diff --git a/src/shared/message_handler.js b/src/shared/message_handler.js
index 88c565775..c0adeb460 100644
--- a/src/shared/message_handler.js
+++ b/src/shared/message_handler.js
@@ -48,14 +48,6 @@ function wrapReason(reason) {
   }
 }
 
-function resolveOrReject(capability, data) {
-  if (data.success) {
-    capability.resolve();
-  } else {
-    capability.reject(wrapReason(data.reason));
-  }
-}
-
 function MessageHandler(sourceName, targetName, comObj) {
   this.sourceName = sourceName;
   this.targetName = targetName;
@@ -80,8 +72,8 @@ function MessageHandler(sourceName, targetName, comObj) {
       if (data.callbackId in callbacksCapabilities) {
         let callback = callbacksCapabilities[callbackId];
         delete callbacksCapabilities[callbackId];
-        if ('error' in data) {
-          callback.reject(wrapReason(data.error));
+        if ('reason' in data) {
+          callback.reject(wrapReason(data.reason));
         } else {
           callback.resolve(data.data);
         }
@@ -109,7 +101,7 @@ function MessageHandler(sourceName, targetName, comObj) {
             targetName,
             isReply: true,
             callbackId: data.callbackId,
-            error: wrapReason(reason),
+            reason: wrapReason(reason),
           });
         });
       } else if (data.streamId) {
@@ -193,6 +185,8 @@ MessageHandler.prototype = {
         this.streamControllers[streamId] = {
           controller,
           startCall: startCapability,
+          pullCall: null,
+          cancelCall: null,
           isClosed: false,
         };
         this.postMessage({
@@ -337,33 +331,43 @@ MessageHandler.prototype = {
   _processStreamMessage(data) {
     let sourceName = this.sourceName;
     let targetName = data.sourceName;
-    let streamId = data.streamId;
+    const streamId = data.streamId;
     const comObj = this.comObj;
 
     let deleteStreamController = () => {
       // Delete the `streamController` only when the start, pull, and cancel
       // capabilities have settled, to prevent `TypeError`s.
       Promise.all([
-        this.streamControllers[data.streamId].startCall,
-        this.streamControllers[data.streamId].pullCall,
-        this.streamControllers[data.streamId].cancelCall
+        this.streamControllers[streamId].startCall,
+        this.streamControllers[streamId].pullCall,
+        this.streamControllers[streamId].cancelCall
       ].map(function(capability) {
         return capability && capability.promise.catch(function() { });
       })).then(() => {
-        delete this.streamControllers[data.streamId];
+        delete this.streamControllers[streamId];
       });
     };
 
     switch (data.stream) {
       case StreamKind.START_COMPLETE:
-        resolveOrReject(this.streamControllers[data.streamId].startCall, data);
+        if (data.success) {
+          this.streamControllers[streamId].startCall.resolve();
+        } else {
+          this.streamControllers[streamId].startCall.reject(
+            wrapReason(data.reason));
+        }
         break;
       case StreamKind.PULL_COMPLETE:
-        resolveOrReject(this.streamControllers[data.streamId].pullCall, data);
+        if (data.success) {
+          this.streamControllers[streamId].pullCall.resolve();
+        } else {
+          this.streamControllers[streamId].pullCall.reject(
+            wrapReason(data.reason));
+        }
         break;
       case StreamKind.PULL:
         // Ignore any pull after close is called.
-        if (!this.streamSinks[data.streamId]) {
+        if (!this.streamSinks[streamId]) {
           comObj.postMessage({
             sourceName,
             targetName,
@@ -376,12 +380,12 @@ MessageHandler.prototype = {
         // Pull increases the desiredSize property of sink,
         // so when it changes from negative to positive,
         // set ready property as resolved promise.
-        if (this.streamSinks[data.streamId].desiredSize <= 0 &&
+        if (this.streamSinks[streamId].desiredSize <= 0 &&
             data.desiredSize > 0) {
-          this.streamSinks[data.streamId].sinkCapability.resolve();
+          this.streamSinks[streamId].sinkCapability.resolve();
         }
         // Reset desiredSize property of sink on every pull.
-        this.streamSinks[data.streamId].desiredSize = data.desiredSize;
+        this.streamSinks[streamId].desiredSize = data.desiredSize;
         const { onPull, } = this.streamSinks[data.streamId];
         new Promise(function(resolve) {
           resolve(onPull && onPull());
@@ -404,35 +408,41 @@ MessageHandler.prototype = {
         });
         break;
       case StreamKind.ENQUEUE:
-        assert(this.streamControllers[data.streamId],
+        assert(this.streamControllers[streamId],
                'enqueue should have stream controller');
-        if (!this.streamControllers[data.streamId].isClosed) {
-          this.streamControllers[data.streamId].controller.enqueue(data.chunk);
-        }
-        break;
-      case StreamKind.CLOSE:
-        assert(this.streamControllers[data.streamId],
-               'close should have stream controller');
-        if (this.streamControllers[data.streamId].isClosed) {
+        if (this.streamControllers[streamId].isClosed) {
           break;
         }
-        this.streamControllers[data.streamId].isClosed = true;
-        this.streamControllers[data.streamId].controller.close();
+        this.streamControllers[streamId].controller.enqueue(data.chunk);
+        break;
+      case StreamKind.CLOSE:
+        assert(this.streamControllers[streamId],
+               'close should have stream controller');
+        if (this.streamControllers[streamId].isClosed) {
+          break;
+        }
+        this.streamControllers[streamId].isClosed = true;
+        this.streamControllers[streamId].controller.close();
         deleteStreamController();
         break;
       case StreamKind.ERROR:
-        assert(this.streamControllers[data.streamId],
+        assert(this.streamControllers[streamId],
                'error should have stream controller');
-        this.streamControllers[data.streamId].controller.
-          error(wrapReason(data.reason));
+        this.streamControllers[streamId].controller.error(
+          wrapReason(data.reason));
         deleteStreamController();
         break;
       case StreamKind.CANCEL_COMPLETE:
-        resolveOrReject(this.streamControllers[data.streamId].cancelCall, data);
+        if (data.success) {
+          this.streamControllers[streamId].cancelCall.resolve();
+        } else {
+          this.streamControllers[streamId].cancelCall.reject(
+            wrapReason(data.reason));
+        }
         deleteStreamController();
         break;
       case StreamKind.CANCEL:
-        if (!this.streamSinks[data.streamId]) {
+        if (!this.streamSinks[streamId]) {
           break;
         }
         const { onCancel, } = this.streamSinks[data.streamId];
@@ -455,10 +465,10 @@ MessageHandler.prototype = {
             reason: wrapReason(reason),
           });
         });
-        this.streamSinks[data.streamId].sinkCapability.
-          reject(wrapReason(data.reason));
-        this.streamSinks[data.streamId].isCancelled = true;
-        delete this.streamSinks[data.streamId];
+        this.streamSinks[streamId].sinkCapability.reject(
+          wrapReason(data.reason));
+        this.streamSinks[streamId].isCancelled = true;
+        delete this.streamSinks[streamId];
         break;
       default:
         throw new Error('Unexpected stream case');