Adding ability to send version info header on HTTP requests.

Added an "extra headers" feature to enable this. I am not a fan
of changing `Connection()` so haphazardly, but I hope to
completely re-factor / destory `Connection()` in the near-term
so I am less worried.

This only adds the storage and datastore header info, for the
purposes of a simple review. Once we agree on the approach,
I can add support in the other subpackages.

Author: dhermes

packages/google-cloud-core/google/cloud/_http.py

@@ -15,7 +15,9 @@
 """Shared implementation of connections to API servers."""
 
 import json
+import platform
 from pkg_resources import get_distribution
+
 import six
 from six.moves.urllib.parse import urlencode
 
@@ -29,6 +31,10 @@
     get_distribution('google-cloud-core').version)
 """The user agent for google-cloud-python requests."""
 
+CLIENT_INFO_HEADER = 'X-Goog-API-Client'
+CLIENT_INFO_TEMPLATE = (
+    'gl-python/' + platform.python_version() + ' gccl/{}')
+
 
 class Connection(object):
     """A generic connection to Google Cloud Platform.
@@ -38,6 +44,11 @@ class Connection(object):
     """
 
     USER_AGENT = DEFAULT_USER_AGENT
+    _EXTRA_HEADERS = {}
+    """Headers to be sent with every request.
+
+    Intended to be over-ridden by subclasses.
+    """
 
     def __init__(self, client):
         self._client = client
@@ -147,7 +158,9 @@ def _make_request(self, method, url, data=None, content_type=None,
         :param content_type: The proper MIME type of the data provided.
 
         :type headers: dict
-        :param headers: A dictionary of HTTP headers to send with the request.
+        :param headers: (Optional) A dictionary of HTTP headers to send with
+                        the request. If passed, will be modified directly
+                        here with added headers.
 
         :type target_object: object
         :param target_object:
@@ -161,6 +174,7 @@ def _make_request(self, method, url, data=None, content_type=None,
                   returned by :meth:`_do_request`.
         """
         headers = headers or {}
+        headers.update(self._EXTRA_HEADERS)
         headers['Accept-Encoding'] = 'gzip'
 
         if data:

packages/google-cloud-core/unit_tests/test__http.py

@@ -287,6 +287,44 @@ def test_api_request_w_headers(self):
         }
         self.assertEqual(http._called_with['headers'], expected_headers)
 
+    def test_api_request_w_extra_headers(self):
+        from six.moves.urllib.parse import urlsplit
+
+        http = _Http(
+            {'status': '200', 'content-type': 'application/json'},
+            b'{}',
+        )
+        client = mock.Mock(_http=http, spec=['_http'])
+        conn = self._make_mock_one(client)
+        conn._EXTRA_HEADERS = {
+            'X-Baz': 'dax-quux',
+            'X-Foo': 'not-bar',  # Collision with ``headers``.
+        }
+        self.assertEqual(
+            conn.api_request('GET', '/', headers={'X-Foo': 'bar'}), {})
+        self.assertEqual(http._called_with['method'], 'GET')
+        uri = http._called_with['uri']
+        scheme, netloc, path, qs, _ = urlsplit(uri)
+        self.assertEqual('%s://%s' % (scheme, netloc), conn.API_BASE_URL)
+        # Intended to emulate self.mock_template
+        PATH = '/'.join([
+            '',
+            'mock',
+            conn.API_VERSION,
+            '',
+        ])
+        self.assertEqual(path, PATH)
+        self.assertEqual(qs, '')
+        self.assertIsNone(http._called_with['body'])
+        expected_headers = {
+            'Accept-Encoding': 'gzip',
+            'Content-Length': '0',
+            'User-Agent': conn.USER_AGENT,
+            'X-Foo': 'not-bar',  # The one passed-in is overridden.
+            'X-Baz': 'dax-quux',
+        }
+        self.assertEqual(http._called_with['headers'], expected_headers)
+
     def test_api_request_w_data(self):
         import json