Send copy of ContentFile.file to upload_fileobj.

AUTHORS

@@ -31,6 +31,7 @@ By order of apparition, thanks:
     * Jody McIntyre (Google Cloud Storage native support)
     * Stanislav Kaledin (Bug fixes in SFTPStorage)
     * Filip Vavera (Google Cloud MIME types support)
+    * João Sampaio (S3 with Boto3)
 
 Extra thanks to Marty for adding this in Django,
 you can buy his very interesting book (Pro Django).

storages/backends/s3boto3.py

@@ -444,10 +444,11 @@ def _save(self, name, content):
         # provided. `File.__bool__`  method is Django-specific and depends on
         # file name, for this reason`botocore.handlers.calculate_md5` can fail
         # even if wrapped file-like object exists. To avoid Django-specific
-        # logic, pass internal file-like object if `content` is `File`
-        # class instance.
+        # logic, pass a copy of internal file-like object if `content` is
+        # `File` class instance.
         if isinstance(content, File):
-            content = content.file
+            content.file.seek(0)
+            content = BytesIO(force_bytes(content.file.read()))
 
         self._save_content(obj, content, parameters=parameters)
         # Note: In boto3, after a put, last_modified is automatically reloaded

tests/test_s3boto3.py

@@ -71,34 +71,42 @@ def test_storage_url_slashes(self):
         self.assertEqual(self.storage.url('path/1'), 'https://example.com/path/1')
         self.assertEqual(self.storage.url('path/1/'), 'https://example.com/path/1/')
 
-    def test_storage_save(self):
+    @mock.patch('storages.backends.s3boto3.BytesIO')
+    def test_storage_save(self, mocked_BytesIO):
         """
         Test saving a file
         """
+        content_file = mock.Mock()
+        mocked_BytesIO.return_value = content_file
+
         name = 'test_storage_save.txt'
         content = ContentFile('new content')
         self.storage.save(name, content)
         self.storage.bucket.Object.assert_called_once_with(name)
 
         obj = self.storage.bucket.Object.return_value
         obj.upload_fileobj.assert_called_with(
-            content.file,
+            content_file,
             ExtraArgs={
                 'ContentType': 'text/plain',
                 'ACL': self.storage.default_acl,
             }
         )
 
-    def test_storage_save_gzipped(self):
+    @mock.patch('storages.backends.s3boto3.BytesIO')
+    def test_storage_save_gzipped(self, mocked_BytesIO):
         """
         Test saving a gzipped file
         """
+        content_file = mock.Mock()
+        mocked_BytesIO.return_value = content_file
+
         name = 'test_storage_save.gz'
         content = ContentFile("I am gzip'd")
         self.storage.save(name, content)
         obj = self.storage.bucket.Object.return_value
         obj.upload_fileobj.assert_called_with(
-            content.file,
+            content_file,
             ExtraArgs={
                 'ContentType': 'application/octet-stream',
                 'ContentEncoding': 'gzip',