[PATCH] Detecting duplicate addresses in listen among different modules

[Sergey Kandaurov]

# HG changeset patch
# User Sergey Kandaurov <pluknet at nginx.com>
# Date 1712349104 -14400
#      Sat Apr 06 00:31:44 2024 +0400
# Node ID 5fe21225ab3105aeea5e381a5d39ec1d3cfc04e6
# Parent  47df39ea9e21c4359e0ca96dcc452f2bc8a82c44
Detecting duplicate addresses in listen among different modules.

This is used to gracefully reject the following configurations during
syntax checking with a "duplicate ... address and port pair" error:

    http {
        server {
            listen  127.0.0.1:8080;
            ...
        }
    }

    stream {
        server {
            listen  127.0.0.1:8080;
            ...
        }
    }

Also for wildcard addresses:

    stream {
        server {
            listen  8080;
            ...
        }
    }

    mail {
        server {
            listen  8080;
            ...
        }
    }

Notably, this won't catch mixed wildcard and non-wildcard addresses as
follows, where http server block with a specific address never accepts
new connections.  The reason is that http will end up listening on the
wildcard address, and stream is configured to listen on the specific
address, which is technically a valid case.

    http {
        server {
            listen  127.0.0.1:8080;
            ...
        }

        server {
            listen  8080;
            ...
        }
    }

    stream {
        server {
            listen  127.0.0.1:8080;
            ...
        }
    }

diff --git a/src/core/ngx_connection.c b/src/core/ngx_connection.c
--- a/src/core/ngx_connection.c
+++ b/src/core/ngx_connection.c
@@ -21,10 +21,27 @@ ngx_create_listening(ngx_conf_t *cf, str
     socklen_t socklen)
 {
     size_t            len;
+    ngx_uint_t        i;
     ngx_listening_t  *ls;
     struct sockaddr  *sa;
     u_char            text[NGX_SOCKADDR_STRLEN];
 
+    ls = cf->cycle->listening.elts;
+    for (i = 0; i < cf->cycle->listening.nelts; i++) {
+
+        if (ngx_cmp_sockaddr(ls[i].sockaddr, ls[i].socklen,
+                             sockaddr, socklen, 1)
+            == NGX_DECLINED)
+        {
+            continue;
+        }
+
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                           "duplicate \"%V\" address and port pair",
+                           &ls[i].addr_text);
+        return NULL;
+    }
+
     ls = ngx_array_push(&cf->cycle->listening);
     if (ls == NULL) {
         return NULL;