fix: refactor mtls logic to standalone method

gapic/templates/%namespace/%name_%version/%sub/services/%service/async_client.py.j2

@@ -5,7 +5,7 @@
 from collections import OrderedDict
 import functools
 import re
-from typing import Dict, {% if service.any_server_streaming %}AsyncIterable, Awaitable, {% endif %}{% if service.any_client_streaming %}AsyncIterator, {% endif %}Sequence, Tuple, Type, Union
+from typing import Dict, Optional, {% if service.any_server_streaming %}AsyncIterable, Awaitable, {% endif %}{% if service.any_client_streaming %}AsyncIterator, {% endif %}Sequence, Tuple, Type, Union
 import pkg_resources
 {% if service.any_deprecated %}
 import warnings
@@ -90,6 +90,40 @@ class {{ service.async_client_name }}:
 
     from_service_account_json = from_service_account_file
 
+    @classmethod
+    def get_mtls_endpoint_and_cert_source(cls, client_options: Optional[ClientOptions] = None):
+        """Return the API endpoint and client cert source for mutual TLS. 
+
+        The client cert source is determined in the following order:
+        (1) if `GOOGLE_API_USE_CLIENT_CERTIFICATE` environment variable is not "true", the
+        client cert source is None.
+        (2) if `client_options.client_cert_source` is provided, use the provided one; if the
+        default client cert source exists, use the default one; otherwise the client cert
+        source is None.
+
+        The API endpoint is determined in the following order:
+        (1) if `client_options.api_endpoint` if provided, use the provided one.
+        (2) if `GOOGLE_API_USE_CLIENT_CERTIFICATE` environment variable is "always", use the
+        default mTLS endpoint; if the environment variabel is "never", use the default API
+        endpoint; otherwise if client cert source exists, use the default mTLS endpoint, otherwise
+        use the default API endpoint.
+
+        More details can be found at https://google.aip.dev/auth/4114.
+
+        Args:
+            client_options (google.api_core.client_options.ClientOptions): Custom options for the
+                client. Only the `api_endpoint` and `client_cert_source` properties may be used
+                in this method.
+
+        Returns:
+            Tuple[str, Callable[[], Tuple[bytes, bytes]]]: returns the API endpoint and the
+                client cert source to use.
+
+        Raises:
+            google.auth.exceptions.MutualTLSChannelError: If any errors happen.
+        """
+        return {{ service.client_name }}.get_mtls_endpoint_and_cert_source.__func__({{ service.async_client_name }}, client_options)  # type: ignore
+
     @property
     def transport(self) -> {{ service.name }}Transport:
         """Returns the transport used by the client instance.

gapic/templates/%namespace/%name_%version/%sub/services/%service/client.py.j2

@@ -200,6 +200,65 @@ class {{ service.client_name }}(metaclass={{ service.client_name }}Meta):
 
     {% endfor %}{# common resources #}
 
+    @classmethod
+    def get_mtls_endpoint_and_cert_source(cls, client_options: Optional[client_options_lib.ClientOptions] = None):
+        """Return the API endpoint and client cert source for mutual TLS. 
+
+        The client cert source is determined in the following order:
+        (1) if `GOOGLE_API_USE_CLIENT_CERTIFICATE` environment variable is not "true", the
+        client cert source is None.
+        (2) if `client_options.client_cert_source` is provided, use the provided one; if the
+        default client cert source exists, use the default one; otherwise the client cert
+        source is None.
+
+        The API endpoint is determined in the following order:
+        (1) if `client_options.api_endpoint` if provided, use the provided one.
+        (2) if `GOOGLE_API_USE_CLIENT_CERTIFICATE` environment variable is "always", use the
+        default mTLS endpoint; if the environment variabel is "never", use the default API
+        endpoint; otherwise if client cert source exists, use the default mTLS endpoint, otherwise
+        use the default API endpoint.
+
+        More details can be found at https://google.aip.dev/auth/4114.
+
+        Args:
+            client_options (google.api_core.client_options.ClientOptions): Custom options for the
+                client. Only the `api_endpoint` and `client_cert_source` properties may be used
+                in this method.
+
+        Returns:
+            Tuple[str, Callable[[], Tuple[bytes, bytes]]]: returns the API endpoint and the
+                client cert source to use.
+
+        Raises:
+            google.auth.exceptions.MutualTLSChannelError: If any errors happen.
+        """
+        if client_options is None:
+            client_options = client_options_lib.ClientOptions()
+        use_client_cert = os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false")
+        use_mtls_endpoint = os.getenv("GOOGLE_API_USE_MTLS_ENDPOINT", "auto")
+        if use_client_cert not in ("true", "false"):
+            raise ValueError("Environment variable `GOOGLE_API_USE_CLIENT_CERTIFICATE` must be either `true` or `false`")
+        if use_mtls_endpoint not in ("auto", "never", "always"):
+            raise MutualTLSChannelError("Environment variable `GOOGLE_API_USE_MTLS_ENDPOINT` must be `never`, `auto` or `always`")
+
+        # Figure out the client cert source to use.
+        client_cert_source = None
+        if use_client_cert == "true":
+            if client_options.client_cert_source:
+                client_cert_source = client_options.client_cert_source
+            elif mtls.has_default_client_cert_source():
+                client_cert_source = mtls.default_client_cert_source()
+
+        # Figure out which api endpoint to use.
+        if client_options.api_endpoint is not None:
+            api_endpoint = client_options.api_endpoint
+        elif use_mtls_endpoint == "always" or (use_mtls_endpoint == "auto" and client_cert_source):
+            api_endpoint = cls.DEFAULT_MTLS_ENDPOINT
+        else:
+            api_endpoint = cls.DEFAULT_ENDPOINT
+
+        return api_endpoint, client_cert_source
+
     def __init__(self, *,
             credentials: Optional[ga_credentials.Credentials] = None,
             transport: Union[str, {{ service.name }}Transport, None] = None,
@@ -248,43 +307,7 @@ class {{ service.client_name }}(metaclass={{ service.client_name }}Meta):
         if client_options is None:
             client_options = client_options_lib.ClientOptions()
 
-        # Create SSL credentials for mutual TLS if needed.
-        if os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false") not in ("true", "false"):
-            raise ValueError("Environment variable `GOOGLE_API_USE_CLIENT_CERTIFICATE` must be either `true` or `false`")
-        use_client_cert = os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false") == "true"
-
-        client_cert_source_func = None
-        is_mtls = False
-        if use_client_cert:
-            if client_options.client_cert_source:
-                is_mtls = True
-                client_cert_source_func = client_options.client_cert_source
-            else:
-                is_mtls = mtls.has_default_client_cert_source()
-                if is_mtls:
-                    client_cert_source_func = mtls.default_client_cert_source()
-                else:
-                    client_cert_source_func = None
-
-        # Figure out which api endpoint to use.
-        if client_options.api_endpoint is not None:
-            api_endpoint = client_options.api_endpoint
-        else:
-            use_mtls_env = os.getenv("GOOGLE_API_USE_MTLS_ENDPOINT", "auto")
-            if use_mtls_env == "never":
-                api_endpoint = self.DEFAULT_ENDPOINT
-            elif use_mtls_env == "always":
-                api_endpoint = self.DEFAULT_MTLS_ENDPOINT
-            elif use_mtls_env == "auto":
-                if is_mtls:
-                    api_endpoint = self.DEFAULT_MTLS_ENDPOINT
-                else:
-                    api_endpoint = self.DEFAULT_ENDPOINT
-            else:
-                raise MutualTLSChannelError(
-                    "Unsupported GOOGLE_API_USE_MTLS_ENDPOINT value. Accepted "
-                    "values: never, auto, always"
-                )
+        api_endpoint, client_cert_source_func = self.get_mtls_endpoint_and_cert_source(client_options)
 
         # Save or instantiate the transport.
         # Ordinarily, we provide the transport, but allowing a custom transport

gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2

@@ -359,6 +359,65 @@ def test_{{ service.client_name|snake_case }}_mtls_env_auto(client_class, transp
                 )
 
 
+@pytest.mark.parametrize("client_class", [
+    {% if 'grpc' in opts.transport %}
+    {{ service.client_name }}, {{ service.async_client_name }}
+    {% elif 'rest' in opts.transport %}
+    {{ service.client_name }}
+    {% endif %}
+])
+@mock.patch.object({{ service.client_name }}, "DEFAULT_ENDPOINT", modify_default_endpoint({{ service.client_name }}))
+{% if 'grpc' in opts.transport %}
+@mock.patch.object({{ service.async_client_name }}, "DEFAULT_ENDPOINT", modify_default_endpoint({{ service.async_client_name }}))
+{% endif %}
+def test_{{ service.client_name|snake_case }}_get_mtls_endpoint_and_cert_source(client_class):
+    mock_client_cert_source = mock.Mock()
+
+    # Test the case GOOGLE_API_USE_CLIENT_CERTIFICATE is "true".
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": "true"}):
+        mock_api_endpoint = "foo"
+        options = client_options.ClientOptions(client_cert_source=mock_client_cert_source, api_endpoint=mock_api_endpoint)
+        api_endpoint, cert_source = client_class.get_mtls_endpoint_and_cert_source(options)
+        assert api_endpoint == mock_api_endpoint
+        assert cert_source == mock_client_cert_source
+
+    # Test the case GOOGLE_API_USE_CLIENT_CERTIFICATE is "false".
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": "false"}):
+        mock_client_cert_source = mock.Mock()
+        mock_api_endpoint = "foo"
+        options = client_options.ClientOptions(client_cert_source=mock_client_cert_source, api_endpoint=mock_api_endpoint)
+        api_endpoint, cert_source = client_class.get_mtls_endpoint_and_cert_source(options)
+        assert api_endpoint == mock_api_endpoint
+        assert cert_source is None
+
+    # Test the case GOOGLE_API_USE_MTLS_ENDPOINT is "never".
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "never"}):
+        api_endpoint, cert_source = client_class.get_mtls_endpoint_and_cert_source()
+        assert api_endpoint == client_class.DEFAULT_ENDPOINT
+        assert cert_source is None
+
+    # Test the case GOOGLE_API_USE_MTLS_ENDPOINT is "always".
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "always"}):
+        api_endpoint, cert_source = client_class.get_mtls_endpoint_and_cert_source()
+        assert api_endpoint == client_class.DEFAULT_MTLS_ENDPOINT
+        assert cert_source is None
+
+    # Test the case GOOGLE_API_USE_MTLS_ENDPOINT is "auto" and default cert doesn't exist.
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": "true"}):
+        with mock.patch('google.auth.transport.mtls.has_default_client_cert_source', return_value=False):
+            api_endpoint, cert_source = client_class.get_mtls_endpoint_and_cert_source()
+            assert api_endpoint == client_class.DEFAULT_ENDPOINT
+            assert cert_source is None
+
+    # Test the case GOOGLE_API_USE_MTLS_ENDPOINT is "auto" and default cert exists.
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": "true"}):
+        with mock.patch('google.auth.transport.mtls.has_default_client_cert_source', return_value=True):
+            with mock.patch('google.auth.transport.mtls.default_client_cert_source', return_value=mock_client_cert_source):
+                api_endpoint, cert_source = client_class.get_mtls_endpoint_and_cert_source()
+                assert api_endpoint == client_class.DEFAULT_MTLS_ENDPOINT
+                assert cert_source == mock_client_cert_source
+
+
 @pytest.mark.parametrize("client_class,transport_class,transport_name", [
     {% if 'grpc' in opts.transport %}
     ({{ service.client_name }}, transports.{{ service.grpc_transport_name }}, "grpc"),

tests/integration/goldens/asset/google/cloud/asset_v1/services/asset_service/async_client.py

@@ -16,7 +16,7 @@
 from collections import OrderedDict
 import functools
 import re
-from typing import Dict, Sequence, Tuple, Type, Union
+from typing import Dict, Optional, Sequence, Tuple, Type, Union
 import pkg_resources
 
 from google.api_core.client_options import ClientOptions
@@ -98,6 +98,40 @@ def from_service_account_file(cls, filename: str, *args, **kwargs):
 
     from_service_account_json = from_service_account_file
 
+    @classmethod
+    def get_mtls_endpoint_and_cert_source(cls, client_options: Optional[ClientOptions] = None):
+        """Return the API endpoint and client cert source for mutual TLS.
+
+        The client cert source is determined in the following order:
+        (1) if `GOOGLE_API_USE_CLIENT_CERTIFICATE` environment variable is not "true", the
+        client cert source is None.
+        (2) if `client_options.client_cert_source` is provided, use the provided one; if the
+        default client cert source exists, use the default one; otherwise the client cert
+        source is None.
+
+        The API endpoint is determined in the following order:
+        (1) if `client_options.api_endpoint` if provided, use the provided one.
+        (2) if `GOOGLE_API_USE_CLIENT_CERTIFICATE` environment variable is "always", use the
+        default mTLS endpoint; if the environment variabel is "never", use the default API
+        endpoint; otherwise if client cert source exists, use the default mTLS endpoint, otherwise
+        use the default API endpoint.
+
+        More details can be found at https://google.aip.dev/auth/4114.
+
+        Args:
+            client_options (google.api_core.client_options.ClientOptions): Custom options for the
+                client. Only the `api_endpoint` and `client_cert_source` properties may be used
+                in this method.
+
+        Returns:
+            Tuple[str, Callable[[], Tuple[bytes, bytes]]]: returns the API endpoint and the
+                client cert source to use.
+
+        Raises:
+            google.auth.exceptions.MutualTLSChannelError: If any errors happen.
+        """
+        return AssetServiceClient.get_mtls_endpoint_and_cert_source.__func__(AssetServiceAsyncClient, client_options)  # type: ignore
+
     @property
     def transport(self) -> AssetServiceTransport:
         """Returns the transport used by the client instance.

tests/integration/goldens/asset/google/cloud/asset_v1/services/asset_service/client.py

@@ -240,6 +240,65 @@ def parse_common_location_path(path: str) -> Dict[str,str]:
         m = re.match(r"^projects/(?P<project>.+?)/locations/(?P<location>.+?)$", path)
         return m.groupdict() if m else {}
 
+    @classmethod
+    def get_mtls_endpoint_and_cert_source(cls, client_options: Optional[client_options_lib.ClientOptions] = None):
+        """Return the API endpoint and client cert source for mutual TLS.
+
+        The client cert source is determined in the following order:
+        (1) if `GOOGLE_API_USE_CLIENT_CERTIFICATE` environment variable is not "true", the
+        client cert source is None.
+        (2) if `client_options.client_cert_source` is provided, use the provided one; if the
+        default client cert source exists, use the default one; otherwise the client cert
+        source is None.
+
+        The API endpoint is determined in the following order:
+        (1) if `client_options.api_endpoint` if provided, use the provided one.
+        (2) if `GOOGLE_API_USE_CLIENT_CERTIFICATE` environment variable is "always", use the
+        default mTLS endpoint; if the environment variabel is "never", use the default API
+        endpoint; otherwise if client cert source exists, use the default mTLS endpoint, otherwise
+        use the default API endpoint.
+
+        More details can be found at https://google.aip.dev/auth/4114.
+
+        Args:
+            client_options (google.api_core.client_options.ClientOptions): Custom options for the
+                client. Only the `api_endpoint` and `client_cert_source` properties may be used
+                in this method.
+
+        Returns:
+            Tuple[str, Callable[[], Tuple[bytes, bytes]]]: returns the API endpoint and the
+                client cert source to use.
+
+        Raises:
+            google.auth.exceptions.MutualTLSChannelError: If any errors happen.
+        """
+        if client_options is None:
+            client_options = client_options_lib.ClientOptions()
+        use_client_cert = os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false")
+        use_mtls_endpoint = os.getenv("GOOGLE_API_USE_MTLS_ENDPOINT", "auto")
+        if use_client_cert not in ("true", "false"):
+            raise ValueError("Environment variable `GOOGLE_API_USE_CLIENT_CERTIFICATE` must be either `true` or `false`")
+        if use_mtls_endpoint not in ("auto", "never", "always"):
+            raise MutualTLSChannelError("Environment variable `GOOGLE_API_USE_MTLS_ENDPOINT` must be `never`, `auto` or `always`")
+
+        # Figure out the client cert source to use.
+        client_cert_source = None
+        if use_client_cert == "true":
+            if client_options.client_cert_source:
+                client_cert_source = client_options.client_cert_source
+            elif mtls.has_default_client_cert_source():
+                client_cert_source = mtls.default_client_cert_source()
+
+        # Figure out which api endpoint to use.
+        if client_options.api_endpoint is not None:
+            api_endpoint = client_options.api_endpoint
+        elif use_mtls_endpoint == "always" or (use_mtls_endpoint == "auto" and client_cert_source):
+            api_endpoint = cls.DEFAULT_MTLS_ENDPOINT
+        else:
+            api_endpoint = cls.DEFAULT_ENDPOINT
+
+        return api_endpoint, client_cert_source
+
     def __init__(self, *,
             credentials: Optional[ga_credentials.Credentials] = None,
             transport: Union[str, AssetServiceTransport, None] = None,
@@ -288,43 +347,7 @@ def __init__(self, *,
         if client_options is None:
             client_options = client_options_lib.ClientOptions()
 
-        # Create SSL credentials for mutual TLS if needed.
-        if os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false") not in ("true", "false"):
-            raise ValueError("Environment variable `GOOGLE_API_USE_CLIENT_CERTIFICATE` must be either `true` or `false`")
-        use_client_cert = os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false") == "true"
-
-        client_cert_source_func = None
-        is_mtls = False
-        if use_client_cert:
-            if client_options.client_cert_source:
-                is_mtls = True
-                client_cert_source_func = client_options.client_cert_source
-            else:
-                is_mtls = mtls.has_default_client_cert_source()
-                if is_mtls:
-                    client_cert_source_func = mtls.default_client_cert_source()
-                else:
-                    client_cert_source_func = None
-
-        # Figure out which api endpoint to use.
-        if client_options.api_endpoint is not None:
-            api_endpoint = client_options.api_endpoint
-        else:
-            use_mtls_env = os.getenv("GOOGLE_API_USE_MTLS_ENDPOINT", "auto")
-            if use_mtls_env == "never":
-                api_endpoint = self.DEFAULT_ENDPOINT
-            elif use_mtls_env == "always":
-                api_endpoint = self.DEFAULT_MTLS_ENDPOINT
-            elif use_mtls_env == "auto":
-                if is_mtls:
-                    api_endpoint = self.DEFAULT_MTLS_ENDPOINT
-                else:
-                    api_endpoint = self.DEFAULT_ENDPOINT
-            else:
-                raise MutualTLSChannelError(
-                    "Unsupported GOOGLE_API_USE_MTLS_ENDPOINT value. Accepted "
-                    "values: never, auto, always"
-                )
+        api_endpoint, client_cert_source_func = self.get_mtls_endpoint_and_cert_source(client_options)
 
         # Save or instantiate the transport.
         # Ordinarily, we provide the transport, but allowing a custom transport