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;

[Tom Sepez, 2014/07/29 16:32:54]

nit: purists might insist on === througout.

[hansmuller, 2014/07/29 19:06:22]

Done.

+  }
+
   // Constants ----------------------------------------------------------------
 
   var kArrayHeaderSize = 8;
   var kStructHeaderSize = 8;
   var kMessageHeaderSize = 16;
   var kMessageWithRequestIDHeaderSize = 24;
 
   // Decoder ------------------------------------------------------------------
 
   function Decoder(buffer, handles, base) {
@@ skipping 318 matching lines @@
     var encodedSize = kArrayHeaderSize + unicode.utf8Length(val);
     var encoder = this.createAndEncodeEncoder(encodedSize);
     encoder.encodeString(val);
   };
 
   // Message ------------------------------------------------------------------
 
   var kMessageExpectsResponse = 1 << 0;
   var kMessageIsResponse      = 1 << 1;
 
+  // Message header is a struct, begins with a struct header.
+  var kNumBytesOffset = 0;

[yzshen1, 2014/07/29 05:59:53]

Maybe we could consider define these in the "constants" section. They are
constants for general struct header, not just for message header.

[hansmuller, 2014/07/29 19:06:22]

Done.

+  var kNumFieldsOffset = 4;
+
   // Skip over num_bytes, num_fields, and message_name.
   var kFlagsOffset = 4 + 4 + 4;

[yzshen1, 2014/07/29 05:59:53]

Some of those 4's (or all of them) could be replaced by constants defined above?

[hansmuller, 2014/07/29 19:06:22]

Done.

 
   // Skip over num_bytes, num_fields, message_name, and flags.
   var kRequestIDOffset = 4 + 4 + 4 + 4;

[yzshen1, 2014/07/29 05:59:53]

ditto.

[hansmuller, 2014/07/29 19:06:22]

Done.

 
   function Message(buffer, handles) {
     this.buffer = buffer;
     this.handles = handles;
   }
 
+  Message.prototype.getHeaderNumBytes = function() {
+    return this.buffer.getUint32(kNumBytesOffset);
+  };
+
+  Message.prototype.getHeaderNumFields = function() {
+    return this.buffer.getUint32(kNumFieldsOffset);
+  };
+
+  Message.prototype.getFlags = function() {
+    return this.buffer.getUint32(kFlagsOffset);
+  };
+
+  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(kRequestIDOffset, requestID);
   };
 
-  Message.prototype.getFlags = function() {
-    return this.buffer.getUint32(kFlagsOffset);
-  };
 
   // 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);
@@ skipping 272 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;
 });