lightningd: close connection when HTLC addition times out.

I noticed this while debugging an issue with ACINQ, that we got upset,
but didn't trigger a reconnect cycle.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Fixed: Protocol: We now close connection with a peer if adding an HTLC times out (which may be a TCP connectivity issue).

lightningd/peer_htlcs.c

@@ -11,6 +11,7 @@
 #include <common/onionreply.h>
 #include <common/timeout.h>
 #include <common/type_to_string.h>
+#include <connectd/connectd_wiregen.h>
 #include <db/exec.h>
 #include <gossipd/gossipd_wiregen.h>
 #include <lightningd/chaintopology.h>
@@ -591,6 +592,14 @@ static void htlc_offer_timeout(struct htlc_out *out)
 	tal_free(channel->owner);
 	channel_set_billboard(channel, false,
 			      "Adding HTLC timed out: killed connection");
+
+	/* Force a disconnect in case the issue is with TCP */
+	if (channel->peer->ld->connectd) {
+		const struct peer *peer = channel->peer;
+		subd_send_msg(peer->ld->connectd,
+			      take(towire_connectd_discard_peer(NULL, &peer->id,
+								peer->connectd_counter)));
+	}
 }
 
 /* Returns failmsg, or NULL on success. */

tests/test_closing.py

@@ -3641,7 +3641,6 @@ def test_close_weight_estimate(node_factory, bitcoind):
     assert signed_weight + 6 >= final_estimate  # 70byte signature
 
 
-@pytest.mark.xfail(strict=True)
 @pytest.mark.developer("needs dev_disconnect")
 def test_onchain_close_upstream(node_factory, bitcoind):
     """https://github.com/ElementsProject/lightning/issues/4649