Add eventstream.ServerListener.getBoundPort() (#491)

Lets users pass 0 to let OS autodetermine the port, and then query which port was selected.

Co-authored-by: Vitaly Khalmansky <[email protected]>

Author: graebm

crt/aws-c-event-stream

@@ -19,6 +19,7 @@ public class ServerListener extends CrtResource {
     private final CompletableFuture<Void> shutdownComplete = new CompletableFuture<>();
     private TlsContext tlsContext = null;
     private final ServerBootstrap serverBootstrap;
+    private int boundPort = -1;
 
     /**
      * Instantiates a server listener. Once this function completes, the server is configured
@@ -36,9 +37,13 @@ public ServerListener(final String hostName, short port, final SocketOptions soc
                           final ServerListenerHandler handler) {
 
         long tlsContextPtr = tlsContext != null ? tlsContext.getNativeHandle(): 0;
-        acquireNativeHandle(serverListenerNew(this, hostName.getBytes(StandardCharsets.UTF_8), port,
+        long serverHandler = serverListenerNew(this, hostName.getBytes(StandardCharsets.UTF_8), port,
                 socketOptions.getNativeHandle(), tlsContextPtr, serverBootstrap.getNativeHandle(),
-                handler));
+                handler);
+
+        boundPort = getBoundPort(serverHandler);
+
+        acquireNativeHandle(serverHandler);
 
         if (tlsContext != null) {
             addReferenceTo(tlsContext);
@@ -60,6 +65,13 @@ protected boolean canReleaseReferencesImmediately() {
         return false;
     }
 
+    /**
+     * @return the port which the listener socket is bound to.
+     */
+    public int getBoundPort() {
+        return boundPort;
+    }
+
     /**
      * Invoked from JNI. Completes the shutdownComplete future.
      */
@@ -78,6 +90,8 @@ private static native long serverListenerNew(ServerListener serverListener, byte
                                                  short port, long socketOptionsHandle,
                                                  long tlsContextHandle, long bootstrapHandle,
                                                  ServerListenerHandler handler);
+    private static native int getBoundPort(long serverListener);
+
     private static native void release(long serverListenerPtr);
 
 }

crt/aws-c-io

@@ -578,6 +578,23 @@ jlong JNICALL Java_software_amazon_awssdk_crt_eventstream_ServerListener_serverL
     return (jlong)NULL;
 }
 
+JNIEXPORT
+jint JNICALL Java_software_amazon_awssdk_crt_eventstream_ServerListener_getBoundPort(
+    JNIEnv *env,
+    jclass jni_class,
+    jlong jni_server_listener) {
+    (void)env;
+    (void)jni_class;
+    struct aws_event_stream_rpc_server_listener *listener =
+        (struct aws_event_stream_rpc_server_listener *)jni_server_listener;
+    if (!listener) {
+        aws_jni_throw_runtime_exception(env, "ServerListener.getBoundPort: Invalid serverListener");
+        return (jshort)-1;
+    }
+
+    return (jint)aws_event_stream_rpc_server_listener_get_bound_port(listener);
+}
+
 JNIEXPORT
 void JNICALL Java_software_amazon_awssdk_crt_eventstream_ServerListener_release(
     JNIEnv *env,

src/main/java/software/amazon/awssdk/crt/eventstream/ServerListener.java

@@ -53,6 +53,34 @@ public void onConnectionShutdown(ServerConnection serverConnection, int errorCod
         socketOptions.close();
     }
 
+    @Test
+    public void testSetupWith0PortAndTearDown() throws ExecutionException, InterruptedException, TimeoutException {
+        SocketOptions socketOptions = new SocketOptions();
+        socketOptions.connectTimeoutMs = 3000;
+        socketOptions.domain = SocketOptions.SocketDomain.IPv4;
+        socketOptions.type = SocketOptions.SocketType.STREAM;
+
+        EventLoopGroup elGroup = new EventLoopGroup(1);
+        ServerBootstrap bootstrap = new ServerBootstrap(elGroup);
+        ServerListener listener = new ServerListener("127.0.0.1", (short)0, socketOptions, null, bootstrap, new ServerListenerHandler() {
+            public ServerConnectionHandler onNewConnection(ServerConnection serverConnection, int errorCode) {
+                return null;
+            }
+
+            public void onConnectionShutdown(ServerConnection serverConnection, int errorCode) {
+            }
+        });
+
+        int boundPort = listener.getBoundPort();
+        assertTrue(boundPort > 0);
+        listener.close();
+        listener.getShutdownCompleteFuture().get(1, TimeUnit.SECONDS);
+        bootstrap.close();
+        elGroup.close();
+        elGroup.getShutdownCompleteFuture().get(1, TimeUnit.SECONDS);
+        socketOptions.close();
+    }
+
     @Test
     public void testBindErrorPropagates() throws ExecutionException, InterruptedException, TimeoutException {
         SocketOptions socketOptions = new SocketOptions();