express-http-proxy

express-http-proxy

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

Install

$ npm install express-http-proxy --save

Usage

proxy(host, options);

Example:

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'));

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The proxy middleware:

• proxies request to your server to an arbitrary server, and
• provide hooks to decorate and filter requests to the proxy target, and
• provide hooks you to decorate and filter proxy responses before returning them to the client.

…

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.

userResHeaderDecorator

When a userResHeaderDecorator is defined, the return of this method will replace (rather than be merged on to) the headers for userRes.

Note that by default, headers from the PROXY response CLOBBER all headers that may have previously been set on the userResponse. Authors have the option of constructing any combination of proxyRes and userRes headers in the userResHeaderDecorator. Check the tests for this method for examples.

app.use('/proxy', proxy('www.google.com', {
  userResHeaderDecorator(headers, userReq, userRes, proxyReq, proxyRes) {
    // recieves an Object of headers, returns an Object of headers.
    return headers;
  }
}));

decorateRequest

REMOVED: See proxyReqOptDecorator and proxyReqBodyDecorator.

skipToNextHandlerFilter(supports Promise form)

(experimental: this interface may change in upcoming versions)

Allows you to inspect the proxy response, and decide if you want to continue processing (via express-http-proxy) or call next() to return control to express.

app.use('/proxy', proxy('www.google.com', {
  skipToNextHandlerFilter: function(proxyRes) {
    return proxyRes.statusCode === 404;
  }
}));

proxyErrorHandler

By default, express-http-proxy will pass any errors except ECONNRESET to next, so that your application can handle or react to them, or just drop through to your default error handling. ECONNRESET errors are immediately returned to the user for historical reasons.

If you would like to modify this behavior, you can provide your own proxyErrorHandler.

// Example of skipping all error handling.

app.use(proxy('localhost:12346', {
  proxyErrorHandler: function(err, res, next) {
    next(err);
  }
}));

// Example of rolling your own

app.use(proxy('localhost:12346', {
  proxyErrorHandler: function(err, res, next) {
    switch (err && err.code) {
      case 'ECONNRESET':    { return res.status(405).send('504 became 405'); }
      case 'ECONNREFUSED':  { return res.status(200).send('gotcher back'); }
      default:              { next(err); }
    }
}}));

proxyReqOptDecorator (supports Promise form)

You can override most request options before issuing the proxyRequest. proxyReqOpt represents the options argument passed to the (http|https).request module.

NOTE: req.path cannot be changed via this method; use proxyReqPathResolver instead. (see https://github.com/villadora/express-http-proxy/issues/243)

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';
    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);
    })
  }
}));

proxyReqBodyDecorator (supports Promise form)

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);
      });
    })
  }
}));

https

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

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

preserveHostHdr

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
}));

parseReqBody

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.

Note: this setting is required for binary uploads. A future version of this library may handle this for you.

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
}));

reqAsBuffer

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
}));

reqBodyEncoding

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
}));

timeout

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
}));

Trace debugging

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.

Upgrade to 1.0, transition guide and breaking changes

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.

When errors occur on your proxy server

When your proxy server responds with an error, express-http-proxy returns a response with the same status code. See test/catchingErrors for syntax details.

When your proxy server times out, express-http-proxy will continue to wait indefinitely for a response, unless you define a timeout as described above.

Questions

Q: Does it support https proxy?

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

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

Q: How can I support non-standard certificate chains?

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

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

Q: How to ignore self-signed certificates ?

You can set the rejectUnauthorized value in proxy request options prior to sending. See proxyReqOptDecorator for more details.

app.use('/', proxy('internalhost.example.com', {
  proxyReqOptDecorator: function(proxyReqOpts, originalReq) {
    proxyReqOpts.rejectUnauthorized = false
    return proxyReqOpts;
  }
}))

Release Notes