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chimurai / http-proxy-middleware

:zap: The one-liner node.js http-proxy middleware for connect, express, next.js and more
MIT License
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http-proxy-middleware

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Node.js proxying made simple. Configure proxy middleware with ease for connect, express, next.js and many more.

Powered by the popular Nodejitsu http-proxy. GitHub stars

⚠️ Note

This page is showing documentation for version v3.x.x (release notes)

See MIGRATION.md for details on how to migrate from v2.x.x to v3.x.x

If you're looking for older documentation. Go to:

TL;DR

Proxy /api requests to http://www.example.org

:bulb: Tip: Set the option changeOrigin to true for name-based virtual hosted sites.

// typescript

import * as express from 'express';
import type { Request, Response, NextFunction } from 'express';

import { createProxyMiddleware } from 'http-proxy-middleware';
import type { Filter, Options, RequestHandler } from 'http-proxy-middleware';

const app = express();

const proxyMiddleware = createProxyMiddleware<Request, Response>({
    target: 'http://www.example.org/api',
    changeOrigin: true,
  }),

app.use('/api', proxyMiddleware);

app.listen(3000);

// proxy and keep the same base path "/api"
// http://127.0.0.1:3000/api/foo/bar -> http://www.example.org/api/foo/bar

All http-proxy options can be used, along with some extra http-proxy-middleware options.

Table of Contents

Install

npm install --save-dev http-proxy-middleware

Basic usage

Create and configure a proxy middleware with: createProxyMiddleware(config).

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

const apiProxy = createProxyMiddleware({
  target: 'http://www.example.org',
  changeOrigin: true,
});

// 'apiProxy' is now ready to be used as middleware in a server.

Express Server Example

An example with express server.

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

const app = express();

// create the proxy
/** @type {import('http-proxy-middleware/dist/types').RequestHandler<express.Request, express.Response>} */
const exampleProxy = createProxyMiddleware({
  target: 'http://www.example.org/api', // target host with the same base path
  changeOrigin: true, // needed for virtual hosted sites
});

// mount `exampleProxy` in web server
app.use('/api', exampleProxy);
app.listen(3000);

app.use(path, proxy)

If you want to use the server's app.use path parameter to match requests. Use pathFilter option to further include/exclude requests which you want to proxy.

app.use(
  createProxyMiddleware({
    target: 'http://www.example.org/api',
    changeOrigin: true,
    pathFilter: '/api/proxy-only-this-path',
  }),
);

app.use documentation:

Options

http-proxy-middleware options:

pathFilter (string, []string, glob, []glob, function)

Narrow down which requests should be proxied. The path used for filtering is the request.url pathname. In Express, this is the path relative to the mount-point of the proxy.

pathRewrite (object/function)

Rewrite target's url path. Object-keys will be used as RegExp to match paths.

// rewrite path
pathRewrite: {'^/old/api' : '/new/api'}

// remove path
pathRewrite: {'^/remove/api' : ''}

// add base path
pathRewrite: {'^/' : '/basepath/'}

// custom rewriting
pathRewrite: function (path, req) { return path.replace('/api', '/base/api') }

// custom rewriting, returning Promise
pathRewrite: async function (path, req) {
  const should_add_something = await httpRequestToDecideSomething(path);
  if (should_add_something) path += "something";
  return path;
}

router (object/function)

Re-target option.target for specific requests.

// Use `host` and/or `path` to match requests. First match will be used.
// The order of the configuration matters.
router: {
    'integration.localhost:3000' : 'http://127.0.0.1:8001',  // host only
    'staging.localhost:3000'     : 'http://127.0.0.1:8002',  // host only
    'localhost:3000/api'         : 'http://127.0.0.1:8003',  // host + path
    '/rest'                      : 'http://127.0.0.1:8004'   // path only
}

// Custom router function (string target)
router: function(req) {
    return 'http://127.0.0.1:8004';
}

// Custom router function (target object)
router: function(req) {
    return {
        protocol: 'https:', // The : is required
        host: '127.0.0.1',
        port: 8004
    };
}

// Asynchronous router function which returns promise
router: async function(req) {
    const url = await doSomeIO();
    return url;
}

plugins (Array)

const simpleRequestLogger = (proxyServer, options) => {
  proxyServer.on('proxyReq', (proxyReq, req, res) => {
    console.log(`[HPM] [${req.method}] ${req.url}`); // outputs: [HPM] GET /users
  });
},

const config = {
  target: `http://example.org`,
  changeOrigin: true,
  plugins: [simpleRequestLogger],
};

ejectPlugins (boolean) default: false

If you're not satisfied with the pre-configured plugins, you can eject them by configuring ejectPlugins: true.

NOTE: register your own error handlers to prevent server from crashing.

// eject default plugins and manually add them back

const {
  debugProxyErrorsPlugin, // subscribe to proxy errors to prevent server from crashing
  loggerPlugin, // log proxy events to a logger (ie. console)
  errorResponsePlugin, // return 5xx response on proxy error
  proxyEventsPlugin, // implements the "on:" option
} = require('http-proxy-middleware');

createProxyMiddleware({
  target: `http://example.org`,
  changeOrigin: true,
  ejectPlugins: true,
  plugins: [debugProxyErrorsPlugin, loggerPlugin, errorResponsePlugin, proxyEventsPlugin],
});

logger (Object)

Configure a logger to output information from http-proxy-middleware: ie. console, winston, pino, bunyan, log4js, etc...

Only info, warn, error are used internally for compatibility across different loggers.

If you use winston, make sure to enable interpolation: https://github.com/winstonjs/winston#string-interpolation

See also logger recipes (recipes/logger.md) for more details.

createProxyMiddleware({
  logger: console,
});

http-proxy events

Subscribe to http-proxy events with the on option:

createProxyMiddleware({
  target: 'http://www.example.org',
  on: {
    proxyReq: (proxyReq, req, res) => {
      /* handle proxyReq */
    },
    proxyRes: (proxyRes, req, res) => {
      /* handle proxyRes */
    },
    error: (err, req, res) => {
      /* handle error */
    },
  },
});

http-proxy options

The following options are provided by the underlying http-proxy library.

WebSocket

// verbose api
createProxyMiddleware({ pathFilter: '/', target: 'http://echo.websocket.org', ws: true });

External WebSocket upgrade

In the previous WebSocket examples, http-proxy-middleware relies on a initial http request in order to listen to the http upgrade event. If you need to proxy WebSockets without the initial http request, you can subscribe to the server's http upgrade event manually.

const wsProxy = createProxyMiddleware({ target: 'ws://echo.websocket.org', changeOrigin: true });

const app = express();
app.use(wsProxy);

const server = app.listen(3000);
server.on('upgrade', wsProxy.upgrade); // <-- subscribe to http 'upgrade'

Intercept and manipulate requests

Intercept requests from downstream by defining onProxyReq in createProxyMiddleware.

Currently the only pre-provided request interceptor is fixRequestBody, which is used to fix proxied POST requests when bodyParser is applied before this middleware.

Example:

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

const proxy = createProxyMiddleware({
  /**
   * Fix bodyParser
   **/
  on: {
    proxyReq: fixRequestBody,
  },
});

Intercept and manipulate responses

Intercept responses from upstream with responseInterceptor. (Make sure to set selfHandleResponse: true)

Responses which are compressed with brotli, gzip and deflate will be decompressed automatically. The response will be returned as buffer (docs) which you can manipulate.

With buffer, response manipulation is not limited to text responses (html/css/js, etc...); image manipulation will be possible too. (example)

NOTE: responseInterceptor disables streaming of target's response.

Example:

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

const proxy = createProxyMiddleware({
  /**
   * IMPORTANT: avoid res.end being called automatically
   **/
  selfHandleResponse: true, // res.end() will be called internally by responseInterceptor()

  /**
   * Intercept response and replace 'Hello' with 'Goodbye'
   **/
  on: {
    proxyRes: responseInterceptor(async (responseBuffer, proxyRes, req, res) => {
      const response = responseBuffer.toString('utf8'); // convert buffer to string
      return response.replace('Hello', 'Goodbye'); // manipulate response and return the result
    }),
  },
});

Check out interception recipes for more examples.

Node.js 17+: ECONNREFUSED issue with IPv6 and localhost (#705)

Node.js 17+ no longer prefers IPv4 over IPv6 for DNS lookups. E.g. It's not guaranteed that localhost will be resolved to 127.0.0.1 – it might just as well be ::1 (or some other IP address).

If your target server only accepts IPv4 connections, trying to proxy to localhost will fail if resolved to ::1 (IPv6).

Ways to solve it:

Note: There’s a thing called Happy Eyeballs which means connecting to both IPv4 and IPv6 in parallel, which Node.js doesn’t have, but explains why for example curl can connect.

Debugging

Configure the DEBUG environment variable enable debug logging.

See debug project for more options.

DEBUG=http-proxy-middleware* node server.js

$ http-proxy-middleware proxy created +0ms
$ http-proxy-middleware proxying request to target: 'http://www.example.org' +359ms

Working examples

View and play around with working examples.

Recipes

View the recipes for common use cases.

Compatible servers

http-proxy-middleware is compatible with the following servers:

Sample implementations can be found in the server recipes.

Tests

Run the test suite:

# install dependencies
$ yarn

# linting
$ yarn lint
$ yarn lint:fix

# building (compile typescript to js)
$ yarn build

# unit tests
$ yarn test

# code coverage
$ yarn cover

# check spelling mistakes
$ yarn spellcheck

Changelog

License

The MIT License (MIT)

Copyright (c) 2015-2022 Steven Chim