Revert "Remove JNR (#5979)" (#6299)

This reverts commit 899d9fb584.

core/src/test/java/hudson/FilePathTest.java

@@ -40,6 +40,7 @@ import static org.mockito.Mockito.when;
 
 import hudson.FilePath.TarCompression;
 import hudson.model.TaskListener;
+import hudson.os.PosixAPI;
 import hudson.os.WindowsUtil;
 import hudson.remoting.VirtualChannel;
 import hudson.slaves.WorkspaceList;
@@ -478,6 +479,25 @@ public class FilePathTest {
             }
     }
 
+    @Test public void copyToWithPermissionSpecialPermissions() throws IOException, InterruptedException {
+        assumeFalse(Functions.isWindows() || Platform.isDarwin());
+        File tmp = temp.getRoot();
+        File original = new File(tmp, "original");
+        FilePath originalP = new FilePath(channels.french, original.getPath());
+        originalP.touch(0);
+        PosixAPI.jnr().chmod(original.getAbsolutePath(), 02777); // Read/write/execute for everyone and setuid.
+
+        File sameChannelCopy = new File(tmp, "sameChannelCopy");
+        FilePath sameChannelCopyP = new FilePath(channels.french, sameChannelCopy.getPath());
+        originalP.copyToWithPermission(sameChannelCopyP);
+        assertEquals("Special permissions should be copied on the same machine", 02777, PosixAPI.jnr().stat(sameChannelCopy.getAbsolutePath()).mode() & 07777);
+
+        File diffChannelCopy = new File(tmp, "diffChannelCopy");
+        FilePath diffChannelCopyP = new FilePath(channels.british, diffChannelCopy.getPath());
+        originalP.copyToWithPermission(diffChannelCopyP);
+        assertEquals("Special permissions should not be copied across machines", 00777, PosixAPI.jnr().stat(diffChannelCopy.getAbsolutePath()).mode() & 07777);
+    }
+
     @Test public void symlinkInTar() throws Exception {
         assumeFalse(Functions.isWindows());