status-go/vendor/github.com/anacrolix/torrent/reader.go

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2022-03-10 09:44:48 +00:00
package torrent
import (
"context"
"errors"
"fmt"
"io"
"sync"
"github.com/anacrolix/log"
"github.com/anacrolix/missinggo/v2"
)
// Accesses Torrent data via a Client. Reads block until the data is available. Seeks and readahead
// also drive Client behaviour.
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
}
var _ io.ReadSeekCloser = (*reader)(nil)
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()
}
func (r *reader) SetReadahead(readahead int64) {
r.mu.Lock()
r.readahead = readahead
r.readaheadFunc = nil
r.posChanged()
r.mu.Unlock()
}
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) {
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
}
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
}
// 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) 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
}
}
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
}
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
}
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
}
r.t.cl.lock()
// 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)
}
r.t.cl.unlock()
}
}
// Hodor
func (r *reader) Close() error {
r.t.cl.lock()
r.t.deleteReader(r)
r.t.cl.unlock()
return nil
}
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 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:
return 0, errors.New("bad whence")
}
if newPos != r.pos {
r.reading = false
r.pos = newPos
r.contiguousReadStartPos = newPos
r.posChanged()
}
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
}