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..5eb5371e5a2825241a3b53d721e977dba7883896 100644
--- a/mojo/public/js/router.js
+++ b/mojo/public/js/router.js
@@ -72,6 +72,9 @@ define("mojo/public/js/router", [
     });
 
     this.setInterfaceIdNamespaceBit_ = setInterfaceIdNamespaceBit;
+    // |cachedMessageData| caches infomation about a message, so it can be
+    // processed later if a client is not yet attached to the target endpoint.
+    this.cachedMessageData = null;
     this.controlMessageHandler_ = new PipeControlMessageHandler(this);
     this.controlMessageProxy_ = new PipeControlMessageProxy(this.connector_);
     this.nextInterfaceIdValue_ = 1;
@@ -132,6 +135,21 @@ define("mojo/public/js/router", [
           endpoint.client.notifyError.bind(endpoint.client));
     }
 
+    if (this.cachedMessageData && interfaceEndpointHandle.id() ===
+            this.cachedMessageData.message.getInterfaceId()) {
+      timer.createOneShot(0, (function() {

[wangjimmy, 2017/04/24 19:04:33]

TODO(wangjimmy): Check endpoint client still exists here.

[yzshen1, 2017/04/24 19:21:49]

I hope this could be addressed in this CL, which shouldn't be too difficult.

When the timer fires, you need to use the interface ID from the
cachedMessageData to loop up the endpoints map, and see whether it has got a
client attached, if yes, you can directly called into client.

[wangjimmy, 2017/04/24 21:16:39]

Done.

+        var ok = interfaceEndpointClient.handleIncomingMessage(
+            this.cachedMessageData.message,
+            this.cachedMessageData.messageValidator);
+
+        if (!ok) {
+          this.handleInvalidIncomingMessage_();
+        }
+        this.cachedMessageData = null;
+        this.connector_.resumeIncomingMethodCallProcessing();
+      }).bind(this));
+    }
+
     return endpoint;
   };
 
@@ -199,9 +217,10 @@ 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.
-          return false;
+          this.cachedMessageData = {message: message,
+              messageValidator: messageValidator};
+          this.connector_.pauseIncomingMethodCallProcessing();
+          return true;
         }
         ok = endpoint.client.handleIncomingMessage(message, messageValidator);
       }