package torrent import ( "errors" "io" "log" "sync" "github.com/anacrolix/missinggo" "golang.org/x/net/context" ) type Reader interface { io.Reader io.Seeker io.Closer missinggo.ReadContexter SetReadahead(int64) SetResponsive() } // Piece range by piece index, [begin, end). type pieceRange struct { begin, end int } // Accesses Torrent data via a Client. Reads block until the data is // available. Seeks and readahead also drive Client behaviour. type reader struct { t *Torrent responsive bool // Adjust the read/seek window to handle Readers locked to File extents // and the like. offset, length int64 // Ensure operations that change the position are exclusive, like Read() // and Seek(). opMu sync.Mutex // Required when modifying pos and readahead, or reading them without // opMu. mu sync.Locker pos int64 readahead 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 } var _ io.ReadCloser = &reader{} // 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() { r.responsive = true r.t.cl.event.Broadcast() } // Disable responsive mode. TODO: Remove? func (r *reader) SetNonResponsive() { r.responsive = false 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.mu.Lock() r.readahead = readahead r.mu.Unlock() r.t.cl.mu.Lock() defer r.t.cl.mu.Unlock() r.posChanged() } func (r *reader) readable(off int64) (ret bool) { if r.t.closed.IsSet() { return true } req, ok := r.t.offsetRequest(r.torrentOffset(off)) if !ok { panic(off) } if r.responsive { return r.t.haveChunk(req) } return r.t.pieceComplete(int(req.Index)) } // How many bytes are available to read. Max is the most we could require. 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.t.haveChunk(req) { break } len1 := int64(req.Length) - (off - r.t.requestOffset(req)) max -= len1 ret += len1 off += len1 } // Ensure that ret hasn't exceeded our original max. if max < 0 { ret += max } return } func (r *reader) waitReadable(off int64) { // We may have been sent back here because we were told we could read but // it failed. 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 ra < 1 { // Needs to be at least 1, because [x, x) means we don't want // anything. ra = 1 } 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) ReadContext(ctx context.Context, b []byte) (n int, err error) { // This is set under the Client lock if the Context is canceled. var ctxErr error if ctx.Done() != nil { ctx, cancel := context.WithCancel(ctx) // Abort the goroutine when the function returns. defer cancel() go func() { <-ctx.Done() r.t.cl.mu.Lock() ctxErr = ctx.Err() r.t.cl.event.Broadcast() r.t.cl.mu.Unlock() }() } // Hmmm, if a Read gets stuck, this means you can't change position for // other purposes. That seems reasonable, but unusual. r.opMu.Lock() defer r.opMu.Unlock() for len(b) != 0 { var n1 int n1, err = r.readOnceAt(b, r.pos, &ctxErr) if n1 == 0 { if err == nil { panic("expected error") } break } b = b[n1:] n += n1 r.mu.Lock() r.pos += int64(n1) r.posChanged() r.mu.Unlock() } if r.pos >= r.length { err = io.EOF } else if err == io.EOF { err = io.ErrUnexpectedEOF } return } // 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(pos, wanted int64, ctxErr *error) (avail int64) { r.t.cl.mu.Lock() defer r.t.cl.mu.Unlock() for !r.readable(pos) && *ctxErr == nil { r.waitReadable(pos) } return r.available(pos, wanted) } func (r *reader) torrentOffset(readerPos int64) int64 { return r.offset + readerPos } // Performs at most one successful read to torrent storage. func (r *reader) readOnceAt(b []byte, pos int64, ctxErr *error) (n int, err error) { if pos >= r.length { err = io.EOF return } for { avail := r.waitAvailable(pos, int64(len(b)), ctxErr) if avail == 0 { if r.t.closed.IsSet() { err = errors.New("torrent closed") return } if *ctxErr != nil { err = *ctxErr return } } pi := int(r.torrentOffset(pos) / r.t.info.PieceLength) ip := r.t.info.Piece(pi) po := r.torrentOffset(pos) % r.t.info.PieceLength b1 := missinggo.LimitLen(b, ip.Length()-po, avail) n, err = r.t.readAt(b1, r.torrentOffset(pos)) if n != 0 { err = nil return } r.t.cl.mu.Lock() log.Printf("error reading torrent %q piece %d offset %d, %d bytes: %s", r.t, pi, po, len(b1), err) r.t.updateAllPieceCompletions() r.t.updateAllPiecePriorities() r.t.cl.mu.Unlock() } } func (r *reader) Close() error { r.t.cl.mu.Lock() defer r.t.cl.mu.Unlock() r.t.deleteReader(r) return nil } func (r *reader) posChanged() { to := r.piecesUncached() from := r.pieces if to == from { return } r.pieces = to r.t.readerPosChanged(from, to) } func (r *reader) Seek(off int64, whence int) (ret int64, err error) { r.opMu.Lock() defer r.opMu.Unlock() r.mu.Lock() defer r.mu.Unlock() switch whence { case io.SeekStart: r.pos = off case io.SeekCurrent: r.pos += off case io.SeekEnd: r.pos = r.length + off default: err = errors.New("bad whence") } ret = r.pos r.posChanged() return }