Absolute links in a self contained STAC Catalog Items

[pomadchin]

Generation of a SELF_CONTAINED catalog produces all correct relative links in catalogs and collections but not in items.

Code example to reproduce:

import pystac
from datetime import datetime, timezone
from shapely.geometry import box, mapping

def tiny():
    # Create a catalog
    catalog = pystac.Catalog(id="example-catalog-id", description="descr")
    collection = pystac.Collection(
        "example-collection-id",
        "descr",
        pystac.Extent(
            spatial=pystac.SpatialExtent([[-180, -90, 180, 90]]),
            temporal=pystac.TemporalExtent(
                [[datetime(2020,7,3, tzinfo=timezone.utc), None]]
            ),
        ),
        license='proprietary'
    )

    item = pystac.Item(
        id="example-item-id",
        stac_extensions=[],
        geometry=mapping(box(0, 0, 90, 90)),
        bbox=[0, 0, 90, 90],
        datetime=datetime(2021,11,1),
        properties={}
    )

    collection.add_item(item)
    catalog.add_child(collection)
    catalog_path = './data/catalog/example-catalog'
    catalog.normalize_hrefs(catalog_path)
    catalog.validate_all()
    print(f'Saving catalog to {catalog_path}...')
    catalog.save(catalog_type=pystac.CatalogType.SELF_CONTAINED)
    print("Done!")

if __name__ == "__main__":
    tiny()

Item json in this case:

{
  "type": "Feature",
  "stac_version": "1.0.0",
  "id": "example-item-id",
  // ...
  "links": [
    {
      "rel": "root",
      "href": "/fullpath/data/catalog/example-catalog/example-collection-id/collection.json",
      "type": "application/json"
    },
    {
      "rel": "collection",
      "href": "/fullpath/data/catalog/example-catalog/example-collection-id/collection.json",
      "type": "application/json"
    },
    {
      "rel": "parent",
      "href": "/fullpath/data/catalog/example-catalog/example-collection-id/collection.json",
      "type": "application/json"
    }
  ],
  // ...
  "collection": "example-collection-id"
}

Gist with the same code, requirements.txt and the output example: https://gist.github.com/pomadchin/7c4c8365e1d3098956acc974f39a4cb6

I will try to prep a PR with a unit test to cover this case as well.

[duckontheweb]

Closed via #658