(节点:45207) UnhandledPromiseRejectionWarning: ERR_HTTP_HEADERS_SENT [ERR_HTTP_HEADERS_SENT]

Question

我正在通过构建一个简单的代码片段应用程序来学习Node.js。它将有两个字段title和snippet。当提交一个新的片段时，我将继续得到这个错误，如下所示。

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:535:11)
    at ServerResponse.header (/myportal/node_modules/express/lib/response.js:771:10)
    at ServerResponse.send (/myportal/node_modules/express/lib/response.js:170:12)
    at /myportal/routes/index.js:99:36
    at processTicksAndRejections (internal/process/task_queues.js:97:5) {
  code: 'ERR_HTTP_HEADERS_SENT'
}
(node:45207) UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:535:11)
    at ServerResponse.header (/myportal/node_modules/express/lib/response.js:771:10)
    at ServerResponse.send (/myportal/node_modules/express/lib/response.js:170:12)
    at /myportal/routes/index.js:102:25
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
(node:45207) 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(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:45207) [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.

index.js

const express = require( "express" );
const mongoose = require( 'mongoose' );

const router = express.Router();
const snippetSchema = mongoose.model( 'snippetSchema' );

const { check, validationResult } = require( 'express-validator' );


router.post( '/newsnippet',
    [
        check( 'title' )
            .isLength( { min: 1 } )
            .withMessage( ' Please enter a valid title name.' ),
        check( 'snippet' )
            .isLength( { min: 1 } )
            .withMessage( ' Please enter a valid snippet.' ),

    ],
    ( req, res ) => {
        const errors = validationResult( req );

        if ( errors.isEmpty() ) {
            res.send( "Thank you for adding new snippet." );
            console.log( "Req Body : " + JSON.stringify( req.body ) );
            const newSnippet = new snippetSchema( req.body );
            console.log( " I am executed till creating newSnippet instantiation" + JSON.stringify( newSnippet ) );
            newSnippet.save()
                .then( () => { res.send( 'Thank you for adding new snippet :)' ); console.log( "Reached till here!" ) } )
                .catch( ( err ) => {
                    console.log( err );
                    res.send( 'Sorry! something went wrong' );

                } );
            //return;
        } else {
            res.render( 'snippets', {
                title: "My Homepage",
                errors: errors.array(),
                data: req.body,
            } );
            //return;
        }

    }

);
module.exports = router;

模型码

const mongoose = require( 'mongoose' );
mongoose.set( 'useCreateIndex', true );

const snippetSchema = new mongoose.Schema( {
  title: {
    type: String,
    trim: true,
    //unique: true,
  },
  snippet_code: {
    type: String,
    trim: true,
    //unique: true,
  }

} );

module.exports = mongoose.model( 'snippetSchema', snippetSchema );

另外一个观察是，即使我的模型在启动新的模型对象时有两个字段，比如title和snippet，但是我没有得到我的代码片段字段。

调试日志如下所示

Req Body : {"title":"Create New Change","snippet":"var r = new Record(); var result = r.createChange({\"short_description\" :\"Sample Changee\"}); print.info(result.number);"}
 I am executed till creating newSnippet instantiation{"_id":"5ea5195c9fcbc0b10ebd7968","title":"Create New Change"}

我搜索了堆栈溢出，发现了error-cant-set-headers-after-they-are-sent-to-the-client，但无法理解。

任何建议，都非常感谢。

谢谢。

Answer 1

不能为同一请求发送两次响应。

router.post( '/newsnippet',
    [
        check( 'title' )
            .isLength( { min: 1 } )
            .withMessage( ' Please enter a valid title name.' ),
        check( 'snippet' )
            .isLength( { min: 1 } )
            .withMessage( ' Please enter a valid snippet.' ),

    ],
    ( req, res ) => {
        const errors = validationResult( req );

        if ( errors.isEmpty() ) {
            const newSnippet = new snippetSchema( req.body );
            console.log( " I am executed till creating newSnippet instantiation" + JSON.stringify( newSnippet ) );
            newSnippet.save()
                .then( () => { res.send( 'Thank you for adding new snippet :)' ); console.log( "Reached till here!" ) } )
                .catch( ( err ) => {
                    console.log( err );
                    res.send( 'Sorry! something went wrong' );

                } );

请始终记住，此错误仅在发送响应后尝试设置标头时才会发生。

因此，在调试时查找res.send()。

这两者是不一样的。

router.get('/', async(req, res) => {
  return res.send('Hello world');
  res.send('Thanks for adding code snippet')!; // this line will not be executed, no errors
);

router.get('/', async(req, res) => {
  res.send('Hello world');
  res.send('Thanks for adding code snippet')!; // this line will be executed, and cause errors
);

next()也是如此。next()将导致代码执行继续进行，而return next()将停止执行并调用下一个中间件。

更多关于最上面的内容。当您从一个return res.send()函数进行middleware时，它将跳过所有其他的中间件，并返回响应。