1 files changed, 40 insertions, 0 deletions
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;
+        }
+    }
+}