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TransactionOutput: Consider the witness discount in getMinNonDustValue().

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This commit is contained in:
Andreas Schildbach 2019-04-28 15:20:47 +02:00
parent fb353d744e
commit 25f36872d5
2 changed files with 30 additions and 14 deletions
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36
core/src/main/java/org/bitcoinj/core/TransactionOutput.java
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@ -193,10 +193,7 @@ public class TransactionOutput extends ChildMessage {
/**
* <p>Gets the minimum value for a txout of this size to be considered non-dust by Bitcoin Core
* (and thus relayed). See: CTxOut::IsDust() in Bitcoin Core. The assumption is that any output that would
* consume more than a third of its value in fees is not something the Bitcoin system wants to deal with right now,
* so we call them "dust outputs" and they're made non standard. The choice of one third is somewhat arbitrary and
* may change in future.</p>
* (and thus relayed). See: CTxOut::IsDust() in Bitcoin Core.</p>
*
* <p>You probably should use {@link TransactionOutput#getMinNonDustValue()} which uses
* a safe fee-per-kb by default.</p>
@ -204,19 +201,34 @@ public class TransactionOutput extends ChildMessage {
* @param feePerKb The fee required per kilobyte. Note that this is the same as Bitcoin Core's -minrelaytxfee * 3
*/
public Coin getMinNonDustValue(Coin feePerKb) {
// A typical output is 33 bytes (pubkey hash + opcodes) and requires an input of 148 bytes to spend so we add
// that together to find out the total amount of data used to transfer this amount of value. Note that this
// formula is wrong for anything that's not a P2PKH output, unfortunately, we must follow Bitcoin Core's
// wrongness in order to ensure we're considered standard. A better formula would either estimate the
// size of data needed to satisfy all different script types, or just hard code 33 below.
final long size = this.unsafeBitcoinSerialize().length + 148;
// "Dust" is defined in terms of dustRelayFee,
// which has units satoshis-per-kilobyte.
// If you'd pay more in fees than the value of the output
// to spend something, then we consider it dust.
// A typical spendable non-segwit txout is 34 bytes big, and will
// need a CTxIn of at least 148 bytes to spend:
// so dust is a spendable txout less than
// 182*dustRelayFee/1000 (in satoshis).
// 546 satoshis at the default rate of 3000 sat/kB.
// A typical spendable segwit txout is 31 bytes big, and will
// need a CTxIn of at least 67 bytes to spend:
// so dust is a spendable txout less than
// 98*dustRelayFee/1000 (in satoshis).
// 294 satoshis at the default rate of 3000 sat/kB.
long size = this.unsafeBitcoinSerialize().length;
final Script script = getScriptPubKey();
if (ScriptPattern.isP2PKH(script) || ScriptPattern.isP2PK(script) || ScriptPattern.isP2SH(script))
size += 32 + 4 + 1 + 107 + 4; // 148
else if (ScriptPattern.isP2WH(script))
size += 32 + 4 + 1 + (107 / 4) + 4; // 68
else
return Coin.ZERO;
return feePerKb.multiply(size).divide(1000);
}
/**
* Returns the minimum value for this output to be considered "not dust", i.e. the transaction will be relayable
* and mined by default miners. For normal pay to address outputs, this is 2730 satoshis, the same as
* {@link Transaction#MIN_NONDUST_OUTPUT}.
* and mined by default miners.
*/
public Coin getMinNonDustValue() {
return getMinNonDustValue(Transaction.REFERENCE_DEFAULT_MIN_TX_FEE.multiply(3));

8
core/src/test/java/org/bitcoinj/core/TransactionOutputTest.java
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@ -86,7 +86,11 @@ public class TransactionOutputTest extends TestWithWallet {
@Test
public void getMinNonDustValue() throws Exception {
TransactionOutput payToAddressOutput = new TransactionOutput(UNITTEST, null, Coin.COIN, myAddress);
assertEquals(Transaction.MIN_NONDUST_OUTPUT, payToAddressOutput.getMinNonDustValue());
TransactionOutput p2pk = new TransactionOutput(UNITTEST, null, Coin.COIN, myKey);
assertEquals(Coin.valueOf(576), p2pk.getMinNonDustValue());
TransactionOutput p2pkh = new TransactionOutput(UNITTEST, null, Coin.COIN, LegacyAddress.fromKey(UNITTEST, myKey));
assertEquals(Coin.valueOf(546), p2pkh.getMinNonDustValue());
TransactionOutput p2wpkh = new TransactionOutput(UNITTEST, null, Coin.COIN, SegwitAddress.fromKey(UNITTEST, myKey));
assertEquals(Coin.valueOf(294), p2wpkh.getMinNonDustValue());
}
}