transaction, function(err, result) {
                           if (err) {
                              return connection.rollback(function() {
                                 console.log(err);
                                 res.send({ paymentSuccess : false });
                              });
                           } else {
                              console.log("Transaction has been recorded!");
                              // Record tournament entries
                              for(j = 0; j < userIDs.length; j++){
                                 var tournamentUser = [userIDs[j], req.body.tournament.chosen, result.insertId, "Temp Val"];
                                 var sql = "INSERT INTO Database.tournamentEntries (userID, tournamentID, transactionID, skillLevel) VALUE (?, ?, ?, ?)";
                                 connection.query(sql, tournamentUser, function(err, result){
                                    if (err) {
                                       return connection.rollback(function() {
                                          console.log(err);
                                          res.send({ paymentSuccess : false });
                                       });
                                    } else {
                                       connection.commit(function(err) {
                                          if (err) {
                                             return connection.rollback(function() {
                                                console.log(err);
                                                res.send({ paymentSuccess: false });
                                             });
                                          } else {
                                             console.log("Tournament entries were successful!");
                                             userIDs.push(result.insertId);
                                             res.send({ paymentSuccess : true });
                                          }
                                       });
                                    }
                                 });
                              }
                           }
                        });
                     }
                  });
               });
            } else { // Payment has failed
               res.send({ paymentSuccess : false });
            }
         });

      });
   });

});

Answer 1

_.each 是一个同步/阻塞调用。然而，在里面你是在进行异步的db.query 调用。所以基本上你不会知道哪些回调正在发送错误或数据，以及你的代码是否应该停止。

由于您的方法的异步特性，即使由于错误或成功调用了res.send 方法之一，其他异步调用也不会终止，因为它们已经由_.each 方法启动。

您需要一个一个或一个并行地触发它们，但最重要的是需要一个最终回调，当它们有任何错误或所有它们都成功完成时应该调用它，然后只有您应该使用res.send 方法。

我建议查看async npm 模块。查看async.each 或async.whilst 方法。这可能可以使用 async 编写如下 -

async.each(req.body.users, function(item, callback){
    // call your db methods here ... 
    // once they are done for error call callback(error) when  successfull call with callback(null)
}, function(err){
    // the final call back 
   // if any of the query produced an error, err would equal that error
   if(error){
     res.send("error");
   }
   else 
   {
      // success
      res.send("success");
   }
});

Answer 2

我看到您在同一条路由中进行了两个注册，并且您正在从它们内部调用 res.send。

因此，在这种情况下，首先完成的是您在客户端得到的响应，而接下来完成的是导致错误的响应。

您可以在回调中调用 res.send 而不是从任何地方调用它，并且在回调中您可以检查两个注册是否都已完成，然后才发送响应。