Fix issues with GceAssertionCredentials in Python 3

Author: charlesccychen

apitools/base/py/credentials_lib.py

@@ -352,7 +352,7 @@ def _ScopesFromMetadataServer(self, scopes):
     def GetServiceAccount(self, account):
         relative_url = 'instance/service-accounts'
         response = _GceMetadataRequest(relative_url)
-        response_lines = [line.rstrip('/\n\r')
+        response_lines = [line.rstrip(b'/\n\r').decode('utf-8')
                           for line in response.readlines()]
         return account in response_lines
 
@@ -395,7 +395,7 @@ def _do_refresh_request(self, unused_http_request):
             raise
         content = response.read()
         try:
-            credential_info = json.loads(content)
+            credential_info = json.loads(content.decode('utf-8'))
         except ValueError:
             raise exceptions.CredentialsError(
                 'Could not parse response as JSON: %s' % content)

apitools/base/py/credentials_lib_test.py

@@ -34,12 +34,12 @@ def __init__(self, scopes=None, service_account_name=None):
 
     def __call__(self, request_url):
         if request_url.endswith('scopes'):
-            return six.StringIO(''.join(self._scopes))
+            return six.BytesIO(''.join(self._scopes).encode('utf-8'))
         elif request_url.endswith('service-accounts'):
-            return six.StringIO(self._sa)
+            return six.BytesIO(self._sa.encode('utf-8'))
         elif request_url.endswith(
                 '/service-accounts/%s/token' % self._sa):
-            return six.StringIO('{"access_token": "token"}')
+            return six.BytesIO('{"access_token": "token"}'.encode('utf-8'))
         self.fail('Unexpected HTTP request to %s' % request_url)
 
 
@@ -132,11 +132,11 @@ def testGetServiceAccount(self):
         creds = self._GetServiceCreds()
         opener = mock.MagicMock()
         opener.open = mock.MagicMock()
-        opener.open.return_value = six.StringIO('default/\nanother')
+        opener.open.return_value = six.BytesIO(b'default/\nanother')
         with mock.patch.object(six.moves.urllib.request, 'build_opener',
                                return_value=opener,
                                autospec=True) as build_opener:
-            creds.GetServiceAccount('default')
+            creds.GetServiceAccount(b'default')
             self.assertEqual(1, build_opener.call_count)
             self.assertEqual(1, opener.open.call_count)
             req = opener.open.call_args[0][0]