From 22eac967502bc465cb63bfcf337e23e552ec0465 Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Tue, 20 Dec 2022 06:42:39 +1030
Subject: [PATCH] connectd: don't ask DNS seeds for addresses on every
 reconnect.

We were stressing the servers if node cannot be found.  Only do lookup
on manual connect commands.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Protocol: lightningd: Only use DNS server address lookup on manual `connect` commands, not normal reconnection attempts.
---
 connectd/connectd.c          | 11 +++++++----
 connectd/connectd_wire.csv   |  1 +
 lightningd/connect_control.c | 18 +++++++++++++-----
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/connectd/connectd.c b/connectd/connectd.c
index debe87693..f66abd13f 100644
--- a/connectd/connectd.c
+++ b/connectd/connectd.c
@@ -1716,7 +1716,8 @@ static void add_gossip_addrs(struct wireaddr_internal **addrs,
 static void try_connect_peer(struct daemon *daemon,
 			     const struct node_id *id,
 			     struct wireaddr *gossip_addrs,
-			     struct wireaddr_internal *addrhint STEALS)
+			     struct wireaddr_internal *addrhint STEALS,
+			     bool dns_fallback)
 {
 	struct wireaddr_internal *addrs;
 	bool use_proxy = daemon->always_use_proxy;
@@ -1762,7 +1763,7 @@ static void try_connect_peer(struct daemon *daemon,
 				                         chainparams_get_ln_port(chainparams));
 				tal_arr_expand(&addrs, unresolved);
 			}
-		} else if (daemon->use_dns) {
+		} else if (daemon->use_dns && dns_fallback) {
 			add_seed_addrs(&addrs, id,
 			               daemon->broken_resolver_response);
 		}
@@ -1804,12 +1805,14 @@ static void connect_to_peer(struct daemon *daemon, const u8 *msg)
 	struct node_id id;
 	struct wireaddr_internal *addrhint;
 	struct wireaddr *addrs;
+	bool dns_fallback;
 
 	if (!fromwire_connectd_connect_to_peer(tmpctx, msg,
-					       &id, &addrs, &addrhint))
+					       &id, &addrs, &addrhint,
+					       &dns_fallback))
 		master_badmsg(WIRE_CONNECTD_CONNECT_TO_PEER, msg);
 
-	try_connect_peer(daemon, &id, addrs, addrhint);
+	try_connect_peer(daemon, &id, addrs, addrhint, dns_fallback);
 }
 
 /* lightningd tells us a peer should be disconnected. */
diff --git a/connectd/connectd_wire.csv b/connectd/connectd_wire.csv
index 16c6953d8..d8b77d0a4 100644
--- a/connectd/connectd_wire.csv
+++ b/connectd/connectd_wire.csv
@@ -50,6 +50,7 @@ msgdata,connectd_connect_to_peer,id,node_id,
 msgdata,connectd_connect_to_peer,len,u32,
 msgdata,connectd_connect_to_peer,addrs,wireaddr,len
 msgdata,connectd_connect_to_peer,addrhint,?wireaddr_internal,
+msgdata,connectd_connect_to_peer,dns_fallback,bool,
 
 # Connectd->master: connect failed.
 msgtype,connectd_connect_failed,2020
diff --git a/lightningd/connect_control.c b/lightningd/connect_control.c
index 61a6bcca8..b85e3bd95 100644
--- a/lightningd/connect_control.c
+++ b/lightningd/connect_control.c
@@ -76,7 +76,8 @@ static void try_connect(const tal_t *ctx,
 			struct lightningd *ld,
 			const struct node_id *id,
 			u32 seconds_delay,
-			const struct wireaddr_internal *addrhint);
+			const struct wireaddr_internal *addrhint,
+			bool dns_fallback);
 
 struct id_and_addr {
 	struct node_id id;
@@ -226,7 +227,7 @@ static struct command_result *json_connect(struct command *cmd,
 					   &peer->addr);
 	}
 
- 	try_connect(cmd, cmd->ld, &id_addr.id, 0, addr);
+	try_connect(cmd, cmd->ld, &id_addr.id, 0, addr, true);
 
 	/* Leave this here for peer_connected, connect_failed or peer_disconnect_done. */
 	new_connect(cmd->ld, &id_addr.id, cmd);
@@ -248,6 +249,7 @@ struct delayed_reconnect {
 	struct lightningd *ld;
 	struct node_id id;
 	struct wireaddr_internal *addrhint;
+	bool dns_fallback;
 };
 
 static void gossipd_got_addrs(struct subd *subd,
@@ -265,7 +267,8 @@ static void gossipd_got_addrs(struct subd *subd,
 	connectmsg = towire_connectd_connect_to_peer(NULL,
 						     &d->id,
 						     addrs,
-						     d->addrhint);
+						     d->addrhint,
+						     d->dns_fallback);
 	subd_send_msg(d->ld->connectd, take(connectmsg));
 	tal_free(d);
 }
@@ -282,7 +285,8 @@ static void try_connect(const tal_t *ctx,
 			struct lightningd *ld,
 			const struct node_id *id,
 			u32 seconds_delay,
-			const struct wireaddr_internal *addrhint)
+			const struct wireaddr_internal *addrhint,
+			bool dns_fallback)
 {
 	struct delayed_reconnect *d;
 	struct peer *peer;
@@ -291,6 +295,7 @@ static void try_connect(const tal_t *ctx,
 	d->ld = ld;
 	d->id = *id;
 	d->addrhint = tal_dup_or_null(d, struct wireaddr_internal, addrhint);
+	d->dns_fallback = dns_fallback;
 
 	if (!seconds_delay) {
 		do_connect(d);
@@ -347,11 +352,14 @@ void try_reconnect(const tal_t *ctx,
 	} else
 		peer->reconnect_delay = INITIAL_WAIT_SECONDS;
 
+	/* We only do DNS fallback lookups for manual connections, to
+	 * avoid stressing DNS servers for private nodes (sorry!) */
 	try_connect(ctx,
 		    peer->ld,
 		    &peer->id,
 		    peer->reconnect_delay,
-		    addrhint);
+		    addrhint,
+		    false);
 }
 
 /* We were trying to connect, but they disconnected. */