Harden YOLO tile inference inputs

backend/app/services/yolo_adapter.py

@@ -1,7 +1,10 @@
 from __future__ import annotations
 
+from contextlib import contextmanager
 from pathlib import Path
+import tempfile
 from typing import Any
+from collections.abc import Iterator
 
 from app.core.config import Settings
 from app.core.errors import AppError
@@ -62,13 +65,24 @@ class YoloDetectionAdapter:
                 details={"tile_path": str(tile_path)},
                 status_code=422,
             )
-        results = model.predict(
-            source=str(tile_path),
-            conf=float(confidence_threshold),
-            imgsz=int(self.settings.yolo_image_size),
-            device=self.settings.yolo_device,
-            verbose=False,
-        )
+        try:
+            with _prediction_source(tile_path) as prediction_source:
+                results = model.predict(
+                    source=prediction_source,
+                    conf=float(confidence_threshold),
+                    imgsz=int(self.settings.yolo_image_size),
+                    device=self.settings.yolo_device,
+                    verbose=False,
+                )
+        except AppError:
+            raise
+        except Exception as exc:
+            raise AppError(
+                code="DETECTION_INFERENCE_FAILED",
+                message="Configured YOLO inference failed for a raster tile",
+                details={"tile_path": str(tile_path), "error": str(exc)},
+                status_code=503,
+            ) from exc
 
         detections: list[dict[str, Any]] = []
         for result in results:
@@ -102,3 +116,35 @@ def _to_list(value: Any) -> list[Any]:
     if hasattr(value, "tolist"):
         return value.tolist()
     return list(value)
+
+
+@contextmanager
+def _prediction_source(tile_path: Path) -> Iterator[str]:
+    temp_path: Path | None = None
+    try:
+        try:
+            from PIL import Image
+        except Exception:
+            yield str(tile_path)
+            return
+
+        try:
+            with Image.open(tile_path) as image:
+                if image.mode == "RGB" and len(image.getbands()) == 3:
+                    yield str(tile_path)
+                    return
+
+                rgb_image = image.convert("RGB")
+                with tempfile.NamedTemporaryFile(suffix=".png", delete=False) as handle:
+                    temp_path = Path(handle.name)
+                rgb_image.save(temp_path)
+                yield str(temp_path)
+                return
+        except Exception:
+            if temp_path is not None:
+                raise
+            yield str(tile_path)
+            return
+    finally:
+        if temp_path is not None:
+            temp_path.unlink(missing_ok=True)