These are supposed to be interpreted caselessly so let's just use the
case insensitive traits throughout. This means we'll understand things
like "Content-Length" even when they send "content-length" etc.
Contrary to popular belief, not every implementation of TLS follows the
specs.
Some of them just drop the connection without sending a proper
close_notify, and we should handle that gracefully.
Apparently servers will feel free to pad their response if they send one
that contains a content-length field.
We should not assume that the entirety of the response is valid data.
