Add method to expose the locally opened port for UdpDataSource.

PiperOrigin-RevId: 341707809

library/core/src/main/java/com/google/android/exoplayer2/upstream/UdpDataSource.java

@@ -45,6 +45,8 @@ public final class UdpDataSource extends BaseDataSource {
   /** The default socket timeout, in milliseconds. */
   public static final int DEFAULT_SOCKET_TIMEOUT_MILLIS = 8 * 1000;
 
+  public static final int UDP_PORT_UNSET = -1;
+
   private final int socketTimeoutMillis;
   private final byte[] packetBuffer;
   private final DatagramPacket packet;
@@ -169,4 +171,15 @@ public final class UdpDataSource extends BaseDataSource {
       transferEnded();
     }
   }
+
+  /**
+   * Returns the local port number opened for the UDP connection, or {@link #UDP_PORT_UNSET} if no
+   * connection is open
+   */
+  public int getLocalPort() {
+    if (socket == null) {
+      return UDP_PORT_UNSET;
+    }
+    return socket.getLocalPort();
+  }
 }