From ddda9c31c76272b8b7e0ee813144abb0bf4dfe56 Mon Sep 17 00:00:00 2001
From: Lukasz Mitusinski <lukasz.mitusinski@xsolve.pl>
Date: Thu, 15 Mar 2018 14:44:06 +0100
Subject: [PATCH] #751 support for converting buffered data in widgets

---
 nbconvert/preprocessors/execute.py | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/nbconvert/preprocessors/execute.py b/nbconvert/preprocessors/execute.py
index 382b336e7..d8e552130 100644
--- a/nbconvert/preprocessors/execute.py
+++ b/nbconvert/preprocessors/execute.py
@@ -3,7 +3,7 @@
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
-
+import base64
 from textwrap import dedent
 from contextlib import contextmanager
 
@@ -335,6 +335,7 @@ def preprocess(self, nb, resources, km=None):
         Preprocess notebook executing each code cell.
 
         The input argument `nb` is modified in-place.
+        self.widget_buffers = {}
 
         Parameters
         ----------
@@ -489,7 +490,10 @@ def run_cell(self, cell, cell_index=0):
                         cell_map[cell_index] = []
                 continue
             elif msg_type.startswith('comm'):
-                self.widget_state.setdefault(content['comm_id'], {}).update(content['data']['state'])
+                data = content['data']
+                self.widget_state.setdefault(content['comm_id'], {}).update(data['state'])
+                if 'buffer_paths' in data and data['buffer_paths']:
+                    self.widget_buffers[content['comm_id']] = _get_buffer_data(msg)
                 continue
 
             display_id = None
@@ -553,3 +557,15 @@ def _serialize_widget_state(state):
         'model_module_version': state.get('_model_module_version'),
         'state': state,
     }
+
+
+def _get_buffer_data(msg):
+    buffers = []
+    path = msg['content']['data']['buffer_paths']
+    for buffer in msg['buffers']:
+        buffers.append({
+            'data': base64.b64encode(buffer.obj).decode('utf-8'),
+            'encoding': 'base64',
+            'path': path
+        })
+    return buffers