Drop root privileges on startup

On rooted devices, switch to user 2000 during startup.

Copy-paste does not work as root (user 0), so switching to 2000 fixes
the issue.

Fixes #6224 <https://github.com/Genymobile/scrcpy/issues/6224>

Suggested-by: Simon Chan <1330321+yume-chan@users.noreply.github.com>

server/src/main/java/com/genymobile/scrcpy/Server.java

@@ -27,6 +27,8 @@ import com.genymobile.scrcpy.video.VideoSource;
 import android.annotation.SuppressLint;
 import android.os.Build;
 import android.os.Looper;
+import android.system.ErrnoException;
+import android.system.Os;
 
 import java.io.File;
 import java.io.IOException;
@@ -233,6 +235,8 @@ public final class Server {
             }
         });
 
+        dropRootPrivileges();
+
         prepareMainLooper();
 
         Options options = Options.parse(args);
@@ -273,4 +277,17 @@ public final class Server {
             // Do not print stack trace, a user-friendly error-message has already been logged
         }
     }
+
+    @SuppressWarnings("deprecation")
+    private static void dropRootPrivileges() {
+        try {
+            if (Os.getuid() == 0) {
+                // Copy-paste does not work with root user
+                // <https://github.com/Genymobile/scrcpy/issues/6224>
+                Os.setuid(2000);
+            }
+        } catch (Exception e) {
+            Ln.w("Cannot set UID", e);
+        }
+    }
 }

server/src/main/java/com/genymobile/scrcpy/video/ScreenCapture.java

@@ -129,26 +129,17 @@ public class ScreenCapture extends SurfaceCapture {
                     .createVirtualDisplay("scrcpy", inputSize.getWidth(), inputSize.getHeight(), displayId, surface);
             Ln.d("Display: using DisplayManager API");
         } catch (Exception displayManagerException) {
-            if (Build.BRAND.equalsIgnoreCase("oculus") && Build.MODEL.equalsIgnoreCase("Quest 3")) {
-                // Workaround for buggy createVirtualDisplay on Quest 3
-                try {
-                    virtualDisplay = (VirtualDisplay) VirtualDisplay.class.getDeclaredConstructors()[0].newInstance(null, null, null, surface);
-                } catch (ReflectiveOperationException e) {
-                    Ln.e("Could not create VirtualDisplay", e);
-                }
-            } else {
-                try {
-                    display = createDisplay();
+            try {
+                display = createDisplay();
 
-                    Size deviceSize = displayInfo.getSize();
-                    int layerStack = displayInfo.getLayerStack();
-                    setDisplaySurface(display, surface, deviceSize.toRect(), inputSize.toRect(), layerStack);
-                    Ln.d("Display: using SurfaceControl API");
-                } catch (Exception surfaceControlException) {
-                    Ln.e("Could not create display using DisplayManager", displayManagerException);
-                    Ln.e("Could not create display using SurfaceControl", surfaceControlException);
-                    throw new AssertionError("Could not create display");
-                }
+                Size deviceSize = displayInfo.getSize();
+                int layerStack = displayInfo.getLayerStack();
+                setDisplaySurface(display, surface, deviceSize.toRect(), inputSize.toRect(), layerStack);
+                Ln.d("Display: using SurfaceControl API");
+            } catch (Exception surfaceControlException) {
+                Ln.e("Could not create display using DisplayManager", displayManagerException);
+                Ln.e("Could not create display using SurfaceControl", surfaceControlException);
+                throw new AssertionError("Could not create display");
             }
         }