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Merge rust-bitcoin/rust-bitcoin#2182: fix: FeeRate::checked_mul_by_weight should scale output down by 1000 

6c6c08ca50 add second test case (conduition)
0c56131819 fix: FeeRate::checked_mul_by_weight should scale output down by 1000 (conduition)

Pull request description:

  Fixes a bug in https://github.com/rust-bitcoin/rust-bitcoin/pull/1864. The `FeeRate::checked_mul_by_weight` and by extension the `FeeRate::fee_wu` methods were returning fee amounts scaled up by a factor of 1000, since the internal representation in `FeeRate` is sats per 1000 weight units.

  This PR fixes `checked_mul_by_weight` and its unit tests by scaling the output of these methods down by 1000, so that `X sat/vbyte * Y vbytes = X * Y sats`, instead of `X * Y * 1000 sats` as before.

  ## Before

  This code would pass without panic before this PR.
  ```rust
  let weight = Weight::from_vb(3).unwrap();
  let rate = FeeRate::from_sat_per_vb(3).unwrap();
  assert_eq!(weight * rate, Amount::from_sat(9));
  assert_eq!(rate.checked_mul_by_weight(weight), Some(Amount::from_sat(9000)));
  ```

  ## After

  ```rust
  let weight = Weight::from_vb(3).unwrap();
  let rate = FeeRate::from_sat_per_vb(3).unwrap();
  assert_eq!(weight * rate, Amount::from_sat(9));
  assert_eq!(rate.checked_mul_by_weight(weight), Some(Amount::from_sat(9)));
  ```

ACKs for top commit:
  Kixunil:
    ACK 6c6c08ca50

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This commit is contained in:
Andrew Poelstra 2023-11-13 21:03:29 +00:00
parent 966b190f23 6c6c08ca50
commit ee787c6481
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1 changed files with 18 additions and 7 deletions
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25
bitcoin/src/blockdata/fee_rate.rs
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@ -82,10 +82,12 @@ impl FeeRate {
/// Checked weight multiplication.
///
/// Computes `self * rhs` where rhs is of type Weight. `None` is returned if an overflow
/// occurred.
/// Computes the absolute fee amount for a given [`Weight`] at this fee rate.
///
/// `None` is returned if an overflow occurred.
pub fn checked_mul_by_weight(self, rhs: Weight) -> Option<Amount> {
self.0.checked_mul(rhs.to_wu()).map(Amount::from_sat)
let sats = self.0.checked_mul(rhs.to_wu())?.checked_add(999)? / 1000;
Some(Amount::from_sat(sats))
}
/// Calculates fee by multiplying this fee rate by weight, in weight units, returning `None`
@ -95,13 +97,14 @@ impl FeeRate {
///
/// # Examples
///
/// ```no_run
/// ```
/// # use bitcoin::{absolute, transaction, FeeRate, Transaction};
/// # // Dummy transaction.
/// # let tx = Transaction { version: transaction::Version::ONE, lock_time: absolute::LockTime::ZERO, input: vec![], output: vec![] };
///
/// let rate = FeeRate::from_sat_per_vb(1).expect("1 sat/vbyte is valid");
/// let fee = rate.fee_wu(tx.weight());
/// let fee = rate.fee_wu(tx.weight()).unwrap();
/// assert_eq!(fee.to_sat(), tx.vsize() as u64);
/// ```
pub fn fee_wu(self, weight: Weight) -> Option<Amount> { self.checked_mul_by_weight(weight) }
@ -209,12 +212,20 @@ mod tests {
#[test]
fn checked_weight_mul_test() {
let weight = Weight::from_wu(10);
let fee: Amount = FeeRate(10).checked_mul_by_weight(weight).expect("expected Amount");
let weight = Weight::from_vb(10).unwrap();
let fee: Amount = FeeRate::from_sat_per_vb(10)
.unwrap()
.checked_mul_by_weight(weight)
.expect("expected Amount");
assert_eq!(Amount::from_sat(100), fee);
let fee = FeeRate(10).checked_mul_by_weight(Weight::MAX);
assert!(fee.is_none());
let weight = Weight::from_vb(3).unwrap();
let fee_rate = FeeRate::from_sat_per_vb(3).unwrap();
let fee = fee_rate.checked_mul_by_weight(weight).unwrap();
assert_eq!(Amount::from_sat(9), fee);
}
#[test]