fix: skip a synced memory card left in an older save archive instead of failing the restore

Author: LoneAngelFayt

webstation_broker/api.py

@@ -105,16 +105,22 @@ def _resolve_callback(body_cb: Optional[CallbackIn], request: Request) -> dict:
     }
 
 
-def _archive_subtrees(emulator, memory_card_synced: bool) -> tuple[str, ...]:
-    """The save subtrees this session ships in its archive.
+def _archive_subtrees(
+    emulator, memory_card_synced: bool
+) -> tuple[tuple[str, ...], tuple[str, ...]]:
+    """The save subtrees this session ships, and the ones it leaves alone.
 
     With the whole card synced, leaving it in the archive too would have the
     restore and the card hydrate writing over each other, and a stale card
     inside an older archive would land on top of the one RomM just laid down.
+    The excluded set is returned rather than simply dropped because archives
+    RomM took before the card was synced still carry it, and a restore has to
+    pass those members over instead of refusing the whole archive.
     """
     if not memory_card_synced or emulator.memory_card_subtree is None:
-        return emulator.save_subtrees
-    return tuple(s for s in emulator.save_subtrees if s != emulator.memory_card_subtree)
+        return emulator.save_subtrees, ()
+    card = emulator.memory_card_subtree
+    return tuple(s for s in emulator.save_subtrees if s != card), (card,)
 
 
 @router.get("/api/health")
@@ -174,7 +180,9 @@ async def activate(
     await anyio.to_thread.run_sync(emulator.clear_working_slot)
     restore_report = None
     save = body.save
-    subtrees = _archive_subtrees(emulator, bool(save and save.memory_card_synced))
+    subtrees, excluded = _archive_subtrees(
+        emulator, bool(save and save.memory_card_synced)
+    )
     if save and save.archive and subtrees:
         archive_path = Path(save.archive)
         if not archive_path.is_file():
@@ -184,7 +192,11 @@ async def activate(
         content = await anyio.to_thread.run_sync(archive_path.read_bytes)
         await anyio.to_thread.run_sync(emulator.prepare_restore)
         restore_report = await anyio.to_thread.run_sync(
-            saves.extract_save_archive, content, emulator.save_root, subtrees
+            saves.extract_save_archive,
+            content,
+            emulator.save_root,
+            subtrees,
+            excluded,
         )
         if restore_report["error"]:
             raise HTTPException(
@@ -252,12 +264,13 @@ async def _do_exit(save_slot: int) -> dict:
     emulator = sess["emulator_obj"]
     exit_report = await anyio.to_thread.run_sync(emulator.save_and_exit, save_slot)
 
+    dump_subtrees, _ = _archive_subtrees(
+        emulator, bool((sess.get("save") or {}).get("memory_card_synced"))
+    )
     dump = await anyio.to_thread.run_sync(
         saves.build_save_archive,
         emulator.save_root,
-        _archive_subtrees(
-            emulator, bool((sess.get("save") or {}).get("memory_card_synced"))
-        ),
+        dump_subtrees,
         sess["save_baseline"],
     )
     cb = sess.get("callback")

webstation_broker/saves.py

@@ -120,16 +120,30 @@ def build_save_archive(
     return report
 
 
+def _under(member: PurePosixPath, subtrees: tuple[str, ...]) -> bool:
+    return any(member.as_posix().startswith(sub + "/") for sub in subtrees)
+
+
 def extract_save_archive(
-    content: bytes, root: Path, subtrees: tuple[str, ...]
+    content: bytes,
+    root: Path,
+    subtrees: tuple[str, ...],
+    excluded: tuple[str, ...] = (),
 ) -> dict:
     """Restore an archive into the emulator's data dir.
 
+    `excluded` names subtrees the emulator owns but this session syncs some
+    other way. Those members are dropped rather than refused: archives taken
+    before that sync was turned on still carry them, and restoring one would
+    undo what the other route just wrote. A member under neither is still a
+    hard error, since that is the guard against an archive writing outside the
+    save area.
+
     Existing files newer than their archive member are skipped so a restore
     can never roll back saves made since the archive was taken. Returns
-    {"written", "skipped", "failed", "error"}.
+    {"written", "skipped", "excluded", "failed", "error"}.
     """
-    result = {"written": 0, "skipped": 0, "failed": 0, "error": None}
+    result = {"written": 0, "skipped": 0, "excluded": 0, "failed": 0, "error": None}
     try:
         zf = zipfile.ZipFile(io.BytesIO(content))
     except zipfile.BadZipFile:
@@ -140,16 +154,21 @@ def extract_save_archive(
         if sum(i.file_size for i in infos) > SAVE_FILE_MAX_BYTES:
             result["error"] = "archive exceeds size limit when extracted"
             return result
+        wanted = []
         for info in infos:
             member = PurePosixPath(info.filename)
             if member.is_absolute() or ".." in member.parts:
                 result["error"] = f"archive member escapes save dir: {info.filename}"
                 return result
-            if not any(member.as_posix().startswith(sub + "/") for sub in subtrees):
+            if _under(member, excluded):
+                result["excluded"] += 1
+                continue
+            if not _under(member, subtrees):
                 result["error"] = f"archive member outside save subtrees: {info.filename}"
                 return result
+            wanted.append(info)
 
-        for info in infos:
+        for info in wanted:
             target = root / PurePosixPath(info.filename)
             mtime = calendar.timegm(info.date_time)
             try: