Add interface versioning. Methods queryVersion and requireVersion.

mojo/public/js/lib/control_message_handler.js

Index: mojo/public/js/lib/control_message_handler.js
diff --git a/mojo/public/js/lib/control_message_handler.js b/mojo/public/js/lib/control_message_handler.js
new file mode 100644
index 0000000000000000000000000000000000000000..81d9002e0bba86a3022ef3c1cc1c5f85256aa7b1
--- /dev/null
+++ b/mojo/public/js/lib/control_message_handler.js
@@ -0,0 +1,111 @@
+// Copyright 2017 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/lib/control_message_handler", [
+  "mojo/public/js/codec",
+  "mojo/public/interfaces/bindings/interface_control_messages.mojom",
+  "mojo/public/js/validator",
+], function(codec, controlMessages, validator) {
+
+  var Validator = validator.Validator;
+
+  function validateControlRequestWithResponse(message) {
+    var messageValidator = new Validator(message);
+    var error = messageValidator.validateMessageIsRequestExpectingResponse();
+    if (error !== validator.validationError.NONE) {
+      throw error;
+    }
+
+    if (message.getName() != controlMessages.kRunMessageId) {

[yzshen1, 2017/02/13 23:44:23]

By the way, I found on the latest JS style guide
(https://google.github.io/styleguide/jsguide.html)
that

"""Braces are required for all control structures (i.e. if, else, for, do,
while, as well as any others), even if the body contains only a single
statement.

Exception: A simple if statement that can fit entirely on a single line with no
wrapping (and that doesn’t have an else) may be kept on a single line with no
braces when it improves readability. This is the only case in which a control
structure may omit braces and newlines."""

On
https://sites.google.com/a/chromium.org/dev/developers/web-development-style-...,
we have
"""Omit curly braces for single-line if statements."""

So my previous comment about "Whether to have {} around single-line body is not
enforced by the style guide." is incorrect with the latest style guide.

[wangjimmy, 2017/02/14 00:06:06]

Acknowledged.

+      throw new Error("Control message name is not kRunMessageId");
+    }
+
+    // Validate payload.
+    error = controlMessages.RunMessageParams.validate(messageValidator,
+        message.getHeaderNumBytes());
+    if (error != validator.validationError.NONE) {
+      throw error;
+    }
+  }
+
+  function validateControlRequestWithoutResponse(message) {
+    var messageValidator = new Validator(message);
+    var error = messageValidator.validateMessageIsRequestWithoutResponse();
+    if (error != validator.validationError.NONE) {
+      throw error;
+    }
+
+    if (message.getName() != controlMessages.kRunOrClosePipeMessageId) {
+      throw new Error("Control message name is not kRunOrClosePipeMessageId");
+    }
+
+    // Validate payload.
+    error = controlMessages.RunOrClosePipeMessageParams.validate(
+        messageValidator, message.getHeaderNumBytes());
+    if (error != validator.validationError.NONE) {
+      throw error;
+    }
+  }
+
+  function runOrClosePipe(message, interface_version) {
+    var reader = new codec.MessageReader(message);
+    var runOrClosePipeMessageParams = reader.decodeStruct(
+        controlMessages.RunOrClosePipeMessageParams);
+    return interface_version >=
+        runOrClosePipeMessageParams.input.require_version.version;
+  }
+
+  function run(message, responder, interface_version) {
+    var reader = new codec.MessageReader(message);
+    var runMessageParams =
+        reader.decodeStruct(controlMessages.RunMessageParams);
+    var runOutput = null;
+
+    if (runMessageParams.input.query_version) {
+      runOutput = new controlMessages.RunOutput();
+      runOutput.query_version_result = new
+          controlMessages.QueryVersionResult({'version': interface_version});
+    }
+
+    var runResponseMessageParams = new
+        controlMessages.RunResponseMessageParams();
+    runResponseMessageParams.output = runOutput;
+
+    var messageName = controlMessages.kRunMessageId;
+    var payloadSize = controlMessages.RunResponseMessageParams.encodedSize;
+    var requestID = reader.requestID;
+    var builder = new codec.MessageWithRequestIDBuilder(messageName,
+        payloadSize, codec.kMessageIsResponse, requestID);
+    builder.encodeStruct(controlMessages.RunResponseMessageParams,
+                         runResponseMessageParams);
+    responder.accept(builder.finish());
+    return true;
+  }
+
+  function isControlMessage(message) {
+    return message.getName() == controlMessages.kRunMessageId ||
+           message.getName() == controlMessages.kRunOrClosePipeMessageId;
+  }
+
+  function ControlMessageHandler(interface_version) {
+    this.interface_version = interface_version;
+  }
+
+  ControlMessageHandler.prototype.accept = function(message) {
+    validateControlRequestWithoutResponse(message);
+    return runOrClosePipe(message, this.interface_version);
+  };
+
+  ControlMessageHandler.prototype.acceptWithResponder = function(message,
+      responder) {
+    validateControlRequestWithResponse(message);
+    return run(message, responder, this.interface_version);
+  };
+
+  var exports = {};
+  exports.ControlMessageHandler = ControlMessageHandler;
+  exports.isControlMessage = isControlMessage;
+
+  return exports;
+});