docs(api-core): address routing review feedback on docstrings, types, and variables

Author: hebaalazzeh

packages/google-api-core/google/api_core/gapic_v1/routing.py

@@ -26,8 +26,10 @@ def get_default_mtls_endpoint(api_endpoint: Optional[str]) -> Optional[str]:
 
     Convert "*.sandbox.googleapis.com" and "*.googleapis.com" to
     "*.mtls.sandbox.googleapis.com" and "*.mtls.googleapis.com" respectively.
+
     Args:
         api_endpoint (Optional[str]): the api endpoint to convert.
+
     Returns:
         Optional[str]: converted mTLS api endpoint.
     """
@@ -52,9 +54,30 @@ def get_api_endpoint(
     use_mtls_endpoint: str,
     default_universe: str,
     default_mtls_endpoint: Optional[str],
-    default_endpoint_template: Optional[str],
-) -> Optional[str]:
-    """Return the API endpoint used by the client."""
+    default_endpoint_template: str,
+) -> str:
+    """Return the API endpoint used by the client.
+
+    Args:
+        api_override (Optional[str]): The API endpoint override. If specified,
+            this is always returned.
+        client_cert_source (Optional[Any]): The client certificate source used by the client.
+        universe_domain (str): The universe domain used by the client.
+        use_mtls_endpoint (str): How to use the mTLS endpoint. Possible values
+            are "always", "auto", or "never".
+        default_universe (str): The default universe domain.
+        default_mtls_endpoint (Optional[str]): The default mTLS endpoint.
+        default_endpoint_template (str): The default endpoint template containing
+            a placeholder `{UNIVERSE_DOMAIN}`.
+
+    Returns:
+        str: The API endpoint to be used by the client.
+
+    Raises:
+        google.auth.exceptions.MutualTLSChannelError: If mTLS is requested but
+            not supported in the configured universe domain.
+        ValueError: If mTLS is requested but no mTLS endpoint is available.
+    """
     if api_override is not None:
         return api_override
     elif use_mtls_endpoint == "always" or (
@@ -64,26 +87,40 @@ def get_api_endpoint(
             raise MutualTLSChannelError(
                 f"mTLS is not supported in any universe other than {default_universe}."
             )
+        if not default_mtls_endpoint:
+            raise ValueError("mTLS endpoint is not available.")
         return default_mtls_endpoint
     else:
-        return (
-            default_endpoint_template.format(UNIVERSE_DOMAIN=universe_domain)
-            if default_endpoint_template
-            else None
-        )
+        return default_endpoint_template.format(UNIVERSE_DOMAIN=universe_domain)
 
 
 def get_universe_domain(
     client_universe_domain: Optional[str],
     universe_domain_env: Optional[str],
     default_universe: str,
 ) -> str:
-    """Return the universe domain used by the client."""
-    universe_domain = default_universe
+    """Return the universe domain used by the client.
+
+    Args:
+        client_universe_domain (Optional[str]): The universe domain configured
+            via client options.
+        universe_domain_env (Optional[str]): The universe domain configured
+            via environment variable.
+        default_universe (str): The default universe domain.
+
+    Returns:
+        str: The universe domain to be used by the client.
+
+    Raises:
+        ValueError: If the resolved universe domain is an empty string.
+    """
     if client_universe_domain is not None:
         universe_domain = client_universe_domain.strip()
     elif universe_domain_env is not None:
         universe_domain = universe_domain_env.strip()
+    else:
+        universe_domain = default_universe
+
     if not universe_domain:
         raise ValueError("Universe Domain cannot be an empty string.")
     return universe_domain

packages/google-api-core/tests/unit/gapic/test_routing.py

@@ -164,6 +164,18 @@ def test__get_api_endpoint():
         == "mTLS is not supported in any universe other than googleapis.com."
     )
 
+    with pytest.raises(ValueError) as excinfo:
+        get_api_endpoint(
+            None,
+            mock_client_cert_source,
+            default_universe,
+            "always",
+            MockClient._DEFAULT_UNIVERSE,
+            None,
+            MockClient._DEFAULT_ENDPOINT_TEMPLATE,
+        )
+    assert str(excinfo.value) == "mTLS endpoint is not available."
+
 
 def test__get_universe_domain():
     client_universe_domain = "foo.com"