Avoid unintended clipboard access (#27215)

shell/platform/android/io/flutter/plugin/platform/PlatformPlugin.java

@@ -7,6 +7,7 @@ package io.flutter.plugin.platform;
 import android.app.Activity;
 import android.app.ActivityManager.TaskDescription;
 import android.content.ClipData;
+import android.content.ClipDescription;
 import android.content.ClipboardManager;
 import android.content.Context;
 import android.os.Build;
@@ -124,10 +125,7 @@ public class PlatformPlugin {
 
         @Override
         public boolean clipboardHasStrings() {
-          CharSequence data =
-              PlatformPlugin.this.getClipboardData(
-                  PlatformChannel.ClipboardContentFormat.PLAIN_TEXT);
-          return data != null && data.length() > 0;
+          return PlatformPlugin.this.clipboardHasStrings();
         }
       };
 
@@ -490,4 +488,20 @@ public class PlatformPlugin {
     ClipData clip = ClipData.newPlainText("text label?", text);
     clipboard.setPrimaryClip(clip);
   }
+
+  private boolean clipboardHasStrings() {
+    ClipboardManager clipboard =
+        (ClipboardManager) activity.getSystemService(Context.CLIPBOARD_SERVICE);
+    // Android 12 introduces a toast message that appears when an app reads the clipboard. To avoid
+    // unintended access, call the appropriate APIs to receive information about the current content
+    // that's on the clipboard (rather than the actual content itself).
+    if (!clipboard.hasPrimaryClip()) {
+      return false;
+    }
+    ClipDescription description = clipboard.getPrimaryClipDescription();
+    if (description == null) {
+      return false;
+    }
+    return description.hasMimeType("text/*");
+  }
 }

shell/platform/android/test/io/flutter/plugin/platform/PlatformPluginTest.java

@@ -7,6 +7,7 @@ import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
@@ -96,10 +97,11 @@ public class PlatformPluginTest {
     assertEquals(dataInputStream.read(), uriInputStream.read());
   }
 
+  @Config(sdk = 28)
   @Test
   public void platformPlugin_hasStrings() {
     ClipboardManager clipboardManager =
-        RuntimeEnvironment.application.getSystemService(ClipboardManager.class);
+        spy(RuntimeEnvironment.application.getSystemService(ClipboardManager.class));
 
     View fakeDecorView = mock(View.class);
     Window fakeWindow = mock(Window.class);
@@ -110,13 +112,44 @@ public class PlatformPluginTest {
     PlatformChannel fakePlatformChannel = mock(PlatformChannel.class);
     PlatformPlugin platformPlugin = new PlatformPlugin(fakeActivity, fakePlatformChannel);
 
+    // Plain text
     ClipData clip = ClipData.newPlainText("label", "Text");
     clipboardManager.setPrimaryClip(clip);
     assertTrue(platformPlugin.mPlatformMessageHandler.clipboardHasStrings());
 
+    // Empty plain text
     clip = ClipData.newPlainText("", "");
     clipboardManager.setPrimaryClip(clip);
+    // Without actually accessing clipboard data (preferred behavior), it is not possible to
+    // distinguish between empty and non-empty string contents.
+    assertTrue(platformPlugin.mPlatformMessageHandler.clipboardHasStrings());
+
+    // HTML text
+    clip = ClipData.newHtmlText("motto", "Don't be evil", "<b>Don't</b> be evil");
+    clipboardManager.setPrimaryClip(clip);
+    assertTrue(platformPlugin.mPlatformMessageHandler.clipboardHasStrings());
+
+    // Text MIME type
+    clip = new ClipData("label", new String[] {"text/something"}, new ClipData.Item("content"));
+    clipboardManager.setPrimaryClip(clip);
+    assertTrue(platformPlugin.mPlatformMessageHandler.clipboardHasStrings());
+
+    // Other MIME type
+    clip =
+        new ClipData(
+            "label", new String[] {"application/octet-stream"}, new ClipData.Item("content"));
+    clipboardManager.setPrimaryClip(clip);
     assertFalse(platformPlugin.mPlatformMessageHandler.clipboardHasStrings());
+
+    if (Build.VERSION.SDK_INT >= 28) {
+      // Empty clipboard
+      clipboardManager.clearPrimaryClip();
+      assertFalse(platformPlugin.mPlatformMessageHandler.clipboardHasStrings());
+    }
+
+    // Verify that the clipboard contents are never accessed.
+    verify(clipboardManager, never()).getPrimaryClip();
+    verify(clipboardManager, never()).getText();
   }
 
   @Config(sdk = 29)