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

[Ruslan Ermilov]

 src/core/ngx_resolver.c |  38 +++++++++++++++++++++++++++++++++++++-
 src/core/ngx_resolver.h |   5 +++++
 2 files changed, 42 insertions(+), 1 deletions(-)


# HG changeset patch
# User Ruslan Ermilov <ru at nginx.com>
# Date 1645589387 -10800
#      Wed Feb 23 07:09:47 2022 +0300
# Node ID 8db4bbd67840e8bebb23f9c6d10c0f633552e616
# Parent  1c19779448db2309d607c74e2628ff98f84569ff
The "sort=" parameter of the "resolver" directive.

diff --git a/src/core/ngx_resolver.c b/src/core/ngx_resolver.c
--- a/src/core/ngx_resolver.c
+++ b/src/core/ngx_resolver.c
@@ -266,6 +266,27 @@ ngx_resolver_create(ngx_conf_t *cf, ngx_
         }
 #endif
 
+        if (ngx_strncmp(names[i].data, "sort=", 5) == 0) {
+
+            if (ngx_strcasecmp(&names[i].data[5], (u_char *) "ipv4") == 0) {
+                r->sort = NGX_RESOLVE_A_FIRST;
+
+#if (NGX_HAVE_INET6)
+            } else if (ngx_strcasecmp(&names[i].data[5], (u_char *) "ipv6")
+                       == 0)
+            {
+                r->sort = NGX_RESOLVE_AAAA_FIRST;
+#endif
+
+            } else {
+                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                                   "invalid parameter: %V", &names[i]);
+                return NULL;
+            }
+
+            continue;
+        }
+
         ngx_memzero(&u, sizeof(ngx_url_t));
 
         u.url = names[i];
@@ -4253,7 +4274,22 @@ ngx_resolver_export(ngx_resolver_t *r, n
     }
 
     i = 0;
-    d = rotate ? ngx_random() % n : 0;
+
+    if (r->sort == NGX_RESOLVE_A_FIRST) {
+        d = 0;
+
+#if (NGX_HAVE_INET6)
+    } else if (r->sort == NGX_RESOLVE_AAAA_FIRST) {
+        d = rn->naddrs6;
+
+        if (d == n) {
+            d = 0;
+        }
+#endif
+
+    } else {
+        d = rotate ? ngx_random() % n : 0;
+    }
 
     if (rn->naddrs) {
         j = rotate ? ngx_random() % rn->naddrs : 0;
diff --git a/src/core/ngx_resolver.h b/src/core/ngx_resolver.h
--- a/src/core/ngx_resolver.h
+++ b/src/core/ngx_resolver.h
@@ -36,6 +36,9 @@
 
 #define NGX_RESOLVER_MAX_RECURSION    50
 
+#define NGX_RESOLVE_A_FIRST           1
+#define NGX_RESOLVE_AAAA_FIRST        2
+
 
 typedef struct ngx_resolver_s  ngx_resolver_t;
 
@@ -185,6 +188,8 @@ struct ngx_resolver_s {
     ngx_queue_t               addr6_expire_queue;
 #endif
 
+    ngx_uint_t                sort;
+
     time_t                    resend_timeout;
     time_t                    tcp_timeout;
     time_t                    expire;