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path: root/compression/rle/read_write.go
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package rle

import (
    "bytes"
    "errors"

    "github.com/ethereum/go-ethereum/crypto"
)

const (
    token             byte = 0xfe
    emptyShaToken          = 0xfd
    emptyListShaToken      = 0xfe
    tokenToken             = 0xff
)

var empty = crypto.Sha3([]byte(""))
var emptyList = crypto.Sha3([]byte{0x80})

func Decompress(dat []byte) ([]byte, error) {
    buf := new(bytes.Buffer)

    for i := 0; i < len(dat); i++ {
        if dat[i] == token {
            if i+1 < len(dat) {
                switch dat[i+1] {
                case emptyShaToken:
                    buf.Write(empty)
                case emptyListShaToken:
                    buf.Write(emptyList)
                case tokenToken:
                    buf.WriteByte(token)
                default:
                    buf.Write(make([]byte, int(dat[i+1]-2)))
                }
                i++
            } else {
                return nil, errors.New("error reading bytes. token encountered without proceeding bytes")
            }
        }
    }

    return buf.Bytes(), nil
}

func Compress(dat []byte) []byte {
    buf := new(bytes.Buffer)

    for i := 0; i < len(dat); i++ {
        if dat[i] == token {
            buf.Write([]byte{token, tokenToken})
        } else if i+1 < len(dat) {
            if dat[i] == 0x0 && dat[i+1] == 0x0 {
                j := 0
                for j <= 254 && i+j < len(dat) {
                    if dat[i+j] != 0 {
                        break
                    }
                    j++
                }
                buf.Write([]byte{token, byte(j + 2)})
                i += (j - 1)
            } else if len(dat[i:]) >= 32 {
                if dat[i] == empty[0] && bytes.Compare(dat[i:i+32], empty) == 0 {
                    buf.Write([]byte{token, emptyShaToken})
                    i += 31
                } else if dat[i] == emptyList[0] && bytes.Compare(dat[i:i+32], emptyList) == 0 {
                    buf.Write([]byte{token, emptyListShaToken})
                    i += 31
                } else {
                    buf.WriteByte(dat[i])
                }
            } else {
                buf.WriteByte(dat[i])
            }
        } else {
            buf.WriteByte(dat[i])
        }
    }

    return buf.Bytes()
}