Don't run EmptyDirTaskTests in a Docker container (#3792)

* Don't run EmptyDirTaskTests in a Docker container

Signed-off-by: Daniel Widdis <widdis@gmail.com>

* Catch possible exceptions

Signed-off-by: Daniel Widdis <widdis@gmail.com>

* Fix newlines with spotless

Signed-off-by: Daniel Widdis <widdis@gmail.com>

* Add comments explaining test incompatibilities

Signed-off-by: Daniel Widdis <widdis@gmail.com>

* IDE incorrectly removed needed imports

Signed-off-by: Daniel Widdis <widdis@gmail.com>

* Manual edit missed a duplicate

Signed-off-by: Daniel Widdis <widdis@gmail.com>
(cherry picked from commit c526b0c)

buildSrc/src/test/java/org/opensearch/gradle/EmptyDirTaskTests.java

@@ -33,6 +33,9 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.InvalidPathException;
+import java.nio.file.Path;
 
 import com.carrotsearch.randomizedtesting.RandomizedTest;
 import org.apache.tools.ant.taskdefs.condition.Os;
@@ -64,7 +67,11 @@ public void testCreateEmptyDir() throws Exception {
     }
 
     public void testCreateEmptyDirNoPermissions() throws Exception {
-        RandomizedTest.assumeFalse("Functionality is Unix specific", Os.isFamily(Os.FAMILY_WINDOWS));
+        // Test depends on Posix file permissions
+        RandomizedTest.assumeFalse("Functionality is Unix-like OS specific", Os.isFamily(Os.FAMILY_WINDOWS));
+        // Java's Files.setPosixFilePermissions is a NOOP inside a Docker container as
+        // files are created by default with UID and GID = 0 (root).
+        RandomizedTest.assumeFalse("Functionality doesn't work in Docker", isRunningInDocker());
 
         Project project = ProjectBuilder.builder().build();
         EmptyDirTask emptyDirTask = project.getTasks().create("emptyDirTask", EmptyDirTask.class);
@@ -92,4 +99,20 @@ private File getNewNonExistingTempFolderFile(Project project) throws IOException
         return newEmptyFolder;
     }
 
+    private static boolean isRunningInDocker() {
+        // Only reliable existing method but may be removed in future
+        if (new File("/.dockerenv").exists()) {
+            return true;
+        }
+        try {
+            // Backup 1: look for 'docker' in one of the paths in /proc/1/cgroup
+            if (Files.lines(Path.of("/proc/1/cgroup")).anyMatch(line -> line.contains("docker"))) {
+                return true;
+            }
+            // Backup 2: look for 'docker' in overlay fs
+            return Files.lines(Path.of("/proc/1/mounts")).anyMatch(line -> line.startsWith("overlay") && line.contains("docker"));
+        } catch (InvalidPathException | IOException e) {
+            return false;
+        }
+    }
 }