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multifundchannel: use excess_as_change flag to simplify logic.

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This was added to fundpsbt/utxopsbt in v0.10, but the spender plugin
didn't take advantage of it, instead calculating its own change amount
and output.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2023-06-29 09:44:09 +09:30
parent 37005b93d3
commit 2f0e13e793
3 changed files with 94 additions and 207 deletions
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275
plugins/spender/multifundchannel.c
View File

@ -15,14 +15,14 @@
extern const struct chainparams *chainparams;
/* Flag set when any of the destinations has a value of "all". */
static bool has_all(const struct multifundchannel_command *mfc)
/* Which destinations has a value of "all", or -1. */
static struct multifundchannel_destination *all_dest(const struct multifundchannel_command *mfc)
{
for (size_t i = 0; i < tal_count(mfc->destinations); i++) {
if (mfc->destinations[i].all)
return true;
return &mfc->destinations[i];
}
return false;
return NULL;
}
size_t dest_count(const struct multifundchannel_command *mfc,
@ -162,19 +162,15 @@ mfc_cleanup_done(struct command *cmd,
return command_still_pending(cmd);
}
/* Cleans up a txid by doing `txdiscard` on it. */
static void
mfc_cleanup_psbt(struct command *cmd,
struct multifundchannel_cleanup *cleanup,
struct wally_psbt *psbt)
static struct command_result *unreserve_call(struct command *cmd,
struct wally_psbt *psbt,
void *cb, void *cbdata)
{
struct wally_psbt *pruned_psbt;
struct out_req *req = jsonrpc_request_start(cmd->plugin,
cmd,
"unreserveinputs",
&mfc_cleanup_done,
&mfc_cleanup_done,
cleanup);
cb, cb, cbdata);
/* We might have peer's inputs on this, get rid of them */
tal_wally_start();
@ -191,7 +187,16 @@ mfc_cleanup_psbt(struct command *cmd,
json_add_psbt(req->js, "psbt", take(pruned_psbt));
json_add_u32(req->js, "reserve", 2016);
send_outreq(cmd->plugin, req);
return send_outreq(cmd->plugin, req);
}
/* Cleans up a txid by doing `txdiscard` on it. */
static void
mfc_cleanup_psbt(struct command *cmd,
struct multifundchannel_cleanup *cleanup,
struct wally_psbt *psbt)
{
unreserve_call(cmd, psbt, mfc_cleanup_done, cleanup);
}
/* Cleans up a `openchannel_init` by doing `openchannel_abort` for the channel*/
@ -820,7 +825,8 @@ perform_fundchannel_complete(struct multifundchannel_command *mfc)
return command_still_pending(mfc->cmd);
}
/*~ The PSBT we are holding currently has no outputs.
/*~ The PSBT we are holding currently has no outputs
(except an optional change output).
We now proceed to filling in those outputs now that
we know what the funding scriptpubkeys are.
@ -856,7 +862,7 @@ perform_funding_tx_finalize(struct multifundchannel_command *mfc)
/* Construct a deck of destinations. */
deck = tal_arr(tmpctx, struct multifundchannel_destination *,
v1_dest_count + mfc->change_needed);
v1_dest_count);
deck_i = 0;
for (i = 0; i < tal_count(mfc->destinations); i++) {
@ -867,10 +873,6 @@ perform_funding_tx_finalize(struct multifundchannel_command *mfc)
deck[deck_i++] = &mfc->destinations[i];
}
/* Add a NULL into the deck as a proxy for change output, if
* needed. */
if (mfc->change_needed)
deck[v1_dest_count] = NULL;
/* Fisher-Yates shuffle. */
for (i = tal_count(deck); i > 1; --i) {
size_t j = pseudorand(i);
@ -884,38 +886,27 @@ perform_funding_tx_finalize(struct multifundchannel_command *mfc)
/* Now that we have our outputs shuffled, add outputs to the PSBT. */
for (unsigned int outnum = 0; outnum < tal_count(deck); ++outnum) {
struct multifundchannel_destination *dest;
if (outnum != 0)
tal_append_fmt(&content, ", ");
if (deck[outnum]) {
/* Funding outpoint. */
struct multifundchannel_destination *dest;
dest = deck[outnum];
(void) psbt_insert_output(mfc->psbt,
dest->funding_script,
dest->amount,
outnum);
/* The actual output index will be based on the
* serial_id if this contains any v2 outputs */
if (v2_dest_count == 0)
dest->outnum = outnum;
tal_append_fmt(&content, "%s: %s",
type_to_string(tmpctx, struct node_id,
&dest->id),
type_to_string(tmpctx,
struct amount_sat,
&dest->amount));
} else {
/* Change output. */
assert(mfc->change_needed);
(void) psbt_insert_output(mfc->psbt,
mfc->change_scriptpubkey,
mfc->change_amount,
outnum);
tal_append_fmt(&content, "change: %s",
type_to_string(tmpctx,
struct amount_sat,
&mfc->change_amount));
}
/* Funding outpoint. */
dest = deck[outnum];
(void) psbt_insert_output(mfc->psbt,
dest->funding_script,
dest->amount,
outnum);
/* The actual output index will be based on the
* serial_id if this contains any v2 outputs */
if (v2_dest_count == 0)
dest->outnum = outnum;
tal_append_fmt(&content, "%s: %s",
type_to_string(tmpctx, struct node_id,
&dest->id),
type_to_string(tmpctx,
struct amount_sat,
&dest->amount));
}
if (v2_dest_count > 0) {
@ -1206,139 +1197,19 @@ mfc_psbt_acquired(struct multifundchannel_command *mfc)
return perform_channel_start(mfc);
}
/* Limited recursion if we discover 'all' is too big for non-wumbo! */
static struct command_result *
after_newaddr(struct command *cmd,
const char *buf,
const jsmntok_t *result,
struct multifundchannel_command *mfc)
{
const jsmntok_t *field;
field = json_get_member(buf, result, "bech32");
if (!field)
plugin_err(cmd->plugin,
"No bech32 field in newaddr result: %.*s",
json_tok_full_len(result),
json_tok_full(buf, result));
if (json_to_address_scriptpubkey(mfc, chainparams, buf, field,
&mfc->change_scriptpubkey)
!= ADDRESS_PARSE_SUCCESS)
plugin_err(cmd->plugin,
"Unparseable bech32 field in newaddr result: %.*s",
json_tok_full_len(result),
json_tok_full(buf, result));
return mfc_psbt_acquired(mfc);
}
perform_fundpsbt(struct multifundchannel_command *mfc, u32 feerate);
static struct command_result *
acquire_change_address(struct multifundchannel_command *mfc)
retry_fundpsbt_capped_all(struct command *cmd,
const char *buf,
const jsmntok_t *result,
struct multifundchannel_command *mfc)
{
struct out_req *req;
req = jsonrpc_request_start(mfc->cmd->plugin, mfc->cmd,
"newaddr",
&after_newaddr, &mfc_forward_error,
mfc);
json_add_string(req->js, "addresstype", "bech32");
return send_outreq(mfc->cmd->plugin, req);
}
static struct command_result *
handle_mfc_change(struct multifundchannel_command *mfc)
{
size_t change_weight;
struct amount_sat change_fee, fee_paid, total_fee;
struct amount_sat change_min_limit;
/* Determine if adding a change output is worth it.
* Get the weight of a change output and how much it
* costs.
*/
change_weight = bitcoin_tx_output_weight(
BITCOIN_SCRIPTPUBKEY_P2WPKH_LEN);
/* To avoid 'off-by-one' errors due to rounding down
* (which we do in `amount_tx_fee`), we find the total calculated
* fees (estimated_weight + change weight @ feerate) and subtract
* the originally calculated fees (estimated_weight @ feerate) */
fee_paid = amount_tx_fee(mfc->feerate_per_kw,
mfc->estimated_final_weight);
total_fee = amount_tx_fee(mfc->feerate_per_kw,
mfc->estimated_final_weight + change_weight);
if (!amount_sat_sub(&change_fee, total_fee, fee_paid))
abort();
/* The limit is equal to the change_fee plus the dust limit. */
if (!amount_sat_add(&change_min_limit,
change_fee, chainparams->dust_limit))
plugin_err(mfc->cmd->plugin,
"Overflow dust limit and change fee.");
/* Is the excess over the limit? */
if (amount_sat_greater(mfc->excess_sat, change_min_limit)) {
bool ok = amount_sat_sub(&mfc->change_amount,
mfc->excess_sat, change_fee);
assert(ok);
mfc->change_needed = true;
if (!mfc->change_scriptpubkey)
return acquire_change_address(mfc);
} else
mfc->change_needed = false;
return mfc_psbt_acquired(mfc);
}
/* If one of the destinations specified "all", figure out how much that is. */
static struct command_result *
compute_mfc_all(struct multifundchannel_command *mfc)
{
size_t all_index = SIZE_MAX;
struct multifundchannel_destination *all_dest;
assert(has_all(mfc));
for (size_t i = 0; i < tal_count(mfc->destinations); ++i) {
struct multifundchannel_destination *dest;
dest = &mfc->destinations[i];
if (dest->all) {
assert(all_index == SIZE_MAX);
all_index = i;
continue;
}
/* Subtract the amount from the excess. */
if (!amount_sat_sub(&mfc->excess_sat,
mfc->excess_sat, dest->amount))
/* Not enough funds! */
return mfc_fail(mfc, FUND_CANNOT_AFFORD,
"Insufficient funds.");
}
assert(all_index != SIZE_MAX);
all_dest = &mfc->destinations[all_index];
/* Is the excess above the dust amount? */
if (amount_sat_less(mfc->excess_sat, chainparams->dust_limit))
return mfc_fail(mfc, FUND_OUTPUT_IS_DUST,
"Output 'all' %s would be dust",
type_to_string(tmpctx, struct amount_sat,
&mfc->excess_sat));
/* Assign the remainder to the 'all' output. */
all_dest->amount = mfc->excess_sat;
if (!feature_negotiated(plugin_feature_set(mfc->cmd->plugin),
all_dest->their_features,
OPT_LARGE_CHANNELS)
&& amount_sat_greater(all_dest->amount,
chainparams->max_funding))
all_dest->amount = chainparams->max_funding;
/* Remove it from the excess. */
bool ok = amount_sat_sub(&mfc->excess_sat,
mfc->excess_sat, all_dest->amount);
assert(ok);
/* Remove the 'all' flag. */
all_dest->all = false;
/* Continue. */
return handle_mfc_change(mfc);
/* We've unreserved this, now free it and try again! */
tal_free(mfc->psbt);
return perform_fundpsbt(mfc, mfc->feerate_per_kw);
}
static struct command_result *
@ -1348,7 +1219,7 @@ after_fundpsbt(struct command *cmd,
struct multifundchannel_command *mfc)
{
const jsmntok_t *field;
struct amount_msat msat;
struct multifundchannel_destination *all;
plugin_log(mfc->cmd->plugin, LOG_DBG,
"mfc %"PRIu64": %s done.",
@ -1379,17 +1250,38 @@ after_fundpsbt(struct command *cmd,
if (!field || !json_to_u32(buf, field, &mfc->estimated_final_weight))
goto fail;
/* msat LOL. */
field = json_get_member(buf, result, "excess_msat");
if (!field || !parse_amount_msat(&msat,
buf + field->start,
field->end - field->start)
|| !amount_msat_to_sat(&mfc->excess_sat, msat))
goto fail;
all = all_dest(mfc);
if (all) {
struct amount_msat msat;
if (has_all(mfc))
return compute_mfc_all(mfc);
return handle_mfc_change(mfc);
/* excess_msat is amount to use for "all". */
field = json_get_member(buf, result, "excess_msat");
if (!field || !parse_amount_msat(&msat,
buf + field->start,
field->end - field->start)
|| !amount_msat_to_sat(&all->amount, msat))
goto fail;
/* Remove the 'all' flag. */
all->all = false;
/* It's first grade, Spongebob! */
if (!feature_negotiated(plugin_feature_set(mfc->cmd->plugin),
all->their_features,
OPT_LARGE_CHANNELS)
&& amount_sat_greater(all->amount,
chainparams->max_funding)) {
/* Oh, crap! Set this amount and retry! */
plugin_log(mfc->cmd->plugin, LOG_INFORM,
"'all' was too large for non-wumbo channel, trimming from %s to %s",
fmt_amount_sat(tmpctx, all->amount),
fmt_amount_sat(tmpctx, chainparams->max_funding));
all->amount = chainparams->max_funding;
return unreserve_call(mfc->cmd, mfc->psbt,
retry_fundpsbt_capped_all, mfc);
}
}
return mfc_psbt_acquired(mfc);
fail:
plugin_err(mfc->cmd->plugin,
@ -1446,7 +1338,7 @@ perform_fundpsbt(struct multifundchannel_command *mfc, u32 feerate)
*/
json_add_u32(req->js, "reserve", 2016);
/* How much do we need to reserve? */
if (has_all(mfc))
if (all_dest(mfc) != NULL)
json_add_string(req->js, "satoshi", "all");
else {
struct amount_sat sum = AMOUNT_SAT(0);
@ -1511,6 +1403,8 @@ perform_fundpsbt(struct multifundchannel_command *mfc, u32 feerate)
tal_fmt(tmpctx, "%u", 110));
}
/* Handle adding a change output if required. */
json_add_bool(req->js, "excess_as_change", true);
return send_outreq(mfc->cmd->plugin, req);
}
@ -2092,7 +1986,6 @@ json_multifundchannel(struct command *cmd,
mfc->minchannels = minchannels ? *minchannels : tal_count(mfc->destinations);
mfc->removeds = tal_arr(mfc, struct multifundchannel_removed, 0);
mfc->psbt = NULL;
mfc->change_scriptpubkey = NULL;
mfc->txid = NULL;
mfc->final_tx = NULL;
mfc->final_txid = NULL;

15
plugins/spender/multifundchannel.h
View File

@ -218,21 +218,6 @@ struct multifundchannel_command {
/* The expected weight of the PSBT after adding in all the outputs.
* In weight units (sipa). */
u32 estimated_final_weight;
/* Excess satoshi from the PSBT.
* If "all" this is the entire amount; if not "all" this is the
* proposed change amount, which if dusty should be donated to
* the miners.
*/
struct amount_sat excess_sat;
/* A convenient change address. NULL at the start, filled in
* if we detect we need it. */
const u8 *change_scriptpubkey;
/* Whether we need a change output. */
bool change_needed;
/* The change amount. */
struct amount_sat change_amount;
/* The txid of the final funding transaction. */
struct bitcoin_txid *txid;

11
tests/test_connection.py
View File

@ -1,5 +1,6 @@
from fixtures import * # noqa: F401,F403
from fixtures import TEST_NETWORK
from decimal import Decimal
from ephemeral_port_reserve import reserve # type: ignore
from pyln.client import RpcError, Millisatoshi
import pyln.proto.wire as wire
@ -1111,6 +1112,7 @@ def test_funding_all_too_much(node_factory):
addr, txid = l1.fundwallet(2**24 + 10000)
l1.rpc.fundchannel(l2.info['id'], "all")
assert l1.daemon.is_in_log("'all' was too large for non-wumbo channel, trimming")
# One reserved, confirmed output spent above, and one change.
outputs = l1.rpc.listfunds()['outputs']
@ -1842,7 +1844,14 @@ def test_multifunding_v1_v2_mixed(node_factory, bitcoind):
{"id": '{}@localhost:{}'.format(l4.info['id'], l4.port),
"amount": 50000}]
l1.rpc.multifundchannel(destinations)
# There should be change!
tx = l1.rpc.multifundchannel(destinations)['tx']
decoded = bitcoind.rpc.decoderawtransaction(tx)
assert len(decoded['vout']) == len(destinations) + 1
# Feerate should be about right, too!
fee = Decimal(2000000) / 10**8 * len(decoded['vin']) - sum(v['value'] for v in decoded['vout'])
assert 7450 < fee * 10**8 / decoded['weight'] * 1000 < 7550
mine_funding_to_announce(bitcoind, [l1, l2, l3, l4], wait_for_mempool=1)
for node in [l1, l2, l3, l4]: