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fundpsbt: make parameters more usable.

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fundpsbt forces the caller to manually add their weight * feerate
to the satoshis they ask for.  That means no named feerates.

Instead, create a startweight parameter and do the calc for them
internally, and return the feerate we used (and, while we're at it,
the estimated final weight).

This API change is best done now, as it would otherwise have to
be appended as a parameter.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2020-07-17 15:15:57 +09:30 committed by Christian Decker
parent fe119fc8fd
commit 73a5f5b313
5 changed files with 110 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
contrib/pyln-client/pyln/client/lightning.py
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@ -1126,13 +1126,14 @@ class LightningRpc(UnixDomainSocketRpc):
}
return self.call("unreserveinputs", payload)
def fundpsbt(self, satoshi, feerate, minconf=None, reserve=True):
def fundpsbt(self, satoshi, feerate, startweight, minconf=None, reserve=True):
"""
Create a PSBT with inputs sufficient to give an output of satoshi.
"""
payload = {
"satoshi": satoshi,
"feerate": feerate,
"startweight": startweight,
"minconf": minconf,
"reserve": reserve,
}

48
doc/lightning-fundpsbt.7 generated
View File

@ -3,7 +3,7 @@
lightning-fundpsbt - Command to populate PSBT inputs from the wallet
.SH SYNOPSIS
\fBfundpsbt\fR \fIsatoshi\fR \fIfeerate\fR [\fIminconf\fR] [\fIreserve\fR]
\fBfundpsbt\fR \fIsatoshi\fR \fIfeerate\fR \fIstartweight\fR [\fIminconf\fR] [\fIreserve\fR]
.SH DESCRIPTION
@ -18,16 +18,18 @@ ending in \fI000msat\fR, or a number with 1 to 8 decimal places ending in
\fIbtc\fR\.
You calculate the value by starting with the amount you want to pay
and adding the fee which will be needed to pay for the base of the
transaction plus that output, and any other outputs and inputs you
will add to the final transaction\.
\fIfeerate\fR can be one of the feerates listed in \fBlightning-feerates\fR(7),
or one of the strings \fIurgent\fR (aim for next block), \fInormal\fR (next 4
blocks or so) or \fIslow\fR (next 100 blocks or so) to use lightningd’s
internal estimates\. It can also be a \fIfeerate\fR is a number, with an
optional suffix: \fIperkw\fR means the number is interpreted as
satoshi-per-kilosipa (weight), and \fIperkb\fR means it is interpreted
bitcoind-style as satoshi-per-kilobyte\. Omitting the suffix is
equivalent to \fIperkb\fR\.
\fIfeerate\fR is a number, with an optional suffix: \fIperkw\fR means the
number is interpreted as satoshi-per-kilosipa (weight), and \fIperkb\fR
means it is interpreted bitcoind-style as
satoshi-per-kilobyte\. Omitting the suffix is equivalent to \fIperkb\fR\.
\fIstartweight\fR is the weight of the transaction before \fIfundpsbt\fR has
added any inputs\.
\fIminconf\fR specifies the minimum number of confirmations that used
@ -37,13 +39,37 @@ outputs should have\. Default is 1\.
\fIreserve\fR is a boolean: if true (the default), then \fIreserveinputs\fR is
called (successfully, with \fIexclusive\fR true) on the returned PSBT\.
.SH EXAMPLE USAGE
Let's assume the caller is trying to produce a 100,000 satoshi output\.
First, the caller estimates the weight of the core (typically 42) and
known outputs of the transaction (typically (9 + scriptlen) * 4)\. For
a simple P2WPKH it's a 22 byte scriptpubkey, so that's 164 weight\.
It calls "\fIfundpsbt\fR 100000sat slow 206", which succeeds, and returns
the \fIpsbt\fR and \fIfeerate_per_kw\fR it used, the \fIestimated_final_weight\fR
and any \fIexcess_msat\fR\.
If \fIexcess_msat\fR is greater than the cost of adding a change output,
the caller adds a change output randomly to position 0 or 1 in the
PSBT\. Say \fIfeerate_per_kw\fR is 253, and the change output is a P2WPKH
(weight 164), that would cost the cost is around 41 sats\. With the
dust limit disallowing payments below 546 satoshis, we would only create
a change output if \fIexcess_msat\fR was greater or equal to 41 + 546\.
.SH RETURN VALUE
On success, returns the \fIpsbt\fR containing the inputs, and
On success, returns the \fIpsbt\fR containing the inputs, \fIfeerate_per_kw\fR
showing the exact numeric feerate it used, \fIestimated_final_weight\fR for
the estimated weight of the transaction once fully signed, and
\fIexcess_msat\fR containing the amount above \fIsatoshi\fR which is
available\. This could be zero, or dust\. If \fIsatoshi\fR was "all",
then \fIexcess_msat\fR is the entire amount once fees are subtracted
for the weights of the inputs\.
for the weights of the inputs and startweight\.
If \fIreserve\fR was true, then a \fIreservations\fR array is returned,

46
doc/lightning-fundpsbt.7.md
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@ -4,7 +4,7 @@ lightning-fundpsbt -- Command to populate PSBT inputs from the wallet
SYNOPSIS
--------
**fundpsbt** *satoshi* *feerate* \[*minconf*\] \[*reserve*\]
**fundpsbt** *satoshi* *feerate* *startweight* \[*minconf*\] \[*reserve*\]
DESCRIPTION
-----------
@ -18,15 +18,17 @@ be a whole number, a whole number ending in *sat*, a whole number
ending in *000msat*, or a number with 1 to 8 decimal places ending in
*btc*.
You calculate the value by starting with the amount you want to pay
and adding the fee which will be needed to pay for the base of the
transaction plus that output, and any other outputs and inputs you
will add to the final transaction.
*feerate* can be one of the feerates listed in lightning-feerates(7),
or one of the strings *urgent* (aim for next block), *normal* (next 4
blocks or so) or *slow* (next 100 blocks or so) to use lightningd’s
internal estimates. It can also be a *feerate* is a number, with an
optional suffix: *perkw* means the number is interpreted as
satoshi-per-kilosipa (weight), and *perkb* means it is interpreted
bitcoind-style as satoshi-per-kilobyte. Omitting the suffix is
equivalent to *perkb*.
*feerate* is a number, with an optional suffix: *perkw* means the
number is interpreted as satoshi-per-kilosipa (weight), and *perkb*
means it is interpreted bitcoind-style as
satoshi-per-kilobyte. Omitting the suffix is equivalent to *perkb*.
*startweight* is the weight of the transaction before *fundpsbt* has
added any inputs.
*minconf* specifies the minimum number of confirmations that used
outputs should have. Default is 1.
@ -34,14 +36,36 @@ outputs should have. Default is 1.
*reserve* is a boolean: if true (the default), then *reserveinputs* is
called (successfully, with *exclusive* true) on the returned PSBT.
EXAMPLE USAGE
-------------
Let's assume the caller is trying to produce a 100,000 satoshi output.
First, the caller estimates the weight of the core (typically 42) and
known outputs of the transaction (typically (9 + scriptlen) * 4). For
a simple P2WPKH it's a 22 byte scriptpubkey, so that's 164 weight.
It calls "*fundpsbt* 100000sat slow 206", which succeeds, and returns
the *psbt* and *feerate_per_kw* it used, the *estimated_final_weight*
and any *excess_msat*.
If *excess_msat* is greater than the cost of adding a change output,
the caller adds a change output randomly to position 0 or 1 in the
PSBT. Say *feerate_per_kw* is 253, and the change output is a P2WPKH
(weight 164), that would cost the cost is around 41 sats. With the
dust limit disallowing payments below 546 satoshis, we would only create
a change output if *excess_msat* was greater or equal to 41 + 546.
RETURN VALUE
------------
On success, returns the *psbt* containing the inputs, and
On success, returns the *psbt* containing the inputs, *feerate_per_kw*
showing the exact numeric feerate it used, *estimated_final_weight* for
the estimated weight of the transaction once fully signed, and
*excess_msat* containing the amount above *satoshi* which is
available. This could be zero, or dust. If *satoshi* was "all",
then *excess_msat* is the entire amount once fees are subtracted
for the weights of the inputs.
for the weights of the inputs and startweight.
If *reserve* was true, then a *reservations* array is returned,
exactly like *reserveinputs*.

32
tests/test_wallet.py
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@ -506,33 +506,45 @@ def test_fundpsbt(node_factory, bitcoind, chainparams):
feerate = '7500perkw'
# Should get one input, plus some excess
funding = l1.rpc.fundpsbt(amount // 2, feerate, reserve=False)
funding = l1.rpc.fundpsbt(amount // 2, feerate, 0, reserve=False)
psbt = bitcoind.rpc.decodepsbt(funding['psbt'])
assert len(psbt['tx']['vin']) == 1
assert funding['excess_msat'] > Millisatoshi(0)
assert funding['excess_msat'] < Millisatoshi(amount // 2 * 1000)
assert funding['feerate_per_kw'] == 7500
assert 'estimated_final_weight' in funding
assert 'reservations' not in funding
# This should add 99 to the weight, but otherwise be identical (might choose different inputs though!)
funding2 = l1.rpc.fundpsbt(amount // 2, feerate, 99, reserve=False)
psbt2 = bitcoind.rpc.decodepsbt(funding2['psbt'])
assert len(psbt2['tx']['vin']) == 1
assert funding2['excess_msat'] < funding['excess_msat']
assert funding2['feerate_per_kw'] == 7500
# Naively you'd expect this to be +99, but it might have selected a non-p2sh output...
assert funding2['estimated_final_weight'] > funding['estimated_final_weight']
# Cannot afford this one (too much)
with pytest.raises(RpcError, match=r"not afford"):
l1.rpc.fundpsbt(amount * total_outs, feerate)
l1.rpc.fundpsbt(amount * total_outs, feerate, 0)
# Nor this (depth insufficient)
with pytest.raises(RpcError, match=r"not afford"):
l1.rpc.fundpsbt(amount // 2, feerate, minconf=2)
l1.rpc.fundpsbt(amount // 2, feerate, 0, minconf=2)
# Should get two inputs.
psbt = bitcoind.rpc.decodepsbt(l1.rpc.fundpsbt(amount, feerate, reserve=False)['psbt'])
psbt = bitcoind.rpc.decodepsbt(l1.rpc.fundpsbt(amount, feerate, 0, reserve=False)['psbt'])
assert len(psbt['tx']['vin']) == 2
# Should not use reserved outputs.
psbt = bitcoind.rpc.createpsbt([{'txid': out[0], 'vout': out[1]} for out in outputs], [])
l1.rpc.reserveinputs(psbt)
with pytest.raises(RpcError, match=r"not afford"):
l1.rpc.fundpsbt(amount // 2, feerate)
l1.rpc.fundpsbt(amount // 2, feerate, 0)
# Will use first one if unreserved.
l1.rpc.unreserveinputs(bitcoind.rpc.createpsbt([{'txid': outputs[0][0], 'vout': outputs[0][1]}], []))
psbt = l1.rpc.fundpsbt(amount // 2, feerate)['psbt']
psbt = l1.rpc.fundpsbt(amount // 2, feerate, 0)['psbt']
# Should have passed to reserveinputs.
with pytest.raises(RpcError, match=r"already reserved"):
@ -540,7 +552,7 @@ def test_fundpsbt(node_factory, bitcoind, chainparams):
# And now we can't afford any more.
with pytest.raises(RpcError, match=r"not afford"):
l1.rpc.fundpsbt(amount // 2, feerate)
l1.rpc.fundpsbt(amount // 2, feerate, 0)
def test_sign_and_send_psbt(node_factory, bitcoind, chainparams):
@ -564,9 +576,10 @@ def test_sign_and_send_psbt(node_factory, bitcoind, chainparams):
bitcoind.generate_block(1)
wait_for(lambda: len(l1.rpc.listfunds()['outputs']) == total_outs)
# Make a PSBT out of our inputs (FIXME: satoshi amount should include fees!)
# Make a PSBT out of our inputs
funding = l1.rpc.fundpsbt(satoshi=Millisatoshi(3 * amount * 1000),
feerate=7500,
startweight=42,
reserve=True)
assert len([x for x in l1.rpc.listfunds()['outputs'] if x['reserved']]) == 4
psbt = bitcoind.rpc.decodepsbt(funding['psbt'])
@ -628,6 +641,7 @@ def test_sign_and_send_psbt(node_factory, bitcoind, chainparams):
wait_for(lambda: len(l2.rpc.listfunds()['outputs']) == total_outs)
l2_funding = l2.rpc.fundpsbt(satoshi=Millisatoshi(3 * amount * 1000),
feerate=7500,
startweight=42,
reserve=True)
# Try to get L1 to sign it
@ -637,6 +651,7 @@ def test_sign_and_send_psbt(node_factory, bitcoind, chainparams):
# Add some of our own PSBT inputs to it
l1_funding = l1.rpc.fundpsbt(satoshi=Millisatoshi(3 * amount * 1000),
feerate=7500,
startweight=42,
reserve=True)
# Join and add an output
@ -652,6 +667,7 @@ def test_sign_and_send_psbt(node_factory, bitcoind, chainparams):
# Send a PSBT that's not ours
l2_funding = l2.rpc.fundpsbt(satoshi=Millisatoshi(3 * amount * 1000),
feerate=7500,
startweight=42,
reserve=True)
psbt = bitcoind.rpc.joinpsbts([l2_funding['psbt'], output_pbst])
l2_signed_psbt = l2.rpc.signpsbt(psbt)['signed_psbt']

15
wallet/reservation.c
View File

@ -184,7 +184,7 @@ static struct command_result *json_fundpsbt(struct command *cmd,
struct json_stream *response;
struct utxo **utxos;
u32 *feerate_per_kw;
u32 *minconf;
u32 *minconf, *weight;
struct amount_sat *amount, input, needed, excess, total_fee;
bool all, *reserve;
u32 locktime, maxheight, current_height;
@ -192,7 +192,8 @@ static struct command_result *json_fundpsbt(struct command *cmd,
if (!param(cmd, buffer, params,
p_req("satoshi", param_sat_or_all, &amount),
p_req("feerate", param_feerate_val, &feerate_per_kw),
p_req("feerate", param_feerate, &feerate_per_kw),
p_req("startweight", param_number, &weight),
p_opt_def("minconf", param_number, &minconf, 1),
p_opt_def("reserve", param_bool, &reserve, true),
NULL))
@ -203,10 +204,15 @@ static struct command_result *json_fundpsbt(struct command *cmd,
current_height = get_block_height(cmd->ld->topology);
/* Can overflow if amount is "all" */
if (!amount_sat_add(amount, *amount,
amount_tx_fee(*feerate_per_kw, *weight)))
;
/* We keep adding until we meet their output requirements. */
input = AMOUNT_SAT(0);
utxos = tal_arr(cmd, struct utxo *, 0);
total_fee = AMOUNT_SAT(0);
total_fee = amount_tx_fee(*feerate_per_kw, *weight);
while (amount_sat_sub(&needed, *amount, input)
&& !amount_sat_eq(needed, AMOUNT_SAT(0))) {
struct utxo *utxo;
@ -227,6 +233,7 @@ static struct command_result *json_fundpsbt(struct command *cmd,
"impossible UTXO value");
/* But increase amount needed, to pay for new input */
*weight += utxo_spend_weight(utxo);
fee = amount_tx_fee(*feerate_per_kw,
utxo_spend_weight(utxo));
if (!amount_sat_add(amount, *amount, fee))
@ -300,6 +307,8 @@ static struct command_result *json_fundpsbt(struct command *cmd,
response = json_stream_success(cmd);
json_add_psbt(response, "psbt", tx->psbt);
json_add_num(response, "feerate_per_kw", *feerate_per_kw);
json_add_num(response, "estimated_final_weight", *weight);
json_add_amount_sat_only(response, "excess_msat", excess);
if (*reserve)
reserve_and_report(response, cmd->ld->wallet, current_height,