Here are the data structures with brief descriptions:

http_authentication_info_s	Structure for Authentication-Info header
http_content_range_s	Content-Range
http_cookie_s	Cookie
http_date_s	Date, Expires, If-Modified-Since, If-Unmodified-Since, Last-Modified
http_header_u	Union representing any HTTP header
http_host_s	Host
http_if_range_s	If-Range
http_location_s	Location, Referer
http_max_forwards_s	Max-Forwards
http_range_s	Range
http_request_s	HTTP request line
http_retry_after_s	Retry-After
http_s	HTTP message object
http_set_cookie_s	Set-Cookie
http_status_s	HTTP status line
http_te_s	TE
http_via_s	Via