ng2-file-upload 500 内部服务器问题

Question

我已经安装了这个 ng2-file-upload 包，但是我在上传图片时遇到了一些问题，它在控制台中显示了以下错误

OPTIONS http://localhost:3000/api/500（内部服务器错误）

XMLHttpRequest 无法加载 http://localhost:3000/api/。对预检请求的响应未通过访问控制检查：请求的资源上不存在“Access-Control-Allow-Origin”标头。因此，不允许访问 Origin 'http://localhost:4200'。响应的 HTTP 状态代码为 500。

我的 api server.js 文件代码是

var express = require('express');
var multer = require('multer');
var fs = require('fs');
var app = express();

var DIR = './uploads/';

var upload = multer({dest: DIR});

app.use(function (req, res, next) {
 res.setHeader("Access-Control-Allow-Methods", 
    "POST, PUT, OPTIONS,   DELETE, GET");
    header('Access-Control-Allow-Origin: http://localhost:4200');

    header('Access-Control-Allow-Methods: GET, POST, PATCH, 
    PUT, DELETE, OPTIONS');

    header('Access-Control-Allow-Headers: Origin, Content-Type');
    next();
});


 app.get('/api', function (req, res) {
  res.end('file catcher example');
 });

app.post('/api', function (req, res) {
 upload(req, res, function (err) {
    if (err) {
      return res.end(err.toString());
    }
    res.end('File is uploaded');
   });
});

var PORT = process.env.PORT || 3000;

app.listen(PORT, function () {
 console.log('Working on port ' + PORT);
});

AdminComponent.ts 代码

 import { FileSelectDirective, FileDropDirective, FileUploader, 
 Headers  } from 'ng2-file-upload/ng2-file-upload';

 const URL = 'http://localhost:3000/api/';

@Component({
  selector  : 'app-admin',
  templateUrl   : './admin.component.html',
  styleUrls : ['./admin.component.css']
})

Answer 1

替换这个：

app.use(function (req, res, next) {
 res.setHeader("Access-Control-Allow-Methods", 
    "POST, PUT, OPTIONS,   DELETE, GET");
    header('Access-Control-Allow-Origin: http://localhost:4200');

    header('Access-Control-Allow-Methods: GET, POST, PATCH, 
    PUT, DELETE, OPTIONS');

    header('Access-Control-Allow-Headers: Origin, Content-Type');
    next();
});

与

app.use(function(req, res, next) {
    res.header("Access-Control-Allow-Origin", 'http://localhost:4200');
    res.header("Access-Control-Allow-Credentials", true);
    res.header('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE,OPTIONS');
    res.header("Access-Control-Allow-Headers", 'Origin,X-Requested-With,Content-Type,Accept,content-type,application/json');
    next();
  });