http-proxy-middleware

What is http-proxy-middleware?

The http-proxy-middleware package is a Node.js package that provides an HTTP proxy as a middleware for use with Node.js applications, particularly in conjunction with frameworks like Express. It allows developers to easily set up proxy rules to forward requests to other servers, which is useful for tasks like API forwarding, logging, handling CORS, and more.

What are http-proxy-middleware's main functionalities?

Proxy requests

This feature allows you to proxy requests to another server. In this example, all requests to '/api' on the local server are forwarded to 'http://www.example.org'.

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

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

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

Path Rewriting

This feature allows you to rewrite the path of the request URL before it gets proxied. In this example, the path '/api' is removed before the request is forwarded to 'http://www.example.org'.

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

const apiProxy = createProxyMiddleware('/api', {
  target: 'http://www.example.org',
  pathRewrite: { '^/api': '' }
});

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

Custom Routing Logic

This feature allows you to implement custom routing logic. In this example, only GET requests to paths starting with '/api' are proxied to 'http://www.example.org'.

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

const apiProxy = createProxyMiddleware((pathname, req) => {
  return pathname.match('^/api') && req.method === 'GET';
}, { target: 'http://www.example.org' });

app.use(apiProxy);

Handling WebSockets

This feature allows you to proxy WebSocket connections. In this example, WebSocket connections to '/socket' are proxied to 'ws://www.example.org'.

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

const wsProxy = createProxyMiddleware('/socket', {
  target: 'ws://www.example.org',
  ws: true
});

app.use('/socket', wsProxy);

Other packages similar to http-proxy-middleware

express-http-proxy

express-http-proxy is similar to http-proxy-middleware but is specifically designed for use with Express. It offers similar features for proxying HTTP requests but may have different configuration options and middleware setup.

node-http-proxy

node-http-proxy is a full-featured HTTP proxy library for Node.js, which http-proxy-middleware is built upon. It provides more low-level control over proxying but requires more setup compared to the convenience middleware layer provided by http-proxy-middleware.

redbird

Redbird is a reverse proxy library for Node.js with built-in support for clustering, HTTP2, LetsEncrypt, and more. It is more feature-rich and suitable for more complex proxying needs compared to http-proxy-middleware, which is simpler and more focused on middleware use cases.

README

http-proxy-middleware

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.

⚠️ 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:

• https://github.com/chimurai/http-proxy-middleware/tree/v2.0.4#readme
• https://github.com/chimurai/http-proxy-middleware/tree/v0.21.0#readme

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
• Basic usage
• Express Server Example
  • app.use(path, proxy)
• Options
  • pathFilter (string, []string, glob, []glob, function)
  • pathRewrite (object/function)
  • router (object/function)
  • plugins (Array)
  • ejectPlugins (boolean) default: false
  • logger (Object)
• http-proxy events
• http-proxy options
• WebSocket
  • External WebSocket upgrade
• Intercept and manipulate requests
• Intercept and manipulate responses
• Node.js 17+: ECONNREFUSED issue with IPv6 and localhost (#705)
• Debugging
• Working examples
• Recipes
• Compatible servers
• Tests
• Changelog
• License

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.

• options.target: target host to proxy to. (protocol + host)

• options.changeOrigin: for virtual hosted sites

• see full list of http-proxy-middleware configuration options

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:

• express: http://expressjs.com/en/4x/api.html#app.use
• connect: https://github.com/senchalabs/connect#mount-middleware
• polka: https://github.com/lukeed/polka#usebase-fn

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.

• path matching

  • createProxyMiddleware({...}) - matches any path, all requests will be proxied when pathFilter is not configured.
  • createProxyMiddleware({ pathFilter: '/api', ...}) - matches paths starting with /api

• multiple path matching

  • createProxyMiddleware({ pathFilter: ['/api', '/ajax', '/someotherpath'], ...})

• wildcard path matching

  For fine-grained control you can use wildcard matching. Glob pattern matching is done by micromatch. Visit micromatch or glob for more globbing examples.

  • createProxyMiddleware({ pathFilter: '**', ...}) matches any path, all requests will be proxied.
  • createProxyMiddleware({ pathFilter: '**/*.html', ...}) matches any path which ends with .html
  • createProxyMiddleware({ pathFilter: '/*.html', ...}) matches paths directly under path-absolute
  • createProxyMiddleware({ pathFilter: '/api/**/*.html', ...}) matches requests ending with .html in the path of /api
  • createProxyMiddleware({ pathFilter: ['/api/**', '/ajax/**'], ...}) combine multiple patterns
  • createProxyMiddleware({ pathFilter: ['/api/**', '!**/bad.json'], ...}) exclusion

  Note: In multiple path matching, you cannot use string paths and wildcard paths together.

• custom matching

  For full control you can provide a custom function to determine which requests should be proxied or not.

  /**
   * @return {Boolean}
   */
  const pathFilter = function (path, req) {
    return path.match('^/api') && req.method === 'GET';
  };
  
  const apiProxy = createProxyMiddleware({
    target: 'http://www.example.org',
    pathFilter: pathFilter,
  });
  

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 */
    },
  },
});

• option.on.error: function, subscribe to http-proxy's error event for custom error handling.

  function onError(err, req, res, target) {
    res.writeHead(500, {
      'Content-Type': 'text/plain',
    });
    res.end('Something went wrong. And we are reporting a custom error message.');
  }
  

• option.on.proxyRes: function, subscribe to http-proxy's proxyRes event.

  function onProxyRes(proxyRes, req, res) {
    proxyRes.headers['x-added'] = 'foobar'; // add new header to response
    delete proxyRes.headers['x-removed']; // remove header from response
  }
  

• option.on.proxyReq: function, subscribe to http-proxy's proxyReq event.

  function onProxyReq(proxyReq, req, res) {
    // add custom header to request
    proxyReq.setHeader('x-added', 'foobar');
    // or log the req
  }
  

• option.on.proxyReqWs: function, subscribe to http-proxy's proxyReqWs event.

  function onProxyReqWs(proxyReq, req, socket, options, head) {
    // add custom header
    proxyReq.setHeader('X-Special-Proxy-Header', 'foobar');
  }
  

• option.on.open: function, subscribe to http-proxy's open event.

  function onOpen(proxySocket) {
    // listen for messages coming FROM the target here
    proxySocket.on('data', hybridParseAndLogMessage);
  }
  

• option.on.close: function, subscribe to http-proxy's close event.

  function onClose(res, socket, head) {
    // view disconnected websocket connections
    console.log('Client disconnected');
  }
  

http-proxy options

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

• option.target: url string to be parsed with the url module

• option.forward: url string to be parsed with the url module

• option.agent: object to be passed to http(s).request (see Node's https agent and http agent objects)

• option.ssl: object to be passed to https.createServer()

• option.ws: true/false: if you want to proxy websockets

• option.xfwd: true/false, adds x-forward headers

• option.secure: true/false, if you want to verify the SSL Certs

• option.toProxy: true/false, passes the absolute URL as the path (useful for proxying to proxies)

• option.prependPath: true/false, Default: true - specify whether you want to prepend the target's path to the proxy path

• option.ignorePath: true/false, Default: false - specify whether you want to ignore the proxy path of the incoming request (note: you will have to append / manually if required).

• option.localAddress : Local interface string to bind for outgoing connections

• option.changeOrigin: true/false, Default: false - changes the origin of the host header to the target URL

• option.preserveHeaderKeyCase: true/false, Default: false - specify whether you want to keep letter case of response header key

• option.auth : Basic authentication i.e. 'user:password' to compute an Authorization header.

• option.hostRewrite: rewrites the location hostname on (301/302/307/308) redirects.

• option.autoRewrite: rewrites the location host/port on (301/302/307/308) redirects based on requested host/port. Default: false.

• option.protocolRewrite: rewrites the location protocol on (301/302/307/308) redirects to 'http' or 'https'. Default: null.

• option.cookieDomainRewrite: rewrites domain of set-cookie headers. Possible values:

  • false (default): disable cookie rewriting

  • String: new domain, for example cookieDomainRewrite: "new.domain". To remove the domain, use cookieDomainRewrite: "".

  • Object: mapping of domains to new domains, use "*" to match all domains.
    For example keep one domain unchanged, rewrite one domain and remove other domains:

    cookieDomainRewrite: {
      "unchanged.domain": "unchanged.domain",
      "old.domain": "new.domain",
      "*": ""
    }
    

• option.cookiePathRewrite: rewrites path of set-cookie headers. Possible values:

  • false (default): disable cookie rewriting

  • String: new path, for example cookiePathRewrite: "/newPath/". To remove the path, use cookiePathRewrite: "". To set path to root use cookiePathRewrite: "/".

  • Object: mapping of paths to new paths, use "*" to match all paths. For example, to keep one path unchanged, rewrite one path and remove other paths:

    cookiePathRewrite: {
      "/unchanged.path/": "/unchanged.path/",
      "/old.path/": "/new.path/",
      "*": ""
    }
    

• option.headers: object, adds request headers. (Example: {host:'www.example.org'})

• option.proxyTimeout: timeout (in millis) when proxy receives no response from target

• option.timeout: timeout (in millis) for incoming requests

• option.followRedirects: true/false, Default: false - specify whether you want to follow redirects

• option.selfHandleResponse true/false, if set to true, none of the webOutgoing passes are called and it's your responsibility to appropriately return the response by listening and acting on the proxyRes event

• option.buffer: stream of data to send as the request body. Maybe you have some middleware that consumes the request stream before proxying it on e.g. If you read the body of a request into a field called 'req.rawbody' you could restream this field in the buffer option:

  'use strict';
  
  const streamify = require('stream-array');
  const HttpProxy = require('http-proxy');
  const proxy = new HttpProxy();
  
  module.exports = (req, res, next) => {
    proxy.web(
      req,
      res,
      {
        target: 'http://127.0.0.1:4003/',
        buffer: streamify(req.rawBody),
      },
      next,
    );
  };
  

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:

• Change target: "http://localhost" to target: "http://127.0.0.1" (IPv4).
• Change the target server to (also) accept IPv6 connections.
• Add this flag when running node: node index.js --dns-result-order=ipv4first. (Not recommended.)

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.

• Browser-Sync (example source)
• express (example source)
• connect (example source)
• WebSocket (example source)
• Response Manipulation (example source)

Recipes

View the recipes for common use cases.

Compatible servers

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

• connect
• express
• next.js
• fastify
• browser-sync
• lite-server
• polka
• grunt-contrib-connect
• grunt-browser-sync
• gulp-connect
• gulp-webserver

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

• View changelog

License

The MIT License (MIT)

Copyright (c) 2015-2024 Steven Chim