New test for Clipboard

Testing the Clipboard can be difficult because there are a lot of system
issues that can interfere, but of particular concern are:

1. System clipboard managers which may take ownership of the clipboard
at unexpected times.
2. Limitations as to when processes can access clipboard, such as on Wayland
where only active window can access clipboard.
3. Different behaviour when copying within a single process than between
processes.

These tests aim to resolve these issues.

For the system clipboard manager there are a lot of extra sleep calls
to allow clipboard manager to complete operations before continuing tests.
In addition, we run all the tests multiple times by default to ensure
stability.

For the process limitations, we carefully control when the shell is created
because we often cannot get focus back when shell ends up in the background.
See the openAndFocusShell and openAndFocusRemote methods.

For the different behaviours, we spin up a simple Swing app in a new
process (the "remote" in openAndFocusRemote above). This app can be
directed, over RMI, to access the clipboard. This allows our test to
place data on the clipboard and ensure that the remote app can read the
data successfully.

For now this test only covers basic text (and a little of RTF). Adding
Image and other transfers is part of the future work as such functionality
is added in GTK4 while working on #2126

For the changes to SwtTestUtil that we required:

1. isGTK4 moved from Test_org_eclipse_swt_widgets_Shell.java to the Utils
2. processEvents was limited to 20 readAndDispatch calls per second due
to the ordering of the targetTimestamp check. This change allows full speed
readAndDispatching.
3. getPath was refactored to allow better control of source and destination
of files extracted. See extracting of class files for remote Swing app
in startRemoteClipboardCommands method

Part of #2126
Split out of #2538

Author: jonahgraham

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/AllNonBrowserTests.java

@@ -47,7 +47,8 @@
 		Test_org_eclipse_swt_accessibility_AccessibleTextEvent.class,
 		Test_org_eclipse_swt_internal_SVGRasterizer.class,
 		DPIUtilTests.class,
-		JSVGRasterizerTest.class})
+		JSVGRasterizerTest.class,
+		Test_org_eclipse_swt_dnd_Clipboard.class,})
 public class AllNonBrowserTests {
 	private static List<Error> leakedResources;
 

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/SwtTestUtil.java

@@ -105,7 +105,8 @@ public class SwtTestUtil {
 
 	public final static boolean isX11 = isGTK
 			&& "x11".equals(System.getProperty("org.eclipse.swt.internal.gdk.backend"));
-
+	public final static boolean isGTK4 = isGTK
+			&& System.getProperty("org.eclipse.swt.internal.gtk.version", "").startsWith("4");
 
 	/**
 	 * The palette used by images. See {@link #getAllPixels(Image)} and {@link #createImage}
@@ -400,13 +401,16 @@ public static void processEvents(int timeoutMs, BooleanSupplier breakCondition)
 	long targetTimestamp = System.currentTimeMillis() + timeoutMs;
 	Display display = Display.getCurrent();
 	while (!breakCondition.getAsBoolean()) {
-		if (!display.readAndDispatch()) {
-			if (System.currentTimeMillis() < targetTimestamp) {
-				Thread.sleep(50);
-			} else {
+		while (display.readAndDispatch()) {
+			if (System.currentTimeMillis() >= targetTimestamp) {
 				return;
 			}
 		}
+		if (System.currentTimeMillis() < targetTimestamp) {
+			Thread.sleep(50);
+		} else {
+			return;
+		}
 	}
 }
 
@@ -583,18 +587,24 @@ public static boolean hasPixelNotMatching(Image image, Color nonMatchingColor, R
 }
 
 public static Path getPath(String fileName, TemporaryFolder tempFolder) {
-	Path filePath = tempFolder.getRoot().toPath().resolve("image-resources").resolve(Path.of(fileName));
-	if (!Files.isRegularFile(filePath)) {
+	Path path = tempFolder.getRoot().toPath();
+	Path filePath = path.resolve("image-resources").resolve(Path.of(fileName));
+	return getPath(fileName, filePath);
+}
+
+public static Path getPath(String sourceFilename, Path destinationPath) {
+	if (!Files.isRegularFile(destinationPath)) {
 		// Extract resource on the classpath to a temporary file to ensure it's
 		// available as plain file, even if this bundle is packed as jar
-		try (InputStream inStream = SwtTestUtil.class.getResourceAsStream(fileName)) {
-			assertNotNull(inStream, "InputStream == null for file " + fileName);
-			Files.createDirectories(filePath.getParent());
-			Files.copy(inStream, filePath);
+		try (InputStream inStream = SwtTestUtil.class.getResourceAsStream(sourceFilename)) {
+			assertNotNull(inStream, "InputStream == null for file " + sourceFilename);
+			Files.createDirectories(destinationPath.getParent());
+			Files.copy(inStream, destinationPath);
 		} catch (IOException e) {
 			throw new IllegalArgumentException(e);
 		}
 	}
-	return filePath;
+	return destinationPath;
 }
+
 }

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_dnd_Clipboard.java

@@ -0,0 +1,319 @@
+/*******************************************************************************
+ * Copyright (c) 2025 Kichwa Coders Canada, Inc.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *******************************************************************************/
+package org.eclipse.swt.tests.junit;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.lang.ProcessBuilder.Redirect;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.rmi.NotBoundException;
+import java.rmi.registry.LocateRegistry;
+import java.rmi.registry.Registry;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+import java.util.function.BooleanSupplier;
+
+import org.eclipse.swt.dnd.Clipboard;
+import org.eclipse.swt.dnd.RTFTransfer;
+import org.eclipse.swt.dnd.TextTransfer;
+import org.eclipse.swt.dnd.Transfer;
+import org.eclipse.swt.widgets.Display;
+import org.eclipse.swt.widgets.Shell;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.RepeatedTest;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import clipboard.ClipboardCommands;
+
+/**
+ * Automated Test Suite for class org.eclipse.swt.dnd.Clipboard
+ *
+ * @see org.eclipse.swt.dnd.Clipboard
+ * @see Test_org_eclipse_swt_custom_StyledText StyledText tests as it also does
+ *      some clipboard tests
+ */
+public class Test_org_eclipse_swt_dnd_Clipboard {
+
+	private static final int REPEAT_COUNT = 3;
+	@TempDir
+	static Path tempFolder;
+	static int uniqueId = 1;
+	private Display display;
+	private Shell shell;
+	private Clipboard clipboard;
+	private TextTransfer textTransfer;
+	private RTFTransfer rtfTransfer;
+	private ClipboardCommands remote;
+	private Process remoteClipboardProcess;
+
+	@BeforeEach
+	public void setUp() {
+		display = Display.getCurrent();
+		if (display == null) {
+			display = Display.getDefault();
+		}
+
+		clipboard = new Clipboard(display);
+		textTransfer = TextTransfer.getInstance();
+		rtfTransfer = RTFTransfer.getInstance();
+	}
+
+	/**
+	 * TODO remove all uses of sleep and change them to processEvents with the
+	 * suitable conditional, or entirely remove them
+	 */
+	private void sleep() throws InterruptedException {
+		SwtTestUtil.processEvents(100, null);
+	}
+
+	/**
+	 * Note: Wayland backend does not allow access to system clipboard from
+	 * non-focussed windows. So we have to create/open and focus a window here so
+	 * that clipboard operations work.
+	 */
+	private void openAndFocusShell() throws InterruptedException {
+		shell = new Shell(display);
+		shell.open();
+		shell.setFocus();
+		sleep();
+	}
+
+	/**
+	 * Note: Wayland backend does not allow access to system clipboard from
+	 * non-focussed windows. So we have to open and focus remote here so that
+	 * clipboard operations work.
+	 */
+	private void openAndFocusRemote() throws Exception {
+		startRemoteClipboardCommands();
+		remote.setFocus();
+		remote.waitUntilReady();
+		sleep();
+	}
+
+	@AfterEach
+	public void tearDown() throws Exception {
+		sleep();
+		try {
+			stopRemoteClipboardCommands();
+		} finally {
+			if (clipboard != null) {
+				clipboard.dispose();
+			}
+			if (shell != null) {
+				shell.dispose();
+			}
+			SwtTestUtil.processEvents();
+		}
+	}
+
+	private void startRemoteClipboardCommands() throws Exception {
+		// TODO: Can I get the jar and run it without extracting it?
+		// TODO: Can I get all the files without having to list them?
+		List.of( //
+				"ClipboardTest", //
+				"ClipboardCommands", //
+				"ClipboardCommandsImpl", //
+				"ClipboardTest$LocalHostOnlySocketFactory" //
+		).forEach((f) -> {
+			// extract the files and put them in the temp directory
+			SwtTestUtil.getPath("/clipboard/" + f + ".class", tempFolder.resolve("clipboard/" + f + ".class"));
+		});
+
+		String javaHome = System.getProperty("java.home");
+		String javaExe = javaHome + "/bin/java";
+		assertTrue(Files.exists(Path.of(javaExe)));
+
+		ProcessBuilder pb = new ProcessBuilder(javaExe, "clipboard.ClipboardTest").directory(tempFolder.toFile());
+		pb.inheritIO();
+		pb.redirectOutput(Redirect.PIPE);
+		remoteClipboardProcess = pb.start();
+
+		// Read server output to find the port
+		BufferedReader reader = new BufferedReader(new InputStreamReader(remoteClipboardProcess.getInputStream()));
+		int port = 0;
+		String line;
+		// TODO: add a timeout here
+		while ((line = reader.readLine()) != null) {
+			if (line.startsWith(ClipboardCommands.PORT_MESSAGE)) {
+				String[] parts = line.split(":");
+				port = Integer.parseInt(parts[1].trim());
+				break;
+			}
+		}
+		assertNotEquals(0, port);
+		Registry reg = LocateRegistry.getRegistry("127.0.0.1", port);
+		long stopTime = System.currentTimeMillis() + 1000;
+		do {
+			try {
+				remote = (ClipboardCommands) reg.lookup(ClipboardCommands.ID);
+				break;
+			} catch (NotBoundException e) {
+				// try again because the remote app probably hasn't bound yet
+			}
+		} while (System.currentTimeMillis() < stopTime);
+
+		// Run a no-op on the Swing event loop so that we know it is idle
+		// and we can continue startup
+		remote.waitUntilReady();
+	}
+
+	private void stopRemoteClipboardCommands() throws Exception {
+		try {
+			if (remote != null) {
+				remote.stop();
+				remote = null;
+			}
+		} finally {
+			if (remoteClipboardProcess != null) {
+				try {
+					remoteClipboardProcess.waitFor(1, TimeUnit.SECONDS);
+				} finally {
+					remoteClipboardProcess.destroyForcibly();
+					remoteClipboardProcess = null;
+				}
+			}
+		}
+	}
+
+	/**
+	 * Make sure to always copy/paste unique strings - this ensures that tests run
+	 * under {@link RepeatedTest}s don't false pass because of clipboard value on
+	 * previous iteration.
+	 */
+	private String getUniqueTestString() {
+		return "Hello World " + uniqueId++;
+	}
+
+	/**
+	 * Test that the remote application clipboard works
+	 */
+	@Test
+	public void test_Remote() throws Exception {
+		openAndFocusRemote();
+		String helloWorld = getUniqueTestString();
+		remote.setContents(helloWorld);
+		assertEquals(helloWorld, remote.getStringContents());
+	}
+
+	/**
+	 * This tests set + get on local clipboard. Remote clipboard can have different
+	 * behaviours and has additional tests.
+	 */
+	@RepeatedTest(value = REPEAT_COUNT)
+	public void test_LocalClipboard() throws Exception {
+		openAndFocusShell();
+
+		String helloWorld = getUniqueTestString();
+		clipboard.setContents(new Object[] { helloWorld }, new Transfer[] { textTransfer });
+		assertEquals(helloWorld, clipboard.getContents(textTransfer));
+		assertNull(clipboard.getContents(rtfTransfer));
+
+		helloWorld = getUniqueTestString();
+		String helloWorldRtf = "{\\rtf1\\b\\i " + helloWorld + "}";
+		clipboard.setContents(new Object[] { helloWorld, helloWorldRtf }, new Transfer[] { textTransfer, rtfTransfer });
+		assertEquals(helloWorld, clipboard.getContents(textTransfer));
+		assertEquals(helloWorldRtf, clipboard.getContents(rtfTransfer));
+
+		helloWorld = getUniqueTestString();
+		helloWorldRtf = "{\\rtf1\\b\\i " + helloWorld + "}";
+		clipboard.setContents(new Object[] { helloWorldRtf }, new Transfer[] { rtfTransfer });
+		assertNull(clipboard.getContents(textTransfer));
+		assertEquals(helloWorldRtf, clipboard.getContents(rtfTransfer));
+	}
+
+	@RepeatedTest(value = REPEAT_COUNT)
+	public void test_setContents() throws Exception {
+		try {
+			openAndFocusShell();
+			String helloWorld = getUniqueTestString();
+
+			clipboard.setContents(new Object[] { helloWorld }, new Transfer[] { textTransfer });
+			sleep();
+
+			openAndFocusRemote();
+			SwtTestUtil.processEvents(1000, () -> helloWorld.equals(runOperationInThread(remote::getStringContents)));
+			String result = runOperationInThread(remote::getStringContents);
+			assertEquals(helloWorld, result);
+		} catch (Exception | AssertionError e) {
+			if (SwtTestUtil.isGTK4 && !SwtTestUtil.isX11) {
+				// TODO make the code + test stable
+				throw new RuntimeException(
+						"This test is really unstable on wayland backend, at least with Ubuntu 25.04", e);
+			}
+			throw e;
+		}
+	}
+
+	@RepeatedTest(value = REPEAT_COUNT)
+	public void test_getContents() throws Exception {
+		openAndFocusRemote();
+		String helloWorld = getUniqueTestString();
+		remote.setContents(helloWorld);
+
+		openAndFocusShell();
+		SwtTestUtil.processEvents(1000, () -> {
+			return helloWorld.equals(clipboard.getContents(textTransfer));
+		});
+		assertEquals(helloWorld, clipboard.getContents(textTransfer));
+	}
+
+	@FunctionalInterface
+	public interface ExceptionalSupplier<T> {
+		T get() throws Exception;
+	}
+
+	/**
+	 * When running some operations, such as requesting remote process read the
+	 * clipboard, we need to have the event queue processing otherwise the remote
+	 * won't be able to read our clipboard contribution.
+	 *
+	 * This method starts the supplier in a new thread and runs the event loop until
+	 * the thread completes.
+	 *
+	 * @throws InterruptedException
+	 */
+	private <T> T runOperationInThread(ExceptionalSupplier<T> supplier) throws RuntimeException {
+		Object[] supplierValue = new Object[1];
+		Exception[] supplierException = new Exception[1];
+		Runnable task = () -> {
+			try {
+				supplierValue[0] = supplier.get();
+			} catch (Exception e) {
+				supplierValue[0] = null;
+				supplierException[0] = e;
+			}
+		};
+		Thread thread = new Thread(task, this.getClass().getName() + ".runOperationInThread");
+		thread.setDaemon(true);
+		thread.start();
+		BooleanSupplier done = () -> !thread.isAlive();
+		try {
+			SwtTestUtil.processEvents(2000, done);
+		} catch (InterruptedException e) {
+			throw new RuntimeException("Failed while running thread", e);
+		}
+		assertTrue(done.getAsBoolean());
+		if (supplierException[0] != null) {
+			throw new RuntimeException("Failed while running thread", supplierException[0]);
+		}
+		@SuppressWarnings("unchecked")
+		T result = (T) supplierValue[0];
+		return result;
+	}
+}