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Date: Tue, 8 Dec 2020 22:46:31 +0000
From: Eric Wong <e@80x24.org>
To: Blake Williams <blake@blakewilliams.me>
Cc: unicorn-public@yhbt.net
Subject: Re: [PATCH] Add rack.after_reply functionality
Message-ID: <20201208224631.GA13148@dcvr>
References: <9873E53C-04D3-4759-9678-CA17DBAEF7B7@blakewilliams.me>
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Blake Williams <blake@blakewilliams.me> wrote:
> This adds `rack.after_reply` functionality which allows rack middleware
> to pass lambdas that will be executed after the client connection has
> been closed.
> 
> This was driven by a need to perform actions in a request that shouldn't
> block the request from completing but also don't make sense as
> background jobs.

Thanks for the patch and explanation.

In the past, I've used response_body.close in middleware for
similar things, and nowadays Rack::BodyProxy exists in rack, too.

So I'm a little skeptical if this is actually needed, but it's
probably too late to do anything about:

> There is prior art of this being supported found in a few gems, as well
> as this functionality existing in other rack based servers.

Citation(s) needed.  Also, are there any proposal(s) to get this
into the Rack specification?

While I can't participate in discussions which requires a
GUI (JS/CAPTCHA) or accepting certain Terms-of-service,
the rack-devel@googlegroups.com mailing list still exists
and I can chime in there.

rack.early_hints could probably be in the Rack spec, too...

More below...

> diff --git a/lib/unicorn/http_server.rb b/lib/unicorn/http_server.rb
> index 05dad99..9889f55 100644
> --- a/lib/unicorn/http_server.rb
> +++ b/lib/unicorn/http_server.rb
> @@ -629,6 +629,8 @@ def process_client(client)
>        end
>      end
>  
> +    env["rack.after_reply"] = []
> +
>      status, headers, body = @app.call(env)
>  
>      begin
> @@ -651,6 +653,8 @@ def process_client(client)
>      end
>    rescue => e
>      handle_error(client, e)
> +  ensure
> +    env["rack.after_reply"].each { |after_reply| after_reply.call }
>    end
>  
>    def nuke_listeners!(readers)

I'll have to squash the following in, since an exception can be
raised if a client truncates the request:

diff --git a/lib/unicorn/http_server.rb b/lib/unicorn/http_server.rb
index 9889f55c..c0f14ba5 100644
--- a/lib/unicorn/http_server.rb
+++ b/lib/unicorn/http_server.rb
@@ -654,7 +654,7 @@ def process_client(client)
   rescue => e
     handle_error(client, e)
   ensure
-    env["rack.after_reply"].each { |after_reply| after_reply.call }
+    env["rack.after_reply"].each(&:call) if env
   end
 
   def nuke_listeners!(readers)

Everything else seems OK.  Thanks.