Basic Mojo message header validation for JavaScript.

mojo/public/js/bindings/validator.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/validator", [
+  "mojo/public/js/bindings/codec",
+  ], function(codec) {
+
+  var validationError = {
+    NONE: 'VALIDATION_ERROR_NONE',
+    MISALIGNED_OBJECT: 'VALIDATION_ERROR_MISALIGNED_OBJECT',
+    ILLEGAL_MEMORY_RANGE: 'VALIDATION_ERROR_ILLEGAL_MEMORY_RANGE',
+    UNEXPECTED_STRUCT_HEADER: 'VALIDATION_ERROR_UNEXPECTED_STRUCT_HEADER',
+    UNEXPECTED_ARRAY_HEADER: 'VALIDATION_ERROR_UNEXPECTED_ARRAY_HEADER',
+    ILLEGAL_HANDLE: 'VALIDATION_ERROR_ILLEGAL_HANDLE',
+    ILLEGAL_POINTER: 'VALIDATION_ERROR_ILLEGAL_POINTER',
+    MESSAGE_HEADER_INVALID_FLAG_COMBINATION:
+        'VALIDATION_ERROR_MESSAGE_HEADER_INVALID_FLAG_COMBINATION',
+    MESSAGE_HEADER_MISSING_REQUEST_ID:
+        'VALIDATION_ERROR_MESSAGE_HEADER_MISSING_REQUEST_ID'
+  };
+
+  function Validator(message) {
+    this.message = message;
+    this.offset = 0;
+  }
+
+  Object.defineProperty(Validator.prototype, "offsetLimit", {
+    get: function() { return this.message.buffer.byteLength; }
+  });
+
+  // True if we can safely allocate a block of bytes from offset + start

[yzshen1, 2014/07/30 17:14:56]

Do you mean |start| is relative to the current |offset| (because offset + start
is used)? That seems confusing.

It might be easier if |start| is relative to a fixed point, such as the
beginning of the message. What do you think?

[hansmuller, 2014/07/30 18:32:30]

I agree, it should be relative to the beginning of the message, offset = 0.

+  // to offset + start + numBytes.
+  Validator.prototype.isValidRange = function(start, numBytes) {
+    if (start < this.offset || numBytes < 0 ||

[yzshen1, 2014/07/30 17:14:56]

start < this.offset: it indicates start and offset are relative to the same
origin. That is inconsistent with start + offset, which indicates start is
relative to offset.

numBytes < 0: The documented algorithm regards an empty range as invalid. It is
better to be consistent.

[hansmuller, 2014/07/30 18:32:30]

Right, that's my mistake (again). The check just needs to verify that
start+offset first between this.offset and this.offsetLimit. In addition to
guarding against overflow.
Yes. The check is now numBytes <= 0.

+        !Number.isSafeInteger(start) ||
+        !Number.isSafeInteger(numBytes))
+      return false;
+
+    var newOffset = this.offset + start + numBytes;
+    if (!Number.isSafeInteger(newOffset) || newOffset > this.offsetLimit)
+      return false;
+
+    return true;
+  }
+
+  Validator.prototype.claimRange = function(start, numBytes) {
+    if (this.isValidRange(start, numBytes)) {
+      this.offset += start + numBytes;
+      return true;
+    }
+    return false;
+  }
+
+  Validator.prototype.validateStructHeader =
+      function(offset, minNumBytes, minNumFields) {
+    if (!codec.isAligned(offset))
+      return validationError.MISALIGNED_OBJECT;
+
+    if (!this.isValidRange(offset, codec.kStructHeaderSize))
+      return validationError.ILLEGAL_MEMORY_RANGE;
+
+    var numBytes = this.message.buffer.getUint32(offset);
+    var numFields = this.message.buffer.getUint32(offset + 4);
+
+    if (numBytes < minNumBytes || numFields < minNumFields)
+      return validationError.UNEXPECTED_STRUCT_HEADER;
+
+    if (!this.claimRange(offset, numBytes))
+      return validationError.ILLEGAL_MEMORY_RANGE;
+
+    return validationError.NONE;
+  }
+
+  Validator.prototype.validateMessageHeader = function() {
+    var numBytes = this.message.getHeaderNumBytes();
+    var numFields = this.message.getHeaderNumFields();
+
+    var validNumFieldsAndNumBytes =
+        (numFields == 2 && numBytes == codec.kMessageHeaderSize) ||
+        (numFields == 3 &&
+         numBytes == codec.kMessageWithRequestIDHeaderSize) ||
+        (numFields > 3 &&
+         numBytes >= codec.kMessageWithRequestIDHeaderSize);
+    if (!validNumFieldsAndNumBytes)
+      return validationError.UNEXPECTED_STRUCT_HEADER;
+
+    var expectsResponse = this.message.expectsResponse();
+    var isResponse = this.message.isResponse();
+
+    if (numFields == 2 && (expectsResponse || isResponse))
+      return validationError.MESSAGE_HEADER_MISSING_REQUEST_ID;
+
+    if (isResponse && expectsResponse)
+      return validationError.MESSAGE_HEADER_INVALID_FLAG_COMBINATION;
+
+    return validationError.NONE;
+  }
+
+  Validator.prototype.validateMessage = function() {
+    var err = this.validateStructHeader(0, codec.kStructHeaderSize, 2);
+    if (err != validationError.NONE)
+      return err;
+
+    return this.validateMessageHeader();
+  }
+
+  var exports = {};
+  exports.validationError = validationError;
+  exports.Validator = Validator;
+  return exports;
+});