package torrent import ( "errors" "io" "log" "os" "sync" "github.com/anacrolix/missinggo" "golang.org/x/net/context" ) // 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 // 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 } // 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(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) { 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) tickleClient() { r.t.readersChanged() } func (r *Reader) waitReadable(off int64) { // We may have been sent back here because we were told we could read but // it failed. r.tickleClient() 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 { ra = 1 } ret.begin, ret.end = r.t.byteRegionPieces(r.pos, ra) return } func (r *Reader) Read(b []byte) (n int, err error) { return r.ReadContext(b, context.Background()) } func (r *Reader) ReadContext(b []byte, ctx context.Context) (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.t.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) } // 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.t.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 } } b1 := b[:avail] pi := int(pos / r.t.Info().PieceLength) ip := r.t.Info().Piece(pi) po := pos % r.t.Info().PieceLength missinggo.LimitLen(&b1, ip.Length()-po) n, err = r.t.readAt(b1, pos) if n != 0 { err = nil return } log.Printf("error reading torrent %q piece %d offset %d, %d bytes: %s", r.t, pi, po, len(b1), err) r.t.cl.mu.Lock() 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) r.t = nil 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 os.SEEK_SET: r.pos = off case os.SEEK_CUR: r.pos += off case os.SEEK_END: r.pos = r.t.info.TotalLength() + off default: err = errors.New("bad whence") } ret = r.pos r.posChanged() return } func (r *Reader) Torrent() *Torrent { return r.t }