index.js

var Thin = require('./lib/thin.js');
var winston = require('winston');
var log = new (winston.Logger)({
  transports: [ new winston.transports.Console() ]
});
var es = require('event-stream');
var proxy = new Thin();

proxy.use(function(req, res, next) {
  console.log(req.headers);
  req.pipe(es.map(function(data, callback) {
    console.log(data);
    callback(null, data);
  }));
  next();
});

proxy.listen(8080, 'localhost', function(err) {
  // .. error handling code ..
});

with_proxy

$ curl --proxy 'http://localhost:8080' httpbin.org/post -F 'hi=there'                   52 ↵
{
  "args": {}, 
  "data": "", 
  "files": {}, 
  "form": {}, 
  "headers": {
    "Connect-Time": "1", 
    "Connection": "close", 
    "Host": "httpbin.org", 
    "Total-Route-Time": "0", 
    "Transfer-Encoding": "chunked", 
    "Via": "1.1 vegur", 
    "X-Request-Id": "0e16080e-c1c6-47dd-8af0-d7da8633fd33"
  }, 
  "json": null, 
  "origin": "xx.xxx.xxx.xx", 
  "url": "http://httpbin.org/post"
}

without_proxy

$ curl  httpbin.org/post -F 'hi=there' 
{
  "args": {}, 
  "data": "", 
  "files": {}, 
  "form": {
    "hi": "there"
  }, 
  "headers": {
    "Accept": "*/*", 
    "Connect-Time": "1", 
    "Connection": "close", 
    "Content-Length": "142", 
    "Content-Type": "multipart/form-data; boundary=------------------------830400dff393ba3b", 
    "Host": "httpbin.org", 
    "Total-Route-Time": "0", 
    "User-Agent": "curl/7.39.0", 
    "Via": "1.1 vegur", 
    "X-Request-Id": "e5d4d482-2bfc-4c04-a34d-2c1b3f37eaac"
  }, 
  "json": null, 
  "origin": "xx.xxx.xxx.xx", 
  "url": "http://httpbin.org/post"
}