commit 69569235c56c682e77dfe878c464217e3b8e4e50
author Maxim Dounin <mdounin@mdounin.ru> Thu Jul 05 22:21:14 2018 +0300
committer Maxim Dounin <mdounin@mdounin.ru> Thu Jul 05 22:21:14 2018 +0300
tree 44e1b2af361346dfe59de4b1e771b0f5804c7d1d
parent 8e488fa2666e72b2aa350ead7e178c893bddc2d4

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().