[PATCH 1 of 2] HTTP: add support for trailers in HTTP responses

[shuxinyang]

> It's "trailer support" for the web serving part of NGINX, just not proxying.
>
>>       - the "get" in "ngx_http_chunked_get_trailers" is sort of misleading.
>> The "get" here actually
>>         means "generate". I thought you are looking for a existing buffer.
> That function name got changed a few times, since I cannot find one
> that I would be 100% happy with... Any suggestions?
I hope you don't call me "make fuss about nothing":-). Being an 
impatient code reader,
I usually take a glimpse the code by reading comment and/or function, 
and imagine
what it tries to do, and stitch them together into a big picture.

the verb "get" did confuse me yesterday and this morning when I took a 
quick look.
I would say "create" or "generate" (or something else) would be better.


Anyway, naming is not big deal, maybe I (and other impatient code 
reader) need change:-)


>
>>    Now go back to the long list of trailer support,  I believe it needs to
>> cover at least:
>>      1) generate trailer headers and sent to downstream/visitor as you just
>> did
>>      2) reverse proxy propagate trailer headers from upstream, which needs
>>          2.0 parse the incoming trailer header, both considering the body is
>> buffered and not buffered,
>>          2.1. make the incoming trailer accessible via variable after content
>> phase,
>>          2.2. if response body is is not buffered, combine incoming trailer
>> header with the generated headers.
>>          2.3. convert incoming trailer to regular header if response body is
>> buffered
>>
>>     3|4|..|n) other features.
>>
>>     I think 2.x is much harder than 1). I only implement 1) and 2.0) and
>> 2.1). While implement 2.1), I left some
>> room for 2.2 and 2.3 for the future. Now that you have plan for 2.x as your
>> email suggests, wouldn't it
>> be nice to submit these code first, and then go ahead with the code of 1). I
>> believe to support 2.2 or 2.3,
>> your existing code in chunk module needs lots of change.
> I don't see how anything you listed in 2.x would require modifications
> to the code I submitted... Actually, everything you listed should be
> handled in upstream and/or proxy modules, not chunking module, and it
> could easily use the API (r->headers_out.trailers) I want to add in
> this commit.

How do you manage to tackle this scenario without changing your existing 
code:

     backend server responses with trailer "lol = 123", and you define 
the same trailer,
"lol = $haha" in *.conf. You have two options as to how to combine them: 
either override the
one from origin, and override the one from your *.conf. It seems to me 
that the
chunk-module is again a best place for such change.

Best Regards
Shuxin


> Best regards,
> Piotr Sikora
>
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