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metainfo.go
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/
metainfo.go
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// Copyright (c) 2016-2019 Uber Technologies, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package core
import (
"bytes"
"encoding/json"
"errors"
"fmt"
"io"
"github.com/jackpal/bencode-go"
)
// info contains the "instructions" for how to download / seed a torrent,
// primarily describing how a blob is broken up into pieces and how to verify
// those pieces (i.e. the piece sums).
type info struct {
// Exported for bencoding.
PieceLength int64
PieceSums []uint32
Name string
Length int64
}
// Hash computes the InfoHash of info.
func (info *info) Hash() (InfoHash, error) {
var b bytes.Buffer
if err := bencode.Marshal(&b, *info); err != nil {
return InfoHash{}, fmt.Errorf("bencode: %s", err)
}
return NewInfoHashFromBytes(b.Bytes()), nil
}
// MetaInfo contains torrent metadata.
type MetaInfo struct {
info info
infoHash InfoHash
digest Digest
}
// NewMetaInfo creates a new MetaInfo. Assumes that d is the valid digest for
// blob (re-computing it is expensive).
func NewMetaInfo(d Digest, blob io.Reader, pieceLength int64) (*MetaInfo, error) {
length, pieceSums, err := calcPieceSums(blob, pieceLength)
if err != nil {
return nil, err
}
info := info{
PieceLength: pieceLength,
PieceSums: pieceSums,
Name: d.Hex(),
Length: length,
}
var buf bytes.Buffer
if err := bencode.Marshal(&buf, info); err != nil {
return nil, fmt.Errorf("bencode: %s", err)
}
h, err := info.Hash()
if err != nil {
return nil, fmt.Errorf("compute info hash: %s", err)
}
return &MetaInfo{
info: info,
infoHash: h,
digest: d,
}, nil
}
// InfoHash returns the torrent InfoHash.
func (mi *MetaInfo) InfoHash() InfoHash {
return mi.infoHash
}
// Digest returns the digest of the original blob.
func (mi *MetaInfo) Digest() Digest {
return mi.digest
}
// Length returns the length of the original blob.
func (mi *MetaInfo) Length() int64 {
return mi.info.Length
}
// NumPieces returns the number of pieces in the torrent.
func (mi *MetaInfo) NumPieces() int {
return len(mi.info.PieceSums)
}
// PieceLength returns the piece length used to break up the original blob. Note,
// the final piece may be shorter than this. Use GetPieceLength for the true
// lengths of each piece.
func (mi *MetaInfo) PieceLength() int64 {
return mi.info.PieceLength
}
// GetPieceLength returns the length of piece i.
func (mi *MetaInfo) GetPieceLength(i int) int64 {
if i < 0 || i >= len(mi.info.PieceSums) {
return 0
}
if i == len(mi.info.PieceSums)-1 {
// Last piece.
return mi.info.Length - mi.info.PieceLength*int64(i)
}
return mi.info.PieceLength
}
// GetPieceSum returns the checksum of piece i. Does not check bounds.
func (mi *MetaInfo) GetPieceSum(i int) uint32 {
return mi.info.PieceSums[i]
}
// metaInfoJSON is used for serializing / deserializing MetaInfo.
type metaInfoJSON struct {
// Only serialize info for backwards compatibility.
Info info `json:"Info"`
}
// Serialize converts mi to a json blob.
func (mi *MetaInfo) Serialize() ([]byte, error) {
return json.Marshal(&metaInfoJSON{mi.info})
}
// DeserializeMetaInfo reconstructs a MetaInfo from a json blob.
func DeserializeMetaInfo(data []byte) (*MetaInfo, error) {
var j metaInfoJSON
if err := json.Unmarshal(data, &j); err != nil {
return nil, fmt.Errorf("json: %s", err)
}
h, err := j.Info.Hash()
if err != nil {
return nil, fmt.Errorf("compute info hash: %s", err)
}
d, err := NewSHA256DigestFromHex(j.Info.Name)
if err != nil {
return nil, fmt.Errorf("parse name: %s", err)
}
return &MetaInfo{
info: j.Info,
infoHash: h,
digest: d,
}, nil
}
// calcPieceSums hashes blob content in pieceLength chunks.
func calcPieceSums(blob io.Reader, pieceLength int64) (length int64, pieceSums []uint32, err error) {
if pieceLength <= 0 {
return 0, nil, errors.New("piece length must be positive")
}
for {
h := PieceHash()
n, err := io.CopyN(h, blob, pieceLength)
if err != nil && err != io.EOF {
return 0, nil, fmt.Errorf("read blob: %s", err)
}
length += n
if n == 0 {
break
}
sum := h.Sum32()
pieceSums = append(pieceSums, sum)
if n < pieceLength {
break
}
}
return length, pieceSums, nil
}