Fix turn screen off on Android 14

On Android 14, execute a separate process with a different classpath and
LD_PRELOAD to execute the methods required to turn the device screen
off.

Fixes #3927 <https://github.com/Genymobile/scrcpy/issues/3927>
Refs #3927 comment <https://github.com/Genymobile/scrcpy/issues/3927#issuecomment-1790031953>

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

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

@@ -4,20 +4,13 @@ import android.annotation.SuppressLint;
 import android.os.IBinder;
 
 import java.io.IOException;
-import java.io.InputStream;
-import java.io.OutputStream;
-import java.io.PrintStream;
 import java.lang.reflect.Method;
 
 /**
  * On Android 14, the methods used to turn the device screen off have been moved from SurfaceControl (in framework.jar) to DisplayControl (a system
  * server class). As a consequence, they could not be called directly. See {@url https://github.com/Genymobile/scrcpy/issues/3927}.
  * <p>
- * Instead, run a separate process with a different classpath and LD_PRELOAD just to set the display power mode. The scrcpy server can request to
- * this process to set the display mode by writing the mode (a single byte, the value of one of the SurfaceControl.POWER_MODE_* constants,
- * typically 0=off, 2=on) to the process stdin. In return, it receives the status of the request (0=ok, 1=error) on the process stdout.
- * <p>
- * This separate process is started on the first display mode request.
+ * Instead, run a separate process with a different classpath and LD_PRELOAD just to set the display power mode.
  * <p>
  * Since the client must not block, and calling/joining a process is blocking (this specific one takes a few hundred milliseconds to complete),
  * this class uses an internal thread to execute the requests asynchronously, and serialize them (so that two successive requests are guaranteed to
@@ -30,26 +23,18 @@ public final class DisplayPowerMode {
 
     private static final class Proxy implements Runnable {
 
-        private Process process;
         private Thread thread;
         private int requestedMode = -1;
         private boolean stopped;
 
-        synchronized boolean requestMode(int mode) {
-            try {
-                if (process == null) {
-                    process = executeDisplayPowerModeDaemon();
-                    thread = new Thread(this, "DisplayPowerModeProxy");
-                    thread.setDaemon(true);
-                    thread.start();
-                }
-                requestedMode = mode;
-                notify();
-                return true;
-            } catch (IOException e) {
-                Ln.e("Could not start display power mode daemon", e);
-                return false;
+        synchronized void requestMode(int mode) {
+            if (thread == null) {
+                thread = new Thread(this, "DisplayPowerModeProxy");
+                thread.setDaemon(true);
+                thread.start();
             }
+            requestedMode = mode;
+            notify();
         }
 
         void stopAndJoin() {
@@ -75,10 +60,8 @@ public final class DisplayPowerMode {
         @Override
         public void run() {
             try {
-                OutputStream out = process.getOutputStream();
-                InputStream in = process.getInputStream();
+                int mode;
                 while (true) {
-                    int mode;
                     synchronized (this) {
                         while (!stopped && requestedMode == -1) {
                             wait();
@@ -93,14 +76,13 @@ public final class DisplayPowerMode {
                     }
 
                     try {
-                        out.write(mode);
-                        out.flush();
-                        int status = in.read();
+                        Process process = executeSystemServerSetDisplayPowerMode(mode);
+                        int status = process.waitFor();
                         if (status != 0) {
                             Ln.e("Set display power mode failed remotely: status=" + status);
                         }
-                    } catch (IOException e) {
-                        Ln.e("Could not request display power mode", e);
+                    } catch (Exception e) {
+                        Ln.e("Failed to execute process", e);
                     }
                 }
             } catch (InterruptedException e) {
@@ -114,8 +96,8 @@ public final class DisplayPowerMode {
     }
 
     // Called from the scrcpy process
-    public static boolean setRemoteDisplayPowerMode(int mode) {
-        return PROXY.requestMode(mode);
+    public static void setRemoteDisplayPowerMode(int mode) {
+        PROXY.requestMode(mode);
     }
 
     public static void stopAndJoin() {
@@ -123,9 +105,9 @@ public final class DisplayPowerMode {
     }
 
     // Called from the proxy thread in the scrcpy process
-    private static Process executeDisplayPowerModeDaemon() throws IOException {
+    private static Process executeSystemServerSetDisplayPowerMode(int mode) throws IOException {
         String[] ldPreloadLibs = {"/system/lib64/libandroid_servers.so"};
-        String[] cmd = {"app_process", "/", DisplayPowerMode.class.getName()};
+        String[] cmd = {"app_process", "/", DisplayPowerMode.class.getName(), String.valueOf(mode)};
 
         ProcessBuilder builder = new ProcessBuilder(cmd);
         builder.environment().put("LD_PRELOAD", String.join(" ", ldPreloadLibs));
@@ -154,31 +136,26 @@ public final class DisplayPowerMode {
     }
 
     public static void main(String... args) {
-        // This process uses stdin/stdout to communicate with the caller, make sure nothing else writes to stdout
-        // (and never use Ln methods other than Ln.w() and Ln.e()).
-        PrintStream nullStream = new PrintStream(new Ln.NullOutputStream());
-        System.setOut(nullStream);
-        PrintStream stdout = Ln.CONSOLE_OUT;
+        Ln.disableSystemStreams();
+        Ln.initLogLevel(Ln.Level.DEBUG);
+
+        int status = run(args) ? 0 : 1;
+        System.exit(status);
+    }
+
+    private static boolean run(String... args) {
+        if (args.length != 1) {
+            Ln.e("Exactly one argument expected: the value of one of the SurfaceControl.POWER_MODE_* constants (typically 0 or 2)");
+            return false;
+        }
 
         try {
-            while (true) {
-                // Wait for requests
-                int request = System.in.read();
-                if (request == -1) {
-                    // EOF
-                    return;
-                }
-                try {
-                    setDisplayPowerModeUsingDisplayControl(request);
-                    stdout.write(0); // ok
-                } catch (Throwable e) {
-                    Ln.e("Could not set display power mode", e);
-                    stdout.write(1); // error
-                }
-                stdout.flush();
-            }
-        } catch (IOException e) {
-            // Expected when the server is dead
+            int mode = Integer.parseInt(args[0]);
+            setDisplayPowerModeUsingDisplayControl(mode);
+            return true;
+        } catch (Throwable e) {
+            Ln.e("Could not set display power mode", e);
+            return false;
         }
     }
 }

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

@@ -16,8 +16,8 @@ public final class Ln {
     private static final String TAG = "scrcpy";
     private static final String PREFIX = "[server] ";
 
-    public static final PrintStream CONSOLE_OUT = new PrintStream(new FileOutputStream(FileDescriptor.out));
-    public static final PrintStream CONSOLE_ERR = new PrintStream(new FileOutputStream(FileDescriptor.err));
+    private static final PrintStream CONSOLE_OUT = new PrintStream(new FileOutputStream(FileDescriptor.out));
+    private static final PrintStream CONSOLE_ERR = new PrintStream(new FileOutputStream(FileDescriptor.err));
 
     enum Level {
         VERBOSE, DEBUG, INFO, WARN, ERROR