Respect VMM flood coverage size limit

backend/app/services/flood_hazard_acquisition_service.py

@@ -14,6 +14,7 @@ from urllib.error import HTTPError, URLError
 from urllib.parse import urlencode
 from urllib.request import Request, urlopen
 from uuid import UUID
+from xml.etree import ElementTree
 
 from geoalchemy2.shape import to_shape
 from pyproj import Transformer
@@ -50,7 +51,9 @@ class FloodHazardAcquisitionService:
     SOURCE_VERSION = "VMM OGRK flood hazard maps"
     ATTRIBUTION = "Bron: VMM"
     LICENSE_NOTE = "Publieke toegang; gebruik en bronvermelding volgens de metadata van VMM/GDI-Vlaanderen."
-    WCS_TILE_SIDE_M = 10_000.0
+    # The VMM WCS rejects generated coverages above 4.88 MB. At the default
+    # 5 metre resolution a 5 km square stays below that provider-side limit.
+    WCS_TILE_SIDE_M = 5_000.0
     WCS_REQUEST_INTERVAL_SECONDS = 1.0
     WCS_RETRY_DELAY_SECONDS = 3.0
     WCS_TRANSIENT_STATUS_CODES = frozenset({400, 429, 502, 503, 504})
@@ -281,10 +284,27 @@ class FloodHazardAcquisitionService:
         if content.startswith((b"II*\x00", b"MM\x00*")):
             return content
         if "multipart" not in content_type.lower():
+            provider_exception = None
+            if "xml" in content_type.lower() or content.lstrip().startswith(b"<"):
+                try:
+                    root = ElementTree.fromstring(content)
+                    exception_texts = [
+                        (element.text or "").strip()
+                        for element in root.iter()
+                        if element.tag.rsplit("}", 1)[-1] in {"ExceptionText", "ServiceException"}
+                        and (element.text or "").strip()
+                    ]
+                    provider_exception = " ".join(exception_texts) or None
+                except ElementTree.ParseError:
+                    pass
             raise AppError(
                 code="FLOOD_HAZARD_PROVIDER_INVALID_RESPONSE",
                 message="The official VMM service did not return a GeoTIFF coverage",
-                details={"content_type": content_type, "response_preview": content[:300].decode("utf-8", errors="replace")},
+                details={
+                    "content_type": content_type,
+                    "provider_exception": provider_exception,
+                    "response_preview": content[:300].decode("utf-8", errors="replace"),
+                },
                 status_code=502,
             )
         message = BytesParser(policy=default).parsebytes(f"Content-Type: {content_type}\r\nMIME-Version: 1.0\r\n\r\n".encode() + content)

backend/tests/test_sprint208_vmm_flood_hazard.py

@@ -137,6 +137,35 @@ def test_flood_hazard_request_is_bounded_and_rejects_arbitrary_products() -> Non
     assert exc_info.value.code == "FLOOD_HAZARD_PRODUCT_NOT_SUPPORTED"
 
 
+def test_flood_hazard_tiles_stay_below_the_observed_vmm_coverage_limit() -> None:
+    prepared = FloodHazardAcquisitionService._prepared_request(flood_payload(side_m=15_000), Settings(_env_file=None))
+    tiles = FloodHazardAcquisitionService._tile_bounds(prepared)
+
+    assert 9 <= len(tiles) <= 16
+    assert all((max_x - min_x) <= 5_000 for min_x, _min_y, max_x, _max_y in tiles)
+    assert all((max_y - min_y) <= 5_000 for _min_x, min_y, _max_x, max_y in tiles)
+    assert all(
+        ((max_x - min_x) / prepared["resolution_m"]) * ((max_y - min_y) / prepared["resolution_m"])
+        <= 1_000_000
+        for min_x, min_y, max_x, max_y in tiles
+    )
+
+
+def test_flood_hazard_xml_provider_error_is_exposed_without_losing_the_canonical_error() -> None:
+    response = b"""<?xml version="1.0"?>
+    <ExceptionReport xmlns="http://www.opengis.net/ows/1.1">
+      <Exception exceptionCode="NoApplicableCode">
+        <ExceptionText>This request is trying to generate too much data</ExceptionText>
+      </Exception>
+    </ExceptionReport>"""
+
+    with pytest.raises(AppError) as exc_info:
+        FloodHazardAcquisitionService._extract_geotiff(response, "application/xml")
+
+    assert exc_info.value.code == "FLOOD_HAZARD_PROVIDER_INVALID_RESPONSE"
+    assert exc_info.value.details["provider_exception"] == "This request is trying to generate too much data"
+
+
 def test_flood_hazard_normalization_converts_centimetres_and_clips_zero_values() -> None:
     payload = flood_payload()
     prepared = FloodHazardAcquisitionService._prepared_request(payload, Settings(_env_file=None))