[dist4]message_header // num_bytes
[u4]1 // version
[u4]0 // interface ID
[u4]0 // name
[u4]1 // flags: kMessageExpectsResponse is set in a request
// for a method that does not take a response.
[u4]0 // padding
[u8]1 // request_id
[anchr]message_header