due to the usage of a hashmap to store headers, when relaying them
to the other side the order was not prevented.
even though correct from a standards point-of-view, this caused
issues with various programs, and it allows to fingerprint the use
of tinyproxy.
to implement this, i imported the MIT-licensed hsearch.[ch] from
https://github.com/rofl0r/htab which was originally taken from
musl libc. it's a simple and efficient hashtable implementation
with far better performance characteristic than the one previously
used by tinyproxy. additionally it has an API much more well-suited
for this purpose.
orderedmap.[ch] was implemented from scratch to address this issue.
behind the scenes it uses an sblist to store string values, and a htab
to store keys and the indices into the sblist.
this allows us to iterate linearly over the sblist and then find the
corresponding key in the hash table, so the headers can be reproduced
in the order they were received.
closes#73
rofl0r