Basic Mojo message header validation for JavaScript.

mojo/public/js/bindings/codec.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 define("mojo/public/js/bindings/codec", [
   "mojo/public/js/bindings/unicode",
   "mojo/public/js/bindings/buffer"
   ], function(unicode, buffer) {
 
   var kErrorUnsigned = "Passing negative value to unsigned";
 
   // Memory -------------------------------------------------------------------
 
   var kAlignment = 8;
 
   function align(size) {
     return size + (kAlignment - (size % kAlignment)) % kAlignment;
   }
 
+  function isAligned(offset) {
+    return offset >= 0 && (offset % kAlignment) === 0;
+  }
+
   // Constants ----------------------------------------------------------------
 
   var kArrayHeaderSize = 8;
   var kStructHeaderSize = 8;
   var kMessageHeaderSize = 16;
   var kMessageWithRequestIDHeaderSize = 24;
 
+  var kStructHeaderNumBytesOffset = 0;
+  var kStructHeaderNumFieldsOffset = 4;
+
   // Decoder ------------------------------------------------------------------
 
   function Decoder(buffer, handles, base) {
     this.buffer = buffer;
     this.handles = handles;
     this.base = base;
     this.next = base;
   }
 
   Decoder.prototype.skip = function(offset) {
@@ skipping 97 matching lines @@
     return val;
   };
 
   Decoder.prototype.decodeBoolArray = function() {
     var numberOfBytes = this.readUint32();
     var numberOfElements = this.readUint32();
 
     var val = new Array(numberOfElements);
     var byte;
     for (var i = 0; i < numberOfElements; ++i) {
-        if (i % 8 == 0)
+        if (i % 8 === 0)
             byte = this.readUint8();
         val[i] = (byte & (1 << i % 8)) ? true : false;
     }
     return val;
   };
 
   Decoder.prototype.decodeStruct = function(cls) {
     return cls.decode(this);
   };
 
@@ skipping 190 matching lines @@
       this.encodePointer(val);
       return;
     }
     var encodedSize = kArrayHeaderSize + unicode.utf8Length(val);
     var encoder = this.createAndEncodeEncoder(encodedSize);
     encoder.encodeString(val);
   };
 
   // Message ------------------------------------------------------------------
 
+  var kMessageNameOffset = kStructHeaderSize;
+  var kMessageFlagsOffset = kMessageNameOffset + 4;
+  var kMessageRequestIDOffset = kMessageFlagsOffset + 4;
+
   var kMessageExpectsResponse = 1 << 0;
   var kMessageIsResponse      = 1 << 1;
 
-  // Skip over num_bytes, num_fields, and message_name.
-  var kFlagsOffset = 4 + 4 + 4;
-
-  // Skip over num_bytes, num_fields, message_name, and flags.
-  var kRequestIDOffset = 4 + 4 + 4 + 4;
-
   function Message(buffer, handles) {
     this.buffer = buffer;
     this.handles = handles;
   }
 
-  Message.prototype.setRequestID = function(requestID) {
-    // TODO(darin): Verify that space was reserved for this field!
-    this.buffer.setUint64(kRequestIDOffset, requestID);
+  Message.prototype.getHeaderNumBytes = function() {
+    return this.buffer.getUint32(kStructHeaderNumBytesOffset);
+  };
+
+  Message.prototype.getHeaderNumFields = function() {
+    return this.buffer.getUint32(kStructHeaderNumFieldsOffset);
   };
 
   Message.prototype.getFlags = function() {
-    return this.buffer.getUint32(kFlagsOffset);
+    return this.buffer.getUint32(kMessageFlagsOffset);
   };
 
+  Message.prototype.isResponse = function() {
+    return (this.getFlags() & kMessageIsResponse) != 0;
+  };
+
+  Message.prototype.expectsResponse = function() {
+    return (this.getFlags() & kMessageExpectsResponse) != 0;
+  };
+
+  Message.prototype.setRequestID = function(requestID) {
+    // TODO(darin): Verify that space was reserved for this field!
+    this.buffer.setUint64(kMessageRequestIDOffset, requestID);
+  };
+
+
   // MessageBuilder -----------------------------------------------------------
 
   function MessageBuilder(messageName, payloadSize) {
     // Currently, we don't compute the payload size correctly ahead of time.
     // Instead, we resize the buffer at the end.
     var numberOfBytes = kMessageHeaderSize + payloadSize;
     this.buffer = new buffer.Buffer(numberOfBytes);
     this.handles = [];
     var encoder = this.createEncoder(kMessageHeaderSize);
     encoder.writeUint32(kMessageHeaderSize);
@@ skipping 271 matching lines @@
   Handle.decode = function(decoder) {
     return decoder.decodeHandle();
   };
 
   Handle.encode = function(encoder, val) {
     encoder.encodeHandle(val);
   };
 
   var exports = {};
   exports.align = align;
+  exports.isAligned = isAligned;
   exports.Message = Message;
   exports.MessageBuilder = MessageBuilder;
   exports.MessageWithRequestIDBuilder = MessageWithRequestIDBuilder;
   exports.MessageReader = MessageReader;
   exports.kArrayHeaderSize = kArrayHeaderSize;
   exports.kStructHeaderSize = kStructHeaderSize;
   exports.kMessageHeaderSize = kMessageHeaderSize;
+  exports.kMessageWithRequestIDHeaderSize = kMessageWithRequestIDHeaderSize;
   exports.kMessageExpectsResponse = kMessageExpectsResponse;
   exports.kMessageIsResponse = kMessageIsResponse;
   exports.Int8 = Int8;
   exports.Uint8 = Uint8;
   exports.Int16 = Int16;
   exports.Uint16 = Uint16;
   exports.Int32 = Int32;
   exports.Uint32 = Uint32;
   exports.Int64 = Int64;
   exports.Uint64 = Uint64;
   exports.Float = Float;
   exports.Double = Double;
   exports.String = String;
   exports.PointerTo = PointerTo;
   exports.ArrayOf = ArrayOf;
   exports.ArrayOfBoolArrayPointers = ArrayOfBoolArrayPointers;
   exports.Handle = Handle;
   return exports;
 });