node.js - 如果我使用 send 或 json， Node 应用程序崩溃

Question

我正在创建一个 IOS 应用程序，在后台我们使用了 Node.js 和 Mongodb。我已经创建了用于创建用户的 Node 应用程序，并通过 json 发送错误和成功响应，但如果使用 res.send 我的 Node 应用程序将崩溃。我试图发现问题，但尚未得到积极的回应。下面是我的所有代码。

Controller :

const nodemailer    = require('nodemailer');
const passport      = require('passport');
const User          = require('../../models/User');





exports.ManuallySave = function(req,res)
{
  if(req.body.my_token !== '')
  {
    User.findOne({ email: req.body.email }, (err, existingUser) => {
      if (existingUser) 
      {
        //res.setHeader('Content-Type', 'text/plain');
        res.json({"status":'error',"msg":'Email address already exists.'});
      }
    });

    User.findOne({ username: req.body.username }, (err, existingUserName) => {
      if (existingUserName) 
      {
        res.send({"status":'error',"msg":'Username already exists.'});
      }
    });

    /* Save Action perform */
  }
  else 
  {
    res.send({"status":'error',"msg":'Token is not available.'});
  }

}

控制台错误。

/var/www/node/MyApplication/node_modules/mongodb/lib/utils.js:98
    process.nextTick(function() { throw err; });
                                  ^

Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:344:11)
    at ServerResponse.header (/var/www/node/MyApplication/node_modules/express/lib/response.js:718:10)
    at ServerResponse.send (/var/www/node/MyApplication/node_modules/express/lib/response.js:163:12)
    at ServerResponse.json (/var/www/node/MyApplication/node_modules/express/lib/response.js:249:15)
    at ServerResponse.send (/var/www/node/MyApplication/node_modules/express/lib/response.js:151:21)
    at /var/www/node/MyApplication/controllers/apis/userAppController.js:55:13
    at model.<anonymous> (/var/www/node/MyApplication/node_modules/mongoose/lib/document.js:1875:20)
    at next_ (/var/www/node/MyApplication/node_modules/hooks-fixed/hooks.js:89:34)
    at fnWrapper (/var/www/node/MyApplication/node_modules/hooks-fixed/hooks.js:186:18)
    at /var/www/node/MyApplication/node_modules/mongoose/lib/model.js:226:5
    at /var/www/node/MyApplication/node_modules/mongoose/lib/model.js:135:7
    at /var/www/node/MyApplication/node_modules/mongodb/lib/collection.js:504:5
    at /var/www/node/MyApplication/node_modules/mongodb/lib/collection.js:666:5
    at handleCallback (/var/www/node/MyApplication/node_modules/mongodb/lib/utils.js:96:12)
    at /var/www/node/MyApplication/node_modules/mongodb/lib/bulk/unordered.js:473:9
    at handleCallback (/var/www/node/MyApplication/node_modules/mongodb/lib/utils.js:96:12)
    at resultHandler (/var/www/node/MyApplication/node_modules/mongodb/lib/bulk/unordered.js:420:5)
    at /var/www/node/MyApplication/node_modules/mongodb-core/lib/wireprotocol/2_4_support.js:544:17
    at nextTickCallbackWith0Args (node.js:420:9)
    at process._tickCallback (node.js:349:13)

我已经使用了 res.send 和 res.json，但在这两种情况下我的应用程序都会崩溃。

Answer 1

当您在已经调用 res.send 的情况下尝试调用 res 上的方法时，会引发该错误。不能保证 res.send 在您的代码中只会被调用一次，而这是必须的。区 block

User.findOne({ email: req.body.email }, (err, existingUser) => {
  if (existingUser) 
  {
    //res.setHeader('Content-Type', 'text/plain');
    res.json({"status":'error',"msg":'Email address already exists.'});
  }
});

User.findOne({ username: req.body.username }, (err, existingUserName) => {
  if (existingUserName) 
  {
    res.send({"status":'error',"msg":'Username already exists.'});
  }
});

如果您已经有一个用户同时拥有该电子邮件地址和该用户名，则将调用 res.send 两次。您必须在第一个回调中执行另一个调用。

User.findOne({ email: req.body.email }, (err, existingUser) => {
  if (existingUser) 
  {
    //res.setHeader('Content-Type', 'text/plain');
    res.json({"status":'error',"msg":'Email address already exists.'});
  } else {
    checkUsername();
  }
});
function checkUsername() {
  User.findOne({ username: req.body.username }, (err, existingUserName) => {
    if (existingUserName) 
    {
      res.send({"status":'error',"msg":'Username already exists.'});
    } else {
      // save action
    }
  });
}

我建议您查看promise chains处理不可避免的即将到来的回调嵌套？