How to listen to node http-proxy traffic? - http

Question

I am using node-http-proxy. However, in addition to relaying HTTP requests, I also need to listen to the incoming and outgoing data.
Intercepting the response data is where I'm struggling. Node's ServerResponse object (and more generically the WritableStream interface) doesn't broadcast a 'data' event. http-proxy seems to create it's own internal request, which produces a ClientResponse object (which does broadcast the 'data' event) however this object is not exposed publically outside the proxy.
Any ideas how to solve this without monkey-patching node-http-proxy or creating a wrapper around the response object?

Answer 1

Related issue in issues of node-http-proxy on Github seems to imply this is not possible. For future attempts by others, here is how I hacked the issue:
you'll quickly find out that the proxy is only calling writeHead(), write() and end() methods of the res object
since res is already an EventEmitter, you can start emitting new custom events
listen for these new events to assemble the response data and then use it
var eventifyResponse = function(res) {
var methods = ['writeHead', 'write', 'end'];
methods.forEach(function(method){
var oldMethod = res[method]; // remember original method
res[method] = function() { // replace with a wrapper
oldMethod.apply(this, arguments); // call original method
arguments = Array.prototype.slice.call(arguments, 0);
arguments.unshift("method_" + method);
this.emit.apply(this, arguments); // broadcast the event
};
});
};
res = eventifyResponse(res), outputData = '';
res.on('method_writeHead', function(statusCode, headers) { saveHeaders(); });
res.on('method_write', function(data) { outputData += data; });
res.on('method_end', function(data) { use_data(outputData + data); });
proxy.proxyRequest(req, res, options)

Answer 2

This is a simple proxy server sniffing the traffic and writing it to console:
var http = require('http'),
httpProxy = require('http-proxy');
//
// Create a proxy server with custom application logic
//
var proxy = httpProxy.createProxyServer({});
// assign events
proxy.on('proxyRes', function (proxyRes, req, res) {
// collect response data
var proxyResData='';
proxyRes.on('data', function (chunk) {
proxyResData +=chunk;
});
proxyRes.on('end',function () {
var snifferData =
{
request:{
data:req.body,
headers:req.headers,
url:req.url,
method:req.method},
response:{
data:proxyResData,
headers:proxyRes.headers,
statusCode:proxyRes.statusCode}
};
console.log(snifferData);
});
// console.log('RAW Response from the target', JSON.stringify(proxyRes.headers, true, 2));
});
proxy.on('proxyReq', function(proxyReq, req, res, options) {
// collect request data
req.body='';
req.on('data', function (chunk) {
req.body +=chunk;
});
req.on('end', function () {
});
});
proxy.on('error',
function(err)
{
console.error(err);
});
// run the proxy server
var server = http.createServer(function(req, res) {
// every time a request comes proxy it:
proxy.web(req, res, {
target: 'http://localhost:4444'
});
});
console.log("listening on port 5556")
server.listen(5556);

Answer 3

I tried your hack but it didn't work for me. My use case is simple: I want to log the in- and outgoing traffic from an Android app to our staging server which is secured by basic auth.
https://github.com/greim/hoxy/
was the solution for me. My node-http-proxy always returned 500 (while the direct request to stage did not). Maybe the authorization headers would not be forwarded correctly or whatever.
Hoxy worked fine right from the start.
npm install hoxy [-g]
hoxy --port=<local-port> --stage=<your stage host>:<port>
As rules for logging I specified:
request: $aurl.log()
request: #log-headers()
request: $method.log()
request: $request-body.log()
response: $url.log()
response: $status-code.log()
response: $response-body.log()
Beware, this prints any binary content.