Refactor torrent

torrent/torrent.go

@@ -12,18 +12,26 @@ import (
 
 const port = 6881
 
-// Info info
-type Info struct {
+// Torrent encodes the metadata from a .torrent file
+type Torrent struct {
+	Announce    string
+	InfoHash    []byte
+	PieceHashes [][]byte
+	PieceLength int
+	Length      int
+	Name        string
+}
+
+type bencodeInfo struct {
 	Pieces      string `bencode:"pieces"`
 	PieceLength int    `bencode:"piece length"`
 	Length      int    `bencode:"length"`
 	Name        string `bencode:"name"`
 }
 
-// Torrent torrent
-type Torrent struct {
-	Announce string `bencode:"announce"`
-	Info     Info   `bencode:"info"`
+type bencodeTorrent struct {
+	Announce string      `bencode:"announce"`
+	Info     bencodeInfo `bencode:"info"`
 }
 
 // Download downloads a torrent
@@ -46,15 +54,19 @@ func (to *Torrent) Download() error {
 
 // Open parses a torrent file
 func Open(r io.Reader) (*Torrent, error) {
-	to := Torrent{}
-	err := bencode.Unmarshal(r, &to)
+	bto := bencodeTorrent{}
+	err := bencode.Unmarshal(r, &bto)
 	if err != nil {
 		return nil, err
 	}
-	return &to, nil
+	to, err := bto.toTorrent()
+	if err != nil {
+		return nil, err
+	}
+	return to, nil
 }
 
-func (i *Info) hash() ([]byte, error) {
+func (i *bencodeInfo) hash() ([]byte, error) {
 	var buf bytes.Buffer
 	err := bencode.Marshal(&buf, *i)
 	if err != nil {
@@ -63,3 +75,39 @@ func (i *Info) hash() ([]byte, error) {
 	h := sha1.Sum(buf.Bytes())
 	return h[:], nil
 }
+
+func (i *bencodeInfo) splitPieceHashes() ([][]byte, error) {
+	hashLen := 20 // Length of SHA-1 hash
+	buf := []byte(i.Pieces)
+	if len(buf)%hashLen != 0 {
+		err := fmt.Errorf("Received malformed pieces of length %d", len(buf))
+		return nil, err
+	}
+	numHashes := len(buf) / hashLen
+	hashes := make([][]byte, numHashes)
+
+	for i := 0; i < numHashes; i++ {
+		hashes[i] = buf[i*hashLen : (i+1)*hashLen]
+	}
+	return hashes, nil
+}
+
+func (bto *bencodeTorrent) toTorrent() (*Torrent, error) {
+	infoHash, err := bto.Info.hash()
+	if err != nil {
+		return nil, err
+	}
+	pieceHashes, err := bto.Info.splitPieceHashes()
+	if err != nil {
+		return nil, err
+	}
+	to := Torrent{
+		Announce:    bto.Announce,
+		InfoHash:    infoHash,
+		PieceHashes: pieceHashes,
+		PieceLength: bto.Info.PieceLength,
+		Length:      bto.Info.Length,
+		Name:        bto.Info.Name,
+	}
+	return &to, nil
+}

torrent/tracker.go

@@ -51,18 +51,14 @@ func (tr *Tracker) buildTrackerURL() (string, error) {
 	if err != nil {
 		return "", err
 	}
-	infoHash, err := tr.Torrent.Info.hash()
-	if err != nil {
-		return "", err
-	}
 	params := url.Values{
-		"info_hash":  []string{string(infoHash)},
+		"info_hash":  []string{string(tr.Torrent.InfoHash)},
 		"peer_id":    []string{string(tr.PeerID)},
 		"port":       []string{strconv.Itoa(int(tr.Port))},
 		"uploaded":   []string{"0"},
 		"downloaded": []string{"0"},
 		"compact":    []string{"1"},
-		"left":       []string{strconv.Itoa(tr.Torrent.Info.Length)},
+		"left":       []string{strconv.Itoa(tr.Torrent.Length)},
 	}
 	base.RawQuery = params.Encode()
 	return base.String(), nil