package torrent
import (
+ "context"
"errors"
+ "fmt"
"io"
- "os"
+ "sync"
+
+ "github.com/anacrolix/log"
+ "github.com/anacrolix/missinggo/v2"
)
-// Accesses torrent data via a client.
-type Reader struct {
- t *clientTorrent
- pos int64
+// Accesses Torrent data via a Client. Reads block until the data is available. Seeks and readahead
+// also drive Client behaviour. Not safe for concurrent use.
+type Reader interface {
+ io.ReadSeekCloser
+ missinggo.ReadContexter
+ // Configure the number of bytes ahead of a read that should also be prioritized in preparation
+ // for further reads. Overridden by non-nil readahead func, see SetReadaheadFunc.
+ SetReadahead(int64)
+ // If non-nil, the provided function is called when the implementation needs to know the
+ // readahead for the current reader. Calls occur during Reads and Seeks, and while the Client is
+ // locked.
+ SetReadaheadFunc(ReadaheadFunc)
+ // Don't wait for pieces to complete and be verified. Read calls return as soon as they can when
+ // the underlying chunks become available.
+ SetResponsive()
+}
+
+// Piece range by piece index, [begin, end).
+type pieceRange struct {
+ begin, end pieceIndex
+}
+
+type ReadaheadContext struct {
+ ContiguousReadStartPos int64
+ CurrentPos int64
+}
+
+// Returns the desired readahead for a Reader.
+type ReadaheadFunc func(ReadaheadContext) int64
+
+type reader struct {
+ t *Torrent
+ // Adjust the read/seek window to handle Readers locked to File extents and the like.
+ offset, length int64
+
+ // Function to dynamically calculate readahead. If nil, readahead is static.
+ readaheadFunc ReadaheadFunc
+
+ // Required when modifying pos and readahead.
+ mu sync.Locker
+
+ readahead, pos int64
+ // Position that reads have continued contiguously from.
+ contiguousReadStartPos int64
+ // The cached piece range this reader wants downloaded. The zero value corresponds to nothing.
+ // We cache this so that changes can be detected, and bubbled up to the Torrent only as
+ // required.
+ pieces pieceRange
+
+ // Reads have been initiated since the last seek. This is used to prevent readaheads occurring
+ // after a seek or with a new reader at the starting position.
+ reading bool
responsive bool
- readahead int64
}
-var _ io.ReadCloser = &Reader{}
+var _ io.ReadSeekCloser = (*reader)(nil)
-// Don't wait for pieces to complete and be verified. Read calls return as
-// soon as they can when the underlying chunks become available.
-func (r *Reader) SetResponsive() {
+func (r *reader) SetResponsive() {
r.responsive = true
+ r.t.cl.event.Broadcast()
}
-// Configure the number of bytes ahead of a read that should also be
-// prioritized in preparation for further reads.
-func (r *Reader) SetReadahead(readahead int64) {
- r.readahead = readahead
+// Disable responsive mode. TODO: Remove?
+func (r *reader) SetNonResponsive() {
+ r.responsive = false
+ r.t.cl.event.Broadcast()
}
-func (r *Reader) raisePriorities(off int64, n int) {
- if r.responsive {
- r.t.cl.addUrgentRequests(r.t.torrent, off, n)
- }
- if !r.responsive || r.readahead != 0 {
- r.t.cl.readRaisePiecePriorities(r.t.torrent, off, int64(n)+r.readahead)
- }
+func (r *reader) SetReadahead(readahead int64) {
+ r.mu.Lock()
+ r.readahead = readahead
+ r.readaheadFunc = nil
+ r.posChanged()
+ r.mu.Unlock()
}
-func (r *Reader) readable(off int64) (ret bool) {
- // log.Println("readable", off)
- // defer func() {
- // log.Println("readable", ret)
- // }()
- if r.t.isClosed() {
- return true
- }
- req, ok := r.t.offsetRequest(off)
- if !ok {
- panic(off)
- }
- if r.responsive {
- return r.t.haveChunk(req)
- }
- return r.t.pieceComplete(int(req.Index))
+func (r *reader) SetReadaheadFunc(f ReadaheadFunc) {
+ r.mu.Lock()
+ r.readaheadFunc = f
+ r.posChanged()
+ r.mu.Unlock()
}
// How many bytes are available to read. Max is the most we could require.
-func (r *Reader) available(off, max int64) (ret int64) {
+func (r *reader) available(off, max int64) (ret int64) {
+ off += r.offset
for max > 0 {
req, ok := r.t.offsetRequest(off)
if !ok {
break
}
+ if !r.responsive && !r.t.pieceComplete(pieceIndex(req.Index)) {
+ break
+ }
if !r.t.haveChunk(req) {
break
}
return
}
-func (r *Reader) waitReadable(off int64) {
- r.t.cl.event.Wait()
+// Calculates the pieces this reader wants downloaded, ignoring the cached value at r.pieces.
+func (r *reader) piecesUncached() (ret pieceRange) {
+ ra := r.readahead
+ if r.readaheadFunc != nil {
+ ra = r.readaheadFunc(ReadaheadContext{
+ ContiguousReadStartPos: r.contiguousReadStartPos,
+ CurrentPos: r.pos,
+ })
+ }
+ if ra < 1 {
+ // Needs to be at least 1, because [x, x) means we don't want
+ // anything.
+ ra = 1
+ }
+ if !r.reading {
+ ra = 0
+ }
+ if ra > r.length-r.pos {
+ ra = r.length - r.pos
+ }
+ ret.begin, ret.end = r.t.byteRegionPieces(r.torrentOffset(r.pos), ra)
+ return
+}
+
+func (r *reader) Read(b []byte) (n int, err error) {
+ return r.ReadContext(context.Background(), b)
}
-func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
- for {
- var n1 int
- n1, err = r.readAt(b, off)
- n += n1
- b = b[n1:]
- off += int64(n1)
- if err != nil || len(b) == 0 || n1 == 0 {
+func (r *reader) ReadContext(ctx context.Context, b []byte) (n int, err error) {
+ if len(b) > 0 {
+ r.reading = true
+ // TODO: Rework reader piece priorities so we don't have to push updates in to the Client
+ // and take the lock here.
+ r.mu.Lock()
+ r.posChanged()
+ r.mu.Unlock()
+ }
+ n, err = r.readOnceAt(ctx, b, r.pos)
+ if n == 0 {
+ if err == nil && len(b) > 0 {
+ panic("expected error")
+ } else {
return
}
}
-}
-func (r *Reader) Read(b []byte) (n int, err error) {
- n, err = r.readAt(b, r.pos)
+ r.mu.Lock()
r.pos += int64(n)
+ r.posChanged()
+ r.mu.Unlock()
+ if r.pos >= r.length {
+ err = io.EOF
+ } else if err == io.EOF {
+ err = io.ErrUnexpectedEOF
+ }
return
}
-// Must only return EOF at the end of the torrent.
-func (r *Reader) readAt(b []byte, pos int64) (n int, err error) {
- // defer func() {
- // log.Println(pos, n, err)
- // }()
- maxLen := r.t.torrent.Info.TotalLength() - pos
- if maxLen <= 0 {
- err = io.EOF
- return
- }
- if int64(len(b)) > maxLen {
- b = b[:maxLen]
- }
-again:
- r.t.cl.mu.Lock()
- r.raisePriorities(pos, len(b))
- for !r.readable(pos) {
- r.raisePriorities(pos, len(b))
- r.waitReadable(pos)
- }
- avail := r.available(pos, int64(len(b)))
- // log.Println("available", avail)
- r.t.cl.mu.Unlock()
- b1 := b[:avail]
- pi := int(pos / r.t.Info().PieceLength)
- tp := &r.t.torrent.Pieces[pi]
- ip := r.t.Info().Piece(pi)
- po := pos % ip.Length()
- if int64(len(b1)) > ip.Length()-po {
- b1 = b1[:ip.Length()-po]
- }
- tp.pendingWritesMutex.Lock()
- for tp.pendingWrites != 0 {
- tp.noPendingWrites.Wait()
- }
- tp.pendingWritesMutex.Unlock()
- n, err = dataReadAt(r.t.data, b1, pos)
- if n != 0 {
- err = nil
- return
- }
- if r.t.isClosed() {
- if err == nil {
+var closedChan = make(chan struct{})
+
+func init() {
+ close(closedChan)
+}
+
+// Wait until some data should be available to read. Tickles the client if it isn't. Returns how
+// much should be readable without blocking.
+func (r *reader) waitAvailable(ctx context.Context, pos, wanted int64, wait bool) (avail int64, err error) {
+ t := r.t
+ for {
+ r.t.cl.rLock()
+ avail = r.available(pos, wanted)
+ readerCond := t.piece(int((r.offset + pos) / t.info.PieceLength)).readerCond.Signaled()
+ r.t.cl.rUnlock()
+ if avail != 0 {
+ return
+ }
+ var dontWait <-chan struct{}
+ if !wait || wanted == 0 {
+ dontWait = closedChan
+ }
+ select {
+ case <-r.t.closed.Done():
err = errors.New("torrent closed")
+ return
+ case <-ctx.Done():
+ err = ctx.Err()
+ return
+ case <-r.t.dataDownloadDisallowed.On():
+ err = errors.New("torrent data downloading disabled")
+ case <-r.t.networkingEnabled.Off():
+ err = errors.New("torrent networking disabled")
+ return
+ case <-dontWait:
+ return
+ case <-readerCond:
}
+ }
+}
+
+// Adds the reader's torrent offset to the reader object offset (for example the reader might be
+// constrainted to a particular file within the torrent).
+func (r *reader) torrentOffset(readerPos int64) int64 {
+ return r.offset + readerPos
+}
+
+// Performs at most one successful read to torrent storage.
+func (r *reader) readOnceAt(ctx context.Context, b []byte, pos int64) (n int, err error) {
+ if pos >= r.length {
+ err = io.EOF
return
}
- if err == io.ErrUnexpectedEOF {
- goto again
+ for {
+ var avail int64
+ avail, err = r.waitAvailable(ctx, pos, int64(len(b)), n == 0)
+ if avail == 0 {
+ return
+ }
+ firstPieceIndex := pieceIndex(r.torrentOffset(pos) / r.t.info.PieceLength)
+ firstPieceOffset := r.torrentOffset(pos) % r.t.info.PieceLength
+ b1 := missinggo.LimitLen(b, avail)
+ n, err = r.t.readAt(b1, r.torrentOffset(pos))
+ if n != 0 {
+ err = nil
+ return
+ }
+ if r.t.closed.IsSet() {
+ err = fmt.Errorf("reading from closed torrent: %w", err)
+ return
+ }
+ r.t.cl.lock()
+ // I think there's a panic here caused by the Client being closed before obtaining this
+ // lock. TestDropTorrentWithMmapStorageWhileHashing seems to tickle occasionally in CI.
+ func() {
+ // Just add exceptions already.
+ defer r.t.cl.unlock()
+ if r.t.closed.IsSet() {
+ // Can't update because Torrent's piece order is removed from Client.
+ return
+ }
+ // TODO: Just reset pieces in the readahead window. This might help
+ // prevent thrashing with small caches and file and piece priorities.
+ r.log(log.Fstr("error reading torrent %s piece %d offset %d, %d bytes: %v",
+ r.t.infoHash.HexString(), firstPieceIndex, firstPieceOffset, len(b1), err))
+ if !r.t.updatePieceCompletion(firstPieceIndex) {
+ r.log(log.Fstr("piece %d completion unchanged", firstPieceIndex))
+ }
+ // Update the rest of the piece completions in the readahead window, without alerting to
+ // changes (since only the first piece, the one above, could have generated the read error
+ // we're currently handling).
+ if r.pieces.begin != firstPieceIndex {
+ panic(fmt.Sprint(r.pieces.begin, firstPieceIndex))
+ }
+ for index := r.pieces.begin + 1; index < r.pieces.end; index++ {
+ r.t.updatePieceCompletion(index)
+ }
+ }()
}
- return
}
-func (r *Reader) Close() error {
- r.t = nil
+// Hodor
+func (r *reader) Close() error {
+ r.t.cl.lock()
+ r.t.deleteReader(r)
+ r.t.cl.unlock()
return nil
}
-func (r *Reader) Seek(off int64, whence int) (ret int64, err error) {
+func (r *reader) posChanged() {
+ to := r.piecesUncached()
+ from := r.pieces
+ if to == from {
+ return
+ }
+ r.pieces = to
+ // log.Printf("reader pos changed %v->%v", from, to)
+ r.t.readerPosChanged(from, to)
+}
+
+func (r *reader) Seek(off int64, whence int) (newPos int64, err error) {
switch whence {
- case os.SEEK_SET:
- r.pos = off
- case os.SEEK_CUR:
- r.pos += off
- case os.SEEK_END:
- r.pos = r.t.torrent.Info.TotalLength() + off
+ case io.SeekStart:
+ newPos = off
+ r.mu.Lock()
+ case io.SeekCurrent:
+ r.mu.Lock()
+ newPos = r.pos + off
+ case io.SeekEnd:
+ newPos = r.length + off
+ r.mu.Lock()
default:
- err = errors.New("bad whence")
+ return 0, errors.New("bad whence")
+ }
+ if newPos != r.pos {
+ r.reading = false
+ r.pos = newPos
+ r.contiguousReadStartPos = newPos
+ r.posChanged()
}
- ret = r.pos
+ r.mu.Unlock()
return
}
+
+func (r *reader) log(m log.Msg) {
+ r.t.logger.LogLevel(log.Debug, m.Skip(1))
+}
+
+// Implementation inspired by https://news.ycombinator.com/item?id=27019613.
+func defaultReadaheadFunc(r ReadaheadContext) int64 {
+ return r.CurrentPos - r.ContiguousReadStartPos
+}