8256461: AbstractFileSystemProvider.getSunPathForSocketCall for empty Path returns '.'

Reviewed-by: dfuchs, alanb

src/java.base/share/classes/sun/nio/ch/UnixDomainSockets.java

@@ -105,6 +105,9 @@ class UnixDomainSockets {
 
     static void bind(FileDescriptor fd, Path addr) throws IOException {
         byte[] path = getPathBytes(addr);
+        if (path.length == 0) {
+            throw new BindException("Server socket cannot bind to unnamed address");
+        }
         bind0(fd, path);
     }
 

src/java.base/share/classes/sun/nio/fs/AbstractFileSystemProvider.java

@@ -158,6 +158,7 @@ public abstract class AbstractFileSystemProvider extends FileSystemProvider {
     /**
      * Returns a path name as bytes for a Unix domain socket.
      * Different encodings may be used for these names on some platforms.
+     * If path is empty, then an empty byte[] is returned.
      */
-    public abstract byte[] getSunPathForSocketFile(Path file);
+    public abstract byte[] getSunPathForSocketFile(Path path);
 }

src/java.base/unix/classes/sun/nio/fs/UnixFileSystemProvider.java

@@ -48,6 +48,7 @@ public abstract class UnixFileSystemProvider
     extends AbstractFileSystemProvider
 {
     private static final String USER_DIR = "user.dir";
+    private static final byte[] EMPTY_PATH = new byte[0];
     private final UnixFileSystem theFileSystem;
 
     public UnixFileSystemProvider() {
@@ -568,6 +569,9 @@ public abstract class UnixFileSystemProvider
     @Override
     public byte[] getSunPathForSocketFile(Path obj) {
         UnixPath file = UnixPath.toUnixPath(obj);
+        if (file.isEmpty()) {
+            return EMPTY_PATH;
+        }
         return file.getByteArrayForSysCalls();
     }
 }

src/java.base/windows/classes/sun/nio/fs/WindowsFileSystemProvider.java

@@ -46,7 +46,7 @@ import static sun.nio.fs.WindowsConstants.*;
 class WindowsFileSystemProvider
     extends AbstractFileSystemProvider
 {
-    private static final Unsafe unsafe = Unsafe.getUnsafe();
+    private static final byte[] EMPTY_PATH = new byte[0];
 
     private final WindowsFileSystem theFileSystem;
 
@@ -628,7 +628,7 @@ class WindowsFileSystemProvider
     public byte[] getSunPathForSocketFile(Path obj) {
         WindowsPath file = WindowsPath.toWindowsPath(obj);
         String s = file.toString();
-        return s.getBytes(StandardCharsets.UTF_8);
+        return s.isEmpty() ? EMPTY_PATH : s.getBytes(StandardCharsets.UTF_8);
     }
 
 }

test/jdk/java/nio/channels/unixdomain/EmptySunPathForSocketFile.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * @test
+ * @bug 8256461
+ * @modules java.base/sun.nio.fs
+ * @run testng EmptySunPathForSocketFile
+ */
+
+import java.nio.file.FileSystems;
+import java.nio.file.Path;
+import java.nio.file.spi.FileSystemProvider;
+import sun.nio.fs.AbstractFileSystemProvider;
+
+import static org.testng.Assert.assertEquals;
+
+/**
+ * Check that AbstractFileSystemProvider.getSunPathForSocketFile with
+ * an empty path returns an empty byte[]
+ */
+public class EmptySunPathForSocketFile {
+    public static void main(String[] args) throws Exception {
+        Path path = Path.of("");
+        FileSystemProvider provider = FileSystems.getDefault().provider();
+        byte[] bb = ((AbstractFileSystemProvider) provider).getSunPathForSocketFile(path);
+        assertEquals(bb, new byte[0]);
+    }
+}