From f62d460d5bb4b89c7932b4193023bee7f522249a Mon Sep 17 00:00:00 2001 From: Maxim Dounin Date: Thu, 5 Jul 2018 22:21:14 +0300 Subject: [PATCH] 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(). --- src/core/ngx_resolver.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/src/core/ngx_resolver.c b/src/core/ngx_resolver.c index d96970434..5d7fe312d 100644 --- a/src/core/ngx_resolver.c +++ b/src/core/ngx_resolver.c @@ -847,7 +847,15 @@ ngx_resolve_name_locked(ngx_resolver_t *r, 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) { @@ -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) {