Emitted after receiving all message headers for a message.
(For a client-side message, this is after receiving the Status-Line and response headers; for a server-side message, it is after receiving the Request-Line and request headers.)
See also add_header_handler and add_status_code_handler, which can be used to connect to a subset of emissions of this signal.
If you cancel or requeue msg
while processing this signal, then the current HTTP I/O will be stopped after this signal
emission finished, and msg
's connection will be closed. (If you need to requeue a message--eg, after handling authentication
or redirection--it is usually better to requeue it from a got_body handler rather
than a got_headers handler, so that the existing HTTP connection can be reused.)