[nginx] Avoid sending "Connection: keep-alive" when shutting down.

[Maxim Dounin]

details:   https://hg.nginx.org/nginx/rev/96ae8e57b3dd
branches:  
changeset: 7993:96ae8e57b3dd
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Tue Jan 11 02:23:49 2022 +0300
description:
Avoid sending "Connection: keep-alive" when shutting down.

When a worker process is shutting down, keepalive is not used: this is checked
before the ngx_http_set_keepalive() call in ngx_http_finalize_connection().
Yet the "Connection: keep-alive" header was still sent, even if we know that
the worker process is shutting down, potentially resulting in additional
requests being sent to the connection which is going to be closed anyway.
While clients are expected to be able to handle asynchronous close events
(see ticket #1022), it is certainly possible to send the "Connection: close"
header instead, informing the client that the connection is going to be closed
and potentially saving some unneeded work.

With this change, we additionally check for worker process shutdown just
before sending response headers, and disable keepalive accordingly.

diffstat:

 src/http/ngx_http_header_filter_module.c |  4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diffs (14 lines):

diff -r e2d07e4ec636 -r 96ae8e57b3dd src/http/ngx_http_header_filter_module.c
--- a/src/http/ngx_http_header_filter_module.c	Thu Dec 30 01:08:46 2021 +0300
+++ b/src/http/ngx_http_header_filter_module.c	Tue Jan 11 02:23:49 2022 +0300
@@ -197,6 +197,10 @@ ngx_http_header_filter(ngx_http_request_
         }
     }
 
+    if (r->keepalive && (ngx_terminate || ngx_exiting)) {
+        r->keepalive = 0;
+    }
+
     len = sizeof("HTTP/1.x ") - 1 + sizeof(CRLF) - 1
           /* the end of the header */
           + sizeof(CRLF) - 1;