lightningd: save outgoing information for more forwards.

There's one case where we can present more infomation, so do that, and
fix documentation.

Changelog-Added: JSON-RPC: `listforwards` now shows `out_channel` in more cases: even if it couldn't actually send to it.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Fixes: #5329

doc/lightning-listforwards.7.md

@@ -27,11 +27,11 @@ On success, an object containing **forwards** is returned.  It is an array of ob
 - **in_msat** (msat): the value of the incoming HTLC
 - **status** (string): still ongoing, completed, failed locally, or failed after forwarding (one of "offered", "settled", "local_failed", "failed")
 - **received_time** (number): the UNIX timestamp when this was received
-- **out_channel** (short_channel_id, optional): the channel that the HTLC was forwarded to
+- **out_channel** (short_channel_id, optional): the channel that the HTLC (trying to) forward to
 - **payment_hash** (hex, optional): payment hash sought by HTLC (always 64 characters)
 - **style** (string, optional): Either a legacy onion format or a modern tlv format (one of "legacy", "tlv")
 
-If **out_channel** is present:
+If **out_msat** is present:
   - **fee_msat** (msat): the amount this paid in fees
   - **out_msat** (msat): the amount we sent out the *out_channel*
 
@@ -59,4 +59,4 @@ RESOURCES
 
 Main web site: <https://github.com/ElementsProject/lightning>
 
-[comment]: # ( SHA256STAMP:131410f052b8a1845c8d3c7eb2d48df0fc7638e7d26817f56863815be86d8f1e)
+[comment]: # ( SHA256STAMP:c8adfa0a6dcae939c5da919d7996261db8663a871210e33b426c3b40c30d7b29)

doc/schemas/listforwards.schema.json

@@ -45,7 +45,7 @@
           },
           "out_channel": {
             "type": "short_channel_id",
-            "description": "the channel that the HTLC was forwarded to"
+            "description": "the channel that the HTLC (trying to) forward to"
           },
           "payment_hash": {
             "type": "hex",
@@ -66,14 +66,15 @@
           {
             "if": {
               "required": [
-                "out_channel"
+                "out_msat"
               ]
             },
             "then": {
               "additionalProperties": false,
               "required": [
                 "fee_msat",
-                "out_msat"
+                "out_msat",
+                "out_channel"
               ],
               "properties": {
                 "in_channel": {},
@@ -116,7 +117,8 @@
                 "resolved_time": {},
                 "payment_hash": {},
                 "failcode": {},
-                "failreason": {}
+                "failreason": {},
+                "out_channel": {}
               }
             }
           },

lightningd/peer_htlcs.c

@@ -538,11 +538,11 @@ static void rcvd_htlc_reply(struct subd *subd, const u8 *msg, const int *fds UNU
 			fail_in_htlc(hout->in, failonion);
 
 			/* here we haven't called connect_htlc_out(),
-			 * so set htlc field with NULL */
+			 * so set htlc field with NULL (db wants it to exist!) */
 			wallet_forwarded_payment_add(ld->wallet,
 					 hout->in,
 					 get_onion_style(hout->in),
-					 NULL, NULL,
+					 channel_scid_or_local_alias(hout->key.channel), NULL,
 					 FORWARD_LOCAL_FAILED,
 						     fromwire_peektype(hout->failmsg));
 		}

tests/test_pay.py

@@ -1383,7 +1383,6 @@ def test_forward_stats(node_factory, bitcoind):
     assert 'received_time' in stats['forwards'][2] and 'resolved_time' not in stats['forwards'][2]
 
 
-@pytest.mark.xfail(strict=True)
 @pytest.mark.developer("too slow without --dev-fast-gossip")
 @pytest.mark.slow_test
 def test_forward_local_failed_stats(node_factory, bitcoind, executor):