Optimize torrent.Length()

diff --git a/torrent.go b/torrent.go
index c046897c366a62ef7284b0c3a24da1cd94afac7b..8ddbe7b7d40e23c60377ea6939e9cbaf2d184e4e 100644 (file)
--- a/torrent.go
+++ b/torrent.go
@@ -49,6 +49,7 @@ type torrent struct {
        Pieces            []*torrentPiece
        PiecesByBytesLeft *OrderedList
        Data              mmap_span.MMapSpan
+       length            int64
        // Prevent mutations to Data memory maps while in use as they're not safe.
        dataLock sync.RWMutex
        Info     *metainfo.Info
@@ -122,6 +123,7 @@ func (t *torrent) setMetadata(md metainfo.Info, dataDir string, infoBytes []byte
        if err != nil {
                return
        }
+       t.length = t.Data.Size()
        t.PiecesByBytesLeft = NewList(func(a, b interface{}) bool {
                apb := t.PieceNumPendingBytes(pp.Integer(a.(int)))
                bpb := t.PieceNumPendingBytes(pp.Integer(b.(int)))
@@ -216,7 +218,6 @@ func (t *torrent) NewMetadataExtensionMessage(c *connection, msgType int, piece
                ExtendedID:      byte(c.PeerExtensionIDs["ut_metadata"]),
                ExtendedPayload: append(p, data...),
        }
-
 }
 
 func (t *torrent) WriteStatus(w io.Writer) {
@@ -293,7 +294,12 @@ func (t *torrent) NumPiecesCompleted() (num int) {
 }
 
 func (t *torrent) Length() int64 {
-       return int64(t.LastPieceSize()) + int64(len(t.Pieces)-1)*int64(t.UsualPieceSize())
+       if t.Data == nil {
+               // Possibly the length might be available before the data is mmapped,
+               // I defer this decision to such a need arising.
+               panic("torrent length not known?")
+       }
+       return t.length
 }
 
 func (t *torrent) isClosed() bool {
@@ -397,7 +403,7 @@ type Peer struct {
 
 func (t *torrent) PieceLength(piece pp.Integer) (len_ pp.Integer) {
        if int(piece) == t.NumPieces()-1 {
-               len_ = pp.Integer(t.Data.Size() % t.Info.PieceLength)
+               len_ = pp.Integer(t.Length() % t.Info.PieceLength)
        }
        if len_ == 0 {
                len_ = pp.Integer(t.Info.PieceLength)