[squid-dev] [RFC] Refactor HttpHeader

[Kinkie]

Hi all,
   I'm starting to work on refactoring HttpHeader to use LookupTable, and
boy that code is a mess..

Since it's going to take significant effort, I'd like to get feedback on
the changes I'd like to implement, so not to end in long discussions later.

Current data structures:
HeadersAttrs: static declaration of header name, header ID, header type
(string/int/etc). Must be sorted by numeric value of ID
Headers: built at initialization time from HeadersAttrs, it's an array of
(name, id, type, stats) structs
ListHeadersArr, GeneralHeadersArr, EntityHeadersArr, RequestHeadersArr,
ReplyHeadersArr, etc: lists of headers ID (possibly overlapping) which are
used to generate..
ListHeadersMask, GeneralHeadersArr, EntityHeadersArr etc: bitmaps used
(only) by HttpHeaderStats to assemble different stats sets

I would like to turn these into:
headerTable: LookupTable<>::Record mapping header name to header ID, used
to generate ...
headerLookupTable: a fast lookup table of header names to ids
headerStatsTable: a std::vector<HttpHeaderFieldStat> indexed by header ID
to collect the statistics currently in Headers[id].stats.
headerDescription: a std::vector keyed by header ID containing header type
(currently in Headers[id].type), possibly header name (if useful), a
bitfield noting if HTTP_HDR{LIST,GENERAL,REQUEST,REPLY,...}.

There are some possible optimizations, but at a minimum this should help
keep information more organized while introducing no performance
regressions.
What do you think?

Thanks
-- 
    Kinkie
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