Causes session to immediately finish processing msg (regardless of its current state) with a final status_code
of status_code. You may call this at any time after handing msg off to session; if session
has started sending the request but has not yet received the complete response, then it will close the request's connection. Note
that with non-idempotent requests (eg, POST, PUT, DELETE) it is possible that you might cancel the request after the
server acts on it, but before it returns a response, leaving the remote resource in an unknown state.
If the message is cancelled while its response body is being read, then the response body in msg will be left
partially-filled-in. The response headers, on the other hand, will always be either empty or complete.
For messages queued with queue_message (and cancelled from the same thread), the callback will be invoked before cancel_message returns.
| msg | the message to cancel |
| status_code | status code to set on msg (generally CANCELLED)
|