tendermint/keys/ecc.go

package keys

import (
	"encoding/binary"
	"errors"
	"hash/crc32"
)

// ECC is used for anything that calculates an error-correcting code
type ECC interface {
	// AddECC calculates an error-correcting code for the input
	// returns an output with the code appended
	AddECC([]byte) []byte

	// CheckECC verifies if the ECC is proper on the input and returns
	// the data with the code removed, or an error
	CheckECC([]byte) ([]byte, error)
}

// NoECC is a no-op placeholder, kind of useless... except for tests
type NoECC struct{}

var _ ECC = NoECC{}

func (_ NoECC) AddECC(input []byte) []byte            { return input }
func (_ NoECC) CheckECC(input []byte) ([]byte, error) { return input, nil }

// CRC32 does the ieee crc32 polynomial check
type CRC32 struct{}

var _ ECC = CRC32{}

func (_ CRC32) AddECC(input []byte) []byte {
	// get crc and convert to some bytes...
	crc := crc32.ChecksumIEEE(input)
	check := make([]byte, 4)
	binary.BigEndian.PutUint32(check, crc)

	// append it to the input
	output := append(input, check...)
	return output
}

func (_ CRC32) CheckECC(input []byte) ([]byte, error) {
	if len(input) <= 4 {
		return nil, errors.New("input too short, no checksum present")
	}
	cut := len(input) - 4
	data, check := input[:cut], input[cut:]
	crc := binary.BigEndian.Uint32(check)
	calc := crc32.ChecksumIEEE(data)
	if crc != calc {
		return nil, errors.New("Checksum does not match")
	}
	return data, nil
}