How to declare STAC Catalog extensions?

[mcucchi9]

As far as I understand, extensions implemented in the STAC Catalog (i.e. STAC extensions) should appear in the stac_extensions field of the STAC API landing page, while STAC API extensions should be listed in the field conformsTo of the same page.

If that's the case, I can't get around how to declare implemented STAC Catalog extension using stac-fastapi.

From a code inspection it looks like this should be possible, in principle, via the extension_schemas argument of the LandingPageMixin._landing_page method here:

stac-fastapi/stac_fastapi/types/stac_fastapi/types/core.py

Line 48 in 7b20977

extension_schemas: List[str],

but it also looks like wherever the method is used it is always harcoded to [], i.e. here:

stac-fastapi/stac_fastapi/types/stac_fastapi/types/core.py

Line 155 in 7b20977

extension_schemas=[],

and here:

stac-fastapi/stac_fastapi/types/stac_fastapi/types/core.py

Line 365 in 7b20977

extension_schemas=[],

What am I missing?

[jonhealy1]

Look at how it's done in SFEOS or stac-fastapi-pgstac app maybe?

I may not be understanding your issue properly though?

[vincentsarago]

I think it's better defined in conformsTo attribute

I think the stac_extensions in the landing page is to define the json-schema for the responses not for the API extensions https://github.com/radiantearth/stac-api-spec/tree/release/v1.0.0/stac-spec/extensions#using-extensions

[mcucchi9]

@vincentsarago I actually want to declare an extension for the responses (i.e. this one -> https://github.com/stac-extensions/version), not for the API (for which I agree the correct place would be the conformsTo attribute). Should it be declared in conformsTo too?

[vincentsarago]

👍

as you mentioned, there is no direct path to set the stac_extensions at the catalog level (landing page)

stac-fastapi/stac_fastapi/types/stac_fastapi/types/core.py

Lines 141 to 156 in 7b20977

	def landing_page(self, **kwargs) -> stac.LandingPage:
	"""Landing page.
	Called with `GET /`.
	Returns:
	API landing page, serving as an entry point to the API.
	"""
	request: Request = kwargs["request"]
	base_url = get_base_url(request)
	landing_page = self._landing_page(
	base_url=base_url,
	conformance_classes=self.conformance_classes(),
	extension_schemas=[],
	)

for collections and items this should be handled by the documents (within the backend).

As fast as I understand, if you are trying to support the version extension for the landing page, you are already customizing the response so you can just add https://stac-extensions.github.io/version/v1.2.0/schema.json to the stac_extensions list

stac-fastapi/stac_fastapi/types/stac_fastapi/types/core.py

Line 97 in 7b20977

stac_extensions=extension_schemas,

[mcucchi9]

Thanks @vincentsarago , that's exactly what I was aiming to do.

What I still do not understand is how to do it. The only way I see given how stac-fastapi is currently structured is redefining the landing_page method of the client and passing to the extension_schemas argument a list containing the extensions I want to expose instead of the hardcoded [] in, e.g.,

stac-fastapi/stac_fastapi/types/stac_fastapi/types/core.py

Line 155 in 7b20977

extension_schemas=[],

Am I getting it right, or is there any easier way to do it?

[mcucchi9]

Or probably I could just show the stac_extensions field at the Items and Collections level, so just setting the values I want (e.g. ["https://stac-extensions.github.io/version/v1.2.0/schema.json"]) in the database entries: now I get this is probably what @vincentsarago was suggesting, thanks.

But in this case I still wonder whether there could be (if there isn't) an easier way to set it at the Catalog level (i.e. in the landing page).

[vincentsarago]

exactly,

I don't see an easy way to do this.

the way to do this is by customizing the Client

@attr.s  # type:ignore
class Client(BaseCoreClient):

    def _landing_page(
        self,
        base_url: str,
        conformance_classes: List[str],
        extension_schemas: List[str],
    ) -> stac.LandingPage:
         
         extension_schemas = extension_schemas or []
         extension_schemas.append("https://stac-extensions.github.io/version/v1.2.0/schema.json")

        landing_page = stac.LandingPage(
            type="Catalog",
            id=self.landing_page_id,
            title=self.title,
            description=self.description,
            stac_version=self.stac_version,
            conformsTo=conformance_classes,
            links=[
                {
                    "rel": Relations.self.value,
                    "type": MimeTypes.json.value,
                    "title": "This document",
                    "href": base_url,
                },
                {
                    "rel": Relations.root.value,
                    "type": MimeTypes.json.value,
                    "title": "Root",
                    "href": base_url,
                },
                {
                    "rel": Relations.data.value,
                    "type": MimeTypes.json.value,
                    "title": "Collections available for this Catalog",
                    "href": urljoin(base_url, "collections"),
                },
                {
                    "rel": Relations.conformance.value,
                    "type": MimeTypes.json.value,
                    "title": "STAC/OGC conformance classes implemented by this server",
                    "href": urljoin(base_url, "conformance"),
                },
                {
                    "rel": Relations.search.value,
                    "type": MimeTypes.geojson.value,
                    "title": "STAC search [GET]",
                    "href": urljoin(base_url, "search"),
                    "method": "GET",
                },
                {
                    "rel": Relations.search.value,
                    "type": MimeTypes.geojson.value,
                    "title": "STAC search [POST]",
                    "href": urljoin(base_url, "search"),
                    "method": "POST",
                },
            ],
            stac_extensions=extension_schemas,
            # custom part
            version="0.1.0",
        )
        return landing_page