From eb0c8951196c637e44daf3c0617b131b997d5d2c Mon Sep 17 00:00:00 2001
From: Lena <lena@omega>
Date: Thu, 1 Jan 2026 00:00:00 +0000
Subject: scrcpy-android: mirror an Android device over wireless ADB

Native Java app for Android 12+ that mirrors another Android
device over wireless ADB, forwarding video, audio, touch input,
and clipboard. Bundles a pinned scrcpy-server.jar and the
vendored libadb-android stack. Supports h264/h265/av1 video and
raw/opus audio with in-app codec selection. No NDK, no Kotlin.
Includes JVM unit tests and a Docker-based emulator e2e rig.
---
 .../main/java/invalid/lena/scrcpy/AtomicFiles.java | 40 ++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 app/src/main/java/invalid/lena/scrcpy/AtomicFiles.java

(limited to 'app/src/main/java/invalid/lena/scrcpy/AtomicFiles.java')

diff --git a/app/src/main/java/invalid/lena/scrcpy/AtomicFiles.java b/app/src/main/java/invalid/lena/scrcpy/AtomicFiles.java
new file mode 100644
index 0000000..6f755b6
--- /dev/null
+++ b/app/src/main/java/invalid/lena/scrcpy/AtomicFiles.java
@@ -0,0 +1,40 @@
+package invalid.lena.scrcpy;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.StandardCopyOption;
+
+// Crash-atomic whole-file write: stage the bytes into a sibling temp file,
+// fsync it, then rename it over the destination. The rename is the only
+// mutation a concurrent reader can observe, so a reader sees either the old
+// file or the new file in full, never a truncated mix. A crash mid-write
+// leaves at most a stale ".tmp", never a damaged destination.
+//
+// Deliberately no fsync of the parent directory: the rename itself may be
+// lost on power failure (the old content survives intact). Callers store
+// re-creatable state, so atomicity matters here and durability does not.
+//
+// android-free (java.io/java.nio only) so it is unit-testable on the JVM.
+final class AtomicFiles {
+
+    private AtomicFiles() {}
+
+    static void write(File dest, byte[] data) throws IOException {
+        File parent = dest.getAbsoluteFile().getParentFile();
+        File tmp = new File(parent, dest.getName() + ".tmp");
+        try (FileOutputStream os = new FileOutputStream(tmp)) {
+            os.write(data);
+            os.flush();
+            os.getFD().sync();
+        }
+        try {
+            Files.move(tmp.toPath(), dest.toPath(),
+                    StandardCopyOption.ATOMIC_MOVE, StandardCopyOption.REPLACE_EXISTING);
+        } catch (IOException e) {
+            tmp.delete();
+            throw e;
+        }
+    }
+}
-- 
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