fix(vision): file non immagine e grafo malformato non escono più come 500 (#15)

Worker: Image.open().convert() in try/except (422 "image is not
decodable"); il grafo deve essere un dict (422 altrimenti); run_graph
distingue costruzione (GraphBuildError -> 422) da esecuzione (500 con
motivo). Router: verifica dei magic bytes (PNG/JPEG/BMP/TIFF/WebP/GIF)
prima di chiamare il worker.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/backend/api/routers/vision.py

@@ -28,6 +28,29 @@ _IMAGE_EXTENSIONS = {
     "image/webp": "webp",
 }
 
+# Sniffed from the first bytes, independent of the declared Content-Type: a
+# text file uploaded as "image/png" passes the header check above and must
+# still be caught before it reaches the worker as a bare 500 (#15). BMP and
+# TIFF are included even though `_IMAGE_EXTENSIONS` does not accept them,
+# because PIL - and so the worker - can decode both; this check only refuses
+# what is not a real image at all, it does not narrow the allow-list above.
+_IMAGE_SIGNATURES: tuple[tuple[bytes, ...], ...] = (
+    (b"\x89PNG\r\n\x1a\n",),         # PNG
+    (b"\xff\xd8\xff",),              # JPEG
+    (b"BM",),                        # BMP
+    (b"II*\x00", b"MM\x00*"),        # TIFF, little- and big-endian
+    (b"GIF87a", b"GIF89a"),          # GIF
+)
+
+
+def _looks_like_an_image(content: bytes) -> bool:
+    """True if `content` starts with a known image format's magic bytes."""
+    for signatures in _IMAGE_SIGNATURES:
+        if any(content.startswith(sig) for sig in signatures):
+            return True
+    # WebP: "RIFF" + 4-byte size + "WEBP", the size in between is not fixed.
+    return len(content) >= 12 and content[:4] == b"RIFF" and content[8:12] == b"WEBP"
+
 
 async def _task_or_404(db: AsyncSession, task_id: int) -> RecipeTask:
     """Shared by the endpoints of this router."""
@@ -60,6 +83,11 @@ async def _read_image(image: UploadFile) -> bytes:
                 f"{settings.max_upload_size_mb}MB"
             ),
         )
+    if not _looks_like_an_image(content):
+        raise HTTPException(
+            status_code=status.HTTP_422_UNPROCESSABLE_CONTENT,
+            detail="the file's content does not match a supported image format",
+        )
     return content
 
 

src/backend/tests/test_vision_upload_limits.py

@@ -102,6 +102,32 @@ async def test_execute_rejects_a_non_image_upload(
     assert (await db_session.execute(select(Measurement))).scalars().all() == []
 
 
+@pytest.mark.asyncio
+async def test_execute_rejects_a_file_whose_bytes_do_not_match_its_declared_type(
+    client, db_session, measurement_tec_user, worker_says,
+):
+    """#15: a text file declared image/png passes the Content-Type check but
+    must still not reach the worker - it is refused on its magic bytes."""
+    recipe = await create_test_recipe(db_session, measurement_tec_user.id)
+    version, task, subtask = await recipe_parts(db_session, recipe.id)
+    task.task_type = "camera_measure"
+    task.vision_json = {"schema_version": 1, "name": "p", "tools": []}
+    subtask.vision_output = "t1.diameter"
+    await db_session.commit()
+    worker_says({"t1.diameter": float(subtask.nominal)})
+
+    response = await client.post(
+        "/api/vision/execute",
+        headers=auth_headers(measurement_tec_user),
+        files={"image": ("p.png", b"i am not an image", "image/png")},
+        data={"task_id": str(task.id)},
+    )
+
+    assert response.status_code == 422
+    assert (await db_session.execute(select(VisionResult))).scalars().all() == []
+    assert (await db_session.execute(select(Measurement))).scalars().all() == []
+
+
 @pytest.mark.asyncio
 async def test_execute_rejects_an_oversized_upload(
     client, db_session, measurement_tec_user, worker_says, monkeypatch,

src/vision/runner.py

@@ -22,6 +22,14 @@ from visionsuite.task import Task
 _SUBMODULE = Path(__file__).resolve().parents[2] / "vendor" / "visionsuite"
 
 
+class GraphBuildError(ValueError):
+    """`Task.from_dict` refused the graph itself - a bad request, not a
+    server fault (a missing "kind", an unknown schema version, a graph that
+    is not even a dict). Kept apart from an error raised once the task is
+    actually running: the worker maps this one to 422, everything else that
+    can go wrong inside `task.run()` to 500."""
+
+
 @dataclass
 class ToolFailure:
     tool_id: str
@@ -103,8 +111,21 @@ def run_graph(
     `image` is whatever the caller already has in hand: a plain numpy array is
     wrapped into the `visionsuite.core.image.Image` that vs-measure's tools
     actually read via `.pixels`; an `Image` passed in is used as-is.
+
+    Two phases, on purpose: building the task from `graph` can fail on
+    nothing but the caller's input (a bad schema version, a tool with no
+    "kind", a graph that is not a dict at all) - that is `GraphBuildError`,
+    a 422 for the worker. Once the task exists, `task.run()` is the engine's
+    own business; an exception from there is not the caller's mistake, and
+    the worker must not call it one.
     """
-    task = Task.from_dict(graph)
+    try:
+        task = Task.from_dict(graph)
+    except (KeyError, TypeError, AttributeError, ValueError) as exc:
+        raise GraphBuildError(
+            f"malformed graph: {type(exc).__name__}: {exc}"
+        ) from exc
+
     wrapped_image = image if isinstance(image, Image) else Image(pixels=np.asarray(image))
     context: dict[str, Any] = {"image": wrapped_image}
     if calibration is not None:

src/vision_worker/main.py

@@ -10,9 +10,9 @@ import json
 
 import numpy as np
 from fastapi import FastAPI, File, Form, HTTPException, UploadFile, status
-from PIL import Image
+from PIL import Image, UnidentifiedImageError
 
-from src.vision.runner import engine_version, run_graph
+from src.vision.runner import GraphBuildError, engine_version, run_graph
 
 app = FastAPI(title="TieMeasureFlow Vision Worker", version="0.1.0")
 
@@ -35,17 +35,36 @@ async def run(
             detail=f"graph is not valid JSON: {exc}",
         ) from exc
 
-    frame = np.array(Image.open(image.file).convert("L"))
+    if not isinstance(parsed_graph, dict):
+        raise HTTPException(
+            status_code=status.HTTP_422_UNPROCESSABLE_CONTENT,
+            detail=f"graph must be a JSON object, got {type(parsed_graph).__name__}",
+        )
+
+    try:
+        frame = np.array(Image.open(image.file).convert("L"))
+    except (UnidentifiedImageError, OSError) as exc:
+        raise HTTPException(
+            status_code=status.HTTP_422_UNPROCESSABLE_CONTENT,
+            detail=f"image is not decodable: {exc}",
+        ) from exc
 
     try:
         outcome = run_graph(frame, parsed_graph)
-    except ValueError as exc:
-        # from_dict refuses a schema version it does not handle; that is a bad
-        # request, not a server fault.
+    except GraphBuildError as exc:
+        # The graph itself is bad (schema version, a tool missing "kind", ...) -
+        # a bad request, not a server fault.
         raise HTTPException(
             status_code=status.HTTP_422_UNPROCESSABLE_CONTENT,
             detail=str(exc),
         ) from exc
+    except Exception as exc:
+        # The graph built fine; something failed while actually running it -
+        # an engine fault, not the caller's. Still named, not a naked 500.
+        raise HTTPException(
+            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+            detail=f"vision run failed: {type(exc).__name__}: {exc}",
+        ) from exc
 
     return {
         # `outcome.outputs` never carries NaN/inf/bool (see runner.run_graph):

src/vision_worker/tests/test_worker.py

@@ -95,3 +95,55 @@ async def test_a_malformed_graph_is_refused_not_crashed():
 
     assert response.status_code == 422
     assert "99" in response.json()["detail"]
+
+
+# ---------------------------------------------------------------------------
+# #15: a non-image upload, a graph that is not a dict, or a tool with no
+# "kind" used to reach the worker as an unhandled exception - a naked 500,
+# and then a 502 with no reason once the backend forwarded it.
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_a_non_image_upload_is_refused_not_crashed():
+    """A text file declared image/png: Image.open() must not escape as 500."""
+    transport = ASGITransport(app=app)
+    async with AsyncClient(transport=transport, base_url="http://worker") as client:
+        response = await client.post(
+            "/run",
+            files={"image": ("piece.png", b"i am not an image", "image/png")},
+            data={"graph": json.dumps(a_circle_graph())},
+        )
+
+    assert response.status_code == 422
+    assert "not decodable" in response.json()["detail"].lower()
+
+
+@pytest.mark.asyncio
+async def test_a_graph_that_is_not_an_object_is_refused():
+    transport = ASGITransport(app=app)
+    async with AsyncClient(transport=transport, base_url="http://worker") as client:
+        response = await client.post(
+            "/run",
+            files={"image": ("piece.png", a_disc_png(), "image/png")},
+            data={"graph": "[]"},
+        )
+
+    assert response.status_code == 422
+    assert "object" in response.json()["detail"].lower()
+
+
+@pytest.mark.asyncio
+async def test_a_tool_without_a_kind_is_refused_not_crashed():
+    graph = {"schema_version": 1, "name": "p", "tools": [{"id": "a", "name": "x"}]}
+    transport = ASGITransport(app=app)
+    async with AsyncClient(transport=transport, base_url="http://worker") as client:
+        response = await client.post(
+            "/run",
+            files={"image": ("piece.png", a_disc_png(), "image/png")},
+            data={"graph": json.dumps(graph)},
+        )
+
+    assert response.status_code == 422
+    assert "malformed graph" in response.json()["detail"].lower()
+    assert "kind" in response.json()["detail"].lower()