relay: On new consensus, reconfigure DNS nameservers

This applies only for relays. Previous commit adds two new consensus
parameters that dictate how libevent is configured with DNS resolution.
And so, with a new consensus, we now look at those values in case they
ever change.

Without this, Exit relay would have to HUP or restart to apply any new
Exit DNS consensus parameters.

Related to #40312

Signed-off-by: David Goulet <dgoulet@torproject.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/feature/relay/dns.c b/src/feature/relay/dns.c
index 9e504a7cfa..8467b9c0a4 100644
--- a/src/feature/relay/dns.c
+++ b/src/feature/relay/dns.c
@@ -213,6 +213,19 @@ evdns_log_cb(int warn, const char *msg)
   tor_log(severity, LD_EXIT, "eventdns: %s", msg);
 }
 
+/** New consensus just appeared, take appropriate actions if need be. */
+void
+dns_new_consensus_params(const networkstatus_t *ns)
+{
+  (void) ns;
+
+  /* Consensus has parameters for the Exit relay DNS side and so we only reset
+   * the DNS nameservers if we are in server mode. */
+  if (server_mode(get_options())) {
+    dns_reset();
+  }
+}
+
 /** Initialize the DNS subsystem; called by the OR process. */
 int
 dns_init(void)