It's got the whole checklist: nginx idiosyncratic module system, inline parsing, custom utf conversion, buffer preallocation and adjustments, linked lists, comments about side effects of custom allocator, and probably other things.
It's not easy to deal with source like that and any serious improvement to that area would effectively be a rewrite anyway.
Since anything doing work in nginx is a module anyway, it wouldn't even have to be a full rewrite in one go.
Anecdotally in the cache module, it's unclear what invariants are supposed to be maintained for a big ol struct full of information about this cache lookup, which functions expect to only be called while holding a lock, etc. The module design and the issues you mentioned also causes suboptimal performance :(
Have a look at:
https://github.com/nginx/nginx/blob/master/src/http/modules/...
It's got the whole checklist: nginx idiosyncratic module system, inline parsing, custom utf conversion, buffer preallocation and adjustments, linked lists, comments about side effects of custom allocator, and probably other things.
It's not easy to deal with source like that and any serious improvement to that area would effectively be a rewrite anyway.
Since anything doing work in nginx is a module anyway, it wouldn't even have to be a full rewrite in one go.