Add open() API to UTransport

Some transports require initialization that should not be done inside of the constructor so we add the open() API that can be implemented to do the async initialization of the underlining transport.

#146

src/main/java/org/eclipse/uprotocol/transport/UTransport.java

@@ -13,22 +13,19 @@
 package org.eclipse.uprotocol.transport;
 
 import java.util.concurrent.CompletionStage;
+import java.util.concurrent.CompletableFuture;
 
 import org.eclipse.uprotocol.v1.UCode;
 import org.eclipse.uprotocol.v1.UMessage;
 import org.eclipse.uprotocol.v1.UStatus;
 import org.eclipse.uprotocol.v1.UUri;
 
 /**
- * UTransport is the uP-L1 interface that provides a common API for uE
- * developers to send and receive messages.
- * UTransport implementations contain the details for connecting to the
- * underlying transport technology and
- * sending UMessage using the configured technology. For more information please
- * refer to
+ * UTransport is the uP-L1 interface that provides a common API for uE developers to send and receive messages.
+ * UTransport implementations contain the details for connecting to the underlying transport technology and
+ * sending UMessage using the configured technology. For more information please refer to
  * https://github.com/eclipse-uprotocol/up-spec/blob/main/up-l1/README.adoc.
  */
-
 public interface UTransport {
 
     /**
@@ -45,6 +42,7 @@ public interface UTransport {
      */
     CompletionStage<UStatus> send(UMessage message);
 
+
     /**
      * Register {@code UListener} for {@code UUri} source filters to be called when
      * a message is received.
@@ -62,6 +60,7 @@ default CompletionStage<UStatus> registerListener(UUri sourceFilter, UListener l
         return registerListener(sourceFilter, null, listener);
     }
 
+
     /**
      * Register {@code UListener} for {@code UUri} source and sink filters to be
      * called when a message is received.
@@ -79,10 +78,10 @@ default CompletionStage<UStatus> registerListener(UUri sourceFilter, UListener l
      */
     CompletionStage<UStatus> registerListener(UUri sourceFilter, UUri sinkFilter, UListener listener);
 
+
     /**
      * Unregister {@code UListener} for {@code UUri} source filters. Messages
-     * arriving on this topic will
-     * no longer be processed by this listener.
+     * arriving on this topic will no longer be processed by this listener.
      * 
      * @param sourceFilter The UAttributes::source address pattern that the message
      *                     to receive needs to match.
@@ -97,10 +96,10 @@ default CompletionStage<UStatus> unregisterListener(UUri sourceFilter, UListener
         return unregisterListener(sourceFilter, null, listener);
     }
 
+
     /**
      * Unregister {@code UListener} for {@code UUri} source and sink filters.
-     * Messages arriving on this topic will
-     * no longer be processed by this listener.
+     * Messages arriving on this topic will no longer be processed by this listener.
      * 
      * @param sourceFilter The UAttributes::source address pattern that the message
      *                     to receive needs to match.
@@ -115,18 +114,31 @@ default CompletionStage<UStatus> unregisterListener(UUri sourceFilter, UListener
      */
     CompletionStage<UStatus> unregisterListener(UUri sourceFilter, UUri sinkFilter, UListener listener);
 
+
     /**
-     * Return the source address for the uE (authority, entity, and resource
-     * information)
+     * Return the source address of the uE.
+     * The Source address is passed to the constructor of a given transport
      * 
      * @return UUri containing the source address
      */
     UUri getSource();
 
 
+    /**
+     * Open the connection to the transport that will trigger any registered listeners
+     * to be registered.
+     * 
+     * @return Returns {@link UStatus} with {@link UCode.OK} if the connection is
+     *         opened correctly, otherwise it returns with the appropriate failure.
+     */
+    default CompletionStage<UStatus> open() {
+        return CompletableFuture.completedFuture(UStatus.newBuilder().setCode(UCode.OK).build());
+    }
+
+
     /**
      * Close the connection to the transport that will trigger any registered listeners
      * to be unregistered.
      */
-    void close();
+    default void close() { }
 }

src/test/java/org/eclipse/uprotocol/transport/UTransportTest.java

@@ -15,6 +15,7 @@
 import java.util.concurrent.CompletionStage;
 import java.util.concurrent.CompletableFuture;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import org.junit.jupiter.api.DisplayName;
@@ -84,6 +85,42 @@ public void test_unhappy_register_unlistener() {
         assertEquals(result.toCompletableFuture().join().getCode(), UCode.INTERNAL);
     }
 
+    @Test
+    @DisplayName("Test happy path calling open() API")
+    public void test_happy_open() {
+        UTransport transport = new HappyUTransport();
+        assertEquals(transport.open().toCompletableFuture().join().getCode(), UCode.OK);
+    }
+
+    @Test
+    @DisplayName("Test default oepn() and close() APIs")
+    public void test_default_open_close() {
+        UTransport transport = new UTransport() {
+            @Override
+            public CompletionStage<UStatus> send(UMessage message) {
+                return CompletableFuture.completedFuture(UStatus.newBuilder().setCode(UCode.OK).build());
+            }
+
+            @Override
+            public CompletionStage<UStatus> registerListener(UUri source, UUri sink, UListener listener) {
+                return CompletableFuture.completedFuture(UStatus.newBuilder().setCode(UCode.OK).build());
+            }
+
+            @Override
+            public CompletionStage<UStatus> unregisterListener(UUri source, UUri sink, UListener listener) {
+                return CompletableFuture.completedFuture(UStatus.newBuilder().setCode(UCode.OK).build());
+            }
+
+            @Override
+            public UUri getSource() {
+                return UUri.getDefaultInstance();
+            }
+        };
+
+        assertDoesNotThrow(() -> transport.close());
+    }
+
+
     class MyListener implements UListener {
         @Override
         public void onReceive(UMessage message) {}