How to get response time of each proxy-request done by node-http-proxy?

Question

i want to compute the response-time for each proxy-request, done by node-http-proxy, like this:

var httpProxy = require('http-proxy');
var proxy = httpProxy.createProxyServer();

require('http').createServer(function(req, res) {
   // start-time for one request
   proxy.web(req, res, { target: 'localhost:80' });
}).listen(3000);

proxy.on('proxyRes', function (res) {
  // end-time for one request to calculate the time
  console.log('RAW Response from the target', JSON.stringify(res.headers, true, 2));
});

so i want to get the time-difference between the start-time and the ent-time. i am be able to catch the proxyRes event, but how to match the proxy-response to the right client-request?

update: i tried the following:

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

var proxy = new httpProxy.createProxyServer({
    target: {
        host: 'localhost',
        port: 80
    }
});

var start_time = 0;
var proxyServer = http.createServer(function (req, res) {


    start_time = new Date().getTime();

    proxy.web(req, res);

    res.on('finish', function() {
        console.log("The request was proxied in " + (new Date().getTime() - start_time) + "ms");
    });
});

proxyServer.listen(3000);

// Proxy-Target server
var n = 0; sleep = 0;
http.createServer(function (req, res) {

    n++;

    var start_time = new Date().getTime();

    res.writeHead(200, {'Content-Type': 'text/plain'});

    if (n % 2 == 0){
        sleep = 2000;
    } else {
        sleep = 5000;
    }

    setTimeout(function(){
        res.end("...");
    }, sleep);

    res.on('finish', function(d) {
        var diff_time = new Date().getTime() - start_time;
        console.log("The request was processed in " + (new Date().getTime() - start_time) + "ms");
    });

}).listen(80);

so, the time of the target-server is measured correctly, cause one request could last either 2 oder 5 seconds, but the proxy measures sometimes response-times of only some milli-seconds. I tried it by using apache-bench like: ab -n 10 -c 3 http://localhost:3000/ and the result of the console:

The request was processed in 2007ms
The request was proxied in 2017ms
The request was processed in 2003ms
The request was proxied in 2006ms
The request was processed in 5002ms
The request was processed in 5001ms
The request was proxied in 980ms
The request was proxied in 981ms
The request was processed in 2002ms
The request was proxied in 2006ms
The request was processed in 2002ms
The request was proxied in 2005ms
The request was processed in 5000ms
The request was proxied in 8ms
The request was processed in 5000ms
The request was proxied in 982ms
The request was processed in 2001ms
The request was proxied in 2005ms
The request was processed in 5002ms
The request was proxied in 4998ms

Answer 1

now it works, got the key hint on the nodejs google-gloup, the cope of start_time was not set locally, so here is the working code:

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

var proxy = new httpProxy.createProxyServer({});

// before: var start_time = 0;
var proxyServer = http.createServer(function (req, res) {

    // now
    var start_time = new Date().getTime();

    proxy.web(req, res, { target: 'http://localhost:80' });

    res.on('finish', function() {
       console.log("The request was proxied in " + (new Date().getTime() - start_time) + "ms");
    });
});
proxyServer.listen(3000);

Answer 2

(untested, but let's see if this works)

var httpProxy = require('http-proxy');
var proxy = httpProxy.createProxyServer();
var startTime = 0;
var endTime = 0;

require('http').createServer(function(req, res) {
   // start-time for one request
   startTime = new Date().getTime();
   proxy.web(req, res, { 
        target: 'localhost:80' 
   });
}).listen(3000);

proxy.on('proxyRes', function (res) {
  // end-time for one request to calculate the time
  endTime = new Date().getTime();
  console.log(endTime - startTime);
  console.log('RAW Response from the target', JSON.stringify(res.headers, true, 2));
});