Omit empty hierarchy data from the response (#18510)

Reduces the payload size for the "Update all labels" action with 40
layouts in BasicPerformanceTest by 16% (from 11087 to 9270 bytes). The
reduction is improved to 22% (1855 to 1455) if the response is gzipped
since the omited data doesn't compress very well.

Change-Id: I1d2837c93222fffa59b14836f162e3e87349e086

3 files changed, 32 insertions, 14 deletions

diff --git a/server/src/com/vaadin/server/communication/ConnectorHierarchyWriter.java b/server/src/com/vaadin/server/communication/ConnectorHierarchyWriter.java
index 1c1a220b5d..503bf8c0ae 100644
--- a/server/src/com/vaadin/server/communication/ConnectorHierarchyWriter.java
+++ b/server/src/com/vaadin/server/communication/ConnectorHierarchyWriter.java
@@ -20,6 +20,7 @@ import java.io.IOException;
 import java.io.Serializable;
 import java.io.Writer;
 import java.util.Collection;
+import java.util.Set;
 
 import com.vaadin.server.AbstractClientConnector;
 import com.vaadin.server.ClientConnector;
@@ -49,10 +50,13 @@ public class ConnectorHierarchyWriter implements Serializable {
      *            The {@link UI} whose hierarchy to write.
      * @param writer
      *            The {@link Writer} used to write the JSON.
+     * @param stateUpdateConnectors
+     *            connector ids with state changes
      * @throws IOException
      *             If the serialization fails.
      */
-    public void write(UI ui, Writer writer) throws IOException {
+    public void write(UI ui, Writer writer, Set<String> stateUpdateConnectors)
+            throws IOException {
 
         Collection<ClientConnector> dirtyVisibleConnectors = ui
                 .getConnectorTracker().getDirtyVisibleConnectors();
@@ -69,13 +73,18 @@ public class ConnectorHierarchyWriter implements Serializable {
                     children.set(children.length(), child.getConnectorId());
                 }
             }
-            try {
-                hierarchyInfo.put(connectorId, children);
-            } catch (JsonException e) {
-                throw new PaintException(
-                        "Failed to send hierarchy information about "
-                                + connectorId + " to the client: "
-                                + e.getMessage(), e);
+
+            // Omit for leaf nodes with state changes
+            if (children.length() > 0
+                    || !stateUpdateConnectors.contains(connectorId)) {
+                try {
+                    hierarchyInfo.put(connectorId, children);
+                } catch (JsonException e) {
+                    throw new PaintException(
+                            "Failed to send hierarchy information about "
+                                    + connectorId + " to the client: "
+                                    + e.getMessage(), e);
+                }
             }
         }
         writer.write(JsonUtil.stringify(hierarchyInfo));
diff --git a/server/src/com/vaadin/server/communication/SharedStateWriter.java b/server/src/com/vaadin/server/communication/SharedStateWriter.java
index 6ef02955f7..06b59ad4cc 100644
--- a/server/src/com/vaadin/server/communication/SharedStateWriter.java
+++ b/server/src/com/vaadin/server/communication/SharedStateWriter.java
@@ -20,6 +20,8 @@ import java.io.IOException;
 import java.io.Serializable;
 import java.io.Writer;
 import java.util.Collection;
+import java.util.HashSet;
+import java.util.Set;
 
 import com.vaadin.server.ClientConnector;
 import com.vaadin.server.PaintException;
@@ -47,31 +49,36 @@ public class SharedStateWriter implements Serializable {
      *            The UI whose state changes should be written.
      * @param writer
      *            The writer to use.
+     * @return a set of connector ids with state changes
      * @throws IOException
      *             If the serialization fails.
      */
-    public void write(UI ui, Writer writer) throws IOException {
+    public Set<String> write(UI ui, Writer writer) throws IOException {
 
         Collection<ClientConnector> dirtyVisibleConnectors = ui
                 .getConnectorTracker().getDirtyVisibleConnectors();
 
+        Set<String> writtenConnectors = new HashSet<String>();
         JsonObject sharedStates = Json.createObject();
         for (ClientConnector connector : dirtyVisibleConnectors) {
             // encode and send shared state
+            String connectorId = connector.getConnectorId();
             try {
                 JsonObject stateJson = connector.encodeState();
 
                 if (stateJson != null && stateJson.keys().length != 0) {
-                    sharedStates.put(connector.getConnectorId(), stateJson);
+                    sharedStates.put(connectorId, stateJson);
+                    writtenConnectors.add(connectorId);
                 }
             } catch (JsonException e) {
                 throw new PaintException(
                         "Failed to serialize shared state for connector "
                                 + connector.getClass().getName() + " ("
-                                + connector.getConnectorId() + "): "
-                                + e.getMessage(), e);
+                                + connectorId + "): " + e.getMessage(), e);
             }
         }
         writer.write(JsonUtil.stringify(sharedStates));
+
+        return writtenConnectors;
     }
 }
diff --git a/server/src/com/vaadin/server/communication/UidlWriter.java b/server/src/com/vaadin/server/communication/UidlWriter.java
index 25b1bdaaf9..b117cb4b4d 100644
--- a/server/src/com/vaadin/server/communication/UidlWriter.java
+++ b/server/src/com/vaadin/server/communication/UidlWriter.java
@@ -159,7 +159,8 @@ public class UidlWriter implements Serializable {
             // processing.
 
             writer.write("\"state\":");
-            new SharedStateWriter().write(ui, writer);
+            Set<String> stateUpdateConnectors = new SharedStateWriter().write(
+                    ui, writer);
             writer.write(", "); // close states
 
             // TODO This should be optimized. The type only needs to be
@@ -179,7 +180,8 @@ public class UidlWriter implements Serializable {
             // child to 0 children)
 
             writer.write("\"hierarchy\":");
-            new ConnectorHierarchyWriter().write(ui, writer);
+            new ConnectorHierarchyWriter().write(ui, writer,
+                    stateUpdateConnectors);
             writer.write(", "); // close hierarchy
 
             // send server to client RPC calls for components in the UI, in call