Express middleware to proxy request to another host and pass response back to original caller.

$ npm install express-http-proxy --save

proxy(host, options);

To proxy URLS starting with '/proxy' to the host 'www.google.com':

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

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

app.use('/proxy', proxy('www.google.com'));

Provide a proxyReqPathResolver function if you'd like to operate on the path before issuing the proxy request. Use a Promise for async operations.

app.use('/proxy', proxy('localhost:12345', {
  proxyReqPathResolver: function(req) {
    return require('url').parse(req.url).path;
  }
}));

Promise form

app.use('/proxy', proxy('localhost:12345', {
  proxyReqPathResolver: function(req) {
    return new Promise(function (resolve, reject) {
      setTimeout(function () {   // do asyncness
        resolve(fancyResults);
      }, 200);
    });
  }
}));

DEPRECATED. See proxyReqPathResolver

DEPRECATED. See proxyReqPathResolver

The filter option can be used to limit what requests are proxied. Return true to execute proxy.

For example, if you only want to proxy get request:

app.use('/proxy', proxy('www.google.com', {
  filter: function(req, res) {
     return req.method == 'GET';
  }
}));

You can modify the proxy's response before sending it to the client.

The intent is that this be used to modify the proxy response data only.

Note: The other arguments (proxyRes, userReq, userRes) are passed by reference, so you can currently exploit this to modify either response's headers, for instance, but this is not a reliable interface. I expect to close this exploit in a future release, while providing an additional hook for mutating the userRes before sending.

If your proxy response is gzipped, this program will automatically unzip it before passing to your function, then zip it back up before piping it to the user response. There is currently no way to short-circuit this behavior.

app.use('/proxy', proxy('www.google.com', {
  userResDecorator: function(proxyRes, proxyResData, userReq, userRes) {
    data = JSON.parse(proxyResData.toString('utf8'));
    data.newProperty = 'exciting data';
    return JSON.stringify(data);
  }
}));

app.use(proxy('httpbin.org', {
  userResDecorator: function(proxyRes, proxyResData) {
    return new Promise(function(resolve) {
      proxyResData.funkyMessage = 'oi io oo ii';
      setTimeout(function() {
        resolve(proxyResData);
      }, 200);
    });
  }
}));

This sets the body size limit (default: 1mb). If the body size is larger than the specified (or default) limit, a 413 Request Entity Too Large error will be returned. See bytes.js for a list of supported formats.

app.use('/proxy', proxy('www.google.com', {
  limit: '5mb'
}));

Defaults to true.

When true, the host argument will be parsed on first request, and memoized for subsequent requests.

When false, host argument will be parsed on each request.

E.g.,

  function coinToss() { return Math.random() > .5 }
  function getHost() { return coinToss() ? 'http://yahoo.com' : 'http://google.com' }

  app.use(proxy(getHost, {
    memoizeHost: false
  }))

In this example, when memoizeHost:false, the coinToss occurs on each request, and each request could get either value.

Conversely, When memoizeHost:true, the coinToss would occur on the first request, and all additional requests would return the value resolved on the first request.

REMOVED: See proxyReqOptDecorator and proxyReqBodyDecorator.

You can mutate the request options before sending the proxyRequest. proxyReqOpt represents the options argument passed to the (http|https).request module.

app.use('/proxy', proxy('www.google.com', {
  proxyReqOptDecorator: function(proxyReqOpts, srcReq) {
    // you can update headers
    proxyReqOpts.headers['Content-Type'] = 'text/html';
    // you can change the method
    proxyReqOpts.method = 'GET';
    // you could change the path
    proxyReqOpts.path = 'http://dev/null'
    return proxyReqOpts;
  }
}));

You can use a Promise for async style.

app.use('/proxy', proxy('www.google.com', {
  proxyReqOptDecorator: function(proxyReqOpts, srcReq) {
    return new Promise(function(resolve, reject) {
      proxyReqOpts.headers['Content-Type'] = 'text/html';
      resolve(proxyReqOpts);
    })
  }
}));

You can mutate the body content before sending the proxyRequest.

app.use('/proxy', proxy('www.google.com', {
  proxyReqBodyDecorator: function(bodyContent, srcReq) {
    return bodyContent.split('').reverse().join('');
  }
}));

You can use a Promise for async style.

app.use('/proxy', proxy('www.google.com', {
  proxyReqBodyDecorator: function(proxyReq, srcReq) {
    return new Promise(function(resolve, reject) {
      http.get('http://dev/null', function (err, res) {
        if (err) { reject(err); }
        resolve(res);
      });
    })
  }
}));

Normally, your proxy request will be made on the same protocol as the original request. If you'd like to force the proxy request to be https, use this option.

app.use('/proxy', proxy('www.google.com', {
  https: true
}));

You can copy the host HTTP header to the proxied express server using the preserveHostHdr option.

app.use('/proxy', proxy('www.google.com', {
  preserveHostHdr: true
}));

The parseReqBody option allows you to control parsing the request body. For example, disabling body parsing is useful for large uploads where it would be inefficient to hold the data in memory.

This defaults to true in order to preserve legacy behavior.

When false, no action will be taken on the body and accordingly req.body will no longer be set.

Note that setting this to false overrides reqAsBuffer and reqBodyEncoding below.

app.use('/proxy', proxy('www.google.com', {
  parseReqBody: false
}));

Note: this is an experimental feature. ymmv

The reqAsBuffer option allows you to ensure the req body is encoded as a Node Buffer when sending a proxied request. Any value for this is truthy.

This defaults to to false in order to preserve legacy behavior. Note that the value of reqBodyEnconding is used as the encoding when coercing strings (and stringified JSON) to Buffer.

Ignored if parseReqBody is set to false.

app.use('/proxy', proxy('www.google.com', {
  reqAsBuffer: true
}));

Encoding used to decode request body. Defaults to utf-8.

Use null to preserve as Buffer when proxied request body is a Buffer. (e.g image upload) Accept any values supported by raw-body.

The same encoding is used in the intercept method.

Ignored if parseReqBody is set to false.

app.use('/post', proxy('httpbin.org', {
  reqBodyEncoding: null
}));

By default, node does not express a timeout on connections.
Use timeout option to impose a specific timeout.
Timed-out requests will respond with 504 status code and a X-Timeout-Reason header.

app.use('/', proxy('httpbin.org', {
  timeout: 2000  // in milliseconds, two seconds
}));

The node-debug module is used to provide a trace debugging capability.

DEBUG=express-http-proxy npm run YOUR_PROGRAM
DEBUG=express-http-proxy npm run YOUR_PROGRAM  | grep 'express-http-proxy'   # to filter down to just these messages

Will trace the execution of the express-http-proxy module in order to aide debugging.

decorateRequest has been REMOVED, and will generate an error when called. See proxyReqOptDecorator and proxyReqBodyDecorator.

Resolution: Most authors will simply need to change the method name for their decorateRequest method; if author was decorating reqOpts and reqBody in the same method, this will need to be split up.

intercept has been REMOVED, and will generate an error when called. See userResDecorator.

Resolution: Most authors will simply need to change the method name from intercept to userResDecorator, and exit the method by returning the value, rather than passing it to a callback. E.g.:

Before:

app.use('/proxy', proxy('www.google.com', {
  intercept: function(proxyRes, proxyResData, userReq, userRes, cb) {
    data = JSON.parse(proxyResData.toString('utf8'));
    data.newProperty = 'exciting data';
    cb(null,  JSON.stringify(data));
  }
}));

Now:

app.use('/proxy', proxy('www.google.com', {
  userResDecorator: function(proxyRes, proxyResData, userReq, userRes) {
    data = JSON.parse(proxyResData.toString('utf8'));
    data.newProperty = 'exciting data';
    return JSON.stringify(data);
  }
}));

forwardPath and forwardPathAsync have been DEPRECATED and will generate a warning when called. See proxyReqPathResolver.

Resolution: Simple update the name of either forwardPath or forwardPathAsync to proxyReqPathResolver.

The library will automatically use https if the provided path has 'https://' or ':443'. You may also set option https to true to alwyas use https.

You can use proxyReqOptDecorator to ammend any auth or challenge headers required to succeed https.

You can use the ability to decorate the proxy request prior to sending. See proxyReqOptDecorators for more details.

app.use('/', proxy('internalhost.example.com', {
  proxyReqOptDecorators: function(proxyReqOpts, originalReq) {
    proxyReqOpts.ca =  [caCert, intermediaryCert]
    return proxyReqOpts;
  }
})

MIT