Bug 1055144 - Implement sendRequestForResult. r=wesj

sendRequestForResult is a promise-based API for messaging Java. It
replaces the callback version of sendMessageToJava.

mobile/android/base/EventDispatcher.java

@@ -27,7 +27,6 @@ import java.util.concurrent.CopyOnWriteArrayList;
 public final class EventDispatcher {
     private static final String LOGTAG = "GeckoEventDispatcher";
     private static final String GUID = "__guid__";
-    private static final String STATUS_CANCEL = "cancel";
     private static final String STATUS_ERROR = "error";
     private static final String STATUS_SUCCESS = "success";
 
@@ -200,10 +199,9 @@ public final class EventDispatcher {
             if (listeners == null || listeners.size() == 0) {
                 Log.w(LOGTAG, "No listeners for " + type);
 
-                // If there are no listeners, cancel the callback to prevent Gecko-side observers
-                // from being leaked.
+                // If there are no listeners, dispatch an error.
                 if (callback != null) {
-                    callback.sendCancel();
+                    callback.sendError("No listeners for request");
                 }
                 return;
             }
@@ -258,10 +256,6 @@ public final class EventDispatcher {
             sendResponse(STATUS_ERROR, response);
         }
 
-        public void sendCancel() {
-            sendResponse(STATUS_CANCEL, null);
-        }
-
         private void sendResponse(final String status, final Object response) {
             if (sent) {
                 throw new IllegalStateException("Callback has already been executed for type=" +

mobile/android/base/tests/testEventDispatcher.java

@@ -68,7 +68,6 @@ public class testEventDispatcher extends UITest
         js.syncCall("send_test_message", NATIVE_EVENT);
         js.syncCall("send_message_for_response", NATIVE_RESPONSE_EVENT, "success");
         js.syncCall("send_message_for_response", NATIVE_RESPONSE_EVENT, "error");
-        js.syncCall("send_message_for_response", NATIVE_RESPONSE_EVENT, "cancel");
         js.syncCall("send_test_message", NATIVE_EXCEPTION_EVENT);
         js.syncCall("finish_test");
     }
@@ -149,8 +148,6 @@ public class testEventDispatcher extends UITest
                 callback.sendSuccess(response);
             } else if ("error".equals(response)) {
                 callback.sendError(response);
-            } else if ("cancel".equals(response)) {
-                callback.sendCancel();
             } else {
                 fFail("Response type should be valid: " + response);
             }

mobile/android/base/util/EventCallback.java

@@ -26,9 +26,4 @@ public interface EventCallback {
      *                 JSONObject#put(String, Object).
      */
     public void sendError(Object response);
-
-    /**
-     * Cancels the request, preventing any Gecko-side callbacks from being executed.
-     */
-    public void sendCancel();
 }

mobile/android/modules/Messaging.jsm

@@ -18,7 +18,13 @@ XPCOMUtils.defineLazyServiceGetter(this, "uuidgen",
 function sendMessageToJava(aMessage, aCallback) {
   Cu.reportError("sendMessageToJava is deprecated. Use Messaging API instead.");
 
-  Messaging.sendRequest(aMessage, aCallback);
+  if (aCallback) {
+    Messaging.sendRequestForResult(aMessage)
+      .then(result => aCallback(result, null),
+            error => aCallback(null, error));
+  } else {
+    Messaging.sendRequest(aMessage);
+  }
 }
 
 let Messaging = {
@@ -71,35 +77,42 @@ let Messaging = {
    * Sends a request to Java.
    *
    * @param aMessage  Message to send; must be an object with a "type" property
-   * @param aCallback Callback function, required if this request expects a response.
    */
-  sendRequest: function (aMessage, aCallback) {
-    if (aCallback) {
+  sendRequest: function (aMessage) {
+    Services.androidBridge.handleGeckoMessage(aMessage);
+  },
+
+  /**
+   * Sends a request to Java, returning a Promise that resolves to the response.
+   *
+   * @param aMessage Message to send; must be an object with a "type" property
+   * @returns A Promise resolving to the response
+   */
+  sendRequestForResult: function (aMessage) {
+    return new Promise((resolve, reject) => {
       let id = uuidgen.generateUUID().toString();
       let obs = {
-        observe: function(aSubject, aTopic, aData) {
+        observe: function (aSubject, aTopic, aData) {
           let data = JSON.parse(aData);
           if (data.__guid__ != id) {
             return;
           }
 
-          Services.obs.removeObserver(obs, aMessage.type + ":Response", false);
+          Services.obs.removeObserver(obs, aMessage.type + ":Response");
 
-          if (data.status === "cancel") {
-            // No Java-side listeners handled our callback.
-            return;
+          if (data.status === "success") {
+            resolve(data.response);
+          } else {
+            reject(data.response);
           }
-
-          aCallback(data.status === "success" ? data.response : null,
-                    data.status === "error"   ? data.response : null);
         }
-      }
+      };
 
       aMessage.__guid__ = id;
       Services.obs.addObserver(obs, aMessage.type + ":Response", false);
-    }
 
-    return Services.androidBridge.handleGeckoMessage(aMessage);
+      this.sendRequest(aMessage);
+    });
   },
 };
 

testing/mochitest/roboextender/bootstrap.js

@@ -29,7 +29,7 @@ var windowListener = {
             height: XPCNativeWrapper.unwrap(e.target).documentElement.scrollHeight,
             cheight: XPCNativeWrapper.unwrap(e.target).documentElement.clientHeight,
           };
-          let retVal = _sendMessageToJava(message);
+          _sendMessageToJava(message);
         });
       }
     }, false);