fix: sanitize nasa_id and filenames to prevent path traversal (#1)

- Add sanitize_filename() to strip path separators and parent refs
- Apply sanitization to nasa_id used in metadata filenames
- Apply sanitization to image filenames derived from asset_href
- Preserve raw nasa_id for API calls to avoid breaking asset lookup

downloader.py

@@ -44,6 +44,7 @@ import argparse
 import datetime
 import json
 import os
+import re
 import sys
 import time
 from pathlib import Path
@@ -180,6 +181,16 @@ def download_file(url: str, dest: Path) -> bool:
         raise RuntimeError(f"Download error for {url}: {e}") from e
 
 
+def sanitize_filename(name: str) -> str:
+    """Sanitize a string for use as a filename, preventing path traversal."""
+    # Strip path separators and parent directory references
+    sanitized = re.sub(r'[\/\\:\*\?"<>|]', "_", name)
+    sanitized = re.sub(r"^\.{1,2}($|_)", "item_", sanitized)
+    # Collapse multiple underscores
+    sanitized = re.sub(r"_+", "_", sanitized)
+    return sanitized.strip(".") or "item"
+
+
 def save_metadata(item: Dict, dest: Path) -> None:
     """Persist the full API item as formatted JSON."""
     with dest.open("w", encoding="utf-8") as f:
@@ -224,12 +235,13 @@ def main() -> None:
 
     for idx, item in enumerate(tqdm(items, desc="Downloading"), start=1):
         data = item.get("data", [{}])[0]
-        nasa_id = data.get("nasa_id") or data.get("title", f"item_{idx}")
+        raw_nasa_id = data.get("nasa_id") or data.get("title", f"item_{idx}")
+        nasa_id = sanitize_filename(str(raw_nasa_id))
 
         # ------------------------------------------------------------------
         # Asset lookup: fetch high‑resolution image URL
         # ------------------------------------------------------------------
-        asset_url = f"{API_ASSET_URL}/{nasa_id}"
+        asset_url = f"{API_ASSET_URL}/{raw_nasa_id}"
         try:
             asset_resp = requests.get(asset_url, timeout=20)
             asset_resp.raise_for_status()
@@ -243,7 +255,7 @@ def main() -> None:
             print(f"[{idx}] Failed asset lookup for {nasa_id}: {e}", file=sys.stderr)
             continue
 
-        filename = Path(asset_href).name
+        filename = sanitize_filename(Path(asset_href).name)
         image_path = IMG_DIR / filename
         meta_path = META_DIR / f"index-{nasa_id}.json"