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'));
Streaming
Proxy requests and user responses are piped/streamed/chunked by default.
If you define a response modifier (userResDecorator, userResHeaderDecorator), or need to inspect the response before continuing (maybeSkipToNext), streaming is disabled, and the request and response are buffered. This can cause performance issues with large payloads.
Promises
Many function hooks support Promises.
If any Promise is rejected, next(x)
is called in the hosting application, where x
is whatever you pass to Promise.reject
;
e.g.
app.use(proxy('/reject-promise', {
proxyReqOptDecorator: function() {
return Promise.reject('An arbitrary rejection message.');
}
}));
eventually calls
next('An arbitrary rejection messasage');
Host
The first positional argument is for the proxy host; in many cases you will use a static string here, eg.
app.use('/', proxy('http://google.com'))
However, this argument can also be a function, and that function can be
memoized or computed on each request, based on the setting of
memoizeHost
.
function selectProxyHost() {
return (new Date() % 2) ? 'http://google.com' : 'http://altavista.com';
}
app.use('/', proxy(selectProxyHost));
Options
proxyReqPathResolver (supports Promises)
Note: In express-http-proxy
, the path
is considered the portion of
the url after the host, and including all query params. E.g. for the URL
http://smoogle.com/search/path?q=123
; the path is
/search/path?q=123
. Authors using this resolver must also handle the query parameter portion of the path.
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('localhost:12345', {
proxyReqPathResolver: function (req) {
var parts = req.url.split('?');
var queryString = parts[1];
var updatedPath = parts[0].replace(/test/, 'tent');
return updatedPath + (queryString ? '?' + queryString : '');
}
}));
Promise form
app.use('/proxy', proxy('localhost:12345', {
proxyReqPathResolver: function(req) {
return new Promise(function (resolve, reject) {
setTimeout(function () { // simulate async
var parts = req.url.split('?');
var queryString = parts[1];
var updatedPath = parts[0].replace(/test/, 'tent');
var resolvedPathValue = updatedPath + (queryString ? '?' + queryString : '');
resolve(resolvedPathValue);
}, 200);
});
}
}));
forwardPath
DEPRECATED. See proxyReqPathResolver
forwardPathAsync
DEPRECATED. See proxyReqPathResolver
filter
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';
}
}));
userResDecorator (was: intercept) (supports Promise)
You can modify the proxy's response before sending it to the client.
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);
});
}
}));
304 - Not Modified
When your proxied service returns 304, not modified, this step will be skipped, since there is no body to decorate.
exploiting references
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.
gzip responses
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.
limit
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'
}));
memoizeHost
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.
userResHeaderDecorator
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 villadora#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
Release | Notes |
---|---|
1.2.0 | Auto-stream when no decorations are made to req/res. Improved docs, fixes issues in maybeSkipToNexthandler, allow authors to manage error handling. |
1.1.0 | Add step to allow response headers to be modified. |
1.0.7 | Update dependencies. Improve docs on promise rejection. Fix promise rejection on body limit. Improve debug output. |
1.0.6 | Fixes preserveHostHdr not working, skip userResDecorator on 304, add maybeSkipToNext, test improvements and cleanup. |
1.0.5 | Minor documentation and test patches |
1.0.4 | Minor documentation, test, and package fixes |
1.0.3 | Fixes 'limit option is not taken into account |
1.0.2 | Minor docs corrections. |
1.0.1 | Minor docs adjustments. |
1.0.0 | Major revision. REMOVE decorateRequest, ADD proxyReqOptDecorator and proxyReqBodyDecorator. REMOVE intercept, ADD userResDecorator userResDecorator supports a Promise form for async operations. General cleanup of structure and application of hooks. Documentation improvements. Update all dependencies. Re-organize code as a series of workflow steps, each (potentially) supporting a promise, and creating a reusable pattern for future development. |
0.11.0 | Allow author to prevent host from being memoized between requests. General program cleanup. |
0.10.1 | Fixed issue where 'body encoding' was being incorrectly set to the character encoding. Dropped explicit support for node 0.10. Intercept can now deal with gziped responses. Author can now 'force https', even if the original request is over http. Do not call next after ECONNRESET catch. |
0.10.0 | Fix regression in forwardPath implementation. |
0.9.1 | Documentation updates. Set 'Accept-Encoding' header to match bodyEncoding. |
0.9.0 | Better handling for request body when body is JSON. |
0.8.0 | Features: add forwardPathAsync option Updates: modernize dependencies Fixes: Exceptions parsing proxied response causes error: Can't set headers after they are sent. (#111) If client request aborts, proxied request is aborted too (#107) |
0.7.4 | Move jscs to devDependencies to avoid conflict with nsp. |
0.7.3 | Adds a timeout option. Code organization and small bug fixes. |
0.7.2 | Collecting many minor documentation and test improvements. |
0.4.0 | Signature of intercept callback changed from function(data, req, res, callback) to function(rsp, data, req, res, callback) where rsp is the original response from the target |
Licence
MIT