feat: port REST transport to Ads templates

Add REST transport tests to Ads generated unit tests
Boost google-api-core dependency version
Minor bugfixes

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

@@ -29,8 +29,13 @@ from google.oauth2 import service_account                         # type: ignore
 {% endfor %}
 {% endfor %}
 {% endfilter %}
+{% if 'grpc' in opts.transport %}
 from .transports.base import {{ service.name }}Transport, DEFAULT_CLIENT_INFO
 from .transports.grpc import {{ service.name }}GrpcTransport
+{% endif %}
+{% if 'rest' in opts.transport %}
+from .transports.rest import {{ service.name }}RestTransport
+{% endif %}
 
 
 class {{ service.client_name }}Meta(type):
@@ -40,8 +45,13 @@ class {{ service.client_name }}Meta(type):
     support objects (e.g. transport) without polluting the client instance
     objects.
     """
+    {% if "grpc" in opts.transport %}
     _transport_registry = OrderedDict()  # type: Dict[str, Type[{{ service.name }}Transport]]
     _transport_registry['grpc'] = {{ service.name }}GrpcTransport
+    {% endif %}
+    {% if "rest" in opts.transport %}
+    _transport_registry["rest"] = {{ service.name }}RestTransport
+    {% endif %}
 
     def get_transport_class(cls,
             label: str = None,

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

@@ -6,16 +6,29 @@ from collections import OrderedDict
 from typing import Dict, Type
 
 from .base import {{ service.name }}Transport
+{% if 'grpc' in opts.transport %}
 from .grpc import {{ service.name }}GrpcTransport
-
+{% endif %}
+{% if 'rest' in opts.transport %}
+from .rest import {{ service.name }}RestTransport
+{% endif %}
 
 # Compile a registry of transports.
 _transport_registry = OrderedDict()  # type: Dict[str, Type[{{ service.name }}Transport]]
+{% if 'grpc' in opts.transport %}
 _transport_registry['grpc'] = {{ service.name }}GrpcTransport
-
+{% endif %}
+{% if 'rest' in opts.transport %}
+_transport_registry['rest'] = {{ service.name }}RestTransport
+{% endif %}
 
 __all__ = (
     '{{ service.name }}Transport',
+    {% if 'grpc' in opts.transport %}
     '{{ service.name }}GrpcTransport',
+    {% endif %}
+    {% if 'rest' in opts.transport %}
+    '{{ service.name }}RestTransport',
+    {% endif %}
 )
 {% endblock %}

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

@@ -4,10 +4,13 @@
 
 import abc
 import typing
+import packaging.version
 import pkg_resources
+from typing import Dict, Optional, {% if service.any_server_streaming %}Iterable, {% endif %}{% if service.any_client_streaming %}Iterator, {% endif %}Sequence, Tuple, Type, Union
 
 import google.auth  # type: ignore
 from google.api_core import gapic_v1    # type: ignore
+from google.api_core import exceptions as core_exceptions  # type: ignore
 from google.api_core import retry as retries  # type: ignore
 {% if service.has_lro %}
 from google.api_core import operations_v1  # type: ignore
@@ -30,6 +33,15 @@ try:
 except pkg_resources.DistributionNotFound:
     DEFAULT_CLIENT_INFO = gapic_v1.client_info.ClientInfo()
 
+try:
+    # google.auth.__version__ was added in 1.26.0
+    _GOOGLE_AUTH_VERSION = google.auth.__version__
+except AttributeError:
+    try:  # try pkg_resources if it is available
+        _GOOGLE_AUTH_VERSION = pkg_resources.get_distribution("google-auth").version
+    except pkg_resources.DistributionNotFound:  # pragma: NO COVER
+        _GOOGLE_AUTH_VERSION = None
+
 
 class {{ service.name }}Transport(metaclass=abc.ABCMeta):
     """Abstract transport class for {{ service.name }}."""
@@ -40,11 +52,17 @@ class {{ service.name }}Transport(metaclass=abc.ABCMeta):
         {% endfor %}
     )
 
+    DEFAULT_HOST: str = {% if service.host %}'{{ service.host }}'{% else %}{{ '' }}{% endif %}
+
     def __init__(
             self, *,
             host: str{% if service.host %} = '{{ service.host }}'{% endif %},
             credentials: ga_credentials.Credentials = None,
+            credentials_file: Optional[str] = None,
+            scopes: Optional[Sequence[str]] = None,
+            quota_project_id: Optional[str] = None,
             client_info: gapic_v1.client_info.ClientInfo = DEFAULT_CLIENT_INFO,
+            always_use_jwt_access: Optional[bool] = False,
             ) -> None:
         """Instantiate the transport.
 
@@ -56,17 +74,47 @@ class {{ service.name }}Transport(metaclass=abc.ABCMeta):
                 credentials identify the application to the service; if none
                 are specified, the client will attempt to ascertain the
                 credentials from the environment.
+            credentials_file (Optional[str]): A file with credentials that can
+                be loaded with :func:`google.auth.load_credentials_from_file`.
+                This argument is mutually exclusive with credentials.
+            scopes (Optional[Sequence[str]]): A list of scopes.
+            quota_project_id (Optional[str]): An optional project to use for billing
+                and quota.
             client_info (google.api_core.gapic_v1.client_info.ClientInfo):
                 The client info used to send a user-agent string along with
                 API requests. If ``None``, then default info will be used.
                 Generally, you only need to set this if you're developing
                 your own client library.
+            always_use_jwt_access (Optional[bool]): Whether self signed JWT should
+                be used for service account credentials.
         """
         # Save the hostname. Default to port 443 (HTTPS) if none is specified.
         if ':' not in host:
             host += ':443'
         self._host = host
 
+        scopes_kwargs = self._get_scopes_kwargs(self._host, scopes)
+
+        # Save the scopes.
+        self._scopes = scopes
+
+        # If no credentials are provided, then determine the appropriate
+        # defaults.
+        if credentials and credentials_file:
+            raise core_exceptions.DuplicateCredentialArgs("'credentials_file' and 'credentials' are mutually exclusive")
+
+        if credentials_file is not None:
+            credentials, _ = google.auth.load_credentials_from_file(
+                                credentials_file,
+                                **scopes_kwargs,
+                                quota_project_id=quota_project_id
+                            )
+        elif credentials is None:
+            credentials, _ = google.auth.default(**scopes_kwargs, quota_project_id=quota_project_id)
+
+        if always_use_jwt_access and isinstance(credentials, service_account.Credentials) and hasattr(service_account.Credentials, "with_always_use_jwt_access"):
+            credentials = credentials.with_always_use_jwt_access(True)
+
         # If no credentials are provided, then determine the appropriate
         # defaults.
         if credentials is None:
@@ -78,6 +126,24 @@ class {{ service.name }}Transport(metaclass=abc.ABCMeta):
         # Lifted into its own function so it can be stubbed out during tests.
         self._prep_wrapped_messages(client_info)
 
+
+    # TODO: Remove this function once google-auth >= 1.25.0 is required
+    @classmethod
+    def _get_scopes_kwargs(cls, host: str, scopes: Optional[Sequence[str]]) -> Dict[str, Optional[Sequence[str]]]:
+        """Returns scopes kwargs to pass to google-auth methods depending on the google-auth version"""
+
+        scopes_kwargs = {}
+
+        if _GOOGLE_AUTH_VERSION and (
+            packaging.version.parse(_GOOGLE_AUTH_VERSION)
+            >= packaging.version.parse("1.25.0")
+        ):
+            scopes_kwargs = {"scopes": scopes, "default_scopes": cls.AUTH_SCOPES}
+        else:
+            scopes_kwargs = {"scopes": scopes or cls.AUTH_SCOPES}
+
+        return scopes_kwargs
+
     def _prep_wrapped_messages(self, client_info):
         # Precomputed wrapped methods
         self._wrapped_methods = {