From 852a8a00273c9128efeed0217a8e5d3fcd8bf780 Mon Sep 17 00:00:00 2001
From: Lena <lena@omega>
Date: Sat, 1 Aug 2026 00:00:00 +0000
Subject: app: harden mirroring lifecycle and state

---
 .../main/java/invalid/lena/scrcpy/AtomicFiles.java | 30 ++++++++++++++--------
 1 file changed, 20 insertions(+), 10 deletions(-)

(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
index 6f755b6..77235f6 100644
--- a/app/src/main/java/invalid/lena/scrcpy/AtomicFiles.java
+++ b/app/src/main/java/invalid/lena/scrcpy/AtomicFiles.java
@@ -10,7 +10,8 @@ import java.nio.file.StandardCopyOption;
 // 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.
+// may leave a stale staging file, never a damaged destination. The next
+// write removes stale staging files before creating its own.
 //
 // Deliberately no fsync of the parent directory: the rename itself may be
 // lost on power failure (the old content survives intact). Callers store
@@ -21,20 +22,29 @@ final class AtomicFiles {
 
     private AtomicFiles() {}
 
-    static void write(File dest, byte[] data) throws IOException {
+    static synchronized 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();
+        if (parent == null || !parent.isDirectory()) {
+            throw new IOException("destination parent is not a directory: " + parent);
         }
+        String prefix = dest.getName() + ".tmp";
+        File[] stale = parent.listFiles((dir, name) ->
+                name.equals(prefix) || name.startsWith(prefix + "-"));
+        if (stale == null) throw new IOException("cannot list destination parent: " + parent);
+        for (File file : stale) Files.deleteIfExists(file.toPath());
+        File tmp = Files.createTempFile(parent.toPath(), dest.getName() + ".tmp-", null).toFile();
+        boolean moved = false;
         try {
+            try (FileOutputStream os = new FileOutputStream(tmp)) {
+                os.write(data);
+                os.flush();
+                os.getFD().sync();
+            }
             Files.move(tmp.toPath(), dest.toPath(),
                     StandardCopyOption.ATOMIC_MOVE, StandardCopyOption.REPLACE_EXISTING);
-        } catch (IOException e) {
-            tmp.delete();
-            throw e;
+            moved = true;
+        } finally {
+            if (!moved) Files.deleteIfExists(tmp.toPath());
         }
     }
 }
-- 
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