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Improve the reasoning for why the Bitcoin DUST constant is set as it is

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Also halves the minimum fee policy, which still may be 2x-4x higher than
necessary due to API limitations within bitcoin-serai (which we can fix as it's
within our scope).
This commit is contained in:
Luke Parker 2023-10-22 17:55:10 -04:00
parent a71a789912
commit 0fff5391a8
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1 changed files with 17 additions and 10 deletions
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27
processor/src/networks/bitcoin.rs
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@ -335,11 +335,14 @@ impl Bitcoin {
fees.sort();
let fee = fees.get(fees.len() / 2).cloned().unwrap_or(0);
// The DUST constant documentation details a 5000 sat/kilo-vbyte minimum fee policy.
// 5000 sat/kilo-vbyte is 5000 sat/4-kilo-weight (1250 sat/kilo-weight).
// Since bitcoin-serai takes fee per weight, use a minimum of 2
// (the ceil div of 1250 by 1000)
Ok(Fee(fee.max(2)))
// The DUST constant documentation notes a relay rule practically enforcing a
// 1000 sat/kilo-vbyte minimum fee.
//
// 1000 sat/kilo-vbyte is 1000 sat/4-kilo-weight (250 sat/kilo-weight).
// Since bitcoin-serai takes fee per weight, we'd need to pass 0.25 to achieve this fee rate.
// Accordingly, setting 1 is 4x the current relay rule minimum (and should be more than safe).
// TODO: Rewrite to fee_per_vbyte, not fee_per_weight?
Ok(Fee(fee.max(1)))
}
async fn make_signable_transaction(
@ -430,9 +433,12 @@ impl Network for Bitcoin {
(4 * (36 + 1 + 4)) + (1 + 1 + 64) = 164 + 66 = 230 weight units
230 ceil div 4 = 57 vbytes
Bitcoin defines multiple minimum feerate constants *per kilo-vbyte*. Currently, these are
1000 and 3000. Since these are solely relay rules, and may be raised, we use a
5000 sat/kilo-vbyte minimum fee rate.
Bitcoin defines multiple minimum feerate constants *per kilo-vbyte*. Currently, these are:
- 1000 sat/kilo-vbyte for a transaction to be relayed
- Each output's value must exceed the fee of the TX spending it at 3000 sat/kilo-vbyte
The DUST constant needs to be determined by the latter.
Since these are solely relay rules, and may be raised, we require all outputs be spendable
under a 5000 sat/kilo-vbyte fee rate.
5000 sat/kilo-vbyte = 5 sat/vbyte
5 * 57 = 285 sats/spent-output
@ -440,7 +446,8 @@ impl Network for Bitcoin {
Even if an output took 100 bytes (it should be just ~29-43), taking 400 weight units, adding
100 vbytes, tripling the transaction size, then the sats/tx would be < 1000.
Increase by an order of magnitude, 10,000 satoshis.
Increase by an order of magnitude, in order to ensure this is actually worth our time, and we
get 10,000 satoshis.
*/
const DUST: u64 = 10_000;
@ -450,7 +457,7 @@ impl Network for Bitcoin {
// issues in the future (if the size decreases or we mis-evaluate it)
// It also offers a minimal amount of benefit when we are able to logarithmically accumulate
// inputs
// For 128-byte inputs (40-byte output specification, 64-byte signature, whatever overhead) and
// For 128-byte inputs (36-byte output specification, 64-byte signature, whatever overhead) and
// 64-byte outputs (40-byte script, 8-byte amount, whatever overhead), they together take up 192
// bytes
// 100,000 / 192 = 520