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// Copyright 2018 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 multihash
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
)
const (
defaultMultihashLength = 32
defaultMultihashTypeCode = 0x1b
)
var (
multihashTypeCode uint8
MultihashLength = defaultMultihashLength
)
func init() {
multihashTypeCode = defaultMultihashTypeCode
MultihashLength = defaultMultihashLength
}
// check if valid swarm multihash
func isSwarmMultihashType(code uint8) bool {
return code == multihashTypeCode
}
// GetMultihashLength returns the digest length of the provided multihash
// It will fail if the multihash is not a valid swarm mulithash
func GetMultihashLength(data []byte) (int, int, error) {
cursor := 0
typ, c := binary.Uvarint(data)
if c <= 0 {
return 0, 0, errors.New("unreadable hashtype field")
}
if !isSwarmMultihashType(uint8(typ)) {
return 0, 0, fmt.Errorf("hash code %x is not a swarm hashtype", typ)
}
cursor += c
hashlength, c := binary.Uvarint(data[cursor:])
if c <= 0 {
return 0, 0, errors.New("unreadable length field")
}
cursor += c
// we cheekily assume hashlength < maxint
inthashlength := int(hashlength)
if len(data[c:]) < inthashlength {
return 0, 0, errors.New("length mismatch")
}
return inthashlength, cursor, nil
}
// FromMulithash returns the digest portion of the multihash
// It will fail if the multihash is not a valid swarm multihash
func FromMultihash(data []byte) ([]byte, error) {
hashLength, _, err := GetMultihashLength(data)
if err != nil {
return nil, err
}
return data[len(data)-hashLength:], nil
}
// ToMulithash wraps the provided digest data with a swarm mulithash header
func ToMultihash(hashData []byte) []byte {
buf := bytes.NewBuffer(nil)
b := make([]byte, 8)
c := binary.PutUvarint(b, uint64(multihashTypeCode))
buf.Write(b[:c])
c = binary.PutUvarint(b, uint64(len(hashData)))
buf.Write(b[:c])
buf.Write(hashData)
return buf.Bytes()
}
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