H2.ResponseSourceResponse
A server-generated message to a Request.t.
create ?headers status creates an HTTP response with the given parameters. Unlike the Response type in http/af, h2 does not define a way for responses to carry reason phrases or protocol version.
See RFC7540§8.1.2.4 for more details.
body_length t is the length of the message body accompanying t.
See RFC7230§3.3.3 for more details.