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diff src/core/ngx_resolver.c @ 7312:54683f650cbd

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Resolver: retry sending queries on errors (ticket #1511). Errors when sending UDP datagrams can happen, e.g., when local IP address changes (see fa0e093b64d7), or an unavailable DNS server on the LAN can cause send() to fail with EHOSTDOWN on BSD systems. If this happens during initial query, retry sending immediately, to a different DNS server when possible. If this is not enough, allow normal resend to happen by ignoring the return code of the second ngx_resolver_send_query() call, much like we do in ngx_resolver_resend().
author Maxim Dounin <mdounin@mdounin.ru>
date Thu, 05 Jul 2018 22:21:14 +0300
parents faf14dc9ab4d
children cbc5dee8d5d2
line wrap: on
line diff
--- a/src/core/ngx_resolver.c
+++ b/src/core/ngx_resolver.c
@@ -847,7 +847,15 @@ ngx_resolve_name_locked(ngx_resolver_t *
     rn->nsrvs = 0;
 
     if (ngx_resolver_send_query(r, rn) != NGX_OK) {
-        goto failed;
+
+        /* immediately retry once on failure */
+
+        rn->last_connection++;
+        if (rn->last_connection == r->connections.nelts) {
+            rn->last_connection = 0;
+        }
+
+        (void) ngx_resolver_send_query(r, rn);
     }
 
     if (ngx_resolver_set_timeout(r, ctx) != NGX_OK) {
@@ -1051,7 +1059,15 @@ ngx_resolve_addr(ngx_resolver_ctx_t *ctx
     rn->nsrvs = 0;
 
     if (ngx_resolver_send_query(r, rn) != NGX_OK) {
-        goto failed;
+
+        /* immediately retry once on failure */
+
+        rn->last_connection++;
+        if (rn->last_connection == r->connections.nelts) {
+            rn->last_connection = 0;
+        }
+
+        (void) ngx_resolver_send_query(r, rn);
     }
 
     if (ngx_resolver_set_timeout(r, ctx) != NGX_OK) {