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Pad initial output if below dust limit #674

Merged
merged 6 commits into from
Oct 19, 2022
Merged

Pad initial output if below dust limit #674

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da1c420
Remove unnecessary Results
casey Oct 19, 2022
6f3798a
Add failing alignment output padding test
casey Oct 19, 2022
fa6f153
Make test pass
casey Oct 19, 2022
74f747a
Refactor into helper function
casey Oct 19, 2022
64b23b5
Add invariant and invariant check
casey Oct 19, 2022
724c378
Merge branch 'master' into avoid-initial-dust-output
casey Oct 19, 2022
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234 changes: 180 additions & 54 deletions src/subcommand/wallet/transaction_builder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -73,13 +73,16 @@ impl TransactionBuilder {
recipient: Address,
change: Vec<Address>,
) -> Result<Transaction> {
Self::new(ranges, ordinal, recipient, change)
.select_ordinal()?
.align_ordinal()?
.add_postage()?
.strip_excess_postage()?
.deduct_fee()?
.build()
Ok(
Self::new(ranges, ordinal, recipient, change)
.select_ordinal()?
.align_ordinal()
.pad_alignment_output()?
.add_postage()?
.strip_excess_postage()
.deduct_fee()
.build(),
)
}

fn new(
Expand Down Expand Up @@ -122,7 +125,7 @@ impl TransactionBuilder {
Ok(self)
}

fn align_ordinal(mut self) -> Result<Self> {
fn align_ordinal(mut self) -> Self {
assert_eq!(self.outputs.len(), 1, "invariant: only one output");

assert_eq!(
Expand All @@ -145,6 +148,19 @@ impl TransactionBuilder {
self.outputs.last_mut().expect("no output").1 -= Amount::from_sat(ordinal_offset);
}

self
}

fn pad_alignment_output(mut self) -> Result<Self> {
if self.outputs[0].0 != self.recipient {
let dust_limit = self.recipient.script_pubkey().dust_value();
if self.outputs[0].1 < dust_limit {
let (utxo, size) = self.select_padding_utxo(dust_limit - self.outputs[0].1)?;
self.inputs.insert(0, utxo);
self.outputs[0].1 += size;
}
}

Ok(self)
}

Expand All @@ -153,28 +169,15 @@ impl TransactionBuilder {
let dust_limit = self.outputs.last().unwrap().0.script_pubkey().dust_value();

if self.outputs.last().unwrap().1 < dust_limit + estimated_fee {
let shortfall = dust_limit + estimated_fee - self.outputs.last().unwrap().1;
let mut found = None;
for utxo in &self.utxos {
let size = self.ranges[utxo]
.iter()
.map(|(start, end)| Amount::from_sat(end - start))
.sum::<Amount>();
if size > shortfall {
found = Some((*utxo, size));
break;
}
}

let (utxo, size) = found.ok_or(Error::InsufficientPadding)?;
let (utxo, size) =
self.select_padding_utxo(dust_limit + estimated_fee - self.outputs.last().unwrap().1)?;
self.inputs.push(utxo);
self.outputs.last_mut().unwrap().1 += size;
self.utxos.remove(&utxo);
}
Ok(self)
}

fn strip_excess_postage(mut self) -> Result<Self> {
fn strip_excess_postage(mut self) -> Self {
let ordinal_offset = self.calculate_ordinal_offset();
let total_output_amount = self
.outputs
Expand All @@ -200,10 +203,10 @@ impl TransactionBuilder {
));
}

Ok(self)
self
}

fn deduct_fee(mut self) -> Result<Self> {
fn deduct_fee(mut self) -> Self {
let ordinal_offset = self.calculate_ordinal_offset();

let fee = self.estimate_fee();
Expand All @@ -226,7 +229,7 @@ impl TransactionBuilder {

*last_output_amount -= fee;

Ok(self)
self
}

fn estimate_fee(&self) -> Amount {
Expand Down Expand Up @@ -256,7 +259,7 @@ impl TransactionBuilder {
Self::TARGET_FEE_RATE * dummy_transaction.vsize().try_into().unwrap()
}

fn build(self) -> Result<Transaction> {
fn build(self) -> Transaction {
let ordinal = self.ordinal.n();
let recipient = self.recipient.script_pubkey();
let transaction = Transaction {
Expand Down Expand Up @@ -380,7 +383,14 @@ impl TransactionBuilder {
target_fee_rate,
);

Ok(transaction)
for tx_out in &transaction.output {
assert!(
Amount::from_sat(tx_out.value) >= tx_out.script_pubkey.dust_value(),
"invariant: all outputs are above dust limit",
);
}

transaction
}

fn calculate_ordinal_offset(&self) -> u64 {
Expand All @@ -395,6 +405,27 @@ impl TransactionBuilder {
}
panic!("Could not find ordinal in inputs");
}

fn select_padding_utxo(&mut self, minimum_amount: Amount) -> Result<(OutPoint, Amount)> {
let mut found = None;

for utxo in &self.utxos {
let amount = self.ranges[utxo]
.iter()
.map(|(start, end)| Amount::from_sat(end - start))
.sum::<Amount>();
if amount >= minimum_amount {
found = Some((*utxo, amount));
break;
}
}

let (utxo, amount) = found.ok_or(Error::InsufficientPadding)?;

self.utxos.remove(&utxo);

Ok((utxo, amount))
}
}

#[cfg(test)]
Expand Down Expand Up @@ -547,7 +578,7 @@ mod tests {
};

assert_eq!(
tx_builder.build().unwrap(),
tx_builder.build(),
Transaction {
version: 1,
lock_time: PackedLockTime::ZERO,
Expand Down Expand Up @@ -679,11 +710,8 @@ mod tests {
.select_ordinal()
.unwrap()
.align_ordinal()
.unwrap()
.strip_excess_postage()
.unwrap()
.deduct_fee()
.unwrap();
.deduct_fee();
}

#[test]
Expand Down Expand Up @@ -932,8 +960,7 @@ mod tests {
.unwrap(),
],
)
.build()
.ok();
.build();
}

#[test]
Expand Down Expand Up @@ -961,8 +988,7 @@ mod tests {
.unwrap(),
],
)
.build()
.ok();
.build();
}

#[test]
Expand Down Expand Up @@ -997,7 +1023,7 @@ mod tests {
.parse()
.unwrap();

builder.build().ok();
builder.build();
}

#[test]
Expand Down Expand Up @@ -1030,7 +1056,7 @@ mod tests {

builder.outputs[0].1 = Amount::from_sat(0);

builder.build().ok();
builder.build();
}

#[test]
Expand Down Expand Up @@ -1116,8 +1142,7 @@ mod tests {
)
.select_ordinal()
.unwrap()
.build()
.unwrap();
.build();
}

#[test]
Expand Down Expand Up @@ -1176,6 +1201,80 @@ mod tests {
)
}

#[test]
fn alignment_output_under_dust_limit_is_padded() {
let utxos = vec![
(
"1111111111111111111111111111111111111111111111111111111111111111:1"
.parse()
.unwrap(),
vec![(0, 10_000)],
),
(
"2222222222222222222222222222222222222222222222222222222222222222:2"
.parse()
.unwrap(),
vec![(10_000, 20_000)],
),
];

pretty_assert_eq!(
TransactionBuilder::build_transaction(
utxos.into_iter().collect(),
Ordinal(1),
"tb1q6en7qjxgw4ev8xwx94pzdry6a6ky7wlfeqzunz"
.parse()
.unwrap(),
vec![
"tb1qjsv26lap3ffssj6hfy8mzn0lg5vte6a42j75ww"
.parse()
.unwrap(),
"tb1qakxxzv9n7706kc3xdcycrtfv8cqv62hnwexc0l"
.parse()
.unwrap(),
]
),
Ok(Transaction {
version: 1,
lock_time: PackedLockTime::ZERO,
input: vec![
TxIn {
previous_output: "2222222222222222222222222222222222222222222222222222222222222222:2"
.parse()
.unwrap(),
script_sig: Script::new(),
sequence: Sequence::ENABLE_RBF_NO_LOCKTIME,
witness: Witness::new(),
},
TxIn {
previous_output: "1111111111111111111111111111111111111111111111111111111111111111:1"
.parse()
.unwrap(),
script_sig: Script::new(),
sequence: Sequence::ENABLE_RBF_NO_LOCKTIME,
witness: Witness::new(),
},
],
output: vec![
TxOut {
value: 10_001,
script_pubkey: "tb1qakxxzv9n7706kc3xdcycrtfv8cqv62hnwexc0l"
.parse::<Address>()
.unwrap()
.script_pubkey(),
},
TxOut {
value: 9_845,
script_pubkey: "tb1q6en7qjxgw4ev8xwx94pzdry6a6ky7wlfeqzunz"
.parse::<Address>()
.unwrap()
.script_pubkey(),
}
],
})
)
}

#[test]
#[should_panic(expected = "invariant: all outputs are either change or recipient")]
fn invariant_all_output_are_recognized() {
Expand Down Expand Up @@ -1204,17 +1303,49 @@ mod tests {
.select_ordinal()
.unwrap()
.align_ordinal()
.unwrap()
.add_postage()
.unwrap()
.strip_excess_postage()
.unwrap()
.deduct_fee()
.unwrap();
.deduct_fee();

builder.change_addresses = BTreeSet::new();

builder.build().ok();
builder.build();
}

#[test]
#[should_panic(expected = "invariant: all outputs are above dust limit")]
fn invariant_all_output_are_above_dust_limit() {
let utxos = vec![(
"1111111111111111111111111111111111111111111111111111111111111111:1"
.parse()
.unwrap(),
vec![(0, 10_000)],
)];

TransactionBuilder::new(
utxos.into_iter().collect(),
Ordinal(1),
"tb1q6en7qjxgw4ev8xwx94pzdry6a6ky7wlfeqzunz"
.parse()
.unwrap(),
vec![
"tb1qjsv26lap3ffssj6hfy8mzn0lg5vte6a42j75ww"
.parse()
.unwrap(),
"tb1qakxxzv9n7706kc3xdcycrtfv8cqv62hnwexc0l"
.parse()
.unwrap(),
],
)
.select_ordinal()
.unwrap()
.align_ordinal()
.add_postage()
.unwrap()
.strip_excess_postage()
.deduct_fee()
.build();
}

#[test]
Expand Down Expand Up @@ -1245,11 +1376,8 @@ mod tests {
.select_ordinal()
.unwrap()
.strip_excess_postage()
.unwrap()
.deduct_fee()
.unwrap()
.build()
.unwrap();
.build();
}

#[test]
Expand Down Expand Up @@ -1280,8 +1408,6 @@ mod tests {
.select_ordinal()
.unwrap()
.strip_excess_postage()
.unwrap()
.build()
.unwrap();
.build();
}
}