[nginx] Core: disabled SO_REUSEADDR on UDP sockets while testing config.

[Maxim Dounin]

details:   https://hg.nginx.org/nginx/rev/46815874bcc6
branches:  
changeset: 7868:46815874bcc6
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Mon May 31 16:36:51 2021 +0300
description:
Core: disabled SO_REUSEADDR on UDP sockets while testing config.

On Linux, SO_REUSEADDR allows completely duplicate UDP sockets, so using
SO_REUSEADDR when testing configuration results in packets being dropped
if there is an existing traffic on the sockets being tested (ticket #2187).
While dropped packets are expected with UDP, it is better to avoid this
when possible.

With this change, SO_REUSEADDR is no longer set on datagram sockets when
testing configuration.

diffstat:

 src/core/ngx_connection.c |  25 ++++++++++++++-----------
 1 files changed, 14 insertions(+), 11 deletions(-)

diffs (39 lines):

diff -r c860f0b7010c -r 46815874bcc6 src/core/ngx_connection.c
--- a/src/core/ngx_connection.c	Mon May 31 16:36:37 2021 +0300
+++ b/src/core/ngx_connection.c	Mon May 31 16:36:51 2021 +0300
@@ -495,21 +495,24 @@ ngx_open_listening_sockets(ngx_cycle_t *
                 return NGX_ERROR;
             }
 
-            if (setsockopt(s, SOL_SOCKET, SO_REUSEADDR,
-                           (const void *) &reuseaddr, sizeof(int))
-                == -1)
-            {
-                ngx_log_error(NGX_LOG_EMERG, log, ngx_socket_errno,
-                              "setsockopt(SO_REUSEADDR) %V failed",
-                              &ls[i].addr_text);
+            if (ls[i].type != SOCK_DGRAM || !ngx_test_config) {
 
-                if (ngx_close_socket(s) == -1) {
+                if (setsockopt(s, SOL_SOCKET, SO_REUSEADDR,
+                               (const void *) &reuseaddr, sizeof(int))
+                    == -1)
+                {
                     ngx_log_error(NGX_LOG_EMERG, log, ngx_socket_errno,
-                                  ngx_close_socket_n " %V failed",
+                                  "setsockopt(SO_REUSEADDR) %V failed",
                                   &ls[i].addr_text);
-                }
 
-                return NGX_ERROR;
+                    if (ngx_close_socket(s) == -1) {
+                        ngx_log_error(NGX_LOG_EMERG, log, ngx_socket_errno,
+                                      ngx_close_socket_n " %V failed",
+                                      &ls[i].addr_text);
+                    }
+
+                    return NGX_ERROR;
+                }
             }
 
 #if (NGX_HAVE_REUSEPORT)