fix: validate ffprobe output structure

src/voice_transcriptor/services/media_probe.py

@@ -50,18 +50,28 @@ def validate_media_path(path: Path) -> Path:
 
 def parse_probe_output(path: Path, size_bytes: int, payload: str) -> MediaInfo:
     try:
-        data: dict[str, Any] = json.loads(payload)
+        data: Any = json.loads(payload)
     except (json.JSONDecodeError, TypeError) as exc:
         raise ProbeOutputError("FFprobe returned invalid data.") from exc
+    if not isinstance(data, dict):
+        raise ProbeOutputError("FFprobe returned invalid data.")
+    format_data = data.get("format", {})
+    streams = data.get("streams", [])
+    if (
+        not isinstance(format_data, dict)
+        or not isinstance(streams, list)
+        or not all(isinstance(stream, dict) for stream in streams)
+    ):
+        raise ProbeOutputError("FFprobe returned invalid data.")
     duration: float | None = None
-    raw_duration = data.get("format", {}).get("duration")
+    raw_duration = format_data.get("duration")
     try:
         if raw_duration is not None:
             duration = float(raw_duration)
     except (TypeError, ValueError):
         duration = None
     codec = next(
-        (stream.get("codec_name") for stream in data.get("streams", []) if stream.get("codec_type") == "audio"),
+        (stream.get("codec_name") for stream in streams if stream.get("codec_type") == "audio"),
         None,
     )
     return MediaInfo(path=path, size_bytes=size_bytes, duration_seconds=duration, audio_codec=codec)

tests/test_media_probe.py

@@ -69,6 +69,12 @@ def test_rejects_malformed_probe_json(tmp_path: Path) -> None:
         parse_probe_output(tmp_path / "bad.mov", 0, "not json")
 
 
+@pytest.mark.parametrize("payload", ["[]", '{"format": []}', '{"streams": [null]}'])
+def test_rejects_structurally_invalid_probe_json(tmp_path: Path, payload: str) -> None:
+    with pytest.raises(ProbeOutputError, match="invalid data"):
+        parse_probe_output(tmp_path / "bad.mov", 0, payload)
+
+
 def test_rejects_missing_file(tmp_path: Path) -> None:
     with pytest.raises(MediaProbeError, match="does not exist"):
         validate_media_path(tmp_path / "missing.mov")