Fifo order should be preserved for messages on associated interfaces.

mojo/public/js/router.js

Index: mojo/public/js/router.js
diff --git a/mojo/public/js/router.js b/mojo/public/js/router.js
index 401a22278958e0736eb7375bf6f458b7fd0c7d19..b86daae43a969f2698e5d495bda4dd710ab09c4c 100644
--- a/mojo/public/js/router.js
+++ b/mojo/public/js/router.js
@@ -72,6 +72,7 @@ define("mojo/public/js/router", [
     });
 
     this.setInterfaceIdNamespaceBit_ = setInterfaceIdNamespaceBit;
+    this.cachedMessageData = null;

[yzshen1, 2017/04/24 17:30:46]

nit: Please consider commenting on the meaning of this field.

[wangjimmy, 2017/04/24 19:03:35]

Done.

     this.controlMessageHandler_ = new PipeControlMessageHandler(this);
     this.controlMessageProxy_ = new PipeControlMessageProxy(this.connector_);
     this.nextInterfaceIdValue_ = 1;
@@ -132,6 +133,18 @@ define("mojo/public/js/router", [
           endpoint.client.notifyError.bind(endpoint.client));
     }
 
+    if (this.cachedMessageData && interfaceEndpointHandle.id() ===
+            this.cachedMessageData.message.getInterfaceId()) {
+      var ok = interfaceEndpointClient.handleIncomingMessage(

[yzshen1, 2017/04/24 17:30:45]

We are not supposed to call it synchronously. Because this will re-enter users'
code.

Imagine the user calls:

var associated_binding = new AssociatedBindings(..., new FooImpl(), ...);

If we call into "handleIncomingMessage" synchronously, that means FooImpl's
methods may be called before newAssociatedBindings() returns.

[wangjimmy, 2017/04/24 19:03:35]

Done.

+          this.cachedMessageData.message,
+          this.cachedMessageData.messageValidator);
+
+      if (!ok) {
+        this.handleInvalidIncomingMessage_();
+      }
+      this.connector_.resumeIncomingMethodCallProcessing();
+    }
+
     return endpoint;
   };
 
@@ -199,8 +212,9 @@ define("mojo/public/js/router", [
         if (!endpoint.client) {
           // We need to wait until a client is attached in order to dispatch
           // further messages.
-          // TODO(wangjimmy): Cache the message and send when the appropriate
-          // endpoint client is attached.
+          this.cachedMessageData = {message: message,
+              messageValidator: messageValidator};
+          this.connector_.pauseIncomingMethodCallProcessing();
           return false;

[yzshen1, 2017/04/24 17:30:45]

I think we should return "true" to mean "the message processing succeeded"?
I understand this return value is not currently used by the Connector.

[wangjimmy, 2017/04/24 19:03:35]

Done.

         }
         ok = endpoint.client.handleIncomingMessage(message, messageValidator);