From 73e497e5a024e03af060643a333ed9f8bf38eef0 Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Thu, 2 May 2019 14:20:27 -0400
Subject: [PATCH 01/14] Add 'user_agent' and 'extra_headers' properties to
 'Connection'.

Deprecate the 'USER_AGENT' and '_EXTRA_HEADERS' class-level attributes.
---
 core/google/cloud/_http.py    |  83 ++++++++++++++++++++++++---
 core/tests/unit/test__http.py | 103 ++++++++++++++++++++++++++++------
 2 files changed, 160 insertions(+), 26 deletions(-)

diff --git a/core/google/cloud/_http.py b/core/google/cloud/_http.py
index d7441e502995..659b1d33f402 100644
--- a/core/google/cloud/_http.py
+++ b/core/google/cloud/_http.py
@@ -16,6 +16,7 @@
 
 import json
 import platform
+import warnings
 
 from pkg_resources import get_distribution
 from six.moves.urllib.parse import urlencode
@@ -34,6 +35,16 @@
 CLIENT_INFO_HEADER = "X-Goog-API-Client"
 CLIENT_INFO_TEMPLATE = "gl-python/" + platform.python_version() + " gccl/{}"
 
+_USER_AGENT_ALL_CAPS_DEPRECATED = """\
+The 'USER_AGENT' class-level attribute is deprecated.  Please use
+'user_agent' instead.
+"""
+
+_EXTRA_HEADERS_ALL_CAPS_DEPRECATED = """\
+The '_EXTRA_HEADERS' class-level attribute is deprecated.  Please use
+'extra_headers' instead.
+"""
+
 
 class Connection(object):
     """A generic connection to Google Cloud Platform.
@@ -42,16 +53,72 @@ class Connection(object):
     :param client: The client that owns the current connection.
     """
 
-    USER_AGENT = DEFAULT_USER_AGENT
-    _EXTRA_HEADERS = {}
-    """Headers to be sent with every request.
-
-    Intended to be over-ridden by subclasses.
-    """
+    _user_agent = DEFAULT_USER_AGENT
+    _extra_headers = None
 
     def __init__(self, client):
         self._client = client
 
+    @property
+    def USER_AGENT(self):
+        """Deprecated:  get / set user agent sent by connection.
+
+        :rtype: str
+        :returns: user agent
+        """
+        warnings.warn(
+            _USER_AGENT_ALL_CAPS_DEPRECATED, DeprecationWarning, stacklevel=2)
+        return self.user_agent
+
+    @USER_AGENT.setter
+    def USER_AGENT(self, value):
+        warnings.warn(
+            _USER_AGENT_ALL_CAPS_DEPRECATED, DeprecationWarning, stacklevel=2)
+        self.user_agent = value
+
+    @property
+    def user_agent(self):
+        """Get / set user agent sent by connection.
+
+        :rtype: str
+        :returns: user agent
+        """
+        return self._user_agent
+
+    @user_agent.setter
+    def user_agent(self, value):
+        self._user_agent = value
+
+    @property
+    def _EXTRA_HEADERS(self):
+        """Deprecated:  get / set extra headers sent by connection.
+
+        :rtype: dict
+        :returns: header keys / values
+        """
+        warnings.warn(
+            _EXTRA_HEADERS_ALL_CAPS_DEPRECATED, DeprecationWarning, stacklevel=2)
+        return self.extra_headers
+
+    @_EXTRA_HEADERS.setter
+    def _EXTRA_HEADERS(self, value):
+        warnings.warn(
+            _EXTRA_HEADERS_ALL_CAPS_DEPRECATED, DeprecationWarning, stacklevel=2)
+        self.extra_headers = value
+
+    @property
+    def extra_headers(self):
+        """Get / set extra headers sent by connection.
+
+        :rtype: dict
+        :returns: header keys / values
+        """
+        return self._extra_headers or {}
+
+    @extra_headers.setter
+    def extra_headers(self, value):
+        self._extra_headers = value
+
     @property
     def credentials(self):
         """Getter for current credentials.
@@ -181,13 +248,13 @@ def _make_request(
         :returns: The HTTP response.
         """
         headers = headers or {}
-        headers.update(self._EXTRA_HEADERS)
+        headers.update(self.extra_headers)
         headers["Accept-Encoding"] = "gzip"
 
         if content_type:
             headers["Content-Type"] = content_type
 
-        headers["User-Agent"] = self.USER_AGENT
+        headers["User-Agent"] = self.user_agent
 
         return self._do_request(method, url, headers, data, target_object)
 
diff --git a/core/tests/unit/test__http.py b/core/tests/unit/test__http.py
index 7c8aec215f22..ffc1d2650714 100644
--- a/core/tests/unit/test__http.py
+++ b/core/tests/unit/test__http.py
@@ -14,6 +14,7 @@
 
 import json
 import unittest
+import warnings
 
 import mock
 import requests
@@ -35,6 +36,81 @@ def test_constructor(self):
         conn = self._make_one(client)
         self.assertIs(conn._client, client)
 
+    def test_user_agent_all_caps_getter_deprecated(self):
+        client = object()
+        conn = self._make_one(client)
+        conn._user_agent = user_agent = 'testing'
+
+        with mock.patch.object(warnings, "warn", autospec=True) as warn:
+            self.assertEqual(conn.USER_AGENT, user_agent)
+
+        warn.assert_called_once_with(mock.ANY, DeprecationWarning, stacklevel=2)
+
+    def test_user_agent_all_caps_setter_deprecated(self):
+        conn = self._make_one(object())
+        user_agent = 'testing'
+
+        with mock.patch.object(warnings, "warn", autospec=True) as warn:
+            conn.USER_AGENT = user_agent
+
+        self.assertEqual(conn._user_agent, user_agent)
+        warn.assert_called_once_with(mock.ANY, DeprecationWarning, stacklevel=2)
+
+    def test_user_agent_getter_default(self):
+        from pkg_resources import get_distribution
+
+        expected = "gcloud-python/{0}".format(
+            get_distribution("google-cloud-core").version
+        )
+        conn = self._make_one(object())
+        self.assertEqual(conn.user_agent, expected)
+
+    def test_user_agent_getter_overridden(self):
+        conn = self._make_one(object())
+        expected = conn._user_agent = "testing"
+        self.assertEqual(conn.user_agent, expected)
+
+    def test_user_agent_setter(self):
+        conn = self._make_one(object())
+        expected = "testing"
+        conn.user_agent = expected
+        self.assertEqual(conn._user_agent, expected)
+
+    def test_extra_headers_all_caps_getter_deprecated(self):
+        client = object()
+        conn = self._make_one(client)
+        expected = conn._extra_headers = {"foo": "bar"}
+
+        with mock.patch.object(warnings, "warn", autospec=True) as warn:
+            self.assertEqual(conn._EXTRA_HEADERS, expected)
+
+        warn.assert_called_once_with(mock.ANY, DeprecationWarning, stacklevel=2)
+
+    def test_extra_headers_all_caps_setter_deprecated(self):
+        conn = self._make_one(object())
+        extra_headers = {"foo": "bar"}
+
+        with mock.patch.object(warnings, "warn", autospec=True) as warn:
+            conn._EXTRA_HEADERS = extra_headers
+
+        self.assertEqual(conn._extra_headers, extra_headers)
+        warn.assert_called_once_with(mock.ANY, DeprecationWarning, stacklevel=2)
+
+    def test_extra_headers_getter_default(self):
+        conn = self._make_one(object())
+        self.assertEqual(conn.extra_headers, {})
+
+    def test_extra_headers_getter_overridden(self):
+        conn = self._make_one(object())
+        expected = conn._extra_headers = {"foo": "bar"}
+        self.assertEqual(conn.extra_headers, expected)
+
+    def test_extra_headers_setter(self):
+        conn = self._make_one(object())
+        expected = {"foo": "bar"}
+        conn.extra_headers = expected
+        self.assertEqual(conn._extra_headers, expected)
+
     def test_credentials_property(self):
         client = mock.Mock(spec=["_credentials"])
         conn = self._make_one(client)
@@ -45,15 +121,6 @@ def test_http_property(self):
         conn = self._make_one(client)
         self.assertIs(conn.http, client._http)
 
-    def test_user_agent_format(self):
-        from pkg_resources import get_distribution
-
-        expected_ua = "gcloud-python/{0}".format(
-            get_distribution("google-cloud-core").version
-        )
-        conn = self._make_one(object())
-        self.assertEqual(conn.USER_AGENT, expected_ua)
-
 
 def make_response(status=http_client.OK, content=b"", headers={}):
     response = requests.Response()
@@ -137,7 +204,7 @@ def test__make_request_no_data_no_content_type_no_headers(self):
         self.assertEqual(response.status_code, http_client.OK)
         self.assertEqual(response.content, b"")
 
-        expected_headers = {"Accept-Encoding": "gzip", "User-Agent": conn.USER_AGENT}
+        expected_headers = {"Accept-Encoding": "gzip", "User-Agent": conn.user_agent}
         http.request.assert_called_once_with(
             method="GET", url=url, headers=expected_headers, data=None
         )
@@ -154,7 +221,7 @@ def test__make_request_w_data_no_extra_headers(self):
         expected_headers = {
             "Accept-Encoding": "gzip",
             "Content-Type": "application/json",
-            "User-Agent": conn.USER_AGENT,
+            "User-Agent": conn.user_agent,
         }
         http.request.assert_called_once_with(
             method="GET", url=url, headers=expected_headers, data=data
@@ -171,7 +238,7 @@ def test__make_request_w_extra_headers(self):
         expected_headers = {
             "Accept-Encoding": "gzip",
             "X-Foo": "foo",
-            "User-Agent": conn.USER_AGENT,
+            "User-Agent": conn.user_agent,
         }
         http.request.assert_called_once_with(
             method="GET", url=url, headers=expected_headers, data=None
@@ -187,7 +254,7 @@ def test_api_request_defaults(self):
 
         self.assertEqual(conn.api_request("GET", path), {})
 
-        expected_headers = {"Accept-Encoding": "gzip", "User-Agent": conn.USER_AGENT}
+        expected_headers = {"Accept-Encoding": "gzip", "User-Agent": conn.user_agent}
         expected_url = "{base}/mock/{version}{path}".format(
             base=conn.API_BASE_URL, version=conn.API_VERSION, path=path
         )
@@ -224,7 +291,7 @@ def test_api_request_w_query_params(self):
 
         self.assertEqual(result, {})
 
-        expected_headers = {"Accept-Encoding": "gzip", "User-Agent": conn.USER_AGENT}
+        expected_headers = {"Accept-Encoding": "gzip", "User-Agent": conn.user_agent}
         http.request.assert_called_once_with(
             method="GET", url=mock.ANY, headers=expected_headers, data=None
         )
@@ -249,7 +316,7 @@ def test_api_request_w_headers(self):
 
         expected_headers = {
             "Accept-Encoding": "gzip",
-            "User-Agent": conn.USER_AGENT,
+            "User-Agent": conn.user_agent,
             "X-Foo": "bar",
         }
         http.request.assert_called_once_with(
@@ -260,7 +327,7 @@ def test_api_request_w_extra_headers(self):
         http = make_requests_session([self.EMPTY_JSON_RESPONSE])
         client = mock.Mock(_http=http, spec=["_http"])
         conn = self._make_mock_one(client)
-        conn._EXTRA_HEADERS = {
+        conn.extra_headers = {
             "X-Baz": "dax-quux",
             "X-Foo": "not-bar",  # Collision with ``headers``.
         }
@@ -271,7 +338,7 @@ def test_api_request_w_extra_headers(self):
 
         expected_headers = {
             "Accept-Encoding": "gzip",
-            "User-Agent": conn.USER_AGENT,
+            "User-Agent": conn.user_agent,
             "X-Foo": "not-bar",  # The one passed-in is overridden.
             "X-Baz": "dax-quux",
         }
@@ -292,7 +359,7 @@ def test_api_request_w_data(self):
         expected_headers = {
             "Accept-Encoding": "gzip",
             "Content-Type": "application/json",
-            "User-Agent": conn.USER_AGENT,
+            "User-Agent": conn.user_agent,
         }
 
         http.request.assert_called_once_with(

From dffc79b7377552365dbb37591075d3b39fbe78c3 Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Thu, 2 May 2019 14:30:18 -0400
Subject: [PATCH 02/14] Add 'client_info' parameter to 'Connection' ctor.

---
 core/google/cloud/_http.py    | 11 ++++++++++-
 core/tests/unit/test__http.py | 11 ++++++++++-
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/core/google/cloud/_http.py b/core/google/cloud/_http.py
index 659b1d33f402..bcc78d3e0844 100644
--- a/core/google/cloud/_http.py
+++ b/core/google/cloud/_http.py
@@ -21,6 +21,7 @@
 from pkg_resources import get_distribution
 from six.moves.urllib.parse import urlencode
 
+from google.api_core.gapic_v1.client_info import ClientInfo
 from google.cloud import exceptions
 
 
@@ -51,14 +52,22 @@ class Connection(object):
 
     :type client: :class:`~google.cloud.client.Client`
     :param client: The client that owns the current connection.
+
+    :type client_info: :class:`~google.api_core.client_info.ClientInfo`
+    :param client_info: (Optional) instance used to generate user agent.
     """
 
     _user_agent = DEFAULT_USER_AGENT
     _extra_headers = None
 
-    def __init__(self, client):
+    def __init__(self, client, client_info=None):
         self._client = client
 
+        if client_info is None:
+            client_info = ClientInfo()
+
+        self._client_info = client_info
+
     @property
     def USER_AGENT(self):
         """Deprecated:  get / set user agent sent by connection.
diff --git a/core/tests/unit/test__http.py b/core/tests/unit/test__http.py
index ffc1d2650714..80d3fec6e352 100644
--- a/core/tests/unit/test__http.py
+++ b/core/tests/unit/test__http.py
@@ -31,10 +31,19 @@ def _get_target_class():
     def _make_one(self, *args, **kw):
         return self._get_target_class()(*args, **kw)
 
-    def test_constructor(self):
+    def test_constructor_defaults(self):
+        from google.api_core.gapic_v1.client_info import ClientInfo
+
         client = object()
         conn = self._make_one(client)
         self.assertIs(conn._client, client)
+        self.assertIsInstance(conn._client_info, ClientInfo)
+
+    def test_constructor_explicit(self):
+        client = object()
+        client_info = object()
+        conn = self._make_one(client, client_info=client_info)
+        self.assertIs(conn._client, client)
 
     def test_user_agent_all_caps_getter_deprecated(self):
         client = object()

From 13aa6775299c121ebfcf1f68f0627ca1307658aa Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Thu, 2 May 2019 14:42:16 -0400
Subject: [PATCH 03/14] Implement 'Connection.user_agent' via its
 '_client_info'.

---
 core/google/cloud/_http.py    |  4 ++--
 core/tests/unit/test__http.py | 27 ++++++++-------------------
 2 files changed, 10 insertions(+), 21 deletions(-)

diff --git a/core/google/cloud/_http.py b/core/google/cloud/_http.py
index bcc78d3e0844..0e4aa2ab637c 100644
--- a/core/google/cloud/_http.py
+++ b/core/google/cloud/_http.py
@@ -92,11 +92,11 @@ def user_agent(self):
         :rtype: str
         :returns: user agent
         """
-        return self._user_agent
+        return self._client_info.to_user_agent()
 
     @user_agent.setter
     def user_agent(self, value):
-        self._user_agent = value
+        self._client_info.user_agent = value
 
     @property
     def _EXTRA_HEADERS(self):
diff --git a/core/tests/unit/test__http.py b/core/tests/unit/test__http.py
index 80d3fec6e352..91e6814497e6 100644
--- a/core/tests/unit/test__http.py
+++ b/core/tests/unit/test__http.py
@@ -48,42 +48,31 @@ def test_constructor_explicit(self):
     def test_user_agent_all_caps_getter_deprecated(self):
         client = object()
         conn = self._make_one(client)
-        conn._user_agent = user_agent = 'testing'
 
         with mock.patch.object(warnings, "warn", autospec=True) as warn:
-            self.assertEqual(conn.USER_AGENT, user_agent)
+            self.assertEqual(conn.USER_AGENT, conn._client_info.to_user_agent())
 
         warn.assert_called_once_with(mock.ANY, DeprecationWarning, stacklevel=2)
 
     def test_user_agent_all_caps_setter_deprecated(self):
         conn = self._make_one(object())
-        user_agent = 'testing'
+        user_agent = "testing"
 
         with mock.patch.object(warnings, "warn", autospec=True) as warn:
             conn.USER_AGENT = user_agent
 
-        self.assertEqual(conn._user_agent, user_agent)
+        self.assertEqual(conn._client_info.user_agent, user_agent)
         warn.assert_called_once_with(mock.ANY, DeprecationWarning, stacklevel=2)
 
-    def test_user_agent_getter_default(self):
-        from pkg_resources import get_distribution
-
-        expected = "gcloud-python/{0}".format(
-            get_distribution("google-cloud-core").version
-        )
-        conn = self._make_one(object())
-        self.assertEqual(conn.user_agent, expected)
-
-    def test_user_agent_getter_overridden(self):
+    def test_user_agent_getter(self):
         conn = self._make_one(object())
-        expected = conn._user_agent = "testing"
-        self.assertEqual(conn.user_agent, expected)
+        self.assertEqual(conn.user_agent, conn._client_info.to_user_agent())
 
     def test_user_agent_setter(self):
         conn = self._make_one(object())
-        expected = "testing"
-        conn.user_agent = expected
-        self.assertEqual(conn._user_agent, expected)
+        user_agent = "testing"
+        conn.user_agent = user_agent
+        self.assertEqual(conn._client_info.user_agent, user_agent)
 
     def test_extra_headers_all_caps_getter_deprecated(self):
         client = object()

From cfed70bdaa4b5a5cfd1811228a5eda5c87fa5013 Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Thu, 2 May 2019 14:57:21 -0400
Subject: [PATCH 04/14] Ensure 'X-Goog-API-Client' header is always passed.

---
 core/google/cloud/_http.py    |  4 ++-
 core/tests/unit/test__http.py | 59 +++++++++++++++++++++++++++++++----
 2 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/core/google/cloud/_http.py b/core/google/cloud/_http.py
index 0e4aa2ab637c..5ffbf02881fe 100644
--- a/core/google/cloud/_http.py
+++ b/core/google/cloud/_http.py
@@ -122,7 +122,9 @@ def extra_headers(self):
         :rtype: dict
         :returns: header keys / values
         """
-        return self._extra_headers or {}
+        result = self._extra_headers.copy() if self._extra_headers else {}
+        result[CLIENT_INFO_HEADER] = self.user_agent
+        return result
 
     @extra_headers.setter
     def extra_headers(self, value):
diff --git a/core/tests/unit/test__http.py b/core/tests/unit/test__http.py
index 91e6814497e6..236d5f964dc9 100644
--- a/core/tests/unit/test__http.py
+++ b/core/tests/unit/test__http.py
@@ -75,9 +75,15 @@ def test_user_agent_setter(self):
         self.assertEqual(conn._client_info.user_agent, user_agent)
 
     def test_extra_headers_all_caps_getter_deprecated(self):
+        from google.cloud._http import CLIENT_INFO_HEADER
+
         client = object()
         conn = self._make_one(client)
-        expected = conn._extra_headers = {"foo": "bar"}
+        conn._extra_headers = {"foo": "bar"}
+        expected = {
+            CLIENT_INFO_HEADER: conn._client_info.to_user_agent(),
+            "foo": "bar",
+        }
 
         with mock.patch.object(warnings, "warn", autospec=True) as warn:
             self.assertEqual(conn._EXTRA_HEADERS, expected)
@@ -95,12 +101,21 @@ def test_extra_headers_all_caps_setter_deprecated(self):
         warn.assert_called_once_with(mock.ANY, DeprecationWarning, stacklevel=2)
 
     def test_extra_headers_getter_default(self):
+        from google.cloud._http import CLIENT_INFO_HEADER
+
         conn = self._make_one(object())
-        self.assertEqual(conn.extra_headers, {})
+        expected = {CLIENT_INFO_HEADER: conn._client_info.to_user_agent()}
+        self.assertEqual(conn.extra_headers, expected)
 
     def test_extra_headers_getter_overridden(self):
+        from google.cloud._http import CLIENT_INFO_HEADER
+
         conn = self._make_one(object())
-        expected = conn._extra_headers = {"foo": "bar"}
+        conn._extra_headers = {"foo": "bar"}
+        expected = {
+            CLIENT_INFO_HEADER: conn._client_info.to_user_agent(),
+            "foo": "bar",
+        }
         self.assertEqual(conn.extra_headers, expected)
 
     def test_extra_headers_setter(self):
@@ -192,6 +207,8 @@ def test_build_api_url_w_extra_query_params(self):
         self.assertEqual(parms["qux"], ["quux", "corge"])
 
     def test__make_request_no_data_no_content_type_no_headers(self):
+        from google.cloud._http import CLIENT_INFO_HEADER
+
         http = make_requests_session([make_response()])
         client = mock.Mock(_http=http, spec=["_http"])
         conn = self._make_one(client)
@@ -202,12 +219,18 @@ def test__make_request_no_data_no_content_type_no_headers(self):
         self.assertEqual(response.status_code, http_client.OK)
         self.assertEqual(response.content, b"")
 
-        expected_headers = {"Accept-Encoding": "gzip", "User-Agent": conn.user_agent}
+        expected_headers = {
+            "Accept-Encoding": "gzip",
+            "User-Agent": conn.user_agent,
+            CLIENT_INFO_HEADER: conn.user_agent,
+        }
         http.request.assert_called_once_with(
             method="GET", url=url, headers=expected_headers, data=None
         )
 
     def test__make_request_w_data_no_extra_headers(self):
+        from google.cloud._http import CLIENT_INFO_HEADER
+
         http = make_requests_session([make_response()])
         client = mock.Mock(_http=http, spec=["_http"])
         conn = self._make_one(client)
@@ -220,12 +243,15 @@ def test__make_request_w_data_no_extra_headers(self):
             "Accept-Encoding": "gzip",
             "Content-Type": "application/json",
             "User-Agent": conn.user_agent,
+            CLIENT_INFO_HEADER: conn.user_agent,
         }
         http.request.assert_called_once_with(
             method="GET", url=url, headers=expected_headers, data=data
         )
 
     def test__make_request_w_extra_headers(self):
+        from google.cloud._http import CLIENT_INFO_HEADER
+
         http = make_requests_session([make_response()])
         client = mock.Mock(_http=http, spec=["_http"])
         conn = self._make_one(client)
@@ -237,12 +263,15 @@ def test__make_request_w_extra_headers(self):
             "Accept-Encoding": "gzip",
             "X-Foo": "foo",
             "User-Agent": conn.user_agent,
+            CLIENT_INFO_HEADER: conn.user_agent,
         }
         http.request.assert_called_once_with(
             method="GET", url=url, headers=expected_headers, data=None
         )
 
     def test_api_request_defaults(self):
+        from google.cloud._http import CLIENT_INFO_HEADER
+
         http = make_requests_session(
             [make_response(content=b"{}", headers=self.JSON_HEADERS)]
         )
@@ -252,7 +281,11 @@ def test_api_request_defaults(self):
 
         self.assertEqual(conn.api_request("GET", path), {})
 
-        expected_headers = {"Accept-Encoding": "gzip", "User-Agent": conn.user_agent}
+        expected_headers = {
+            "Accept-Encoding": "gzip",
+            "User-Agent": conn.user_agent,
+            CLIENT_INFO_HEADER: conn.user_agent,
+        }
         expected_url = "{base}/mock/{version}{path}".format(
             base=conn.API_BASE_URL, version=conn.API_VERSION, path=path
         )
@@ -280,6 +313,7 @@ def test_api_request_wo_json_expected(self):
     def test_api_request_w_query_params(self):
         from six.moves.urllib.parse import parse_qs
         from six.moves.urllib.parse import urlsplit
+        from google.cloud._http import CLIENT_INFO_HEADER
 
         http = make_requests_session([self.EMPTY_JSON_RESPONSE])
         client = mock.Mock(_http=http, spec=["_http"])
@@ -289,7 +323,11 @@ def test_api_request_w_query_params(self):
 
         self.assertEqual(result, {})
 
-        expected_headers = {"Accept-Encoding": "gzip", "User-Agent": conn.user_agent}
+        expected_headers = {
+            "Accept-Encoding": "gzip",
+            "User-Agent": conn.user_agent,
+            CLIENT_INFO_HEADER: conn.user_agent,
+        }
         http.request.assert_called_once_with(
             method="GET", url=mock.ANY, headers=expected_headers, data=None
         )
@@ -305,6 +343,8 @@ def test_api_request_w_query_params(self):
         self.assertEqual(parms["baz"], ["qux", "quux"])
 
     def test_api_request_w_headers(self):
+        from google.cloud._http import CLIENT_INFO_HEADER
+
         http = make_requests_session([self.EMPTY_JSON_RESPONSE])
         client = mock.Mock(_http=http, spec=["_http"])
         conn = self._make_mock_one(client)
@@ -316,12 +356,15 @@ def test_api_request_w_headers(self):
             "Accept-Encoding": "gzip",
             "User-Agent": conn.user_agent,
             "X-Foo": "bar",
+            CLIENT_INFO_HEADER: conn.user_agent,
         }
         http.request.assert_called_once_with(
             method="GET", url=mock.ANY, headers=expected_headers, data=None
         )
 
     def test_api_request_w_extra_headers(self):
+        from google.cloud._http import CLIENT_INFO_HEADER
+
         http = make_requests_session([self.EMPTY_JSON_RESPONSE])
         client = mock.Mock(_http=http, spec=["_http"])
         conn = self._make_mock_one(client)
@@ -339,12 +382,15 @@ def test_api_request_w_extra_headers(self):
             "User-Agent": conn.user_agent,
             "X-Foo": "not-bar",  # The one passed-in is overridden.
             "X-Baz": "dax-quux",
+            CLIENT_INFO_HEADER: conn.user_agent,
         }
         http.request.assert_called_once_with(
             method="GET", url=mock.ANY, headers=expected_headers, data=None
         )
 
     def test_api_request_w_data(self):
+        from google.cloud._http import CLIENT_INFO_HEADER
+
         http = make_requests_session([self.EMPTY_JSON_RESPONSE])
         client = mock.Mock(_http=http, spec=["_http"])
         conn = self._make_mock_one(client)
@@ -358,6 +404,7 @@ def test_api_request_w_data(self):
             "Accept-Encoding": "gzip",
             "Content-Type": "application/json",
             "User-Agent": conn.user_agent,
+            CLIENT_INFO_HEADER: conn.user_agent,
         }
 
         http.request.assert_called_once_with(

From 78035033539d8d2e7258841586cd37d97dac02df Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Thu, 2 May 2019 15:13:01 -0400
Subject: [PATCH 05/14] Avoid relying on systest envvars in a unit test.

---
 bigquery/tests/unit/test_client.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/bigquery/tests/unit/test_client.py b/bigquery/tests/unit/test_client.py
index 08c36e0ac277..6f001889164d 100644
--- a/bigquery/tests/unit/test_client.py
+++ b/bigquery/tests/unit/test_client.py
@@ -4518,7 +4518,9 @@ def test_list_rows_with_missing_schema(self):
             self.assertIsNone(rows[2].age, msg=repr(table))
 
     def test_list_rows_error(self):
-        client = self._make_one()
+        creds = _make_credentials()
+        http = object()
+        client = self._make_one(project=self.PROJECT, credentials=creds, _http=http)
 
         # neither Table nor tableReference
         with self.assertRaises(TypeError):

From ce60f3ab92dcf75f7d55ce0116f36501c90a0dcb Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Thu, 2 May 2019 15:13:43 -0400
Subject: [PATCH 06/14] Rely on base connection class for user_agent,
 extra_headers support.

---
 bigquery/google/cloud/bigquery/_http.py | 32 ++-----------------
 bigquery/tests/unit/test__http.py       | 42 +++++--------------------
 2 files changed, 10 insertions(+), 64 deletions(-)

diff --git a/bigquery/google/cloud/bigquery/_http.py b/bigquery/google/cloud/bigquery/_http.py
index 0e5475f5f54b..78fa4a6a3ea6 100644
--- a/bigquery/google/cloud/bigquery/_http.py
+++ b/bigquery/google/cloud/bigquery/_http.py
@@ -28,17 +28,10 @@ class Connection(_http.JSONConnection):
     """
 
     def __init__(self, client, client_info=None):
-        super(Connection, self).__init__(client)
+        super(Connection, self).__init__(client, client_info)
 
-        if client_info is None:
-            client_info = google.api_core.gapic_v1.client_info.ClientInfo(
-                gapic_version=__version__, client_library_version=__version__
-            )
-        else:
-            client_info.gapic_version = __version__
-            client_info.client_library_version = __version__
-        self._client_info = client_info
-        self._extra_headers = {}
+        self._client_info.gapic_version = __version__
+        self._client_info.client_library_version = __version__
 
     API_BASE_URL = "https://www.googleapis.com"
     """The base of the API call URL."""
@@ -48,22 +41,3 @@ def __init__(self, client, client_info=None):
 
     API_URL_TEMPLATE = "{api_base_url}/bigquery/{api_version}{path}"
     """A template for the URL of a particular API call."""
-
-    @property
-    def USER_AGENT(self):
-        return self._client_info.to_user_agent()
-
-    @USER_AGENT.setter
-    def USER_AGENT(self, value):
-        self._client_info.user_agent = value
-
-    @property
-    def _EXTRA_HEADERS(self):
-        self._extra_headers[
-            _http.CLIENT_INFO_HEADER
-        ] = self._client_info.to_user_agent()
-        return self._extra_headers
-
-    @_EXTRA_HEADERS.setter
-    def _EXTRA_HEADERS(self, value):
-        self._extra_headers = value
diff --git a/bigquery/tests/unit/test__http.py b/bigquery/tests/unit/test__http.py
index d7d25ea445a0..939b5668e1e2 100644
--- a/bigquery/tests/unit/test__http.py
+++ b/bigquery/tests/unit/test__http.py
@@ -57,49 +57,21 @@ def test_user_agent(self):
         client = mock.Mock(_http=http, spec=["_http"])
 
         conn = self._make_one(client)
-        conn.USER_AGENT = "my-application/1.2.3"
+        conn.user_agent = "my-application/1.2.3"
         req_data = "req-data-boring"
         result = conn.api_request("GET", "/rainbow", data=req_data, expect_json=False)
         self.assertEqual(result, data)
 
         expected_headers = {
             "Accept-Encoding": "gzip",
-            base_http.CLIENT_INFO_HEADER: conn.USER_AGENT,
-            "User-Agent": conn.USER_AGENT,
-        }
-        expected_uri = conn.build_api_url("/rainbow")
-        http.request.assert_called_once_with(
-            data=req_data, headers=expected_headers, method="GET", url=expected_uri
-        )
-        self.assertIn("my-application/1.2.3", conn.USER_AGENT)
-
-    def test_extra_headers(self):
-        from google.cloud import _http as base_http
-
-        http = mock.create_autospec(requests.Session, instance=True)
-        response = requests.Response()
-        response.status_code = 200
-        data = b"brent-spiner"
-        response._content = data
-        http.request.return_value = response
-        client = mock.Mock(_http=http, spec=["_http"])
-
-        conn = self._make_one(client)
-        conn._EXTRA_HEADERS["x-test-header"] = "a test value"
-        req_data = "req-data-boring"
-        result = conn.api_request("GET", "/rainbow", data=req_data, expect_json=False)
-        self.assertEqual(result, data)
-
-        expected_headers = {
-            "Accept-Encoding": "gzip",
-            base_http.CLIENT_INFO_HEADER: conn.USER_AGENT,
-            "User-Agent": conn.USER_AGENT,
-            "x-test-header": "a test value",
+            base_http.CLIENT_INFO_HEADER: conn.user_agent,
+            "User-Agent": conn.user_agent,
         }
         expected_uri = conn.build_api_url("/rainbow")
         http.request.assert_called_once_with(
             data=req_data, headers=expected_headers, method="GET", url=expected_uri
         )
+        self.assertIn("my-application/1.2.3", conn.user_agent)
 
     def test_extra_headers_replace(self):
         from google.cloud import _http as base_http
@@ -113,15 +85,15 @@ def test_extra_headers_replace(self):
         client = mock.Mock(_http=http, spec=["_http"])
 
         conn = self._make_one(client)
-        conn._EXTRA_HEADERS = {"x-test-header": "a test value"}
+        conn.extra_headers = {"x-test-header": "a test value"}
         req_data = "req-data-boring"
         result = conn.api_request("GET", "/rainbow", data=req_data, expect_json=False)
         self.assertEqual(result, data)
 
         expected_headers = {
             "Accept-Encoding": "gzip",
-            base_http.CLIENT_INFO_HEADER: conn.USER_AGENT,
-            "User-Agent": conn.USER_AGENT,
+            base_http.CLIENT_INFO_HEADER: conn.user_agent,
+            "User-Agent": conn.user_agent,
             "x-test-header": "a test value",
         }
         expected_uri = conn.build_api_url("/rainbow")

From 551a76b505a8be6586a081966a44b4ff0bac3ff5 Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Thu, 2 May 2019 19:44:47 -0400
Subject: [PATCH 07/14] Lint.

---
 bigquery/google/cloud/bigquery/_http.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/bigquery/google/cloud/bigquery/_http.py b/bigquery/google/cloud/bigquery/_http.py
index 78fa4a6a3ea6..e1c8e9fd9c86 100644
--- a/bigquery/google/cloud/bigquery/_http.py
+++ b/bigquery/google/cloud/bigquery/_http.py
@@ -14,7 +14,6 @@
 
 """Create / interact with Google BigQuery connections."""
 
-import google.api_core.gapic_v1.client_info
 from google.cloud import _http
 
 from google.cloud.bigquery import __version__

From e6dc855ec64cf8d2dcca2f163c3cb562d11f64c4 Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Fri, 3 May 2019 12:28:28 -0400
Subject: [PATCH 08/14] Move 'X-Goog-API-Client' header generation out of
 'extra_headers'.

---
 core/google/cloud/_http.py    |  7 +++----
 core/tests/unit/test__http.py | 20 +++-----------------
 2 files changed, 6 insertions(+), 21 deletions(-)

diff --git a/core/google/cloud/_http.py b/core/google/cloud/_http.py
index 5ffbf02881fe..d766900256ae 100644
--- a/core/google/cloud/_http.py
+++ b/core/google/cloud/_http.py
@@ -58,7 +58,6 @@ class Connection(object):
     """
 
     _user_agent = DEFAULT_USER_AGENT
-    _extra_headers = None
 
     def __init__(self, client, client_info=None):
         self._client = client
@@ -67,6 +66,7 @@ def __init__(self, client, client_info=None):
             client_info = ClientInfo()
 
         self._client_info = client_info
+        self._extra_headers = {}
 
     @property
     def USER_AGENT(self):
@@ -122,9 +122,7 @@ def extra_headers(self):
         :rtype: dict
         :returns: header keys / values
         """
-        result = self._extra_headers.copy() if self._extra_headers else {}
-        result[CLIENT_INFO_HEADER] = self.user_agent
-        return result
+        return self._extra_headers
 
     @extra_headers.setter
     def extra_headers(self, value):
@@ -265,6 +263,7 @@ def _make_request(
         if content_type:
             headers["Content-Type"] = content_type
 
+        headers[CLIENT_INFO_HEADER] = self.user_agent
         headers["User-Agent"] = self.user_agent
 
         return self._do_request(method, url, headers, data, target_object)
diff --git a/core/tests/unit/test__http.py b/core/tests/unit/test__http.py
index 236d5f964dc9..c00fabcf0e46 100644
--- a/core/tests/unit/test__http.py
+++ b/core/tests/unit/test__http.py
@@ -75,15 +75,9 @@ def test_user_agent_setter(self):
         self.assertEqual(conn._client_info.user_agent, user_agent)
 
     def test_extra_headers_all_caps_getter_deprecated(self):
-        from google.cloud._http import CLIENT_INFO_HEADER
-
         client = object()
         conn = self._make_one(client)
-        conn._extra_headers = {"foo": "bar"}
-        expected = {
-            CLIENT_INFO_HEADER: conn._client_info.to_user_agent(),
-            "foo": "bar",
-        }
+        expected = conn._extra_headers = {"foo": "bar"}
 
         with mock.patch.object(warnings, "warn", autospec=True) as warn:
             self.assertEqual(conn._EXTRA_HEADERS, expected)
@@ -101,21 +95,13 @@ def test_extra_headers_all_caps_setter_deprecated(self):
         warn.assert_called_once_with(mock.ANY, DeprecationWarning, stacklevel=2)
 
     def test_extra_headers_getter_default(self):
-        from google.cloud._http import CLIENT_INFO_HEADER
-
         conn = self._make_one(object())
-        expected = {CLIENT_INFO_HEADER: conn._client_info.to_user_agent()}
+        expected = {}
         self.assertEqual(conn.extra_headers, expected)
 
     def test_extra_headers_getter_overridden(self):
-        from google.cloud._http import CLIENT_INFO_HEADER
-
         conn = self._make_one(object())
-        conn._extra_headers = {"foo": "bar"}
-        expected = {
-            CLIENT_INFO_HEADER: conn._client_info.to_user_agent(),
-            "foo": "bar",
-        }
+        expected = conn._extra_headers = {"foo": "bar"}
         self.assertEqual(conn.extra_headers, expected)
 
     def test_extra_headers_setter(self):

From 0276af155ae73c3e435d748eac5bed2e324e6a42 Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Fri, 3 May 2019 12:34:26 -0400
Subject: [PATCH 09/14] Add unit test showing that item assingment to
 'extra_headers' property works.

---
 core/tests/unit/test__http.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/core/tests/unit/test__http.py b/core/tests/unit/test__http.py
index c00fabcf0e46..da038fe524ba 100644
--- a/core/tests/unit/test__http.py
+++ b/core/tests/unit/test__http.py
@@ -104,6 +104,12 @@ def test_extra_headers_getter_overridden(self):
         expected = conn._extra_headers = {"foo": "bar"}
         self.assertEqual(conn.extra_headers, expected)
 
+    def test_extra_headers_item_assignment(self):
+        conn = self._make_one(object())
+        expected = {"foo": "bar"}
+        conn.extra_headers["foo"] = "bar"
+        self.assertEqual(conn._extra_headers, expected)
+
     def test_extra_headers_setter(self):
         conn = self._make_one(object())
         expected = {"foo": "bar"}

From dfa12fe5458947fa0f60896cecedaf38847101f1 Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Fri, 3 May 2019 12:51:58 -0400
Subject: [PATCH 10/14] Document the 'client_info' parameter to
 'bigquery._http.Connection'.

---
 bigquery/google/cloud/bigquery/_http.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/bigquery/google/cloud/bigquery/_http.py b/bigquery/google/cloud/bigquery/_http.py
index e1c8e9fd9c86..643b24920bee 100644
--- a/bigquery/google/cloud/bigquery/_http.py
+++ b/bigquery/google/cloud/bigquery/_http.py
@@ -24,6 +24,9 @@ class Connection(_http.JSONConnection):
 
     :type client: :class:`~google.cloud.bigquery.client.Client`
     :param client: The client that owns the current connection.
+
+    :type client_info: :class:`~google.api_core.client_info.ClientInfo`
+    :param client_info: (Optional) instance used to generate user agent.
     """
 
     def __init__(self, client, client_info=None):

From 85977418b1f7c350039706c9df311c169024fca9 Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Fri, 3 May 2019 13:30:00 -0400
Subject: [PATCH 11/14] Create/use non-GAPIC-specific 'ClientInfo' class FBO
 HTTP/JSON clients.

Derive the existing GAPIC class from it.
---
 api_core/google/api_core/client_info.py       | 96 +++++++++++++++++++
 .../google/api_core/gapic_v1/client_info.py   | 54 +----------
 api_core/tests/unit/gapic/test_client_info.py | 53 ----------
 api_core/tests/unit/test_client_info.py       | 69 +++++++++++++
 core/google/cloud/_http.py                    |  2 +-
 core/tests/unit/test__http.py                 |  2 +-
 6 files changed, 169 insertions(+), 107 deletions(-)
 create mode 100644 api_core/google/api_core/client_info.py
 create mode 100644 api_core/tests/unit/test_client_info.py

diff --git a/api_core/google/api_core/client_info.py b/api_core/google/api_core/client_info.py
new file mode 100644
index 000000000000..b196b7a987e4
--- /dev/null
+++ b/api_core/google/api_core/client_info.py
@@ -0,0 +1,96 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helpers for providing client information.
+
+Client information is used to send information about the calling client,
+such as the library and Python version, to API services.
+"""
+
+import platform
+
+import pkg_resources
+
+_PY_VERSION = platform.python_version()
+_API_CORE_VERSION = pkg_resources.get_distribution("google-api-core").version
+
+try:
+    _GRPC_VERSION = pkg_resources.get_distribution("grpcio").version
+except pkg_resources.DistributionNotFound:  # pragma: NO COVER
+    _GRPC_VERSION = None
+
+
+class ClientInfo(object):
+    """Client information used to generate a user-agent for API calls.
+
+    This user-agent information is sent along with API calls to allow the
+    receiving service to do analytics on which versions of Python and Google
+    libraries are being used.
+
+    Args:
+        python_version (str): The Python interpreter version, for example,
+            ``'2.7.13'``.
+        grpc_version (Optional[str]): The gRPC library version.
+        api_core_version (str): The google-api-core library version.
+        gapic_version (Optional[str]): The sversion of gapic-generated client
+            library, if the library was generated by gapic.
+        client_library_version (Optional[str]): The version of the client
+            library, generally used if the client library was not generated
+            by gapic or if additional functionality was built on top of
+            a gapic client library.
+        user_agent (Optional[str]): Prefix to the user agent header. This is
+            used to supply information such as application name or partner tool.
+            Recommended format: ``application-or-tool-ID/major.minor.version``.
+    """
+
+    def __init__(
+        self,
+        python_version=_PY_VERSION,
+        grpc_version=_GRPC_VERSION,
+        api_core_version=_API_CORE_VERSION,
+        gapic_version=None,
+        client_library_version=None,
+        user_agent=None,
+    ):
+        self.python_version = python_version
+        self.grpc_version = grpc_version
+        self.api_core_version = api_core_version
+        self.gapic_version = gapic_version
+        self.client_library_version = client_library_version
+        self.user_agent = user_agent
+
+    def to_user_agent(self):
+        """Returns the user-agent string for this client info."""
+
+        # Note: the order here is important as the internal metrics system
+        # expects these items to be in specific locations.
+        ua = ""
+
+        if self.user_agent is not None:
+            ua += "{user_agent} "
+
+        ua += "gl-python/{python_version} "
+
+        if self.grpc_version is not None:
+            ua += "grpc/{grpc_version} "
+
+        ua += "gax/{api_core_version} "
+
+        if self.gapic_version is not None:
+            ua += "gapic/{gapic_version} "
+
+        if self.client_library_version is not None:
+            ua += "gccl/{client_library_version} "
+
+        return ua.format(**self.__dict__).strip()
diff --git a/api_core/google/api_core/gapic_v1/client_info.py b/api_core/google/api_core/gapic_v1/client_info.py
index 069e0194ab31..bdc2ce440de3 100644
--- a/api_core/google/api_core/gapic_v1/client_info.py
+++ b/api_core/google/api_core/gapic_v1/client_info.py
@@ -18,22 +18,13 @@
 such as the library and Python version, to API services.
 """
 
-import platform
+from google.api_core import client_info
 
-import pkg_resources
-
-_PY_VERSION = platform.python_version()
-_API_CORE_VERSION = pkg_resources.get_distribution("google-api-core").version
-
-try:
-    _GRPC_VERSION = pkg_resources.get_distribution("grpcio").version
-except pkg_resources.DistributionNotFound:  # pragma: NO COVER
-    _GRPC_VERSION = None
 
 METRICS_METADATA_KEY = "x-goog-api-client"
 
 
-class ClientInfo(object):
+class ClientInfo(client_info.ClientInfo):
     """Client information used to generate a user-agent for API calls.
 
     This user-agent information is sent along with API calls to allow the
@@ -56,47 +47,6 @@ class ClientInfo(object):
             Recommended format: ``application-or-tool-ID/major.minor.version``.
     """
 
-    def __init__(
-        self,
-        python_version=_PY_VERSION,
-        grpc_version=_GRPC_VERSION,
-        api_core_version=_API_CORE_VERSION,
-        gapic_version=None,
-        client_library_version=None,
-        user_agent=None,
-    ):
-        self.python_version = python_version
-        self.grpc_version = grpc_version
-        self.api_core_version = api_core_version
-        self.gapic_version = gapic_version
-        self.client_library_version = client_library_version
-        self.user_agent = user_agent
-
-    def to_user_agent(self):
-        """Returns the user-agent string for this client info."""
-
-        # Note: the order here is important as the internal metrics system
-        # expects these items to be in specific locations.
-        ua = ""
-
-        if self.user_agent is not None:
-            ua += "{user_agent} "
-
-        ua += "gl-python/{python_version} "
-
-        if self.grpc_version is not None:
-            ua += "grpc/{grpc_version} "
-
-        ua += "gax/{api_core_version} "
-
-        if self.gapic_version is not None:
-            ua += "gapic/{gapic_version} "
-
-        if self.client_library_version is not None:
-            ua += "gccl/{client_library_version} "
-
-        return ua.format(**self.__dict__).strip()
-
     def to_grpc_metadata(self):
         """Returns the gRPC metadata for this client info."""
         return (METRICS_METADATA_KEY, self.to_user_agent())
diff --git a/api_core/tests/unit/gapic/test_client_info.py b/api_core/tests/unit/gapic/test_client_info.py
index 0cca47905988..64080ffdbccd 100644
--- a/api_core/tests/unit/gapic/test_client_info.py
+++ b/api_core/tests/unit/gapic/test_client_info.py
@@ -16,59 +16,6 @@
 from google.api_core.gapic_v1 import client_info
 
 
-def test_constructor_defaults():
-    info = client_info.ClientInfo()
-
-    assert info.python_version is not None
-    assert info.grpc_version is not None
-    assert info.api_core_version is not None
-    assert info.gapic_version is None
-    assert info.client_library_version is None
-
-
-def test_constructor_options():
-    info = client_info.ClientInfo(
-        python_version="1",
-        grpc_version="2",
-        api_core_version="3",
-        gapic_version="4",
-        client_library_version="5",
-        user_agent="6"
-    )
-
-    assert info.python_version == "1"
-    assert info.grpc_version == "2"
-    assert info.api_core_version == "3"
-    assert info.gapic_version == "4"
-    assert info.client_library_version == "5"
-    assert info.user_agent == "6"
-
-
-def test_to_user_agent_minimal():
-    info = client_info.ClientInfo(
-        python_version="1", api_core_version="2", grpc_version=None
-    )
-
-    user_agent = info.to_user_agent()
-
-    assert user_agent == "gl-python/1 gax/2"
-
-
-def test_to_user_agent_full():
-    info = client_info.ClientInfo(
-        python_version="1",
-        grpc_version="2",
-        api_core_version="3",
-        gapic_version="4",
-        client_library_version="5",
-        user_agent="app-name/1.0",
-    )
-
-    user_agent = info.to_user_agent()
-
-    assert user_agent == "app-name/1.0 gl-python/1 grpc/2 gax/3 gapic/4 gccl/5"
-
-
 def test_to_grpc_metadata():
     info = client_info.ClientInfo()
 
diff --git a/api_core/tests/unit/test_client_info.py b/api_core/tests/unit/test_client_info.py
new file mode 100644
index 000000000000..0eb17c5feb1c
--- /dev/null
+++ b/api_core/tests/unit/test_client_info.py
@@ -0,0 +1,69 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+from google.api_core import client_info
+
+
+def test_constructor_defaults():
+    info = client_info.ClientInfo()
+
+    assert info.python_version is not None
+    assert info.grpc_version is not None
+    assert info.api_core_version is not None
+    assert info.gapic_version is None
+    assert info.client_library_version is None
+
+
+def test_constructor_options():
+    info = client_info.ClientInfo(
+        python_version="1",
+        grpc_version="2",
+        api_core_version="3",
+        gapic_version="4",
+        client_library_version="5",
+        user_agent="6"
+    )
+
+    assert info.python_version == "1"
+    assert info.grpc_version == "2"
+    assert info.api_core_version == "3"
+    assert info.gapic_version == "4"
+    assert info.client_library_version == "5"
+    assert info.user_agent == "6"
+
+
+def test_to_user_agent_minimal():
+    info = client_info.ClientInfo(
+        python_version="1", api_core_version="2", grpc_version=None
+    )
+
+    user_agent = info.to_user_agent()
+
+    assert user_agent == "gl-python/1 gax/2"
+
+
+def test_to_user_agent_full():
+    info = client_info.ClientInfo(
+        python_version="1",
+        grpc_version="2",
+        api_core_version="3",
+        gapic_version="4",
+        client_library_version="5",
+        user_agent="app-name/1.0",
+    )
+
+    user_agent = info.to_user_agent()
+
+    assert user_agent == "app-name/1.0 gl-python/1 grpc/2 gax/3 gapic/4 gccl/5"
diff --git a/core/google/cloud/_http.py b/core/google/cloud/_http.py
index d766900256ae..653e43138e3a 100644
--- a/core/google/cloud/_http.py
+++ b/core/google/cloud/_http.py
@@ -21,7 +21,7 @@
 from pkg_resources import get_distribution
 from six.moves.urllib.parse import urlencode
 
-from google.api_core.gapic_v1.client_info import ClientInfo
+from google.api_core.client_info import ClientInfo
 from google.cloud import exceptions
 
 
diff --git a/core/tests/unit/test__http.py b/core/tests/unit/test__http.py
index da038fe524ba..d50494e8eadc 100644
--- a/core/tests/unit/test__http.py
+++ b/core/tests/unit/test__http.py
@@ -32,7 +32,7 @@ def _make_one(self, *args, **kw):
         return self._get_target_class()(*args, **kw)
 
     def test_constructor_defaults(self):
-        from google.api_core.gapic_v1.client_info import ClientInfo
+        from google.api_core.client_info import ClientInfo
 
         client = object()
         conn = self._make_one(client)

From 08b316fd9be0baff573a7b7dcc0ed53be8fbf2ad Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Fri, 3 May 2019 13:39:12 -0400
Subject: [PATCH 12/14] Avoid use of deprecated 'USER_AGENT' attr of
 connection.

---
 bigquery/google/cloud/bigquery/client.py | 4 ++--
 bigquery/tests/unit/test_client.py       | 6 +++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/bigquery/google/cloud/bigquery/client.py b/bigquery/google/cloud/bigquery/client.py
index db53dab9ef11..791c6e3a5de8 100644
--- a/bigquery/google/cloud/bigquery/client.py
+++ b/bigquery/google/cloud/bigquery/client.py
@@ -1363,7 +1363,7 @@ def _initiate_resumable_upload(self, stream, metadata, num_retries):
         """
         chunk_size = _DEFAULT_CHUNKSIZE
         transport = self._http
-        headers = _get_upload_headers(self._connection.USER_AGENT)
+        headers = _get_upload_headers(self._connection.user_agent)
         upload_url = _RESUMABLE_URL_TEMPLATE.format(project=self.project)
         # TODO: modify ResumableUpload to take a retry.Retry object
         # that it can use for the initial RPC.
@@ -1409,7 +1409,7 @@ def _do_multipart_upload(self, stream, metadata, size, num_retries):
             msg = _READ_LESS_THAN_SIZE.format(size, len(data))
             raise ValueError(msg)
 
-        headers = _get_upload_headers(self._connection.USER_AGENT)
+        headers = _get_upload_headers(self._connection.user_agent)
 
         upload_url = _MULTIPART_URL_TEMPLATE.format(project=self.project)
         upload = MultipartUpload(upload_url, headers=headers)
diff --git a/bigquery/tests/unit/test_client.py b/bigquery/tests/unit/test_client.py
index 6f001889164d..13889f90d7e8 100644
--- a/bigquery/tests/unit/test_client.py
+++ b/bigquery/tests/unit/test_client.py
@@ -54,7 +54,7 @@ def _make_connection(*responses):
     from google.cloud.exceptions import NotFound
 
     mock_conn = mock.create_autospec(google.cloud.bigquery._http.Connection)
-    mock_conn.USER_AGENT = "testing 1.2.3"
+    mock_conn.user_agent = "testing 1.2.3"
     mock_conn.api_request.side_effect = list(responses) + [NotFound("miss")]
     return mock_conn
 
@@ -2752,7 +2752,7 @@ def _initiate_resumable_upload_helper(self, num_retries=None):
             + "/jobs?uploadType=resumable"
         )
         self.assertEqual(upload.upload_url, upload_url)
-        expected_headers = _get_upload_headers(conn.USER_AGENT)
+        expected_headers = _get_upload_headers(conn.user_agent)
         self.assertEqual(upload._headers, expected_headers)
         self.assertFalse(upload.finished)
         self.assertEqual(upload._chunk_size, _DEFAULT_CHUNKSIZE)
@@ -2830,7 +2830,7 @@ def _do_multipart_upload_success_helper(self, get_boundary, num_retries=None):
             + b"\r\n"
             + b"--==0==--"
         )
-        headers = _get_upload_headers(conn.USER_AGENT)
+        headers = _get_upload_headers(conn.user_agent)
         headers["content-type"] = b'multipart/related; boundary="==0=="'
         fake_transport.request.assert_called_once_with(
             "POST", upload_url, data=payload, headers=headers

From 5a7da2e605afd8687a4a23645874f819cf11667a Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Fri, 3 May 2019 14:48:53 -0400
Subject: [PATCH 13/14] Fix class reference for client_info.

---
 bigquery/google/cloud/bigquery/client.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/bigquery/google/cloud/bigquery/client.py b/bigquery/google/cloud/bigquery/client.py
index 791c6e3a5de8..f61c18f11bd4 100644
--- a/bigquery/google/cloud/bigquery/client.py
+++ b/bigquery/google/cloud/bigquery/client.py
@@ -128,7 +128,7 @@ class Client(ClientWithProject):
         default_query_job_config (google.cloud.bigquery.job.QueryJobConfig):
             (Optional) Default ``QueryJobConfig``.
             Will be merged into job configs passed into the ``query`` method.
-        client_info (google.api_core.gapic_v1.client_info.ClientInfo):
+        client_info (google.api_core.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 library

From 443a82262850d5e31dbd356d4270ae362b195542 Mon Sep 17 00:00:00 2001
From: Tres Seaver <tseaver@palladion.com>
Date: Tue, 7 May 2019 11:16:34 -0400
Subject: [PATCH 14/14] Document 'ClientInfo' classes.

---
 docs/core/client_info.rst | 11 +++++++++++
 docs/core/index.rst       |  7 ++++---
 2 files changed, 15 insertions(+), 3 deletions(-)
 create mode 100644 docs/core/client_info.rst

diff --git a/docs/core/client_info.rst b/docs/core/client_info.rst
new file mode 100644
index 000000000000..e976b1863c7c
--- /dev/null
+++ b/docs/core/client_info.rst
@@ -0,0 +1,11 @@
+Client Information Helpers
+==========================
+
+.. automodule:: google.api_core.client_info
+  :members:
+  :show-inheritance:
+
+.. automodule:: google.api_core.gapic_v1.client_info
+  :members:
+  :show-inheritance:
+
diff --git a/docs/core/index.rst b/docs/core/index.rst
index 5b44ddcb071d..45c68ad08ee2 100644
--- a/docs/core/index.rst
+++ b/docs/core/index.rst
@@ -5,15 +5,16 @@ Core
     config
     auth
     client
+    client_info
     exceptions
     helpers
-    retry
-    timeout
-    page_iterator
     iam
     operation
     operations_client
+    page_iterator
     path_template
+    retry
+    timeout
 
 Changelog
 ~~~~~~~~~