bkpr: properly account for onchain fees for channel closes

onchain fees are weird at channel close because:

- you may be missing an trimmed htlc (which went to fees)
- the balance from close may have been rounded (msats cant land on
chain)
- the close might have been a past state and you've actually
  ended up with more money onchain than you had in the channel. wut

This commit accounts for all of this appropriately, with some tests.

channel_close.debit should equal onchain_fee.credit (for that txid)
plus sum(chain_event.credit [wallet/channel_acct]).

In the penalty case, channel_close.debit becomes channel_close.debit +
penalty_adj.debit, i.e.

	channel-close.debit + (penalty_adj.debit) =
		onchain_fee.credit
	      + sum(chain_event.credit [wallet/channel_acct])

tests/test_closing.py

@@ -479,6 +479,107 @@ def test_closing_negotiation_step_700sat(node_factory, bitcoind, chainparams):
     closing_negotiation_step(node_factory, bitcoind, chainparams, opts)
 
 
+# FIXME: move to bookkeeper tests
+@pytest.mark.developer("dev-ignore-htlcs")
+def test_closing_trimmed_htlcs(node_factory, bitcoind, executor):
+    l1, l2 = node_factory.line_graph(2)
+
+    # give l2 an output!?
+    l1.pay(l2, 11000000)
+
+    l1.rpc.dev_ignore_htlcs(id=l2.info['id'], ignore=True)
+    # This will get stuck due to l3 ignoring htlcs
+    executor.submit(l2.pay, l1, 100001)
+    l1.daemon.wait_for_log('their htlc 0 dev_ignore_htlcs')
+
+    l1.rpc.dev_fail(l2.info['id'])
+    l1.wait_for_channel_onchain(l2.info['id'])
+
+    bitcoind.generate_block(1)
+    l1.daemon.wait_for_log(' to ONCHAIN')
+    l2.daemon.wait_for_log(' to ONCHAIN')
+
+    bitcoind.generate_block(5)
+    l1.daemon.wait_for_log('Broadcasting OUR_DELAYED_RETURN_TO_WALLET')
+    bitcoind.generate_block(20)
+    l1.daemon.wait_for_log('All outputs resolved')
+
+    def _find_tags(evs, tag):
+        return [e for e in evs if e['tag'] == tag]
+
+    def _find_first_tag(evs, tag):
+        ev = _find_tags(evs, tag)
+        assert len(ev) > 0
+        return ev[0]
+
+    evs = l1.rpc.listaccountevents()['events']
+    close = _find_first_tag(evs, 'channel_close')
+    delayed_to = _find_first_tag(evs, 'delayed_to_us')
+
+    # find the chain fee entry for the channel close
+    fees = _find_tags(evs, 'onchain_fee')
+    close_fee = [e for e in fees if e['txid'] == close['txid']]
+    assert len(close_fee) == 1
+    assert Millisatoshi(close_fee[0]['credit']) + Millisatoshi(delayed_to['credit']) == Millisatoshi(close['debit'])
+
+    # l2's fees should equal the trimmed htlc out
+    evs = l2.rpc.listaccountevents()['events']
+    close = _find_first_tag(evs, 'channel_close')
+    deposit = _find_first_tag(evs, 'deposit')
+    fees = _find_tags(evs, 'onchain_fee')
+    close_fee = [e for e in fees if e['txid'] == close['txid']]
+    assert len(close_fee) == 1
+    # sent htlc was too small, we lose it, rounded up to nearest sat
+    assert close_fee[0]['credit'] == '101000msat'
+    assert Millisatoshi(close_fee[0]['credit']) + Millisatoshi(deposit['credit']) == Millisatoshi(close['debit'])
+
+
+# FIXME: move to bookkeeper tests
+def test_closing_subsat_htlcs(node_factory, bitcoind, chainparams):
+    """Test closing balances when HTLCs are: sub 1-satoshi"""
+    l1, l2 = node_factory.line_graph(2)
+
+    l1.pay(l2, 111)
+    l1.pay(l2, 222)
+    l1.pay(l2, 4000000)
+
+    l2.stop()
+    l1.rpc.close(l2.info['id'], 1)
+    bitcoind.generate_block(5)
+    l2.start()
+    sync_blockheight(bitcoind, [l1])
+    l1.daemon.wait_for_log('Broadcasting OUR_DELAYED_RETURN_TO_WALLET')
+    bitcoind.generate_block(80)
+
+    def _find_tags(evs, tag):
+        return [e for e in evs if e['tag'] == tag]
+
+    def _find_first_tag(evs, tag):
+        ev = _find_tags(evs, tag)
+        assert len(ev) > 0
+        return ev[0]
+
+    sync_blockheight(bitcoind, [l1, l2])
+    evs = l1.rpc.listaccountevents()['events']
+    # check that closing equals onchain deposits + fees
+    close = _find_first_tag(evs, 'channel_close')
+    delayed_to = _find_first_tag(evs, 'delayed_to_us')
+    fees = _find_tags(evs, 'onchain_fee')
+    close_fee = [e for e in fees if e['txid'] == close['txid']]
+    assert len(close_fee) == 1
+    assert Millisatoshi(close_fee[0]['credit']) + Millisatoshi(delayed_to['credit']) == Millisatoshi(close['debit'])
+
+    evs = l2.rpc.listaccountevents()['events']
+    close = _find_first_tag(evs, 'channel_close')
+    deposit = _find_first_tag(evs, 'deposit')
+    fees = _find_tags(evs, 'onchain_fee')
+    close_fee = [e for e in fees if e['txid'] == close['txid']]
+    assert len(close_fee) == 1
+    # too small to fit, we lose them as miner fees
+    assert close_fee[0]['credit'] == '333msat'
+    assert Millisatoshi(close_fee[0]['credit']) + Millisatoshi(deposit['credit']) == Millisatoshi(close['debit'])
+
+
 @pytest.mark.developer("needs dev-disable-commit-after")
 def test_penalty_inhtlc(node_factory, bitcoind, executor, chainparams):
     """Test penalty transaction with an incoming HTLC"""