github.com/clem109/go-ethereum@v1.8.3-0.20180316121352-fe6cf00f480a/compression/rle/read_write.go (about)

     1  // Copyright 2014 The go-ethereum Authors
     2  // This file is part of the go-ethereum library.
     3  //
     4  // The go-ethereum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The go-ethereum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  // Package rle implements the run-length encoding used for Ethereum data.
    18  package rle
    19  
    20  import (
    21  	"bytes"
    22  	"errors"
    23  
    24  	"github.com/ethereum/go-ethereum/crypto"
    25  )
    26  
    27  const (
    28  	token             byte = 0xfe
    29  	emptyShaToken          = 0xfd
    30  	emptyListShaToken      = 0xfe
    31  	tokenToken             = 0xff
    32  )
    33  
    34  var empty = crypto.Keccak256([]byte(""))
    35  var emptyList = crypto.Keccak256([]byte{0x80})
    36  
    37  func Decompress(dat []byte) ([]byte, error) {
    38  	buf := new(bytes.Buffer)
    39  
    40  	for i := 0; i < len(dat); i++ {
    41  		if dat[i] == token {
    42  			if i+1 < len(dat) {
    43  				switch dat[i+1] {
    44  				case emptyShaToken:
    45  					buf.Write(empty)
    46  				case emptyListShaToken:
    47  					buf.Write(emptyList)
    48  				case tokenToken:
    49  					buf.WriteByte(token)
    50  				default:
    51  					buf.Write(make([]byte, int(dat[i+1]-2)))
    52  				}
    53  				i++
    54  			} else {
    55  				return nil, errors.New("error reading bytes. token encountered without proceeding bytes")
    56  			}
    57  		} else {
    58  			buf.WriteByte(dat[i])
    59  		}
    60  	}
    61  
    62  	return buf.Bytes(), nil
    63  }
    64  
    65  func compressChunk(dat []byte) (ret []byte, n int) {
    66  	switch {
    67  	case dat[0] == token:
    68  		return []byte{token, tokenToken}, 1
    69  	case len(dat) > 1 && dat[0] == 0x0 && dat[1] == 0x0:
    70  		j := 0
    71  		for j <= 254 && j < len(dat) {
    72  			if dat[j] != 0 {
    73  				break
    74  			}
    75  			j++
    76  		}
    77  		return []byte{token, byte(j + 2)}, j
    78  	case len(dat) >= 32:
    79  		if dat[0] == empty[0] && bytes.Equal(dat[:32], empty) {
    80  			return []byte{token, emptyShaToken}, 32
    81  		} else if dat[0] == emptyList[0] && bytes.Equal(dat[:32], emptyList) {
    82  			return []byte{token, emptyListShaToken}, 32
    83  		}
    84  		fallthrough
    85  	default:
    86  		return dat[:1], 1
    87  	}
    88  }
    89  
    90  func Compress(dat []byte) []byte {
    91  	buf := new(bytes.Buffer)
    92  
    93  	i := 0
    94  	for i < len(dat) {
    95  		b, n := compressChunk(dat[i:])
    96  		buf.Write(b)
    97  		i += n
    98  	}
    99  
   100  	return buf.Bytes()
   101  }