listpeers: add latest feerate and actual last fee amount.

Users have no idea what they would pay for unilateral closes.
At least this gives them a clue!

Reported-by: @Az0re on IRC.

Changelog-Added: JSON-RPC: `listpeers` now shows latest feerate and unilaral close fee.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

doc/lightning-listpeers.7.md

@@ -202,6 +202,10 @@ state, or in various circumstances:
 * *out\_fulfilled\_msat*: A string describing the total amount of all
   outgoing HTLCs offered *and successfully claimed* over this channel;
   a number followed by a string unit.
+* *scratch_txid*: The txid of the latest transaction (what we would sign and
+  send to chain if the channel were to fail now).
+* *last_tx_fee*: The fee on that latest transaction.
+* *feerate*: An object containing the latest feerate as both *perkw* and *perkb*.
 * *htlcs*: An array of objects describing the HTLCs currently in-flight
   in the channel.
 

lightningd/peer_control.c

@@ -698,6 +698,7 @@ static void json_add_channel(struct lightningd *ld,
 	struct amount_sat peer_funded_sats;
 	struct peer *p = channel->peer;
 	struct state_change_entry *state_changes;
+	u32 feerate;
 
 	json_object_start(response, key);
 	json_add_string(response, "state", channel_state_name(channel));
@@ -706,7 +707,17 @@ static void json_add_channel(struct lightningd *ld,
 		bitcoin_txid(channel->last_tx, &txid);
 
 		json_add_txid(response, "scratch_txid", &txid);
+		json_add_amount_sat_only(response, "last_tx_fee",
+					 bitcoin_tx_compute_fee(channel->last_tx));
 	}
+
+	json_object_start(response, "feerate");
+	feerate = get_feerate(channel->fee_states, channel->opener, LOCAL);
+	json_add_u32(response, feerate_style_name(FEERATE_PER_KSIPA), feerate);
+	json_add_u32(response, feerate_style_name(FEERATE_PER_KBYTE),
+		     feerate_to_style(feerate, FEERATE_PER_KBYTE));
+	json_object_end(response);
+
 	if (channel->owner)
 		json_add_string(response, "owner", channel->owner->name);
 

lightningd/test/run-invoice-select-inchan.c

@@ -267,6 +267,12 @@ void json_add_amount_sat_compat(struct json_stream *result UNNEEDED,
 				const char *msatfieldname)
 
 { fprintf(stderr, "json_add_amount_sat_compat called!\n"); abort(); }
+/* Generated stub for json_add_amount_sat_only */
+void json_add_amount_sat_only(struct json_stream *result UNNEEDED,
+			 const char *msatfieldname UNNEEDED,
+			 struct amount_sat sat)
+
+{ fprintf(stderr, "json_add_amount_sat_only called!\n"); abort(); }
 /* Generated stub for json_add_bolt11 */
 void json_add_bolt11(struct json_stream *response UNNEEDED,
 		     const struct bolt11 *b11 UNNEEDED)

tests/test_connection.py

@@ -1606,7 +1606,8 @@ def test_multifunding_feerates(node_factory, bitcoind):
     Test feerate parameters for multifundchannel
     '''
     funding_tx_feerate = '10000perkw'
-    commitment_tx_feerate = '2000perkw'
+    commitment_tx_feerate_int = 2000
+    commitment_tx_feerate = str(commitment_tx_feerate_int) + 'perkw'
 
     l1, l2, l3 = node_factory.get_nodes(3, opts={'log-level': 'debug'})
 
@@ -1626,6 +1627,11 @@ def _connect_str(node):
     expected_fee = int(funding_tx_feerate[:-5]) * weight // 1000
     assert expected_fee == entry['fees']['base'] * 10 ** 8
 
+    assert only_one(only_one(l1.rpc.listpeers(l2.info['id'])['peers'])['channels'])['feerate']['perkw'] == commitment_tx_feerate_int
+    assert only_one(only_one(l1.rpc.listpeers(l2.info['id'])['peers'])['channels'])['feerate']['perkb'] == commitment_tx_feerate_int * 4
+
+    txfee = only_one(only_one(l1.rpc.listpeers(l2.info['id'])['peers'])['channels'])['last_tx_fee']
+
     # We get the expected close txid, force close the channel, then fish
     # the details about the transaction out of the mempoool entry
     close_txid = only_one(only_one(l1.rpc.listpeers(l2.info['id'])['peers'])['channels'])['scratch_txid']
@@ -1652,6 +1658,7 @@ def _connect_str(node):
         expected_fee += 330
 
     assert expected_fee == entry['fees']['base'] * 10 ** 8
+    assert Millisatoshi(str(expected_fee) + 'sat') == Millisatoshi(txfee)
 
 
 def test_multifunding_param_failures(node_factory):

wallet/test/run-wallet.c

@@ -268,6 +268,12 @@ void json_add_amount_sat_compat(struct json_stream *result UNNEEDED,
 				const char *msatfieldname)
 
 { fprintf(stderr, "json_add_amount_sat_compat called!\n"); abort(); }
+/* Generated stub for json_add_amount_sat_only */
+void json_add_amount_sat_only(struct json_stream *result UNNEEDED,
+			 const char *msatfieldname UNNEEDED,
+			 struct amount_sat sat)
+
+{ fprintf(stderr, "json_add_amount_sat_only called!\n"); abort(); }
 /* Generated stub for json_add_bool */
 void json_add_bool(struct json_stream *result UNNEEDED, const char *fieldname UNNEEDED,
 		   bool value UNNEEDED)