benchmark: Add net-pipe benchmark

Just sends a buffer to a server, which echoes it back, and then measures
the Gbits/second.  Very similar to throughput.js, but using a single
process, so that it's possible to dtrace and get the jsstack frames for
profile comparison.

benchmark/net-pipe.js

@@ -0,0 +1,95 @@
+// test the speed of .pipe() with sockets
+
+var net = require('net');
+var start;
+
+function Writer() {
+  this.start = null;
+  this.received = 0;
+  this.writable = true;
+  this.printStats = this.printStats.bind(this);
+  this.interval = setInterval(this.printStats, 1000);
+}
+
+Writer.prototype.write = function(chunk, encoding, cb) {
+  if (!this.start)
+    this.start = process.hrtime();
+
+  this.received += chunk.length;
+
+  if (typeof encoding === 'function')
+    encoding();
+  else if (typeof cb === 'function')
+    cb();
+
+  return true;
+};
+
+// doesn't matter, never emits anything.
+Writer.prototype.on = function() {};
+
+Writer.prototype.emit = function() {};
+
+var statCounter = 0;
+Writer.prototype.printStats = function() {
+  if (!this.start || !this.received)
+    return;
+  var elapsed = process.hrtime(this.start);
+  elapsed = elapsed[0] * 1E9 + elapsed[1];
+  var bits = this.received * 8;
+  var gbits = bits / (1024 * 1024 * 1024);
+  var rate = (gbits / elapsed * 1E9).toFixed(4);
+  console.log('%s Gbits/sec (%d bits / %d ns)', rate, bits, elapsed);
+
+  // reset to keep getting instant time.
+  this.start = process.hrtime();
+  this.received = 0;
+
+  // 100 seconds is enough time to get a few GC runs and stabilize.
+  if (statCounter++ === 100)
+    process.exit(0);
+};
+
+var len = process.env.LENGTH || 16 * 1024 * 1024;
+var chunk = new Buffer(len);
+for (var i = 0; i < len; i++) {
+  chunk[i] = i % 256;
+}
+
+function Reader() {
+  this.flow = this.flow.bind(this);
+  this.readable = true;
+}
+
+Reader.prototype.pipe = function(dest) {
+  this.dest = dest;
+  this.flow();
+  return dest;
+};
+
+Reader.prototype.flow = function() {
+  var dest = this.dest;
+  var res = dest.write(chunk);
+  if (!res)
+    dest.once('drain', this.flow);
+  else
+    process.nextTick(this.flow);
+};
+
+
+var reader = new Reader();
+var writer = new Writer();
+
+// the actual benchmark.
+var server = net.createServer(function(socket) {
+  socket.pipe(socket);
+});
+
+server.listen(1337, function() {
+  var socket = net.connect(1337);
+  socket.on('connect', function() {
+    reader.pipe(socket);
+    socket.pipe(writer);
+  });
+});
+