Lingering close for connections with pipelined requests. This is expected to help with clients using pipelining with some constant depth, such as apt[1][2]. When downloading many resources, apt uses pipelining with some constant depth, a number of requests in flight. This essentially means that after receiving a response it sends an additional request to the server, and this can result in requests arriving to the server at any time. Further, additional requests are sent one-by-one, and can be easily seen as such (neither as pipelined, nor followed by pipelined requests). The only safe approach to close such connections (for example, when keepalive_requests is reached) is with lingering. To do so, now nginx monitors if pipelining was used on the connection, and if it was, closes the connection with lingering. [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=973861#10 [2] https://mailman.nginx.org/pipermail/nginx-devel/2023-January/ZA2SP5SJU55LHEBCJMFDB2AZVELRLTHI.html

--- a/src/core/ngx_connection.h
+++ b/src/core/ngx_connection.h
@@ -172,6 +172,7 @@ struct ngx_connection_s {
     unsigned            timedout:1;
     unsigned            error:1;
     unsigned            destroyed:1;
+    unsigned            pipeline:1;
 
     unsigned            idle:1;
     unsigned            reusable:1;