fix: no stream serialization without uis (#15287)

Do not serialize the streamResourceRegistry
if UIs are not serialized.

Fixes #14893

flow-server/src/main/java/com/vaadin/flow/server/VaadinSession.java

@@ -131,7 +131,7 @@ public class VaadinSession implements HttpSessionBindingListener, Serializable {
 
     private final Attributes attributes = new Attributes();
 
-    private final StreamResourceRegistry resourceRegistry;
+    private transient StreamResourceRegistry resourceRegistry;
 
     private long lastUnlocked;
 
@@ -1056,6 +1056,7 @@ private void readObject(ObjectInputStream stream)
         try {
             stream.defaultReadObject();
             uIs = (Map<Integer, UI>) stream.readObject();
+            resourceRegistry = (StreamResourceRegistry) stream.readObject();
             pendingAccessQueue = new ConcurrentLinkedQueue<>();
         } finally {
             CurrentInstance.restoreInstances(old);
@@ -1081,8 +1082,10 @@ private void writeObject(java.io.ObjectOutputStream stream)
         stream.defaultWriteObject();
         if (serializeUIs) {
             stream.writeObject(uIs);
+            stream.writeObject(resourceRegistry);
         } else {
             stream.writeObject(new HashMap<>());
+            stream.writeObject(new StreamResourceRegistry(this));
         }
     }
 

flow-server/src/test/java/com/vaadin/tests/server/SerializationTest.java

@@ -13,6 +13,8 @@
 import org.junit.Test;
 import org.mockito.Mockito;
 
+import com.vaadin.flow.server.StreamRegistration;
+import com.vaadin.flow.server.StreamResource;
 import com.vaadin.flow.server.VaadinContext;
 import com.vaadin.flow.server.VaadinRequest;
 import com.vaadin.flow.server.VaadinService;
@@ -49,6 +51,43 @@ public void testSerializeVaadinSession_notProductionMode_disableDevModeSerializa
                 session.getUIs().isEmpty());
     }
 
+    @Test
+    public void testSerializeVaadinSession_notProductionMode_disableDevModeSerialization_streamResources_deserializedSessionHasNoUIs()
+            throws Exception {
+
+        VaadinService vaadinService = new MockVaadinService(false, false);
+        VaadinSession session = new VaadinSession(vaadinService);
+        // This is done only for test purpose to init the session lock,
+        // should be called by Flow internally as soon as the session has
+        // been created.
+        session.refreshTransients(null, vaadinService);
+        MockUI ui = new MockUI(session);
+        ui.doInit(null, 42);
+        session.addUI(ui);
+
+        session.lock();
+        final StreamRegistration name = session.getResourceRegistry()
+                .registerResource(new StreamResource("name",
+                        () -> new ByteArrayInputStream(new byte[0])));
+        session.unlock();
+
+        session = serializeAndDeserialize(session);
+        // This is done only for test purpose to refresh the session lock,
+        // should be called by Flow internally as soon as the session has
+        // been retrieved from http session.
+        session.refreshTransients(null, vaadinService);
+
+        Assert.assertNotNull(
+                "UIs map should be available after devmode deserialization",
+                session.getUIs());
+        Assert.assertTrue("UIs should be empty after devmode deserialization",
+                session.getUIs().isEmpty());
+        Assert.assertTrue(
+                "StreamResources should be empty after devmode deserialization",
+                session.getResourceRegistry().getResource(name.getResourceUri())
+                        .isEmpty());
+    }
+
     @Test
     public void testSerializeVaadinSession_notProductionMode_enableDevModeSerialization_deserializedSessionHasUI()
             throws Exception {