错误 [ERR_HTTP_HEADERS_SENT] 发送给客户端后无法设置 headers

Question

    at ServerResponse.setHeader (_http_outgoing.js:470:11)
    at ServerResponse.header (C:\root\node_modules\express\lib\response.js:771:10)
    at ServerResponse.send (C:\root\node_modules\express\lib\response.js:170:12)
    at ServerResponse.json (C:\root\node_modules\express\lib\response.js:267:15)
    at ServerResponse.send (C:\root\node_modules\express\lib\response.js:158:21)
    at grade.save (C:\root\route\api\listsData.js:223:32)
    at C:\root\node_modules\mongoose\lib\model.js:4604:16
    at C:\root\node_modules\mongoose\lib\utils.js:268:11
    at $__save.error (C:\root\node_modules\mongoose\lib\model.js:472:16)
    at C:\root\node_modules\kareem\index.js:246:48
    at next (C:\root\node_modules\kareem\index.js:167:27)
    at next (C:\root\node_modules\kareem\index.js:169:9)
    at Kareem.execPost (C:\root\node_modules\kareem\index.js:217:3)
    at _handleWrapError (C:\root\node_modules\kareem\index.js:245:21)
    at C:\root\node_modules\kareem\index.js:272:14
    at _next (C:\root\node_modules\kareem\index.js:94:14)
Emitted 'error' event at:

请帮忙，我已经面临这个问题将近 3 天了，下面是我的后端 nodejs 代码：等级模型

const mongoose = require('mongoose');

const GradeSchema = new mongoose.Schema({
  name: {
    type: String,
    maxlength: 100,
    required: true,
    unique: true
  }
})

module.exports = Grade = mongoose.model('Grade', GradeSchema);

添加等级路线

  '/add/grade',
  [
    check('name', 'grade name is require')
      .not()
      .isEmpty()
  ],
  auth,
  admin,
  (req, res) => {
    const errors = validationResult(req);
    if (!errors.isEmpty()) res.status(400).send({ errors: errors.array() });

    const grade = new Grade(req.body);

    grade.save((err, doc) => {
      if (err) res.status(400).send({ success: false, err });
      return res.status(200).send({
        success: true,
        grade: doc,
        msg: 'Grade add successfully'
      });
    });
  }
);

问题是当我尝试使用 post 请求添加成绩时它工作正常，但如果我输入空白字段并再次发送请求，应用程序崩溃并且它 returns 'Cannot set headers after they are sent to the client' 以上的错误。谢谢。

Answer 1

一旦发生错误，您需要return您的错误响应，否则您的函数将保持运行并在错误发生后执行以下代码。

  '/add/grade',
  [
   check('name', 'grade name is require')
  .not()
  .isEmpty()
],
auth,
admin,
(req, res) => {
const errors = validationResult(req);
if (!errors.isEmpty()) return res.status(400).send({ errors: errors.array() });

const grade = new Grade(req.body);

grade.save((err, doc) => {
  if (err) return res.status(400).send({ success: false, err });
  return res.status(200).send({
    success: true,
    grade: doc,
    msg: 'Grade add successfully'
  });
});
}
);

因为如果发生错误或任何验证失败，API 会发送响应但不会 returned，因此该函数会继续运行并执行它下面的所有其他代码。

您应该知道，在 HTTP 请求中，响应只能发送一次，当函数在出错后再次发送响应时，它会向您显示在将响应发送到客户端后无法发送响应 headers .

希望这对您有所帮助。祝你好运:)

Answer 2

当发送多次会产生错误时，您只能向客户端发送一次响应

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

我遇到了同样的错误。就我而言，我发送了两次回复。 1)保存用户前

res.send(user);//<----after removing this statement my problem was fixed.

2)保存用户后

await user.save().then(result=>{
       return res.send(result);
        
    }).catch(err=>{
        return res.sendStatus(500).send({
            message:err.message|| "some error occured"
        });
        
    })

错误 [ERR_HTTP_HEADERS_SENT] 发送给客户端后无法设置 headers

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

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