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)