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, browser-sync and many more.

Powered by the popular Nodejitsu http-proxy.

TL;DR

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

var express = require('express');
var proxy = require('http-proxy-middleware');

var app = express();

app.use(
  '/api',
  proxy({ target: 'http://www.example.org', changeOrigin: true })
);
app.listen(3000);

// http://localhost: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.

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

Table of Contents

• Install
• Core concept
• Example
• Context matching
• Options
  • http-proxy-middleware options
  • http-proxy events
  • http-proxy options
• Shorthand
  • app.use(path, proxy)
• WebSocket
  • External WebSocket upgrade
• Working examples
• Recipes
• Compatible servers
• Tests
• Changelog
• License

Install

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

Core concept

Proxy middleware configuration.

proxy([context,] config)

var proxy = require('http-proxy-middleware');

var apiProxy = proxy('/api', { target: 'http://www.example.org' });
//                   \____/   \_____________________________/
//                     |                    |
//                   context             options

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

• context: Determine which requests should be proxied to the target host. (more on context matching)
• options.target: target host to proxy to. (protocol + host)

(full list of http-proxy-middleware configuration options)

proxy(uri [, config])

// shorthand syntax for the example above:
var apiProxy = proxy('http://www.example.org/api');

More about the shorthand configuration.

Example

An example with express server.

// include dependencies
var express = require('express');
var proxy = require('http-proxy-middleware');

// proxy middleware options
var options = {
  target: 'http://www.example.org', // target host
  changeOrigin: true, // needed for virtual hosted sites
  ws: true, // proxy websockets
  pathRewrite: {
    '^/api/old-path': '/api/new-path', // rewrite path
    '^/api/remove/path': '/path' // remove base path
  },
  router: {
    // when request.headers.host == 'dev.localhost:3000',
    // override target 'http://www.example.org' to 'http://localhost:8000'
    'dev.localhost:3000': 'http://localhost:8000'
  }
};

// create the proxy (without context)
var exampleProxy = proxy(options);

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

Context matching

Providing an alternative way to decide which requests should be proxied; In case you are not able to use the server's path parameter to mount the proxy or when you need more flexibility.

RFC 3986 path is used for context matching.

         foo://example.com:8042/over/there?name=ferret#nose
         \_/   \______________/\_________/ \_________/ \__/
          |           |            |            |        |
       scheme     authority       path        query   fragment

• path matching

  • proxy({...}) - matches any path, all requests will be proxied.
  • proxy('/', {...}) - matches any path, all requests will be proxied.
  • proxy('/api', {...}) - matches paths starting with /api

• multiple path matching

  • proxy(['/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.

  • proxy('**', {...}) matches any path, all requests will be proxied.
  • proxy('**/*.html', {...}) matches any path which ends with .html
  • proxy('/*.html', {...}) matches paths directly under path-absolute
  • proxy('/api/**/*.html', {...}) matches requests ending with .html in the path of /api
  • proxy(['/api/**', '/ajax/**'], {...}) combine multiple patterns
  • proxy(['/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}
   */
  var filter = function(pathname, req) {
    return pathname.match('^/api') && req.method === 'GET';
  };
  
  var apiProxy = proxy(filter, { target: 'http://www.example.org' });
  

Options

http-proxy-middleware options

• option.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') }
  

• option.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://localhost:8001',  // host only
      'staging.localhost:3000'     : 'http://localhost:8002',  // host only
      'localhost:3000/api'         : 'http://localhost:8003',  // host + path
      '/rest'                      : 'http://localhost:8004'   // path only
  }
  
  // Custom router function
  router: function(req) {
      return 'http://localhost:8004';
  }
  

• option.logLevel: string, ['debug', 'info', 'warn', 'error', 'silent']. Default: 'info'

• option.logProvider: function, modify or replace log provider. Default: console.

  // simple replace
  function logProvider(provider) {
    // replace the default console log provider.
    return require('winston');
  }
  

  // verbose replacement
  function logProvider(provider) {
    var logger = new (require('winston')).Logger();
  
    var myCustomProvider = {
      log: logger.log,
      debug: logger.debug,
      info: logger.info,
      warn: logger.warn,
      error: logger.error
    };
    return myCustomProvider;
  }
  

http-proxy events

Subscribe to http-proxy events:

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

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

• option.onProxyRes: 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.onProxyReq: 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.onProxyReqWs: 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.onOpen: function, subscribe to http-proxy's open event.

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

• option.onClose: 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://localhost:4003/',
      buffer: streamify(req.rawBody)
    }, next);
  
  };
  

Shorthand

Use the shorthand syntax when verbose configuration is not needed. The context and option.target will be automatically configured when shorthand is used. Options can still be used if needed.

proxy('http://www.example.org:8000/api');
// proxy('/api', {target: 'http://www.example.org:8000'});

proxy('http://www.example.org:8000/api/books/*/**.json');
// proxy('/api/books/*/**.json', {target: 'http://www.example.org:8000'});

proxy('http://www.example.org:8000/api', { changeOrigin: true });
// proxy('/api', {target: 'http://www.example.org:8000', changeOrigin: true});

app.use(path, proxy)

If you want to use the server's app.use path parameter to match requests; Create and mount the proxy without the http-proxy-middleware context parameter:

app.use(
  '/api',
  proxy({ target: 'http://www.example.org', changeOrigin: true })
);

app.use documentation:

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

WebSocket

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

// shorthand
proxy('http://echo.websocket.org', { ws: true });

// shorter shorthand
proxy('ws://echo.websocket.org');

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.

var wsProxy = proxy('ws://echo.websocket.org', { changeOrigin: true });

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

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

Working examples

View and play around with working examples.

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

Recipes

View the recipes for common use cases.

Compatible servers

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

• connect
• express
• browser-sync
• lite-server
• 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

Changelog

• View changelog

License

The MIT License (MIT)

Copyright (c) 2015-2019 Steven Chim

Changelog

v0.20.0

• fix(ws): concurrent websocket requests do not get upgraded (#335)
• chore: drop node 6 (BREAKING CHANGE)
• chore: update to micromatch@4 (BREAKING CHANGE)
• chore: update dev dependencies
• refactor: migrate to typescript (#328)
• feat(middleware): Promise / async support (#328)
• refactor: remove legacy options proxyHost and proxyTable (BREAKING CHANGE)