channeld: only enable option_data_loss_protect if EXPERIMENTAL_FEATURES.

We have an incompatibility with lnd it seems: I've lost channels on
reconnect with 'sync error'.  Since I never got this code to be reliable,
disable it for next release since I suspect it's our fault :(

And reenable the check which didn't work, for others to untangle.

I couldn't get option_data_loss_protect to be reliable, and I disabled
the check.  This was a mistake, I should have either spent even more
time trying to get to the bottom of this (especially, writing test
vectors for the spec and testing against other implementations).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

CHANGELOG.md

@@ -30,6 +30,8 @@ changes.
 
 ### Removed
 
+- option_data_loss_protect is now only offered if EXPERIMENTAL_FEATURES is enabled, since it seems incompatible with lnd and has known bugs.
+
 ### Fixed
 
 - JSON API: uppercase invoices now parsed correctly (broken in 0.6.2).

channeld/channeld.c

@@ -1986,7 +1986,6 @@ static void check_current_dataloss_fields(struct peer *peer,
 			    type_to_string(tmpctx, struct secret,
 					   &old_commit_secret));
 
-#if 0 /* FIXME: This isn't reliable! */
 	/* FIXME: We don't keep really old per_commit numbers, so we can't
 	 * check this 'needs retransmit' case! */
 	if (next_remote_revocation_number == peer->next_index[REMOTE]) {
@@ -2010,7 +2009,6 @@ static void check_current_dataloss_fields(struct peer *peer,
 					    remote_current_per_commitment_point),
 			     next_remote_revocation_number,
 			     peer->next_index[REMOTE]);
-#endif
 
 	status_trace("option_data_loss_protect: fields are correct");
 }

common/features.c

@@ -4,7 +4,9 @@
 #include <wire/peer_wire.h>
 
 static const u32 our_localfeatures[] = {
+#if EXPERIMENTAL_FEATURES
 	LOCAL_DATA_LOSS_PROTECT,
+#endif
 	LOCAL_INITIAL_ROUTING_SYNC,
 	LOCAL_GOSSIP_QUERIES
 };

tests/test_connection.py

@@ -1,7 +1,7 @@
 from collections import namedtuple
 from fixtures import *  # noqa: F401,F403
 from lightning import RpcError
-from utils import DEVELOPER, only_one, wait_for, sync_blockheight, VALGRIND
+from utils import DEVELOPER, only_one, wait_for, sync_blockheight, VALGRIND, EXPERIMENTAL_FEATURES
 
 
 import os
@@ -1004,11 +1004,14 @@ def test_forget_channel(node_factory):
 
 def test_peerinfo(node_factory, bitcoind):
     l1, l2 = node_factory.line_graph(2, fundchannel=False, opts={'may_reconnect': True})
+    if EXPERIMENTAL_FEATURES:
+        lfeatures = '8a'
+    else:
+        lfeatures = '88'
     # Gossiping but no node announcement yet
     assert l1.rpc.getpeer(l2.info['id'])['connected']
     assert len(l1.rpc.getpeer(l2.info['id'])['channels']) == 0
-    assert l1.rpc.getpeer(l2.info['id'])['localfeatures'] == '8a'
-    assert l1.rpc.getpeer(l2.info['id'])['globalfeatures'] == ''
+    assert l1.rpc.getpeer(l2.info['id'])['localfeatures'] == lfeatures
 
     # Fund a channel to force a node announcement
     chan = l1.fund_channel(l2, 10**6)
@@ -1025,15 +1028,15 @@ def test_peerinfo(node_factory, bitcoind):
     assert only_one(nodes1)['globalfeatures'] == peer1['globalfeatures']
     assert only_one(nodes2)['globalfeatures'] == peer2['globalfeatures']
 
-    assert l1.rpc.getpeer(l2.info['id'])['localfeatures'] == '8a'
-    assert l2.rpc.getpeer(l1.info['id'])['localfeatures'] == '8a'
+    assert l1.rpc.getpeer(l2.info['id'])['localfeatures'] == lfeatures
+    assert l2.rpc.getpeer(l1.info['id'])['localfeatures'] == lfeatures
 
     # If it reconnects after db load, it should know features.
     l1.restart()
     wait_for(lambda: l1.rpc.getpeer(l2.info['id'])['connected'])
     wait_for(lambda: l2.rpc.getpeer(l1.info['id'])['connected'])
-    assert l1.rpc.getpeer(l2.info['id'])['localfeatures'] == '8a'
-    assert l2.rpc.getpeer(l1.info['id'])['localfeatures'] == '8a'
+    assert l1.rpc.getpeer(l2.info['id'])['localfeatures'] == lfeatures
+    assert l2.rpc.getpeer(l1.info['id'])['localfeatures'] == lfeatures
 
     # Close the channel to forget the peer
     with pytest.raises(RpcError, match=r'Channel close negotiation not finished'):
@@ -1247,6 +1250,7 @@ def test_funder_simple_reconnect(node_factory, bitcoind):
 
 
 @unittest.skipIf(not DEVELOPER, "needs LIGHTNINGD_DEV_LOG_IO")
+@unittest.skipIf(not EXPERIMENTAL_FEATURES, "needs option_dataloss_protect")
 def test_dataloss_protection(node_factory, bitcoind):
     l1 = node_factory.get_node(may_reconnect=True, log_all_io=True)
     l2 = node_factory.get_node(may_reconnect=True, log_all_io=True)