path: root/compression/rle/read_write.go

// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// Package rle implements the run-length encoding used for Ethereum data.
package rle

import (
    "bytes"
    "errors"

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

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

var empty = crypto.Keccak256([]byte(""))
var emptyList = crypto.Keccak256([]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")
            }
        } else {
            buf.WriteByte(dat[i])
        }
    }

    return buf.Bytes(), nil
}

func compressChunk(dat []byte) (ret []byte, n int) {
    switch {
    case dat[0] == token:
        return []byte{token, tokenToken}, 1
    case len(dat) > 1 && dat[0] == 0x0 && dat[1] == 0x0:
        j := 0
        for j <= 254 && j < len(dat) {
            if dat[j] != 0 {
                break
            }
            j++
        }
        return []byte{token, byte(j + 2)}, j
    case len(dat) >= 32:
        if dat[0] == empty[0] && bytes.Equal(dat[:32], empty) {
            return []byte{token, emptyShaToken}, 32
        } else if dat[0] == emptyList[0] && bytes.Equal(dat[:32], emptyList) {
            return []byte{token, emptyListShaToken}, 32
        }
        fallthrough
    default:
        return dat[:1], 1
    }
}

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

    i := 0
    for i < len(dat) {
        b, n := compressChunk(dat[i:])
        buf.Write(b)
        i += n
    }

    return buf.Bytes()
}