fix: prevent URL-encoding of $alt query parameter in REST transport

gapic/ads-templates/%namespace/%name/%version/%sub/services/%service/_shared_macros.j2

@@ -171,16 +171,23 @@ def _get_http_options():
     timeout,
     transcoded_request,
     body=None):
-    
+
     uri = transcoded_request['uri']
     method = transcoded_request['method']
     headers = dict(metadata)
     headers['Content-Type'] = 'application/json'
+    # Build query string manually to avoid URL-encoding special characters like '$'.
+    # The `requests` library encodes '$' as '%24' when using the `params` argument,
+    # which causes API errors for parameters like '$alt'. See:
+    # https://github.com/googleapis/gapic-generator-python/issues/2514
+    _query_params = rest_helpers.flatten_query_params(query_params, strict=True)
+    _request_url = "{host}{uri}".format(host=host, uri=uri)
+    if _query_params:
+        _request_url = "{}?{}".format(_request_url, urlencode(_query_params, safe="$"))
     response = {{ await_prefix }}getattr(session, method)(
-        "{host}{uri}".format(host=host, uri=uri),
+        _request_url,
         timeout=timeout,
         headers=headers,
-        params=rest_helpers.flatten_query_params(query_params, strict=True),
         {% if body_spec %}
         data=body,
         {% endif %}

gapic/ads-templates/%namespace/%name/%version/%sub/services/%service/transports/rest.py.j2

@@ -33,11 +33,13 @@ from google.iam.v1 import policy_pb2  # type: ignore
 from google.cloud.location import locations_pb2 # type: ignore
 {% endif %}
 
-from requests import __version__ as requests_version
 import dataclasses
 from typing import Any, Callable, Dict, List, Optional, Sequence, Tuple, Union
+from urllib.parse import urlencode
 import warnings
 
+from requests import __version__ as requests_version
+
 {{ shared_macros.operations_mixin_imports(api, service, opts) }}
 
 from .rest_base import _Base{{ service.name }}RestTransport

gapic/ads-templates/tests/unit/gapic/%name_%version/%sub/_test_mixins.py.j2

@@ -997,3 +997,346 @@ def test_test_iam_permissions_from_dict():
 {% endif %}
 
 {% endif %}
+
+{# REST transport tests for mixin URL query params encoding #}
+{% if 'rest' in opts.transport %}
+
+{# Operations mixin REST URL encoding tests #}
+{% if api.has_operations_mixin %}
+
+{% if "ListOperations" in api.mixin_api_methods %}
+def test_list_operations_rest_url_query_params_encoding():
+    # Verify that special characters like '$' are correctly preserved (not URL-encoded)
+    # when building the URL query string for mixin methods.
+    transport = transports.{{ service.rest_transport_name }}(credentials=ga_credentials.AnonymousCredentials())
+    method_class = transport.list_operations.__class__
+    get_response_fn = method_class._get_response
+
+    mock_session = mock.Mock()
+    mock_response = mock.Mock()
+    mock_response.status_code = 200
+    mock_session.get.return_value = mock_response
+
+    with mock.patch.object(rest_helpers, 'flatten_query_params') as mock_flatten:
+        mock_flatten.return_value = [('$alt', 'json;enum-encoding=int'), ('foo', 'bar')]
+
+        transcoded_request = {
+            'uri': '/v1/test/operations',
+            'method': 'get',
+        }
+
+        get_response_fn(
+            host='https://example.com',
+            metadata=[],
+            query_params={},
+            session=mock_session,
+            timeout=None,
+            transcoded_request=transcoded_request,
+        )
+
+        assert mock_session.get.called
+        call_url = mock_session.get.call_args.args[0]
+        assert '$alt=json' in call_url
+        assert '%24alt' not in call_url
+        assert 'foo=bar' in call_url
+{% endif %}
+
+{% if "GetOperation" in api.mixin_api_methods %}
+def test_get_operation_rest_url_query_params_encoding():
+    transport = transports.{{ service.rest_transport_name }}(credentials=ga_credentials.AnonymousCredentials())
+    method_class = transport.get_operation.__class__
+    get_response_fn = method_class._get_response
+
+    mock_session = mock.Mock()
+    mock_response = mock.Mock()
+    mock_response.status_code = 200
+    mock_session.get.return_value = mock_response
+
+    with mock.patch.object(rest_helpers, 'flatten_query_params') as mock_flatten:
+        mock_flatten.return_value = [('$alt', 'json;enum-encoding=int'), ('foo', 'bar')]
+
+        transcoded_request = {
+            'uri': '/v1/test/operations/op1',
+            'method': 'get',
+        }
+
+        get_response_fn(
+            host='https://example.com',
+            metadata=[],
+            query_params={},
+            session=mock_session,
+            timeout=None,
+            transcoded_request=transcoded_request,
+        )
+
+        assert mock_session.get.called
+        call_url = mock_session.get.call_args.args[0]
+        assert '$alt=json' in call_url
+        assert '%24alt' not in call_url
+        assert 'foo=bar' in call_url
+{% endif %}
+
+{% if "DeleteOperation" in api.mixin_api_methods %}
+def test_delete_operation_rest_url_query_params_encoding():
+    transport = transports.{{ service.rest_transport_name }}(credentials=ga_credentials.AnonymousCredentials())
+    method_class = transport.delete_operation.__class__
+    get_response_fn = method_class._get_response
+
+    mock_session = mock.Mock()
+    mock_response = mock.Mock()
+    mock_response.status_code = 200
+    mock_session.delete.return_value = mock_response
+
+    with mock.patch.object(rest_helpers, 'flatten_query_params') as mock_flatten:
+        mock_flatten.return_value = [('$alt', 'json;enum-encoding=int'), ('foo', 'bar')]
+
+        transcoded_request = {
+            'uri': '/v1/test/operations/op1',
+            'method': 'delete',
+        }
+
+        get_response_fn(
+            host='https://example.com',
+            metadata=[],
+            query_params={},
+            session=mock_session,
+            timeout=None,
+            transcoded_request=transcoded_request,
+        )
+
+        assert mock_session.delete.called
+        call_url = mock_session.delete.call_args.args[0]
+        assert '$alt=json' in call_url
+        assert '%24alt' not in call_url
+        assert 'foo=bar' in call_url
+{% endif %}
+
+{% if "CancelOperation" in api.mixin_api_methods %}
+def test_cancel_operation_rest_url_query_params_encoding():
+    transport = transports.{{ service.rest_transport_name }}(credentials=ga_credentials.AnonymousCredentials())
+    method_class = transport.cancel_operation.__class__
+    get_response_fn = method_class._get_response
+
+    mock_session = mock.Mock()
+    mock_response = mock.Mock()
+    mock_response.status_code = 200
+    mock_session.post.return_value = mock_response
+
+    with mock.patch.object(rest_helpers, 'flatten_query_params') as mock_flatten:
+        mock_flatten.return_value = [('$alt', 'json;enum-encoding=int'), ('foo', 'bar')]
+
+        transcoded_request = {
+            'uri': '/v1/test/operations/op1:cancel',
+            'method': 'post',
+            'body': {},
+        }
+
+        get_response_fn(
+            host='https://example.com',
+            metadata=[],
+            query_params={},
+            session=mock_session,
+            timeout=None,
+            transcoded_request=transcoded_request,
+            body={},
+        )
+
+        assert mock_session.post.called
+        call_url = mock_session.post.call_args.args[0]
+        assert '$alt=json' in call_url
+        assert '%24alt' not in call_url
+        assert 'foo=bar' in call_url
+{% endif %}
+
+{% endif %} {# operations_mixin #}
+
+{# Location mixin REST URL encoding tests #}
+{% if api.has_location_mixin %}
+
+{% if "ListLocations" in api.mixin_api_methods %}
+def test_list_locations_rest_url_query_params_encoding():
+    transport = transports.{{ service.rest_transport_name }}(credentials=ga_credentials.AnonymousCredentials())
+    method_class = transport.list_locations.__class__
+    get_response_fn = method_class._get_response
+
+    mock_session = mock.Mock()
+    mock_response = mock.Mock()
+    mock_response.status_code = 200
+    mock_session.get.return_value = mock_response
+
+    with mock.patch.object(rest_helpers, 'flatten_query_params') as mock_flatten:
+        mock_flatten.return_value = [('$alt', 'json;enum-encoding=int'), ('foo', 'bar')]
+
+        transcoded_request = {
+            'uri': '/v1/projects/p1/locations',
+            'method': 'get',
+        }
+
+        get_response_fn(
+            host='https://example.com',
+            metadata=[],
+            query_params={},
+            session=mock_session,
+            timeout=None,
+            transcoded_request=transcoded_request,
+        )
+
+        assert mock_session.get.called
+        call_url = mock_session.get.call_args.args[0]
+        assert '$alt=json' in call_url
+        assert '%24alt' not in call_url
+        assert 'foo=bar' in call_url
+{% endif %}
+
+{% if "GetLocation" in api.mixin_api_methods %}
+def test_get_location_rest_url_query_params_encoding():
+    transport = transports.{{ service.rest_transport_name }}(credentials=ga_credentials.AnonymousCredentials())
+    method_class = transport.get_location.__class__
+    get_response_fn = method_class._get_response
+
+    mock_session = mock.Mock()
+    mock_response = mock.Mock()
+    mock_response.status_code = 200
+    mock_session.get.return_value = mock_response
+
+    with mock.patch.object(rest_helpers, 'flatten_query_params') as mock_flatten:
+        mock_flatten.return_value = [('$alt', 'json;enum-encoding=int'), ('foo', 'bar')]
+
+        transcoded_request = {
+            'uri': '/v1/projects/p1/locations/l1',
+            'method': 'get',
+        }
+
+        get_response_fn(
+            host='https://example.com',
+            metadata=[],
+            query_params={},
+            session=mock_session,
+            timeout=None,
+            transcoded_request=transcoded_request,
+        )
+
+        assert mock_session.get.called
+        call_url = mock_session.get.call_args.args[0]
+        assert '$alt=json' in call_url
+        assert '%24alt' not in call_url
+        assert 'foo=bar' in call_url
+{% endif %}
+
+{% endif %} {# location_mixin #}
+
+{# IAM mixin REST URL encoding tests #}
+{% if api.has_iam_mixin or opts.add_iam_methods %}
+
+{% if "SetIamPolicy" in api.mixin_api_methods or opts.add_iam_methods %}
+def test_set_iam_policy_rest_url_query_params_encoding():
+    transport = transports.{{ service.rest_transport_name }}(credentials=ga_credentials.AnonymousCredentials())
+    method_class = transport.set_iam_policy.__class__
+    get_response_fn = method_class._get_response
+
+    mock_session = mock.Mock()
+    mock_response = mock.Mock()
+    mock_response.status_code = 200
+    mock_session.post.return_value = mock_response
+
+    with mock.patch.object(rest_helpers, 'flatten_query_params') as mock_flatten:
+        mock_flatten.return_value = [('$alt', 'json;enum-encoding=int'), ('foo', 'bar')]
+
+        transcoded_request = {
+            'uri': '/v1/resource:setIamPolicy',
+            'method': 'post',
+            'body': {},
+        }
+
+        get_response_fn(
+            host='https://example.com',
+            metadata=[],
+            query_params={},
+            session=mock_session,
+            timeout=None,
+            transcoded_request=transcoded_request,
+            body={},
+        )
+
+        assert mock_session.post.called
+        call_url = mock_session.post.call_args.args[0]
+        assert '$alt=json' in call_url
+        assert '%24alt' not in call_url
+        assert 'foo=bar' in call_url
+{% endif %}
+
+{% if "GetIamPolicy" in api.mixin_api_methods or opts.add_iam_methods %}
+def test_get_iam_policy_rest_url_query_params_encoding():
+    transport = transports.{{ service.rest_transport_name }}(credentials=ga_credentials.AnonymousCredentials())
+    method_class = transport.get_iam_policy.__class__
+    get_response_fn = method_class._get_response
+
+    mock_session = mock.Mock()
+    mock_response = mock.Mock()
+    mock_response.status_code = 200
+    mock_session.get.return_value = mock_response
+
+    with mock.patch.object(rest_helpers, 'flatten_query_params') as mock_flatten:
+        mock_flatten.return_value = [('$alt', 'json;enum-encoding=int'), ('foo', 'bar')]
+
+        transcoded_request = {
+            'uri': '/v1/resource:getIamPolicy',
+            'method': 'get',
+        }
+
+        get_response_fn(
+            host='https://example.com',
+            metadata=[],
+            query_params={},
+            session=mock_session,
+            timeout=None,
+            transcoded_request=transcoded_request,
+        )
+
+        assert mock_session.get.called
+        call_url = mock_session.get.call_args.args[0]
+        assert '$alt=json' in call_url
+        assert '%24alt' not in call_url
+        assert 'foo=bar' in call_url
+{% endif %}
+
+{% if "TestIamPermissions" in api.mixin_api_methods or opts.add_iam_methods %}
+def test_test_iam_permissions_rest_url_query_params_encoding():
+    transport = transports.{{ service.rest_transport_name }}(credentials=ga_credentials.AnonymousCredentials())
+    method_class = transport.test_iam_permissions.__class__
+    get_response_fn = method_class._get_response
+
+    mock_session = mock.Mock()
+    mock_response = mock.Mock()
+    mock_response.status_code = 200
+    mock_session.post.return_value = mock_response
+
+    with mock.patch.object(rest_helpers, 'flatten_query_params') as mock_flatten:
+        mock_flatten.return_value = [('$alt', 'json;enum-encoding=int'), ('foo', 'bar')]
+
+        transcoded_request = {
+            'uri': '/v1/resource:testIamPermissions',
+            'method': 'post',
+            'body': {},
+        }
+
+        get_response_fn(
+            host='https://example.com',
+            metadata=[],
+            query_params={},
+            session=mock_session,
+            timeout=None,
+            transcoded_request=transcoded_request,
+            body={},
+        )
+
+        assert mock_session.post.called
+        call_url = mock_session.post.call_args.args[0]
+        assert '$alt=json' in call_url
+        assert '%24alt' not in call_url
+        assert 'foo=bar' in call_url
+{% endif %}
+
+{% endif %} {# iam_mixin #}
+
+{% endif %} {# rest transport #}