REST: list_namespaces double-encodes the parent namespace query parameter #4111

Apache Iceberg version

main (development)

Please describe the bug 🐞

RestCatalog.list_namespaces(parent) URL-encodes each part of the parent namespace with quote() (via _encode_namespace_path) and then hands the result to requests as a query parameter, which encodes it again. Any namespace part that contains a space, /, % or a non-ASCII character is therefore sent double-encoded, and the server looks up the wrong parent namespace (typically a 404 / NoSuchNamespaceError, or an empty listing).

This started when list_namespaces moved from building the query string by hand to params= in #3347.

Minimal reproduction (no server required):

from urllib.parse import parse_qs, urlsplit

import requests_mock

from pyiceberg.catalog.rest import RestCatalog

with requests_mock.Mocker() as m:
    m.get("http://srv/v1/config", json={"defaults": {}, "overrides": {}})
    m.get("http://srv/v1/namespaces", json={"namespaces": []})
    cat = RestCatalog("r", uri="http://srv", token="t")
    for ns in [("my namespace",), ("dept/finance",), ("café",), ("100%",)]:
        cat.list_namespaces(ns)
        url = m.request_history[-1].url
        print(ns, url, parse_qs(urlsplit(url).query)["parent"])

Output:

('my namespace',) http://srv/v1/namespaces?parent=my%2520namespace ['my%20namespace']
('dept/finance',) http://srv/v1/namespaces?parent=dept%252Ffinance ['dept%2Ffinance']
('café',) http://srv/v1/namespaces?parent=caf%25C3%25A9 ['caf%C3%A9']
('100%',) http://srv/v1/namespaces?parent=100%2525 ['100%25']

Expected: after the server decodes the query string, parent is the namespace parts joined by the namespace separator (my namespace, dept/finance, ...). This is what the Java client sends: RESTUtil.namespaceToQueryParam joins the raw levels with the separator and leaves encoding to the HTTP client, and the server parses the value with RESTUtil.namespaceFromQueryParam without decoding it again.

Actual: the server receives my%20namespace, dept%2Ffinance, and so on. Plain ASCII names such as accounting are unaffected, which is why the existing tests pass.

Environment: pyiceberg main (b32392d), Python 3.12.13, requests 2.34.2, macOS.