code: func writeTxIn(w io.Writer, pver uint32, version int32, ti *TxIn) error {
  	err := writeOutPoint(w, pver, version, &ti.PreviousOutPoint)
  	if err != nil {
  		return err
  	}
  
  	err = WriteVarBytes(w, pver, ti.SignatureScript)
  	if err != nil {
  		return err
  	}
  
  	return binarySerializer.PutUint32(w, littleEndian, ti.Sequence)
  }
docs: // writeTxIn encodes ti to the bitcoin protocol encoding for a transaction
  // input (TxIn) to w.