Raise ValueError if text-mode file is passed to 'upload_from_file'.

Addresses:
#1779 (comment)

gcloud/bigquery/table.py

@@ -809,8 +809,9 @@ def upload_from_file(self,
         :rtype: :class:`gcloud.bigquery.jobs.LoadTableFromStorageJob`
         :returns: the job instance used to load the data (e.g., for
                   querying status)
-        :raises: :class:`ValueError` if size is not passed in and can not be
-                 determined
+        :raises: :class:`ValueError` if ``size`` is not passed in and can not
+                 be determined, or if the ``file_obj`` can be detected to be
+                 a file opened in text mode.
         """
         client = self._require_client(client)
         connection = client.connection
@@ -820,6 +821,12 @@ def upload_from_file(self,
         if rewind:
             file_obj.seek(0, os.SEEK_SET)
 
+        mode = getattr(file_obj, 'mode', None)
+        if mode is not None and mode != 'rb':
+            raise ValueError(
+                "Cannot upload files opened in text mode:  use "
+                "open(filename, mode='rb')")
+
         # Get the basic stats about the file.
         total_bytes = size
         if total_bytes is None:

gcloud/bigquery/test_table.py

@@ -1289,6 +1289,19 @@ def _row_data(row):
         self.assertEqual(req['path'], '/%s' % PATH)
         self.assertEqual(req['data'], SENT)
 
+    def test_upload_from_file_text_mode_file_failure(self):
+
+        class TextModeFile(object):
+            mode = 'r'
+
+        conn = _Connection()
+        client = _Client(project=self.PROJECT, connection=conn)
+        dataset = _Dataset(client)
+        file_obj = TextModeFile()
+        table = self._makeOne(self.TABLE_NAME, dataset=dataset)
+        with self.assertRaises(ValueError):
+            table.upload_from_file(file_obj, 'CSV', size=1234)
+
     def test_upload_from_file_size_failure(self):
         conn = _Connection()
         client = _Client(project=self.PROJECT, connection=conn)