node.js duplex proxy for load testing with production traffic

proxyproxy.js

/* A node.js proxy that forwards requests to two upstream servers, but only
 * returns the response from one.  Might be useful for load testing with
 * production traffic.
 */
var http = require('http');

/* The request is forwarded to both proxies, but only the response from proxy1
 * is returned.
 */
var proxy1 = [8001, 'localhost'],
    proxy2 = [8002, 'localhost'];

var server = function(request, response) {
    var p1 = http.createClient(proxy1[0], proxy1[1]),
        p2 = http.createClient(proxy2[0], proxy2[1]),
        r1 = p1.request(request.method, request.url, request.headers),
        r2 = p2.request(request.method, request.url, request.headers),
        start = new(Date), p1Time, p2Time;

    /* Write request data to both proxies. */
    request.on('data', function(chunk) {
        r1.write(chunk, 'binary');
        r2.write(chunk, 'binary');
    });

    /* Send the primary response back to the client. */
    r1.on('response', function(proxy_response) {
        response.writeHead(proxy_response.statusCode, proxy_response.headers);
        proxy_response.on('data', function(chunk) {
            response.write(chunk, 'binary');
        });
        proxy_response.on('end', function() {
            response.end();
            p1Time = new(Date) - start;
            status();
        });
    });

    /* Only track the timing for the duplicate request. */
    r2.on('response', function(proxy_response) {
        proxy_response.on('end', function() {
            p2Time = new(Date) - start;
            status();
        });
    });

    /* Log response times once both requests are complete. */
    var status = function() {
        if (p1Time && p2Time) {
            console.log(request.method + ' "' + request.url + '" ' +
                        'p1: ' + p1Time / 1000 + '; p2: ' + p2Time / 1000);
        }
    }

    /* 500 response if something goes wrong with the proxy1. */
    var error = function(err) {
        response.writeHead(500, {'content-type': 'text/plain'});
        if (request.method !== 'HEAD') {
            response.write('Internal Server Error');
        }
        response.end();
    };

    /* Log issues with the proxy2. */
    var busted = function(err) {
        console.log('Error in proxy 2:\n' + JSON.stringify(err));
    };

    /* Oh joy, error handling. */
    p1.on('error', error), p2.on('error', busted);
    r1.on('error', error), r2.on('error', busted);
    r1.end(), r2.end();
};

http.createServer(server).listen(8000);
console.log('running on :8000');