// EstFee gives a fee estimate based on a tx and a sat/Byte target.
// The TX should have all outputs, including the change address already
// populated (with potentially 0 amount. Also it should have all inputs
// populated, but inputs don't need to have sigscripts or witnesses
// (it'll guess the sizes of sigs/wits that arent' filled in).
func EstFee(otx *wire.MsgTx, spB int64) int64 {
mtsig := make([]byte, 72)
mtpub := make([]byte, 33)
tx := otx.Copy()
// iterate through txins, replacing subscript sigscripts with noise
// sigs or witnesses
for _, txin := range tx.TxIn {
// check wpkh
if len(txin.SignatureScript) == 22 &&
txin.SignatureScript[0] == 0x00 && txin.SignatureScript[1] == 0x14 {
txin.SignatureScript = nil
txin.Witness = make([][]byte, 2)
txin.Witness[0] = mtsig
txin.Witness[1] = mtpub
} else if len(txin.SignatureScript) == 34 &&
txin.SignatureScript[0] == 0x00 && txin.SignatureScript[1] == 0x20 {
// p2wsh -- sig lenght is a total guess!
txin.SignatureScript = nil
txin.Witness = make([][]byte, 3)
// 3 sigs? totally guessing here
txin.Witness[0] = mtsig
txin.Witness[1] = mtsig
txin.Witness[2] = mtsig
} else {
// assume everything else is p2pkh. Even though it's not
txin.Witness = nil
txin.SignatureScript = make([]byte, 105) // len of p2pkh sigscript
}
}
fmt.Printf(TxToString(tx))
size := int64(blockchain.GetTxVirtualSize(btcutil.NewTx(tx)))
fmt.Printf("%d spB, est vsize %d, fee %d\n", spB, size, size*spB)
return size * spB
}
