diff --git a/lib/protocol.js b/lib/protocol.js
index 4d86f5e..a349b3b 100644
--- a/lib/protocol.js
+++ b/lib/protocol.js
@@ -633,20 +633,21 @@ var packetStates = {toClient: {}, toServer: {}};
 
 
 var types = {
-  'int': [readInt, writeInt, 4],
-  'short': [readShort, writeShort, 2],
-  'ushort': [readUShort, writeUShort, 2],
   'byte': [readByte, writeByte, 1],
   'ubyte': [readUByte, writeUByte, 1],
-  'string': [readString, writeString, sizeOfString],
-  'ustring': [readString, writeString, sizeOfUString],
-  'byteArray16': [readByteArray16, writeByteArray16, sizeOfByteArray16],
-  'bool': [readBool, writeBool, 1],
-  'double': [readDouble, writeDouble, 8],
-  'float': [readFloat, writeFloat, 4],
-  'slot': [readSlot, writeSlot, sizeOfSlot],
+  'short': [readShort, writeShort, 2],
+  'ushort': [readUShort, writeUShort, 2],
+  'int': [readInt, writeInt, 4],
   'long': [readLong, writeLong, 8],
   'varint': [readVarInt, writeVarInt, sizeOfVarInt],
+  'float': [readFloat, writeFloat, 4],
+  'double': [readDouble, writeDouble, 8],
+  'bool': [readBool, writeBool, 1],
+  'string': [readString, writeString, sizeOfString],
+  'ustring': [readString, writeString, sizeOfUString], // TODO : remove ustring
+  // TODO : remove type-specific, replace with generic containers and arrays.
+  'slot': [readSlot, writeSlot, sizeOfSlot],
+  'byteArray16': [readByteArray16, writeByteArray16, sizeOfByteArray16],
   'ascii': [readAscii, writeAscii, sizeOfAscii],
   'entityMetadata': [readEntityMetadata, writeEntityMetadata, sizeOfEntityMetadata],
   'byteArray32': [readByteArray32, writeByteArray32, sizeOfByteArray32],
@@ -728,7 +729,7 @@ function sizeOfEntityMetadata(value) {
   var item;
   for (var i = 0; i < value.length; ++i) {
     item = value[i];
-    size += sizeOf(item.type, item.value);
+    size += sizeOf(item.value, { type: item.type }, {});
   }
   return size;
 }
@@ -1599,6 +1600,50 @@ function writeMatchArray(value, buffer, offset) {
     return offset;
 }
 
+function read(buffer, cursor, fieldInfo, rootNodes) {
+  if (fieldInfo.condition && !fieldInfo.condition(rootNodes)) {
+    return null;
+  }
+  var type = types[fieldInfo.type];
+  if (!type) {
+    return {
+      error: new Error("missing data type: " + fieldInfo.type)
+    };
+  }
+  var readResults = type[0](buffer, cursor, fieldInfo.typeArgs, rootNodes);
+  if (readResults.error) return { error: readResults.error };
+
+  return readResults;
+}
+
+function write(value, buffer, offset, fieldInfo, rootNodes) {
+  if (fieldInfo.condition && !fieldInfo.condition(rootNodes)) {
+    return null;
+  }
+  var type = types[fieldInfo.type];
+  if (!type) {
+    return {
+      error: new Error("missing data type: " + fieldInfo.type)
+    };
+  }
+  return type[1](value, buffer, offset, fieldInfo.typeArgs);
+}
+
+function sizeOf(value, fieldInfo, rootNodes) {
+  if (fieldInfo.condition && !fieldInfo.condition(rootNodes)) {
+    return 0;
+  }
+  var type = types[fieldInfo.type];
+  if (!type) {
+    throw new Error("missing data type: " + fieldInfo.type);
+  }
+  if (typeof type[2] === 'function') {
+    return type[2](value, fieldInfo.typeArgs);
+  } else {
+    return type[2];
+  }
+}
+
 function get(packetId, state, toServer) {
   var direction = toServer ? "toServer" : "toClient";
   var packetInfo = packetFields[state][direction][packetId];
@@ -1608,17 +1653,6 @@ function get(packetId, state, toServer) {
   return packetInfo;
 }
 
-function sizeOf(type, value) {
-  var dataType = types[type];
-  assert.ok(dataType, "unknown data type " + type);
-  var size = dataType[2];
-  if (typeof size === "function") {
-    return size(value);
-  } else {
-    return size;
-  }
-}
-
 function createPacketBuffer(packetId, state, params, isServer) {
   var length = 0;
   if (typeof packetId === 'string' && typeof state !== 'string' && !params) {
@@ -1632,10 +1666,7 @@ function createPacketBuffer(packetId, state, params, isServer) {
   var packet = get(packetId, state, !isServer);
   assert.notEqual(packet, null);
   packet.forEach(function(fieldInfo) {
-    var condition = fieldInfo.condition;
-    if (typeof condition != "undefined" && !condition(params))
-      return;
-    length += sizeOf(fieldInfo.type, params[fieldInfo.name]);
+    length += sizeOf(params[fieldInfo.name], fieldInfo, params);
   });
   length += sizeOfVarInt(packetId);
   var size = length + sizeOfVarInt(length);
@@ -1643,32 +1674,14 @@ function createPacketBuffer(packetId, state, params, isServer) {
   var offset = writeVarInt(length, buffer, 0);
   offset = writeVarInt(packetId, buffer, offset);
   packet.forEach(function(fieldInfo) {
-    var condition = fieldInfo.condition;
-    if (typeof condition != "undefined" && !condition(params))
-      return;
-    var write = types[fieldInfo.type][1];
     var value = params[fieldInfo.name];
-    if(typeof value === "undefined") value = 0;
-    offset = write(value, buffer, offset);
+    if(typeof value === "undefined") value = 0; // TODO : Why ?
+    offset = write(value, buffer, offset, fieldInfo, params);
   });
   return buffer;
 }
 
 function parsePacket(buffer, state, isServer) {
-
-  function readPacketField(fieldInfo) {
-    var read = types[fieldInfo.type][0];
-    if (!read) {
-      return {
-        error: new Error("missing reader for data type: " + fieldInfo.type)
-      }
-    }
-    var readResults = read(buffer, cursor);
-    if (! readResults) return null; // buffer needs to be more full
-    if (readResults.error) return { error: readResults.error };
-
-    return readResults;
-  }
   if (state == null) state == states.PLAY;
   var cursor = 0;
   var lengthField = readVarInt(buffer, 0);
@@ -1697,13 +1710,10 @@ function parsePacket(buffer, state, isServer) {
   var i, fieldInfo, readResults;
   for (i = 0; i < packetInfo.length; ++i) {
     fieldInfo = packetInfo[i];
-    var condition = fieldInfo.condition;
-    if (typeof condition != "undefined" && !condition(results)) {
-      results[fieldInfo.name] = null;
-      continue;
-    }
-    readResults = readPacketField(fieldInfo);
-    if (!!!readResults) {
+    readResults = read(buffer, cursor, fieldInfo, results);
+    /* A deserializer cannot return null anymore. Besides, read() returns
+     * null when the condition is not fulfilled.
+     if (!!!readResults) {
         var error = new Error("A deserializer returned null");
         error.packetId = packetId;
         error.fieldInfo = fieldInfo.name;
@@ -1712,7 +1722,8 @@ function parsePacket(buffer, state, isServer) {
             error: error,
             results: results
         };
-    }
+    }*/
+    if (readResults === null) continue;
     if (readResults.error) {
       return readResults;
     }
diff --git a/test/test.js b/test/test.js
index ff74845..8923326 100644
--- a/test/test.js
+++ b/test/test.js
@@ -164,7 +164,9 @@ describe("packets", function() {
     // empty object uses default values
     var packet = {};
     packetInfo.forEach(function(field) {
-      packet[field.name] = values[field.type];
+      if (!field.hasOwnProperty("condition") || field.condition(packet)) {
+        packet[field.name] = values[field.type];
+      }
     });
     if (toServer) {
       serverClient.once([state, packetId], function(receivedPacket) {