[farkhalit]

new_batch_http_request() builds its endpoint as rootUrl + batchPath straight from the discovery document, while every ordinary method request goes through self._baseUrl, which already carries the universe domain substitution, the client_options.api_endpoint override and the mTLS endpoint choice. A client configured for a non-default universe, a restricted or private api_endpoint, or GOOGLE_API_USE_MTLS_ENDPOINT=always therefore POSTs its batch, with each sub-request's bearer token inside the multipart body, to the public www.googleapis.com host. The universe check in _validate_credentials does not catch this because it compares the configured universes rather than the host the batch is actually sent to. The batch URI now takes its host from _baseUrl through the same _fix_up_media_path_base_url correction that media upload URLs already get, and the three new tests fail on main and pass with the change.

• Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

[gemini-code-assist]

Code Review

This pull request ensures that batch request URIs correctly respect custom API endpoints, mTLS endpoints, and universe domains by using the base URL in googleapiclient/discovery.py. It also adds comprehensive unit tests to verify these scenarios. The feedback suggests improving code readability by using f-strings instead of % formatting for string interpolation.

[gemini-code-assist]

In accordance with the general rules, f-strings are preferred over % formatting for string interpolation in Python.

Suggested change

	"%s%s" % (rootDesc["rootUrl"], rootDesc.get("batchPath", "batch")),
	f"{rootDesc['rootUrl']}{rootDesc.get('batchPath', 'batch')}",

References

1. Prefer using f-strings for string interpolation in Python.