Add a metadata attribute to zeromq stdout/stderr stream messages

IPython/zmq/iostream.py

@@ -28,10 +28,15 b' class OutStream(object):'
         self.name = name
         self.parent_header = {}
         self._new_buffer()
+        self.metadata = {}
 
     def set_parent(self, parent):
         self.parent_header = extract_header(parent)
 
+    def set_metadata(self, metadata):
+        self.flush()
+        self.metadata = metadata
+
     def close(self):
         self.pub_socket = None
 
@@ -43,6 +48,8 b' class OutStream(object):'
             data = self._buffer.getvalue()
             if data:
                 content = {u'name':self.name, u'data':data}
+                if self.metadata:
+                    content['metadata'] = self.metadata
                 msg = self.session.send(self.pub_socket, u'stream', content=content,
                                        parent=self.parent_header, ident=self.topic)