FileDescriptors: Return empty array instead of null; code cleanup

junixsocket-common/src/main/java/org/newsclub/net/unix/AFUNIXSocketExtensions.java

@@ -62,9 +62,9 @@ public interface AFUNIXSocketExtensions {
    * along with a call to {@link InputStream#read()}, etc.
    * 
    * NOTE: Another call to this method will not return the same file descriptors again (most likely,
-   * {@code null} will be returned).
+   * an empty array will be returned).
    * 
-   * @return The file descriptors, or {@code null} if none were available.
+   * @return The file descriptors, or an empty array if none were available.
    * @throws IOException if the operation fails.
    */
   FileDescriptor[] getReceivedFileDescriptors() throws IOException;

junixsocket-common/src/main/java/org/newsclub/net/unix/AncillaryDataSupport.java

@@ -32,6 +32,7 @@
 
 class AncillaryDataSupport implements Closeable {
   private static final ByteBuffer EMPTY_BUFFER = ByteBuffer.allocate(0);
+  private static final FileDescriptor[] NO_FILE_DESCRIPTORS = new FileDescriptor[0];
 
   protected final Map<FileDescriptor, Integer> openReceivedFileDescriptors = Collections
       .synchronizedMap(new HashMap<FileDescriptor, Integer>());
@@ -106,19 +107,19 @@ final void clearReceivedFileDescriptors() {
 
   FileDescriptor[] getReceivedFileDescriptors() {
     if (receivedFileDescriptors.isEmpty()) {
-      return null;
+      return NO_FILE_DESCRIPTORS;
     }
     List<FileDescriptor[]> copy = new ArrayList<>(receivedFileDescriptors);
     if (copy.isEmpty()) {
-      return null;
+      return NO_FILE_DESCRIPTORS;
     }
     receivedFileDescriptors.removeAll(copy);
     int count = 0;
     for (FileDescriptor[] fds : copy) {
       count += fds.length;
     }
     if (count == 0) {
-      return null;
+      return NO_FILE_DESCRIPTORS;
     }
     FileDescriptor[] oneArray = new FileDescriptor[count];
     int offset = 0;

junixsocket-common/src/main/java/org/newsclub/net/unix/FileDescriptorCast.java

@@ -105,7 +105,6 @@ public ReadableByteChannel provideAs(FileDescriptorCast fdc,
       });
 
       addProvider(FileChannel.class, new CastingProvider<FileChannel>() {
-        @SuppressWarnings("resource")
         @Override
         public FileChannel provideAs(FileDescriptorCast fdc, Class<? super FileChannel> desiredType)
             throws IOException {

junixsocket-common/src/main/java/org/newsclub/net/unix/NativeUnixSocket.java

@@ -78,24 +78,23 @@ static void checkSupported() {
 
   static native byte[] sockname(FileDescriptor fd, boolean peer);
 
-  static native long bind(final byte[] socketAddr, final FileDescriptor fd, final int options)
-      throws IOException;
+  static native long bind(byte[] socketAddr, FileDescriptor fd, int options) throws IOException;
 
-  static native void listen(final FileDescriptor fd, final int backlog) throws IOException;
+  static native void listen(FileDescriptor fd, int backlog) throws IOException;
 
-  static native boolean accept(final byte[] socketAddr, final FileDescriptor fdServer,
-      final FileDescriptor fd, long inode, int timeout) throws IOException;
+  static native boolean accept(byte[] socketAddr, FileDescriptor fdServer, FileDescriptor fd,
+      long inode, int timeout) throws IOException;
 
-  static native boolean connect(final byte[] socketAddr, final FileDescriptor fd, long inode)
+  static native boolean connect(byte[] socketAddr, FileDescriptor fd, long inode)
       throws IOException;
 
   static native boolean finishConnect(FileDescriptor fd) throws IOException;
 
-  static native void disconnect(final FileDescriptor fd) throws IOException;
+  static native void disconnect(FileDescriptor fd) throws IOException;
 
-  static native int socketStatus(final FileDescriptor fd) throws IOException;
+  static native int socketStatus(FileDescriptor fd) throws IOException;
 
-  static native Class<?> primaryType(final FileDescriptor fd) throws IOException;
+  static native Class<?> primaryType(FileDescriptor fd) throws IOException;
 
   /**
    * Reads data from an {@link AFUNIXSocketImpl}.
@@ -109,7 +108,7 @@ static native boolean connect(final byte[] socketAddr, final FileDescriptor fd,
    *         {@code buf} was {@code null}.
    * @throws IOException upon error.
    */
-  static native int read(final FileDescriptor fd, byte[] buf, int off, int len,
+  static native int read(FileDescriptor fd, byte[] buf, int off, int len,
       AncillaryDataSupport ancillaryDataSupport, int timeoutMillis) throws IOException;
 
   /**
@@ -123,37 +122,37 @@ static native int read(final FileDescriptor fd, byte[] buf, int off, int len,
    * @return The number of bytes written (which could be 0).
    * @throws IOException upon error.
    */
-  static native int write(final FileDescriptor fd, byte[] buf, int off, int len,
+  static native int write(FileDescriptor fd, byte[] buf, int off, int len,
       AncillaryDataSupport ancillaryDataSupport) throws IOException;
 
-  static native int receive(final FileDescriptor fd, ByteBuffer directBuffer, int offset,
-      int length, ByteBuffer directSocketAddressOut, int options,
-      AncillaryDataSupport ancillaryDataSupport, int timeoutMillis) throws IOException;
+  static native int receive(FileDescriptor fd, ByteBuffer directBuffer, int offset, int length,
+      ByteBuffer directSocketAddressOut, int options, AncillaryDataSupport ancillaryDataSupport,
+      int timeoutMillis) throws IOException;
 
-  static native int send(final FileDescriptor fd, ByteBuffer directBuffer, int offset, int length,
+  static native int send(FileDescriptor fd, ByteBuffer directBuffer, int offset, int length,
       ByteBuffer directSocketAddress, int options, AncillaryDataSupport ancillaryDataSupport)
       throws IOException;
 
-  static native void close(final FileDescriptor fd) throws IOException;
+  static native void close(FileDescriptor fd) throws IOException;
 
-  static native void shutdown(final FileDescriptor fd, int mode) throws IOException;
+  static native void shutdown(FileDescriptor fd, int mode) throws IOException;
 
-  static native int getSocketOptionInt(final FileDescriptor fd, int optionId) throws IOException;
+  static native int getSocketOptionInt(FileDescriptor fd, int optionId) throws IOException;
 
-  static native void setSocketOptionInt(final FileDescriptor fd, int optionId, int value)
+  static native void setSocketOptionInt(FileDescriptor fd, int optionId, int value)
       throws IOException;
 
-  static native int available(final FileDescriptor fd) throws IOException;
+  static native int available(FileDescriptor fd) throws IOException;
 
   static native AFUNIXSocketCredentials peerCredentials(FileDescriptor fd,
       AFUNIXSocketCredentials creds) throws IOException;
 
-  static native void initServerImpl(final ServerSocket serverSocket, final AFUNIXSocketImpl impl)
+  static native void initServerImpl(ServerSocket serverSocket, AFUNIXSocketImpl impl)
       throws IOException;
 
   static native void createSocket(FileDescriptor fdesc, int type) throws IOException;
 
-  static native void setPort(final AFUNIXSocketAddress addr, int port);
+  static native void setPort(AFUNIXSocketAddress addr, int port);
 
   static native void initFD(FileDescriptor fdesc, int fd) throws IOException;
 

junixsocket-common/src/test/java/org/newsclub/net/unix/AFUNIXSocketTest.java

@@ -17,14 +17,15 @@
  */
 package org.newsclub.net.unix;
 
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotEquals;
-import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.io.Closeable;
+import java.io.FileDescriptor;
 import java.io.IOException;
 import java.net.InetSocketAddress;
 import java.net.Socket;
@@ -155,7 +156,7 @@ public void testBindBadArguments() throws Exception {
   public void testReceivedFileDescriptorsUnconnected() throws Exception {
     try (AFUNIXSocket sock = AFUNIXSocket.newInstance()) {
       // We don't check socket status, so these calls are perfectly fine for unconnected sockets.
-      assertNull(sock.getReceivedFileDescriptors());
+      assertArrayEquals(new FileDescriptor[0], sock.getReceivedFileDescriptors());
       sock.clearReceivedFileDescriptors();
     }
   }

junixsocket-common/src/test/java/org/newsclub/net/unix/FileDescriptorsTest.java

@@ -17,9 +17,9 @@
  */
 package org.newsclub.net.unix;
 
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTimeoutPreemptively;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -73,7 +73,7 @@ protected void handleConnection(final AFUNIXSocket socket) throws IOException {
         FileDescriptor[] fds;
         int numRead;
         fds = socket.getReceivedFileDescriptors();
-        assertNull(fds, "Initially, there are no file descriptors");
+        assertArrayEquals(new FileDescriptor[0], fds, "Initially, there are no file descriptors");
 
         numRead = in.read(buf);
         assertEquals(5, numRead, "'HELLO' is five bytes long");
@@ -83,13 +83,13 @@ protected void handleConnection(final AFUNIXSocket socket) throws IOException {
         assertEquals(2, fds.length, "Now, we should have two file descriptors");
 
         fds = socket.getReceivedFileDescriptors();
-        assertNull(fds, "If we ask again, these new file descriptors should be gone");
+        assertArrayEquals(new FileDescriptor[0], fds, "If we ask again, these new file descriptors should be gone");
 
         try (InputStream is = socket.getInputStream()) {
           numRead = is.read(buf);
           assertEquals(-1, numRead, "There shouldn't be anything left to read");
           fds = socket.getReceivedFileDescriptors();
-          assertNull(fds, "There shouldn't be any new file descriptors");
+          assertArrayEquals(new FileDescriptor[0], fds, "There shouldn't be any new file descriptors");
         }
       }
     });
@@ -202,7 +202,7 @@ protected void handleConnection(final AFUNIXSocket socket) throws IOException {
         } catch (SocketException e) {
           // on Linux, a SocketException may be thrown (an ancillary message was sent, but not read)
         }
-        assertNull(socket.getReceivedFileDescriptors());
+        assertArrayEquals(new FileDescriptor[0], socket.getReceivedFileDescriptors());
         assertEquals(0, socket.getAncillaryReceiveBufferSize());
       }
     });
@@ -235,7 +235,7 @@ protected void handleConnection(final AFUNIXSocket socket) throws IOException {
         try {
           assertEquals(123, inputStream.read());
           FileDescriptor[] fds = socket.getReceivedFileDescriptors();
-          if (fds != null) {
+          if (fds.length != 0) {
             if (fds.length == 2) {
               // space was sufficient
             } else if (fds.length == 1) {
@@ -250,7 +250,7 @@ protected void handleConnection(final AFUNIXSocket socket) throws IOException {
         } catch (SocketException e) {
           // expected
         }
-        assertNull(socket.getReceivedFileDescriptors());
+        assertArrayEquals(new FileDescriptor[0], socket.getReceivedFileDescriptors());
       }
     });
   }

junixsocket-common/src/test/java/org/newsclub/net/unix/SocketTestBase.java

@@ -158,7 +158,7 @@ public void shutdown() throws IOException {
      * @param sock The socket to handle.
      * @throws IOException upon error.
      */
-    protected abstract void handleConnection(final AFUNIXSocket sock) throws IOException;
+    protected abstract void handleConnection(AFUNIXSocket sock) throws IOException;
 
     /**
      * Called from within {@link #handleConnection(AFUNIXSocket)} to tell the server to no longer