/// <summary>
/// Check whether an output amount is considered dust for a given transaction relay fee.
/// Transactions with dust outputs are rejected by mempool.
/// </summary>
/// <param name="amount">Output amount</param>
/// <param name="scriptSize">Size of the output script in bytes</param>
/// <param name="relayFeePerKb">Mempool relay fee/kB</param>
/// <returns>Whether the output is dust</returns>
public static bool IsDustAmount(Amount amount, int scriptSize, Amount relayFeePerKb)
{
// Calculate the total (estimated) cost to the network. This is
// calculated using the serialize size of the output plus the serial
// size of a transaction input which redeems it. The output is assumed
// to be compressed P2PKH as this is the most common script type. Use
// the average size of a compressed P2PKH redeem input (165) rather than
// the largest possible (Transaction.RedeemPayToPubKeyHashInputSize).
var totalSize = 8 + 2 + CompactInt.SerializeSize((ulong)scriptSize) + scriptSize + 165;
// Dust is defined as an output value where the total cost to the network
// (output size + input size) is greater than 1/3 of the relay fee.
return(amount * 1000 / (3 * totalSize) < relayFeePerKb);
}
/// <summary>
/// Estimates the signed serialize size of an unsigned transaction, assuming all
/// inputs spend P2PKH outputs. The estimate is a worst case, so the actual
/// serialize size after signing should always be less than or equal to this value.
/// </summary>
/// <param name="inputCount">Number of P2PKH outputs the transaction will redeem</param>
/// <param name="outputs">Transaction output array</param>
/// <param name="addChangeOutput">Add the serialize size for an additional P2PKH change output</param>
/// <returns>Estimated signed serialize size of the transaction</returns>
public static int EstimateSerializeSize(int inputCount, Output[] outputs, bool addChangeOutput)
{
if (outputs == null)
{
throw new ArgumentNullException(nameof(outputs));
}
var changeSize = 0;
var outputCount = outputs.Length;
if (addChangeOutput)
{
changeSize = PayToPubKeyHashOutputSize;
outputCount++;
}
return
(12 + (2 * CompactInt.SerializeSize((ulong)inputCount)) + CompactInt.SerializeSize((ulong)outputCount) +
inputCount * RedeemPayToPubKeyHashInputSize +
outputs.Sum(o => o.SerializeSize) +
changeSize);
}