/// <summary>
/// Constructs an unsigned transaction by referencing previous unspent outputs.
/// A change output is added when necessary to return extra value back to the wallet.
/// </summary>
/// <param name="outputs">Transaction output array without change.</param>
/// <param name="changeScript">Output script to pay change to.</param>
/// <param name="fetchInputsAsync">Input selection source.</param>
/// <returns>Unsigned transaction and total input amount.</returns>
/// <exception cref="InsufficientFundsException">Input source was unable to provide enough input value.</exception>
public static async Task <Tuple <Transaction, Amount> > BuildUnsignedTransaction(Transaction.Output[] outputs,
Amount feePerKb,
InputSource fetchInputsAsync,
ChangeSource fetchChangeAsync)
{
if (outputs == null)
{
throw new ArgumentNullException(nameof(outputs));
}
if (fetchInputsAsync == null)
{
throw new ArgumentNullException(nameof(fetchInputsAsync));
}
if (fetchChangeAsync == null)
{
throw new ArgumentNullException(nameof(fetchChangeAsync));
}
var targetAmount = outputs.Sum(o => o.Amount);
var estimatedSize = Transaction.EstimateSerializeSize(1, outputs, true);
var targetFee = TransactionFees.FeeForSerializeSize(feePerKb, estimatedSize);
while (true)
{
var funding = await fetchInputsAsync(targetAmount + targetFee);
var inputAmount = funding.Item1;
var inputs = funding.Item2;
if (inputAmount < targetAmount + targetFee)
{
throw new InsufficientFundsException();
}
var maxSignedSize = Transaction.EstimateSerializeSize(inputs.Length, outputs, true);
var maxRequiredFee = TransactionFees.FeeForSerializeSize(feePerKb, maxSignedSize);
var remainingAmount = inputAmount - targetAmount;
if (remainingAmount < maxRequiredFee)
{
targetFee = maxRequiredFee;
continue;
}
var unsignedTransaction = new Transaction(Transaction.SupportedVersion, inputs, outputs, 0, 0);
var changeAmount = inputAmount - targetAmount - maxRequiredFee;
if (changeAmount != 0 && !TransactionRules.IsDustAmount(changeAmount, Transaction.PayToPubKeyHashPkScriptSize, feePerKb))
{
var changeScript = await fetchChangeAsync();
if (changeScript.Script.Length > Transaction.PayToPubKeyHashPkScriptSize)
{
throw new Exception("Fee estimation requires change scripts no larger than P2PKH output scripts");
}
var changeOutput = new Transaction.Output(changeAmount, Transaction.Output.LatestPkScriptVersion, changeScript.Script);
var outputList = unsignedTransaction.Outputs.ToList();
outputList.Add(changeOutput);
var outputsWithChange = outputList.ToArray();
unsignedTransaction = new Transaction(unsignedTransaction.Version, unsignedTransaction.Inputs, outputsWithChange,
unsignedTransaction.LockTime, unsignedTransaction.Expiry);
}
return(Tuple.Create(unsignedTransaction, inputAmount));
}
}
/// <summary>
/// Builds a transaction that sends value from one address to another.
/// Change is spent to the source address, if necessary.
/// </summary>
/// <param name="request"></param>
/// <param name="feeFactor"></param>
/// <returns></returns>
/// <exception cref="BusinessException"></exception>
public async Task <BuildTransactionResponse> BuildSingleTransactionAsync(BuildSingleTransactionRequest request, decimal feeFactor)
{
if (string.IsNullOrWhiteSpace(request.FromAddress))
{
throw new BusinessException(ErrorReason.BadRequest, "FromAddress missing");
}
if (string.IsNullOrWhiteSpace(request.ToAddress))
{
throw new BusinessException(ErrorReason.BadRequest, "ToAddress missing");
}
if (!long.TryParse(request.Amount, out var amount) || amount <= 0)
{
throw new BusinessException(ErrorReason.BadRequest, $"Invalid amount {amount}");
}
var feePerKb = await _feeService.GetFeePerKb();
if (TransactionRules.IsDustAmount(amount, Transaction.PayToPubKeyHashPkScriptSize, new Amount(feePerKb)))
{
throw new BusinessException(ErrorReason.AmountTooSmall, "Amount is dust");
}
const int outputVersion = 0;
const int lockTime = 0;
const int expiry = 0;
// Number of outputs newly build tx will contain,
// not including the change address
const int numOutputs = 1;
// Lykke api doesn't have option to specify a change address.
var changeAddress = Address.Decode(request.FromAddress);
var toAddress = Address.Decode(request.ToAddress);
var allInputs = (await GetUtxosForAddress(request.FromAddress)).ToList();
long estFee = 0;
long totalSpent = 0;
var consumedInputs = new List <Transaction.Input>();
bool HasEnoughInputs(out long fee)
{
var calculateWithChange = false;
while (true)
{
var changeCount = calculateWithChange ? 1 : 0;
fee = _feeService.CalculateFee(feePerKb, consumedInputs.Count, numOutputs + changeCount, feeFactor);
var estAmount = amount + (request.IncludeFee ? 0 : fee);
if (totalSpent < estAmount)
{
return(false);
}
if (totalSpent == estAmount)
{
return(true);
}
if (totalSpent > estAmount && calculateWithChange)
{
return(true);
}
// Loop one more time but make sure change is accounted for this time.
if (totalSpent > estAmount)
{
calculateWithChange = true;
}
}
}
// Accumulate inputs until we have enough to cover the cost
// of the amount + fee
foreach (var input in allInputs)
{
// Don't consume an outpoint if it's spent.
if (await IsBroadcastedUtxo(input.PreviousOutpoint))
{
continue;
}
consumedInputs.Add(input);
totalSpent += input.InputAmount;
if (HasEnoughInputs(out estFee))
{
break;
}
}
// If all inputs do not have enough value to fund the transaction.
if (totalSpent < amount + (request.IncludeFee ? 0 : estFee))
{
throw new BusinessException(ErrorReason.NotEnoughBalance, "Address balance too low");
}
// The fee either comes from the change or the sent amount
var send = amount - (request.IncludeFee ? estFee : 0);
var change = (totalSpent - amount) - (request.IncludeFee ? 0 : estFee);
// If all inputs do not have enough value to fund the transaction, throw error.
if (request.IncludeFee && estFee > amount)
{
throw new BusinessException(ErrorReason.AmountTooSmall, "Amount not enough to include fee");
}
// If all inputs do not have enough value to fund the transaction, throw error.
if (totalSpent < amount + (request.IncludeFee ? 0 : estFee))
{
throw new BusinessException(ErrorReason.NotEnoughBalance, "Address balance too low");
}
// Build outputs to address + change address.
// If any of the outputs is zero value, exclude it. For example, if there is no change.
var outputs = new[] {
new Transaction.Output(send, outputVersion, toAddress.BuildScript().Script),
new Transaction.Output(change, outputVersion, changeAddress.BuildScript().Script)
}.Where(o => o.Amount != 0).ToArray();
var newTx = new Transaction(
Transaction.SupportedVersion,
consumedInputs.ToArray(),
outputs,
lockTime,
expiry
);
return(new BuildTransactionResponse
{
TransactionContext = HexUtil.FromByteArray(newTx.Serialize())
});
}