Server push (#111)

* Asynchronous bidirectional communication
* Use Atmosphere as a backend
* Use websockets if available, fallback to HTTP streaming
* Push mode (disabled, manual, automatic)
  * Configurable via servlet parameter pushMode
  * Disabled: The default; regular AJAX communication
  * Manual: Need explicit UI.push() call
  * Automatic: push all UIs in session when lock released
* UI.push()
  * Push pending state and RPC to client asynchronously
  * Must hold session lock when invoking

Change-Id: Idb5978ac81f7ff1e66665df4e3f96e29e4c419d4

2 files changed, 57 insertions, 0 deletions

diff --git a/shared/src/com/vaadin/shared/ApplicationConstants.java b/shared/src/com/vaadin/shared/ApplicationConstants.java
index 220679e69c..5f23a3dc38 100644
--- a/shared/src/com/vaadin/shared/ApplicationConstants.java
+++ b/shared/src/com/vaadin/shared/ApplicationConstants.java
@@ -28,6 +28,8 @@ public class ApplicationConstants implements Serializable {
 
     public static final String HEARTBEAT_PATH = "HEARTBEAT";
 
+    public static final String PUSH_PATH = "PUSH";
+
     public static final String PUBLISHED_FILE_PATH = APP_PATH + '/'
             + "PUBLISHED";
 
diff --git a/shared/src/com/vaadin/shared/communication/PushMode.java b/shared/src/com/vaadin/shared/communication/PushMode.java
new file mode 100644
index 0000000000..f7414a89ea
--- /dev/null
+++ b/shared/src/com/vaadin/shared/communication/PushMode.java
@@ -0,0 +1,55 @@
+/*
+ * Copyright 2000-2013 Vaadin Ltd.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package com.vaadin.shared.communication;
+
+/**
+ * The mode of bidirectional ("push") communication that is in use.
+ * 
+ * @see com.vaadin.server.DeploymentConfiguration#getPushMode()
+ * 
+ * @author Vaadin Ltd
+ * @since 7.1
+ */
+public enum PushMode {
+    /**
+     * Push is disabled. Regular AJAX requests are used to communicate between
+     * the client and the server. Asynchronous messages from the server are not
+     * possible. {@link com.vaadin.ui.UI#push() ui.push()} throws
+     * IllegalStateException.
+     * <p>
+     * This is the default mode unless
+     * {@link com.vaadin.server.DeploymentConfiguration#getPushMode()
+     * configured} otherwise.
+     */
+    DISABLED,
+
+    /**
+     * Push is enabled. A bidirectional channel is established between the
+     * client and server and used to communicate state changes and RPC
+     * invocations. The client is not automatically updated if the server-side
+     * state is asynchronously changed; {@link com.vaadin.ui.UI#push()
+     * ui.push()} must be explicitly called.
+     */
+    MANUAL,
+
+    /**
+     * Push is enabled. Like {@link #MANUAL}, but asynchronous changes to the
+     * server-side state are automatically pushed to the client once the session
+     * lock is released.
+     */
+    AUTOMATIC;
+}