[MapProxy] internal error when using clip with datasource

[Lars-Daniel Weber]

Hi there!

I'd like to narrow down to the visible area of my tiles to a BBOX.

When using pure BBOX in source-coverage, the tiles don't get limited, they still can be requested outside the BBOX:
sources:
  src_distribution:
    type: mapnik
    mapfile: data/mapnik.xml
    layers: lyr_distribution
    transparent: true
    coverage:
      bbox: 'xxxx'
      srs: 'EPSG:3857'

Adding "clip: true" to bbox doesn't work, it directly leads to "internal error".
The only way seems to be a datasource with the geometry of the bbox, then "clip: true" works:

sources:
  src_distribution:
    type: mapnik
    mapfile: data/mapnik.xml
    layers: lyr_distribution
    transparent: true
    coverage:
      clip: true
      datasource: 'distribution_bbox.geojson'
      srs: 'EPSG:3857'


The tiles are perfectly within this bbox only, but I'm getting hundrets of "internal error" as text around the bbox. On areas very far outside the bbox, I'm getting the normal XML error that the requested tile is out of boundary.

Is this a bug?

Best regards,
Lars-Daniel