Replace hidden getFileDescriptor$()

It's the preparation for the incoming ConnectivityService
mainline. The mainline modules can not access hidden APIs.
Thus, the hidden APIs usage should be removed.

The getFileDescriptor$() in Socket or DatagramSocket is
hidden for internal usage. It should be used in a module and
not prefer to expose as an API. Thus, replace it with
ParcelFileDescriptor APIs to get the fd via
ParcelFileDescriptor.

Bug: 170598012
Test: atest FrameworksNetTests
Change-Id: I05b31a48315e7e6d95e22123103e544a7136a449
diff --git a/core/java/android/net/Network.java b/core/java/android/net/Network.java
index fbca7f1..b07bd68 100644
--- a/core/java/android/net/Network.java
+++ b/core/java/android/net/Network.java
@@ -21,6 +21,7 @@
 import android.compat.annotation.UnsupportedAppUsage;
 import android.os.Build;
 import android.os.Parcel;
+import android.os.ParcelFileDescriptor;
 import android.os.Parcelable;
 import android.system.ErrnoException;
 import android.system.Os;
@@ -380,7 +381,13 @@
         // Query a property of the underlying socket to ensure that the socket's file descriptor
         // exists, is available to bind to a network and is not closed.
         socket.getReuseAddress();
-        bindSocket(socket.getFileDescriptor$());
+        final ParcelFileDescriptor pfd = ParcelFileDescriptor.fromDatagramSocket(socket);
+        bindSocket(pfd.getFileDescriptor());
+        // ParcelFileDescriptor.fromSocket() creates a dup of the original fd. The original and the
+        // dup share the underlying socket in the kernel. The socket is never truly closed until the
+        // last fd pointing to the socket being closed. So close the dup one after binding the
+        // socket to control the lifetime of the dup fd.
+        pfd.close();
     }
 
     /**
@@ -392,7 +399,13 @@
         // Query a property of the underlying socket to ensure that the socket's file descriptor
         // exists, is available to bind to a network and is not closed.
         socket.getReuseAddress();
-        bindSocket(socket.getFileDescriptor$());
+        final ParcelFileDescriptor pfd = ParcelFileDescriptor.fromSocket(socket);
+        bindSocket(pfd.getFileDescriptor());
+        // ParcelFileDescriptor.fromSocket() creates a dup of the original fd. The original and the
+        // dup share the underlying socket in the kernel. The socket is never truly closed until the
+        // last fd pointing to the socket being closed. So close the dup one after binding the
+        // socket to control the lifetime of the dup fd.
+        pfd.close();
     }
 
     /**