Coverages: don't parse absent scale-factor as 1

The OGC standard allows an implementation to downscale by default
if no scale-factor is given, so handling of absent scale-factor
parameter has been moved from the request parser to the controller
(though for the moment we are still defaulting to 1).

test/webapi/ows/coverages/test_request.py

@@ -95,7 +95,7 @@ def test_parse_properties(self):
         )
 
     def test_parse_scale_factor(self):
-        self.assertEqual(1, CoveragesRequest({}).scale_factor)
+        self.assertEqual(None, CoveragesRequest({}).scale_factor)
         self.assertEqual(
             1.5, CoveragesRequest({'scale-factor': ['1.5']}).scale_factor
         )

xcube/webapi/ows/coverages/controllers.py

@@ -134,17 +134,21 @@ def get_coverage_data(
     if request.bbox is not None:
         ds = _apply_bbox(ds, request.bbox, bbox_crs, always_xy=False)
 
-    _assert_coverage_size_ok(ds, request.scale_factor)
+    # NB: a default scale factor of 1 is not compulsory. We may in future
+    # choose to downscale by default if a large coverage is requested.
+    scale_factor = 1 if request.scale_factor is None else request.scale_factor
+    _assert_coverage_size_ok(ds, scale_factor)
 
     source_gm = GridMapping.from_dataset(ds, crs=native_crs)
     target_gm = None
 
     if native_crs != final_crs:
         target_gm = source_gm.transform(final_crs).to_regular()
-    if request.scale_factor != 1:
+
+    if scale_factor != 1:
         if target_gm is None:
             target_gm = source_gm
-        target_gm = target_gm.scale(1. / request.scale_factor)
+        target_gm = target_gm.scale(1. / scale_factor)
     if request.scale_axes is not None:
         # TODO implement scale-axes
         raise ApiError.NotImplemented(

xcube/webapi/ows/coverages/request.py

@@ -127,7 +127,9 @@ def _parse_scale_factor(self):
             except ValueError:
                 raise ValueError(f'Invalid scale-factor {scale_factor_str}')
         else:
-            self.scale_factor = 1
+            # We don't default to 1, since (per the standard) an implementation
+            # may choose to downscale by default.
+            self.scale_factor = None
 
     def _parse_scale_axes(self):
         self.scale_axes = (