From 538141eb7e590bc94c043b43b5e5483b13bc9c5e Mon Sep 17 00:00:00 2001
From: Azat Khuzhin <azat@libevent.org>
Date: Sat, 15 Jun 2019 23:18:05 +0300
Subject: [PATCH] evdns: add new options -- so-rcvbuf/so-sndbuf

This will allow to customize SO_RCVBUF/SO_SNDBUF for nameservers in this
evdns_base, you may want to adjust them if the kernel starts dropping
udp packages.
---
 evdns.c              | 30 ++++++++++++++++++++++++++++++
 include/event2/dns.h |  3 ++-
 test/regress_dns.c   | 23 +++++++++++++++++++++++
 3 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/evdns.c b/evdns.c
index 1b815366..0a0e1ba6 100644
--- a/evdns.c
+++ b/evdns.c
@@ -346,6 +346,9 @@ struct evdns_base {
 
 	struct timeval global_getaddrinfo_allow_skew;
 
+	int so_rcvbuf;
+	int so_sndbuf;
+
 	int getaddrinfo_ipv4_timeouts;
 	int getaddrinfo_ipv6_timeouts;
 	int getaddrinfo_ipv4_answered;
@@ -2538,6 +2541,23 @@ evdns_nameserver_add_impl_(struct evdns_base *base, const struct sockaddr *addre
 		}
 	}
 
+	if (base->so_rcvbuf) {
+		if (setsockopt(ns->socket, SOL_SOCKET, SO_RCVBUF,
+		    (void *)&base->so_rcvbuf, sizeof(base->so_rcvbuf))) {
+			log(EVDNS_LOG_WARN, "Couldn't set SO_RCVBUF to %i", base->so_rcvbuf);
+			err = -SO_RCVBUF;
+			goto out2;
+		}
+	}
+	if (base->so_sndbuf) {
+		if (setsockopt(ns->socket, SOL_SOCKET, SO_SNDBUF,
+		    (void *)&base->so_sndbuf, sizeof(base->so_sndbuf))) {
+			log(EVDNS_LOG_WARN, "Couldn't set SO_SNDBUF to %i", base->so_sndbuf);
+			err = -SO_SNDBUF;
+			goto out2;
+		}
+	}
+
 	memcpy(&ns->address, address, addrlen);
 	ns->addrlen = addrlen;
 	ns->state = 1;
@@ -3531,6 +3551,16 @@ evdns_base_set_option_impl(struct evdns_base *base,
 		    val);
 		memcpy(&base->global_nameserver_probe_initial_timeout, &tv,
 		    sizeof(tv));
+	} else if (str_matches_option(option, "so-rcvbuf:")) {
+		int buf = strtoint(val);
+		if (!(flags & DNS_OPTION_MISC)) return 0;
+		log(EVDNS_LOG_DEBUG, "Setting SO_RCVBUF to %s", val);
+		base->so_rcvbuf = buf;
+	} else if (str_matches_option(option, "so-sndbuf:")) {
+		int buf = strtoint(val);
+		if (!(flags & DNS_OPTION_MISC)) return 0;
+		log(EVDNS_LOG_DEBUG, "Setting SO_SNDBUF to %s", val);
+		base->so_sndbuf = buf;
 	}
 	return 0;
 }
diff --git a/include/event2/dns.h b/include/event2/dns.h
index 3c548a1e..13ce027e 100644
--- a/include/event2/dns.h
+++ b/include/event2/dns.h
@@ -455,7 +455,8 @@ void evdns_cancel_request(struct evdns_base *base, struct evdns_request *req);
   The currently available configuration options are:
 
     ndots, timeout, max-timeouts, max-inflight, attempts, randomize-case,
-    bind-to, initial-probe-timeout, getaddrinfo-allow-skew.
+    bind-to, initial-probe-timeout, getaddrinfo-allow-skew,
+    so-rcvbuf, so-sndbuf.
 
   In versions before Libevent 2.0.3-alpha, the option name needed to end with
   a colon.
diff --git a/test/regress_dns.c b/test/regress_dns.c
index b080f341..c0c31729 100644
--- a/test/regress_dns.c
+++ b/test/regress_dns.c
@@ -2369,6 +2369,26 @@ end:
 }
 #endif
 
+static void
+test_set_so_rcvbuf_so_sndbuf(void *arg)
+{
+	struct basic_test_data *data = arg;
+	struct evdns_base *dns_base;
+
+	dns_base = evdns_base_new(data->base, 0);
+	tt_assert(dns_base);
+
+	tt_assert(!evdns_base_set_option(dns_base, "so-rcvbuf", "10240"));
+	tt_assert(!evdns_base_set_option(dns_base, "so-sndbuf", "10240"));
+
+	/* actually check SO_RCVBUF/SO_SNDBUF not fails */
+	tt_assert(!evdns_base_nameserver_ip_add(dns_base, "127.0.0.1"));
+
+end:
+	if (dns_base)
+		evdns_base_free(dns_base, 0);
+}
+
 #define DNS_LEGACY(name, flags)					       \
 	{ #name, run_legacy_test_fn, flags|TT_LEGACY, &legacy_setup,   \
 		    dns_##name }
@@ -2440,6 +2460,9 @@ struct testcase_t dns_testcases[] = {
 	  TT_FORK|TT_OFF_BY_DEFAULT, NULL, NULL },
 #endif
 
+	{ "set_SO_RCVBUF_SO_SNDBUF", test_set_so_rcvbuf_so_sndbuf,
+	  TT_FORK|TT_NEED_BASE, &basic_setup, NULL },
+
 	END_OF_TESTCASES
 };
 
-- 
2.40.0