93 lines
2.6 KiB
Go
93 lines
2.6 KiB
Go
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// Copyright 2018 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package multihash
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import (
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"bytes"
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"encoding/binary"
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"errors"
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"fmt"
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)
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const (
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defaultMultihashLength = 32
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defaultMultihashTypeCode = 0x1b
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)
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var (
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multihashTypeCode uint8
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MultihashLength = defaultMultihashLength
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)
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func init() {
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multihashTypeCode = defaultMultihashTypeCode
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MultihashLength = defaultMultihashLength
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}
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// check if valid swarm multihash
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func isSwarmMultihashType(code uint8) bool {
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return code == multihashTypeCode
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}
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// GetMultihashLength returns the digest length of the provided multihash
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// It will fail if the multihash is not a valid swarm mulithash
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func GetMultihashLength(data []byte) (int, int, error) {
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cursor := 0
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typ, c := binary.Uvarint(data)
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if c <= 0 {
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return 0, 0, errors.New("unreadable hashtype field")
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}
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if !isSwarmMultihashType(uint8(typ)) {
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return 0, 0, fmt.Errorf("hash code %x is not a swarm hashtype", typ)
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}
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cursor += c
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hashlength, c := binary.Uvarint(data[cursor:])
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if c <= 0 {
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return 0, 0, errors.New("unreadable length field")
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}
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cursor += c
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// we cheekily assume hashlength < maxint
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inthashlength := int(hashlength)
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if len(data[c:]) < inthashlength {
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return 0, 0, errors.New("length mismatch")
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}
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return inthashlength, cursor, nil
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}
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// FromMulithash returns the digest portion of the multihash
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// It will fail if the multihash is not a valid swarm multihash
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func FromMultihash(data []byte) ([]byte, error) {
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hashLength, _, err := GetMultihashLength(data)
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if err != nil {
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return nil, err
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}
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return data[len(data)-hashLength:], nil
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}
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// ToMulithash wraps the provided digest data with a swarm mulithash header
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func ToMultihash(hashData []byte) []byte {
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buf := bytes.NewBuffer(nil)
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b := make([]byte, 8)
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c := binary.PutUvarint(b, uint64(multihashTypeCode))
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buf.Write(b[:c])
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c = binary.PutUvarint(b, uint64(len(hashData)))
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buf.Write(b[:c])
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buf.Write(hashData)
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return buf.Bytes()
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}
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