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Make TransactionOutput.getMinNonDustValue() more documented and provide a simpler function for it.

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Mike Hearn 2013-06-18 13:56:53 +02:00
parent 215a131f8b
commit f98088221e
1 changed files with 24 additions and 4 deletions
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28
core/src/main/java/com/google/bitcoin/core/TransactionOutput.java
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@ -173,18 +173,38 @@ public class TransactionOutput extends ChildMessage implements Serializable {
} }
/** /**
* Gets the minimum value for a txout of this size to be considered non-dust by a reference client (and thus relayed). * <p>Gets the minimum value for a txout of this size to be considered non-dust by a reference client
* See: CTxOut::IsDust() in the reference client. * (and thus relayed). See: CTxOut::IsDust() in the reference client. 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>
*
* <p>You probably should use {@link com.google.bitcoin.core.TransactionOutput#getMinNonDustValue()} which uses
* a safe fee-per-kb by default.</p>
* *
* @param feePerKbRequired The fee required per kilobyte. Note that this is the same as the reference client's -minrelaytxfee * 3 * @param feePerKbRequired The fee required per kilobyte. Note that this is the same as the reference client's -minrelaytxfee * 3
* If you want a safe default, use {@link Transaction#REFERENCE_DEFAULT_MIN_TX_FEE}*3 * If you want a safe default, use {@link Transaction#REFERENCE_DEFAULT_MIN_TX_FEE}*3
*/ */
public BigInteger getMinNonDustValue(BigInteger feePerKbRequired) { public BigInteger getMinNonDustValue(BigInteger feePerKbRequired) {
// Note we skip the *3 as that should be considered in the parameter // A typical output is 33 bytes (pubkey hash + opcodes) and requires an input of 148 bytes to spend so we add
BigInteger[] nonDustAndRemainder = feePerKbRequired.multiply(BigInteger.valueOf(this.bitcoinSerialize().length + 148)).divideAndRemainder(BigInteger.valueOf(1000)); // 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 pay-to-address output, unfortunately, we must follow the reference
// clients 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 BigInteger size = BigInteger.valueOf(this.bitcoinSerialize().length + 148);
BigInteger[] nonDustAndRemainder = feePerKbRequired.multiply(size).divideAndRemainder(BigInteger.valueOf(1000));
return nonDustAndRemainder[1].equals(BigInteger.ZERO) ? nonDustAndRemainder[0] : nonDustAndRemainder[0].add(BigInteger.ONE); return nonDustAndRemainder[1].equals(BigInteger.ZERO) ? nonDustAndRemainder[0] : nonDustAndRemainder[0].add(BigInteger.ONE);
} }
/**
* 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 5460 satoshis, the same as
* {@link Transaction#MIN_NONDUST_OUTPUT}.
*/
public BigInteger getMinNonDustValue() {
return getMinNonDustValue(Transaction.REFERENCE_DEFAULT_MIN_TX_FEE.multiply(BigInteger.valueOf(3)));
}
/** /**
* Sets this objects availableForSpending flag to false and the spentBy pointer to the given input. * Sets this objects availableForSpending flag to false and the spentBy pointer to the given input.
* If the input is null, it means this output was signed over to somebody else rather than one of our own keys. * If the input is null, it means this output was signed over to somebody else rather than one of our own keys.