Client.get_collection() doesn't work with GeoServer OSEO STAC API

[EetuHuuskoCSC]

We have an issue with using pystac-client with our GeoServer OSEO STAC API.
The Client.get_collection() function doesn't work as it assumes there are no query parameters in the URL and builds the URL manually based on that.

The generated URL looks like <host-adress>/geoserver/ogc/stac/v1/collections?f=application%2Fjson/<collection-id> where ?f=application%2Fjson is left in the middle.

import pystac_client

catalog_client = pystac_client.Client.open("https://paituli.csc.fi/geoserver/ogc/stac/v1")
collection = catalog_client.get_collection("sentinel2-l2a")

Traceback (most recent call last):
  File "/home/ehuusko/Documents/paituli/stac/testing_get_colletion.py", line 6, in <module>
    catalog_client.get_collection('sentinel2-l2a')
  File "/home/ehuusko/miniconda3/envs/paituli-stac/lib/python3.12/site-packages/pystac_client/client.py", line 399, in get_collection
    self._stac_io.read_json(url),
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ehuusko/miniconda3/envs/paituli-stac/lib/python3.12/site-packages/pystac/stac_io.py", line 205, in read_json
    txt = self.read_text(source, *args, **kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ehuusko/miniconda3/envs/paituli-stac/lib/python3.12/site-packages/pystac_client/stac_api_io.py", line 168, in read_text
    return self.request(href, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ehuusko/miniconda3/envs/paituli-stac/lib/python3.12/site-packages/pystac_client/stac_api_io.py", line 217, in request
    raise APIError.from_response(resp)
pystac_client.exceptions.APIError: {"code":"NoApplicableCode","description":"Invalid mime type \"application/json/sentinel2-l2a\": Invalid token character '/' in token \"json/sentinel2-l2a\"\nInvalid mime type \"application/json/sentinel2-l2a\": Invalid token character '/' in token \"json/sentinel2-l2a\""}

Using pystac.catalog.Catalog.get_child() works:

import pystac

catalog = pystac.catalog.Catalog.from_file("https://paituli.csc.fi/geoserver/ogc/stac/v1")
collection = catalog.get_child("sentinel2-l2a")

<Collection id=sentinel2-l2a>

[gadomski]

Thanks for the report! PR to fix here: #746