Finish adding compression to pipeline (see note)

It's 3 AM and I know theres a pretty big chance none of this code makes sense.
Everything needs to be tested, as well as I need to figure out if encryption
comes after compression or not.

lib/client.js

@@ -4,6 +4,7 @@ var net = require('net')
   , protocol = require('./protocol')
   , dns = require('dns')
   , createPacketBuffer = protocol.createPacketBuffer
+  , compressPacketBuffer = protocol.compressPacketBuffer
   , parsePacket = protocol.parsePacket
   , states = protocol.states
   , debug = protocol.debug
@@ -154,18 +155,38 @@ Client.prototype.write = function(packetId, params) {
     packetId = packetId[1];
   }
 
-  var buffer = createPacketBuffer(packetId, this.state, params, this.isServer);
+  // TODO: Which comes first, encryption or compression?
+
+  var finishWriting = function(buffer) {
       debug("writing packetId " + packetId + " (0x" + packetId.toString(16) + ")");
       debug(params);
       var out = this.encryptionEnabled ? new Buffer(this.cipher.update(buffer), 'binary') : buffer;
       this.socket.write(out);
       return true;
+  }
+
+  var buffer = createPacketBuffer(packetId, this.state, params, this.isServer);
+  if(this.compressionThreshold != -1 && buffer.length > this.compressionThreshold) {
+      compressPacketBuffer(buffer, finishWriting);
+  } else {
+      finishWriting(buffer);
+  }
+
 };
 
 Client.prototype.writeRaw = function(buffer, shouldEncrypt) {
     if (shouldEncrypt === null) {
         shouldEncrypt = true;
     }
+
+    var finishWriting = function(buffer) {
         var out = (shouldEncrypt && this.encryptionEnabled) ? new Buffer(this.cipher.update(buffer), 'binary') : buffer;
         this.socket.write(out);
     };
+
+    if(this.compressionThreshold != -1 && buffer.length > this.compressionThreshold) {
+        compressPacketBuffer(buffer, finishWriting);
+    } else {
+        finishWriting(buffer);
+    }
+};

lib/protocol.js

@@ -1,5 +1,6 @@
 var assert = require('assert');
 var util = require('util');
+var zlib = require('zlib');
 
 var STRING_MAX_LENGTH = 240;
 var SRV_STRING_MAX_LENGTH = 32767;
@@ -1289,6 +1290,19 @@ function createPacketBuffer(packetId, state, params, isServer) {
   return buffer;
 }
 
+function compressPacketBuffer(buffer, callback) {
+    var dataLength   = buffer.length;
+    var packetLength = dataLength + sizeOfVarInt(dataLength);
+    var data = zlib.deflateRaw(buffer, function(compressedBuffer) {
+        var size = sizeOfVarInt(packetLength) + sizeOfVarInt(packetLength) + compressedBuffer.length;
+        var packetBuffer = new Buffer(size);
+        var offset = writeVarInt(packetLength, packetBuffer, 0);
+        offset = writeVarInt(dataLength, packetBuffer, offset);
+        writeVarInt(compressedBuffer, packetBuffer, offset);
+        callback(packetBuffer);
+    });
+}
+
 function parsePacket(buffer, state, isServer, packetsToParse) {
   if (state == null) state = states.PLAY;
   var cursor = 0;
@@ -1365,6 +1379,7 @@ module.exports = {
   sessionVersion: 13,
   parsePacket: parsePacket,
   createPacketBuffer: createPacketBuffer,
+  compressPacketBuffer: compressPacketBuffer,
   STRING_MAX_LENGTH: STRING_MAX_LENGTH,
   packetIds: packetIds,
   packetNames: packetNames,