update BinaryCapsule class to include data content type

splash/kernel/kernel.py

@@ -159,7 +159,7 @@ def done(result):
                     'text/plain': result if isinstance(result, basestring) else str(result),
                 }
                 if isinstance(result, BinaryCapsule):
-                    data["image/png"] = result.as_b64()
+                    data[result.content_type] = result.as_b64()
                 self._publish_execute_result(parent, data, {}, self.execution_count)
 
             super(SplashKernel, self).send_execute_reply(stream, ident, parent, md, reply)

splash/qtrender_lua.py

@@ -386,7 +386,7 @@ def png(self, width=None, height=None, render_all=False,
             height = int(height)
         result = self.tab.png(width, height, b64=False, render_all=render_all,
                               scale_method=scale_method)
-        return BinaryCapsule(result)
+        return BinaryCapsule(result, 'image/png')
 
     @command()
     def jpeg(self, width=None, height=None, render_all=False,
@@ -399,7 +399,7 @@ def jpeg(self, width=None, height=None, render_all=False,
             quality = int(quality)
         result = self.tab.jpeg(width, height, b64=False, render_all=render_all,
                                scale_method=scale_method, quality=quality)
-        return BinaryCapsule(result)
+        return BinaryCapsule(result, 'image/jpeg')
 
     @command()
     def har(self):

splash/utils.py

@@ -20,8 +20,9 @@ class BadRequest(Exception):
 
 class BinaryCapsule(object):
     """ A wrapper for passing binary data. """
-    def __init__(self, data):
+    def __init__(self, data, content_type):
         self.data = data
+        self.content_type = content_type
 
     def as_b64(self):
         return base64.b64encode(self.data)