channeld: fix fee calculation.

Funder can't spend the fee it needs to pay for the commitment transaction:
we were not converting to millisatoshis, however!

This breaks our routeboost test, which no longer has sufficient funds
to make payment.

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

CHANGELOG.md

@@ -37,8 +37,10 @@ changes.
 - JSON API: uppercase invoices now parsed correctly (broken in 0.6.2).
 - JSON API: commands are once again read even if one hasn't responded yet (broken in 0.6.2).
 - Protocol: allow lnd to send `update_fee` before `funding_locked`.
+- Protocol: fix limit on how much funder can send (fee was 1000x too small)
 - pylightning: handle multiple simultanous RPC replies reliably.
 
+
 ### Security
 
 

channeld/full_channel.c

@@ -414,7 +414,7 @@ static enum channel_add_err add_htlc(struct channel *channel,
 			- commit_tx_num_untrimmed(removing, feerate, dust,
 						  recipient);
 
-		fee_msat = commit_tx_base_fee(feerate, untrimmed);
+		fee_msat = commit_tx_base_fee(feerate, untrimmed) * 1000;
 	} else
 		fee_msat = 0;
 
@@ -684,7 +684,7 @@ static int change_htlcs(struct channel *channel,
 u32 approx_max_feerate(const struct channel *channel)
 {
 	size_t num;
-	u64 weight;
+	u64 weight, avail_msat;
 	const struct htlc **committed, **adding, **removing;
 
 	gather_htlcs(tmpctx, channel, !channel->funder,
@@ -695,8 +695,12 @@ u32 approx_max_feerate(const struct channel *channel)
 
 	weight = 724 + 172 * num;
 
-	return channel->view[!channel->funder].owed_msat[channel->funder]
-		/ weight * 1000;
+	/* We should never go below reserve. */
+	avail_msat = channel->view[!channel->funder].owed_msat[channel->funder]
+		- channel_reserve_msat(channel, channel->funder);
+
+	/* We have to pay fee from onchain funds, so it's in satoshi. */
+	return avail_msat / 1000 / weight * 1000;
 }
 
 bool can_funder_afford_feerate(const struct channel *channel, u32 feerate_per_kw)
@@ -714,7 +718,7 @@ bool can_funder_afford_feerate(const struct channel *channel, u32 feerate_per_kw
 			- commit_tx_num_untrimmed(removing, feerate_per_kw, dust,
 						  !channel->funder);
 
-	fee_msat = commit_tx_base_fee(feerate_per_kw, untrimmed);
+	fee_msat = commit_tx_base_fee(feerate_per_kw, untrimmed) * 1000;
 
 	/* BOLT #2:
 	 *

tests/test_invoices.py

@@ -120,7 +120,7 @@ def test_invoice_preimage(node_factory):
 def test_invoice_routeboost(node_factory, bitcoind):
     """Test routeboost 'r' hint in bolt11 invoice.
     """
-    l1, l2 = node_factory.line_graph(2, fundamount=10**4)
+    l1, l2 = node_factory.line_graph(2, fundamount=2 * (10**4))
 
     # Won't get reference to route until channel is public.
     inv = l2.rpc.invoice(msatoshi=123456, label="inv0", description="?")
@@ -147,8 +147,8 @@ def test_invoice_routeboost(node_factory, bitcoind):
     l1.rpc.pay(inv['bolt11'])
     wait_channel_quiescent(l1, l2)
 
-    # Due to reserve, l1 doesn't have capacity to pay this.
-    inv = l2.rpc.invoice(msatoshi=10**7 - 123456, label="inv2", description="?")
+    # Due to reserve & fees, l1 doesn't have capacity to pay this.
+    inv = l2.rpc.invoice(msatoshi=2 * (10**7) - 123456, label="inv2", description="?")
     # Check warning
     assert 'warning_capacity' in inv
     assert 'warning_offline' not in inv

tests/test_pay.py

@@ -446,7 +446,7 @@ def test_sendpay_cant_afford(node_factory):
         pay(l1, l2, 10**9 + 1)
 
     # This is the fee, which needs to be taken into account for l1.
-    available = 10**9 - 13440
+    available = 10**9 - 13440000
     # Reserve is 1%.
     reserve = 10**7