If there is no start-line, this offset is set to -1. Otherwise, it is the
relative address where the start-line is stored in the data block. When the
start-line is added, replaced or removed, this offset is updated accordingly. On
remove, if the start-line is no set and if the next block is a start-line, the
offset is updated. Finally, when an HTX structure is defragmented, the offset is
also updated accordingly.
The HTX start-line is now a struct. It will be easier to extend, if needed. Same
info can be found, of course. In addition it is now possible to set flags on
it. It will be used to set some infos about the message.
Some macros and functions have been added in proto/htx.h to help accessing
different parts of the start-line.
The internal representation of an HTTP message, called HTX, is a structured
representation, unlike the old one which is a raw representation of
messages. Idea is to have a version-agnostic representation of the HTTP
messages, which can be easily used by to handle HTTP/1, HTTP/2 and hopefully
QUIC messages, and communication from one of them to another.
In this patch, we add types to define the internal representation itself and the
main functions to manipulate them.
