How to build a nodejs(express) proxy using http-proxy-middleware?

Question

I try to proxy all interfaces of http://A.com to http://B.com. And then I want to change the result of interface '/api/v2'. But what i do is not worked for the interface '/api/v2'. My logs in proxyRes don't run. Here is the code in my server.

const express = require('express');
const { createProxyMiddleware } = require('http-proxy-middleware');

const app = express();

app.use('/api/v2', createProxyMiddleware({
  target: 'http://B.com',
  changeOrigin: true,
  on: {
    proxyRes: (proxyRes, req, res) => {
      console.log('proxy res here =====');
      proxyRes.headers['x-added'] = 'foobar';
    }
  }
}));

app.use('/', createProxyMiddleware({ target: 'http://B.com', changeOrigin: true }));

// 启动服务器
const port = 3000;
app.listen(port, () => {
  console.log(`Server is running on port ${port}`);
});

Is there anything wrong with my code? Proxy A.com to B.com is worked. But it seems app.use('/api/v2', ......) is not worked at all. I want to change its response header and response data.

env

• node: 14.18.3
• express: 4.18.2
• http-proxy-middleware: 2.0.6

Answer 1

From the http-proxy events documentation, it should be option.onProxyRes.

const express = require('express');
const { createProxyMiddleware } = require('http-proxy-middleware');

const app = express();

app.use(
    '/api/v2',
    createProxyMiddleware({
        target: 'https://jsonplaceholder.typicode.com',
        pathRewrite: {
            '^/api/v2': '',
        },
        changeOrigin: true,
        onProxyRes: (proxyRes, req, res) => {
            console.log('proxy res here =====');
            proxyRes.headers['x-added'] = 'foobar';
        },
    }),
);

// 启动服务器
const port = 3000;
app.listen(port, () => {
    console.log(`Server is running on port ${port}`);
});

Test:

✗ curl -i --request GET http://localhost:3000/api/v2/todos/1
HTTP/1.1 200 OK
x-powered-by: Express
date: Tue, 28 Nov 2023 08:48:31 GMT
content-type: application/json; charset=utf-8
content-length: 83
connection: close
report-to: {"group":"heroku-nel","max_age":3600,"endpoints":[{"url":"https://nel.heroku.com/reports?ts=1700986863&sid=e11707d5-02a7-43ef-b45e-2cf4d2036f7d&s=FwLcy2E2TneWtDma4sLiQRIGzoY%2FlU%2BGZ83naoahnso%3D"}]}
reporting-endpoints: heroku-nel=https://nel.heroku.com/reports?ts=1700986863&sid=e11707d5-02a7-43ef-b45e-2cf4d2036f7d&s=FwLcy2E2TneWtDma4sLiQRIGzoY%2FlU%2BGZ83naoahnso%3D
nel: {"report_to":"heroku-nel","max_age":3600,"success_fraction":0.005,"failure_fraction":0.05,"response_headers":["Via"]}
x-ratelimit-limit: 1000
x-ratelimit-remaining: 999
x-ratelimit-reset: 1700986910
vary: Origin, Accept-Encoding
access-control-allow-credentials: true
cache-control: max-age=43200
pragma: no-cache
expires: -1
x-content-type-options: nosniff
etag: W/"53-hfEnumeNh6YirfjyjaujcOPPT+s"
via: 1.1 vegur
cf-cache-status: HIT
age: 691
accept-ranges: bytes
server: cloudflare
cf-ray: 82d15a340e1a48c9-LHR
alt-svc: h3=":443"; ma=86400
x-added: foobar

{
  "userId": 1,
  "id": 1,
  "title": "delectus aut autem",
  "completed": false
}% 

The x-added: foobar response header is added.