Add a method to JavaScriptExecutor to return a value

bundles/org.eclipse.rap.rwt/js/rwt/client/JavaScriptExecutor.js

@@ -7,6 +7,7 @@
  *
  * Contributors:
  *    EclipseSource - initial API and implementation
+ *    Kyle Smith - Add evaluate method
  ******************************************************************************/
 
 namespace( "rwt.client" );
@@ -17,6 +18,15 @@ rwt.client.JavaScriptExecutor = function() {
     eval( code );
   };
 
+  this.evaluate = function( futureId, code ) {
+    const remote = rwt.remote.Connection.getInstance().getRemoteObject( this );
+    const retval = eval( code );
+    remote.call( "complete", {
+        futureId : futureId,
+        retval: retval
+    } );
+  };
+
 };
 
 rwt.client.JavaScriptExecutor.getInstance = function() {

bundles/org.eclipse.rap.rwt/js/rwt/remote/handler/JavaScriptExecutorHandler.js

@@ -7,6 +7,7 @@
  *
  * Contributors:
  *    EclipseSource - initial API and implementation
+ *    Kyle Smith - Add evaluate method
  ******************************************************************************/
 
 rwt.remote.HandlerRegistry.add( "rwt.client.JavaScriptExecutor", {
@@ -20,12 +21,16 @@ rwt.remote.HandlerRegistry.add( "rwt.client.JavaScriptExecutor", {
   destructor : rwt.util.Functions.returnTrue,
 
   methods : [
-    "execute"
+    "execute",
+    "evaluate"
   ],
 
   methodHandler : {
     "execute" : function( object, args ) {
       object.execute( args.content );
+    },
+    "evaluate" : function( object, args ) {
+      object.evaluate( args.futureId, args.content );
     }
   }
 

bundles/org.eclipse.rap.rwt/src/org/eclipse/rap/rwt/client/service/JavaScriptExecutor.java

@@ -7,9 +7,12 @@
  *
  * Contributors:
  *    EclipseSource - initial API and implementation
+ *    Kyle Smith - Add evalute method
  ******************************************************************************/
 package org.eclipse.rap.rwt.client.service;
 
+import java.util.concurrent.CompletableFuture;
+
 
 /**
  * The JavaScriptExecuter service allows executing JavaScript code on the client.
@@ -20,13 +23,35 @@
 public interface JavaScriptExecutor extends ClientService {
 
   /**
-   * Evaluate the JavaScript code on the client
-   *
-   * If the code throws an error, it will crash the web client.
-   * Accessing internals of the web client is strongly discouraged.
+   * Executes the JavaScript code on the client.
+   * <p>
+   * If the code throws an error, it will crash the web client. Accessing internals of the web
+   * client is strongly discouraged.
    *
    * @param code the JavaScript code to evaluate
    */
   public void execute( String code );
 
+  /**
+   * Evaluates the JavaScript code on the client. Unlike {@link #execute(String)}, this method
+   * returns a value (asynchronously) if the specified JavaScript code returns a value. The returned
+   * {@link CompletableFuture} is completed when the client object sends the return value, if any,
+   * in the next remote call, which may never happen. If the JavaScript code does not return a
+   * value, the future is completed with {@code null}.
+   * <p>
+   * <b>Important:</b> Do not wait for the future to complete in the UI thread or it will cause a
+   * deadlock. The code to execute is only sent to the client once the UI thread is available, which
+   * will not happen if the future is blocking it. Instead, use another thread or
+   * {@link java.util.concurrent.ExecutorService ExecutorService}.
+   * <p>
+   * If the code throws an error, it will crash the web client. Accessing internals of the web
+   * client is strongly discouraged.
+   *
+   * @param code the JavaScript code to evaluate
+   * @return a future that will be completed with the result of the JavaScript code, or a future
+   *         that will be completed with {@code null} if the given JavaScript code does not return a
+   *         value (i.e., returns {@code undefined})
+   * @since 4.3
+   */
+  public CompletableFuture<String> evaluate( String code );
 }

bundles/org.eclipse.rap.rwt/src/org/eclipse/rap/rwt/internal/client/JavaScriptExecutorImpl.java

@@ -7,29 +7,71 @@
  *
  * Contributors:
  *    EclipseSource - initial API and implementation
+ *    Kyle Smith - Add evalute method
  ******************************************************************************/
 package org.eclipse.rap.rwt.internal.client;
 
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+
 import org.eclipse.rap.json.JsonObject;
+import org.eclipse.rap.json.JsonValue;
 import org.eclipse.rap.rwt.RWT;
 import org.eclipse.rap.rwt.client.service.JavaScriptExecutor;
 import org.eclipse.rap.rwt.internal.remote.ConnectionImpl;
+import org.eclipse.rap.rwt.remote.AbstractOperationHandler;
 import org.eclipse.rap.rwt.remote.RemoteObject;
+import org.eclipse.swt.internal.widgets.IdGenerator;
 
 
 public final class JavaScriptExecutorImpl implements JavaScriptExecutor {
 
   private static final String REMOTE_ID = "rwt.client.JavaScriptExecutor";
   private final RemoteObject remoteObject;
+  private final Map<String, CompletableFuture<String>> futures;
 
   public JavaScriptExecutorImpl() {
     ConnectionImpl connection = ( ConnectionImpl )RWT.getUISession().getConnection();
+    futures = new HashMap<>();
     remoteObject = connection.createServiceObject( REMOTE_ID );
+    remoteObject.setHandler( new EvaluateHandler() );
   }
 
   @Override
   public void execute( String code ) {
     remoteObject.call( "execute", new JsonObject().add( "content", code.trim() ) );
   }
 
+  @Override
+  public CompletableFuture<String> evaluate( String code ) {
+    CompletableFuture<String> future = new CompletableFuture<>();
+    String id = IdGenerator.getInstance( RWT.getUISession() ).createId( future );
+    futures.put( id, future );
+    remoteObject.call( "evaluate",
+                       new JsonObject().add( "futureId", id ).add( "content", code.trim() ) );
+    return future;
+  }
+
+  private final class EvaluateHandler extends AbstractOperationHandler {
+
+    @Override
+    public void handleCall( String method, JsonObject properties ) {
+      if( "complete".equals( method ) ) {
+        JsonValue idJson = properties.get( "futureId" );
+        JsonValue retvalJson = properties.get( "retval" );
+        if( idJson != null && idJson.isString() ) {
+          CompletableFuture<String> future = futures.get( idJson.asString() );
+          if( future != null ) {
+            if( retvalJson != null ) {
+              future.complete( retvalJson.toString() );
+            } else {
+              future.complete( null );
+            }
+            futures.remove( idJson.asString() );
+          }
+        }
+      }
+    }
+  }
 }

tests/org.eclipse.rap.rwt.test/src/org/eclipse/rap/rwt/internal/client/JavaScriptExecutorImpl_Test.java

@@ -18,6 +18,8 @@
 import static org.mockito.Mockito.verifyNoMoreInteractions;
 import static org.mockito.Mockito.when;
 
+import java.util.concurrent.CompletableFuture;
+
 import org.eclipse.rap.json.JsonObject;
 import org.eclipse.rap.rwt.internal.remote.ConnectionImpl;
 import org.eclipse.rap.rwt.remote.RemoteObject;
@@ -75,12 +77,38 @@ public void testExecute_createsSeparateOperationForEveryCall() {
     verify( remoteObject ).call( eq( "execute" ), eq( new JsonObject().add( "content", "code 2" ) ) );
     verifyNoMoreInteractions( remoteObject );
   }
+
+  @Test
+  public void testEvaluate_createsCallOperation() {
+    RemoteObject remoteObject = mock( RemoteObject.class );
+    fakeConnection( remoteObject );
+    JavaScriptExecutorImpl executor = new JavaScriptExecutorImpl();
+
+    CompletableFuture<String> future = executor.evaluate( "5 + 6" );
+
+    verify( remoteObject ).call( eq( "evaluate" ), eq( new JsonObject().add( "content", "5+6" ) ) );
+    verifyNoMoreInteractions( remoteObject );
+  }
+
+  @Test
+  public void testEvaluate_createsSeparateOperationForEveryCall() {
+    RemoteObject remoteObject = mock( RemoteObject.class );
+    fakeConnection( remoteObject );
+    JavaScriptExecutorImpl executor = new JavaScriptExecutorImpl();
+
+    CompletableFuture<String> future = executor.evaluate( "5 + 6" );
+    CompletableFuture<String> future2 = executor.evaluate( "Date.now()" );
+
+    verify( remoteObject ).call( eq( "evaluate" ), eq( new JsonObject().add( "content", "5+6" ) ) );
+    verify( remoteObject ).call( eq( "evaluate" ), eq( new JsonObject().add( "content", "Date.now()" ) ) );
+
+    verifyNoMoreInteractions( remoteObject );
+  }
 
   private static ConnectionImpl fakeConnection( RemoteObject remoteObject ) {
     ConnectionImpl connection = mock( ConnectionImpl.class );
     when( connection.createServiceObject( anyString() ) ).thenReturn( remoteObject );
     Fixture.fakeConnection( connection );
     return connection;
   }
-
 }