Causes this 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 this; if
this has started sending the request but has not yet received the complete response, then it will close
the request's connection. Note that with requests that have side effects (eg, <literal>POST</literal>, <literal>PUT<
/literal>, <literal>DELETE</literal>) 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.
Beware that with the deprecated SessionAsync, messages queued with queue_message will have their callbacks invoked before cancel_message returns. The plain Session does not have this behavior; cancelling an asynchronous message will merely queue its callback to be run after returning to the main loop.
| this |
a Session |
| msg |
the message to cancel |
| status_code |
status code to set on |