// calcPriority returns a transaction priority given a transaction and the sum
// of each of its input values multiplied by their age (# of confirmations).
// Thus, the final formula for the priority is:
// sum(inputValue * inputAge) / adjustedTxSize
func calcPriority(tx *wire.MsgTx, txStore blockchain.TxStore, nextBlockHeight int32) float64 {
// In order to encourage spending multiple old unspent transaction
// outputs thereby reducing the total set, don't count the constant
// overhead for each input as well as enough bytes of the signature
// script to cover a pay-to-script-hash redemption with a compressed
// pubkey. This makes additional inputs free by boosting the priority
// of the transaction accordingly. No more incentive is given to avoid
// encouraging gaming future transactions through the use of junk
// outputs. This is the same logic used in the reference
// implementation.
//
// The constant overhead for a txin is 41 bytes since the previous
// outpoint is 36 bytes + 4 bytes for the sequence + 1 byte the
// signature script length.
//
// A compressed pubkey pay-to-script-hash redemption with a maximum len
// signature is of the form:
// [OP_DATA_73 <73-byte sig> + OP_DATA_35 + {OP_DATA_33
// <33 byte compresed pubkey> + OP_CHECKSIG}]
//
// Thus 1 + 73 + 1 + 1 + 33 + 1 = 110
overhead := 0
for _, txIn := range tx.TxIn {
// Max inputs + size can't possibly overflow here.
overhead += 41 + minInt(110, len(txIn.SignatureScript))
}
serializedTxSize := tx.SerializeSize()
if overhead >= serializedTxSize {
return 0.0
}
inputValueAge := calcInputValueAge(tx, txStore, nextBlockHeight)
return inputValueAge / float64(serializedTxSize-overhead)
}
// NewTxRecordFromMsgTx creates a new transaction record that may be inserted
// into the store.
func NewTxRecordFromMsgTx(msgTx *wire.MsgTx, received time.Time) (*TxRecord, error) {
buf := bytes.NewBuffer(make([]byte, 0, msgTx.SerializeSize()))
err := msgTx.Serialize(buf)
if err != nil {
str := "failed to serialize transaction"
return nil, storeError(ErrInput, str, err)
}
rec := &TxRecord{
MsgTx: *msgTx,
Received: received,
SerializedTx: buf.Bytes(),
}
copy(rec.Hash[:], wire.DoubleSha256(rec.SerializedTx))
return rec, nil
}
