input.go

package bt

import (
	"encoding/binary"
	"encoding/hex"
	"fmt"
	"io"

	"github.com/libsv/go-bt/v2/bscript"
	"github.com/pkg/errors"
)

/*
Field	                     Description                                                   Size
--------------------------------------------------------------------------------------------------------
Previous Transaction hash  doubled SHA256-hashed of a (previous) to-be-used transaction	 32 bytes
Previous Txout-index       non-negative integer indexing an output of the to-be-used      4 bytes
                           transaction
Txin-script length         non-negative integer VI = VarInt                               1-9 bytes
Txin-script / scriptSig	   Script	                                                        <in-script length>-many bytes
sequence_no	               normally 0xFFFFFFFF; irrelevant unless transaction's           4 bytes
                           lock_time is > 0
*/

// DefaultSequenceNumber is the default starting sequence number
const DefaultSequenceNumber uint32 = 0xFFFFFFFF

// Input is a representation of a transaction input
//
// DO NOT CHANGE ORDER - Optimised for memory via maligned
//
type Input struct {
	previousTxID       []byte
	PreviousTxSatoshis uint64
	PreviousTxScript   *bscript.Script
	UnlockingScript    *bscript.Script
	PreviousTxOutIndex uint32
	SequenceNumber     uint32
}

// ReadFrom reads from the `io.Reader` into the `bt.Input`.
func (i *Input) ReadFrom(r io.Reader) (int64, error) {
	*i = Input{}
	var bytesRead int64

	previousTxID := make([]byte, 32)
	n, err := io.ReadFull(r, previousTxID)
	bytesRead += int64(n)
	if err != nil {
		return bytesRead, errors.Wrapf(err, "previousTxID(32): got %d bytes", n)
	}

	prevIndex := make([]byte, 4)
	n, err = io.ReadFull(r, prevIndex)
	bytesRead += int64(n)
	if err != nil {
		return bytesRead, errors.Wrapf(err, "previousTxID(4): got %d bytes", n)
	}

	var l VarInt
	n64, err := l.ReadFrom(r)
	bytesRead += n64
	if err != nil {
		return bytesRead, err
	}

	script := make([]byte, l)
	n, err = io.ReadFull(r, script)
	bytesRead += int64(n)
	if err != nil {
		return bytesRead, errors.Wrapf(err, "script(%d): got %d bytes", l, n)
	}

	sequence := make([]byte, 4)
	n, err = io.ReadFull(r, sequence)
	bytesRead += int64(n)
	if err != nil {
		return bytesRead, errors.Wrapf(err, "sequence(4): got %d bytes", n)
	}

	i.previousTxID = ReverseBytes(previousTxID)
	i.PreviousTxOutIndex = binary.LittleEndian.Uint32(prevIndex)
	i.UnlockingScript = bscript.NewFromBytes(script)
	i.SequenceNumber = binary.LittleEndian.Uint32(sequence)

	return bytesRead, nil
}

// PreviousTxIDAdd will add the supplied txID bytes to the Input,
// if it isn't a valid transaction id an ErrInvalidTxID error will be returned.
func (i *Input) PreviousTxIDAdd(txID []byte) error {
	if !IsValidTxID(txID) {
		return ErrInvalidTxID
	}
	i.previousTxID = txID
	return nil
}

// PreviousTxIDAddStr will validate and add the supplied txID string to the Input,
// if it isn't a valid transaction id an ErrInvalidTxID error will be returned.
func (i *Input) PreviousTxIDAddStr(txID string) error {
	bb, err := hex.DecodeString(txID)
	if err != nil {
		return err
	}
	return i.PreviousTxIDAdd(bb)
}

// PreviousTxID will return the PreviousTxID if set.
func (i *Input) PreviousTxID() []byte {
	return i.previousTxID
}

// PreviousTxIDStr returns the Previous TxID as a hex string.
func (i *Input) PreviousTxIDStr() string {
	return hex.EncodeToString(i.previousTxID)
}

// String implements the Stringer interface and returns a string
// representation of a transaction input.
func (i *Input) String() string {
	return fmt.Sprintf(
		`prevTxHash:   %s
prevOutIndex: %d
scriptLen:    %d
script:       %s
sequence:     %x
`,
		hex.EncodeToString(i.previousTxID),
		i.PreviousTxOutIndex,
		len(*i.UnlockingScript),
		i.UnlockingScript,
		i.SequenceNumber,
	)
}

// Bytes encodes the Input into a hex byte array.
func (i *Input) Bytes(clear bool) []byte {
	h := make([]byte, 0)

	h = append(h, ReverseBytes(i.previousTxID)...)
	h = append(h, LittleEndianBytes(i.PreviousTxOutIndex, 4)...)
	if clear {
		h = append(h, 0x00)
	} else {
		if i.UnlockingScript == nil {
			h = append(h, VarInt(0).Bytes()...)
		} else {
			h = append(h, VarInt(uint64(len(*i.UnlockingScript))).Bytes()...)
			h = append(h, *i.UnlockingScript...)
		}
	}

	return append(h, LittleEndianBytes(i.SequenceNumber, 4)...)
}