fix: validate upload date, close upload races (REQ-178)

backend/library.py

@@ -104,13 +104,17 @@ class LibraryConflict(LibraryError):
 
 
 def create_date(video_root: str, date: str) -> str:
-    """Make a YYYY-MM-DD folder; never touch an existing one (REQ-171)."""
+    """Make a YYYY-MM-DD folder; never touch an existing one (REQ-178)."""
     if not re.fullmatch(r"\d{4}-\d{2}-\d{2}", date):
         raise LibraryError("Folder name must be YYYY-MM-DD")
     folder = _safe_join(_effective_root(video_root), date)
     if os.path.exists(folder):
         raise LibraryConflict(f"Folder already exists: {date}")
-    os.makedirs(folder)
+    try:
+        os.makedirs(folder)
+    except FileExistsError:
+        # Lost the race against a concurrent mkdir; same 409 as above.
+        raise LibraryConflict(f"Folder already exists: {date}")
     return folder
 
 
@@ -119,6 +123,8 @@ def upload_video(video_root: str, date: str, filename: str, chunks) -> str:
     name = os.path.basename(filename or "")
     if not name or name != filename or not name.lower().endswith(video.VIDEO_EXTS):
         raise LibraryError(f"Unsupported file: {filename}")
+    if not re.fullmatch(r"\d{4}-\d{2}-\d{2}", date):
+        raise LibraryError("Folder name must be YYYY-MM-DD")
     root = _effective_root(video_root)
     if not os.path.isdir(_safe_join(root, date)):
         raise LibraryError(f"No such date in the archive: {date}")
@@ -127,13 +133,22 @@ def upload_video(video_root: str, date: str, filename: str, chunks) -> str:
         raise LibraryConflict(f"Already exists: {date}/{name}")
     part = dest + ".part"
     try:
-        with open(part, "wb") as handle:
+        fd = os.open(part, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o644)
+    except FileExistsError:
+        raise LibraryConflict(f"Already exists: {date}/{name}")
+    try:
+        with os.fdopen(fd, "wb") as handle:
             for chunk in chunks:
                 handle.write(chunk)
+        if os.path.exists(dest):
+            raise LibraryConflict(f"Already exists: {date}/{name}")
         os.replace(part, dest)
     except BaseException:
         if os.path.exists(part):
-            os.unlink(part)
+            try:
+                os.unlink(part)
+            except OSError:
+                pass
         raise
     return f"{date}/{name}"