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..0634cdeeaea5d27b2ac21cd4334bdd5caababca2 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 +135,30 @@ define("mojo/public/js/router", [
           endpoint.client.notifyError.bind(endpoint.client));
     }
 
+    if (this.cachedMessageData && interfaceEndpointHandle.id() ===
+        this.cachedMessageData.message.getInterfaceId()) {
+      timer.createOneShot(0, (function() {
+        if (!this.cachedMessageData) {
+          return;
+        }
+
+        var targetEndpoint = this.endpoints_.get(
+            this.cachedMessageData.message.getInterfaceId());
+        // Check that the target endpoint's client still exists.
+        if (targetEndpoint && targetEndpoint.client) {
+          var ok = endpoint.client.handleIncomingMessage(
+              this.cachedMessageData.message,

[yzshen1, 2017/04/26 16:40:00]

nit: please move the contents of cachedMessageData to a local variable and
resumeIncomingMethodCallProcessing() before calling handleIncomingMessage().
Because that method may re-enter the router, it is a little more robust to do
things this way.

[wangjimmy, 2017/04/26 17:54:07]

Done.

+              this.cachedMessageData.messageValidator);
+
+          if (!ok) {
+            this.handleInvalidIncomingMessage_();
+          }
+          this.cachedMessageData = null;
+          this.connector_.resumeIncomingMethodCallProcessing();
+        }
+      }).bind(this));
+    }
+
     return endpoint;
   };
 
@@ -199,9 +226,10 @@ 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);
       }
@@ -290,6 +318,14 @@ define("mojo/public/js/router", [
     if (!types.isMasterInterfaceId(interfaceId) || reason) {
       this.controlMessageProxy_.notifyPeerEndpointClosed(interfaceId, reason);
     }
+
+    if (this.cachedMessageData && interfaceId ===
+        this.cachedMessageData.message.getInterfaceId()) {
+      timer.createOneShot(0, (function() {

[yzshen1, 2017/04/26 16:40:00]

no need to use timer: resumeIncomingMethodCallProcessing() won't receive message
synchronously.

[wangjimmy, 2017/04/26 17:54:07]

Done.

+        this.cachedMessageData = null;
+        this.connector_.resumeIncomingMethodCallProcessing();
+      }).bind(this));
+    }
   };
 
   Router.prototype.updateEndpointStateMayRemove = function(endpoint,