http-array-of-buffers.js

var http = require('http');

var data = [];
var length;

var req = http.request('http://mail.yandex.ru', function(res) {
    res.on('data', function (chunk) {
        data.push(chunk);
    });

    res.on('end', function() {
        length = data.length;
        startServer();
    });
});

req.end();

function startServer() {
    http.createServer(function(req, res) {
        res.writeHead( 200, { 'Content-Type': 'text/html' } );
        for (var i = 0; i < length; i++) {
            res.write( data[i] );
        }
        res.end();
    }).listen(9000, '127.0.0.1');
}

http-buffer.js

var http = require('http');

var length = 0;
var data = [];
var buffer;

var req = http.request('http://mail.yandex.ru', function(res) {
    res.on('data', function (chunk) {
        length += chunk.length;
        data.push(chunk);
    });

    res.on('end', function() {
        buffer = Buffer.concat(data, length);
        startServer();
    });
});

req.end();

function startServer() {
    http.createServer(function(req, res) {
        res.writeHead( 200, { 'Content-Type': 'text/html' } );
        res.end(buffer);
    }).listen(9000, '127.0.0.1');
}

http-string.js

var http = require('http');

var result = '';

var req = http.request('http://mail.yandex.ru', function(res) {
    res.on('data', function (chunk) {
        result += chunk;
    });

    res.on('end', startServer);
});

req.end();

function startServer() {
    http.createServer(function(req, res) {
        res.writeHead( 200, { 'Content-Type': 'text/html' } );
        res.end(result);
    }).listen(9000, '127.0.0.1');
}

Да, тестил тупо через ab:

ab -n 10000 -c 100 http://127.0.0.1:9000/