[PATCH 2 of 2] The "sort=" parameter of the "resolver" directive

[Sergey Kandaurov]

# HG changeset patch
# User Ruslan Ermilov <ru at nginx.com>
# Date 1645589387 -10800
#      Wed Feb 23 07:09:47 2022 +0300
# Node ID e80adbf788f6796c6bdf415938abb19b7aa43e3e
# Parent  04e314eb6b4d20a48c5d7bab0609e1b03b51b406
The "sort=" parameter of the "resolver" directive.

diff -r 04e314eb6b4d -r e80adbf788f6 src/core/ngx_resolver.c
--- a/src/core/ngx_resolver.c	Wed Feb 23 07:08:37 2022 +0300
+++ b/src/core/ngx_resolver.c	Wed Feb 23 07:09:47 2022 +0300
@@ -227,6 +227,7 @@ ngx_resolver_create(ngx_conf_t *cf, ngx_
         }
 
 #if (NGX_HAVE_INET6)
+
         if (ngx_strncmp(names[i].data, "ipv4=", 5) == 0) {
 
             if (ngx_strcmp(&names[i].data[5], "on") == 0) {
@@ -260,6 +261,24 @@ ngx_resolver_create(ngx_conf_t *cf, ngx_
 
             continue;
         }
+
+        if (ngx_strncmp(names[i].data, "prefer=", 7) == 0) {
+
+            if (ngx_strcmp(&names[i].data[7], "ipv4") == 0) {
+                r->prefer = NGX_RESOLVE_PREFER_A;
+
+            } else if (ngx_strcmp(&names[i].data[7], "ipv6") == 0) {
+                r->prefer = NGX_RESOLVE_PREFER_AAAA;
+
+            } else {
+                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                                   "invalid parameter: %V", &names[i]);
+                return NULL;
+            }
+
+            continue;
+        }
+
 #endif
 
         ngx_memzero(&u, sizeof(ngx_url_t));
@@ -4250,7 +4269,27 @@ ngx_resolver_export(ngx_resolver_t *r, n
     }
 
     i = 0;
-    d = rotate ? ngx_random() % n : 0;
+
+    switch (r->prefer) {
+
+#if (NGX_HAVE_INET6)
+    case NGX_RESOLVE_PREFER_A:
+        d = 0;
+        break;
+
+    case NGX_RESOLVE_PREFER_AAAA:
+        d = rn->naddrs6;
+
+        if (d == n) {
+            d = 0;
+        }
+
+        break;
+#endif
+
+    default:
+        d = rotate ? ngx_random() % n : 0;
+    }
 
     if (rn->naddrs) {
         j = rotate ? ngx_random() % rn->naddrs : 0;
diff -r 04e314eb6b4d -r e80adbf788f6 src/core/ngx_resolver.h
--- a/src/core/ngx_resolver.h	Wed Feb 23 07:08:37 2022 +0300
+++ b/src/core/ngx_resolver.h	Wed Feb 23 07:09:47 2022 +0300
@@ -36,6 +36,9 @@
 
 #define NGX_RESOLVER_MAX_RECURSION    50
 
+#define NGX_RESOLVE_PREFER_A          1
+#define NGX_RESOLVE_PREFER_AAAA       2
+
 
 typedef struct ngx_resolver_s  ngx_resolver_t;
 
@@ -175,6 +178,8 @@ struct ngx_resolver_s {
     ngx_queue_t               srv_expire_queue;
     ngx_queue_t               addr_expire_queue;
 
+    unsigned                  prefer:2;
+
     unsigned                  ipv4:1;
 
 #if (NGX_HAVE_INET6)