Failing to download pieces different than 0 #nd2

Challenges
1

This is the traffic I receive when I ask for piece 0:

peer: 165.232.35.114:51531
...
recv: [0 0 0 2 5 224] # bitfield message receive
send: [0 0 0 2 2 0] # respond with an interested
recv: [0 0 0 1 1] # receive an unchoke
send: [0 0 0 13 6 0 0 0 0 0 0 0 0 0 0 64 0] # I ask for piece 0
recv[ block 0 ]: 16397 length
recv[ block 1 ]: 16397 length

but when I ask for piece 1 I just get length 0 messages but not the piece block

peer: 165.232.35.114:51531
...
recv: [0 0 0 2 5 224] # bitfield message receive
send: [0 0 0 2 2 0] # respond with an interested
recv: [0 0 0 1 1] # receive an unchoke
send: [0 0 0 13 6 0 0 0 1 0 0 0 0 0 0 64 0] # I ask for piece 1
recv[ block 0 ]: 0 length
send: [0 0 0 13 6 0 0 0 1 0 0 0 0 0 0 64 0] # I ask again for piece 1
recv[ block 0 ]: 0 length
3

Hey @adecora, would you mind pushing your latest code so that I can take a closer look?

5

Yes here is the code,sorry about the mess I’m hardcoding few things in order to try to get some answer for the peers

peerMsg := PeerMessage{}
		peerMsg.Read(conn)
		fmt.Println("recv:", peerMsg.Bytes())
		assert(peerMsg.Id == 5, "First message must always be os type 5 bitfield")

		// We send an interested message
		peerMsg = PeerMessage{
			Length:  2,
			Id:      2,
			Payload: make([]byte, 1),
		}

		_, err = conn.Write(peerMsg.Bytes())
		if err != nil {
			return err
		}
		fmt.Println("send:", peerMsg.Bytes())
		peerMsg.Read(conn)
		fmt.Println("recv:", peerMsg.Bytes())
		assert(peerMsg.Id == 1, "Peer always send unchoke")

		allPiece := make([]byte, torrent.Info.PieceLength)
               
                // BlockSize = 2**14
 		// + (BlockSize - 1) rounds up
		PieceLength := torrent.Info.PieceLength
		if piece == len(piecesHash)-1 {
			PieceLength = torrent.Info.Length % torrent.Info.PieceLength
		}
		fmt.Println(pieceAddress)
		fmt.Println("piece lenght:", PieceLength)
		var nblocks uint = (uint(PieceLength) + (BlockSize - 1)) / BlockSize
		for block := uint(0); block < nblocks; block++ {
			length := BlockSize
			if (block == nblocks-1) && (uint(PieceLength)%BlockSize != 0) {
				length = uint(PieceLength) % BlockSize
			}

			for {
				reqPayload := PieceRequest{}
				reqPayload.New(piece, block*BlockSize, length)

				peerMsg = PeerMessage{
					Length:  13,
					Id:      6,
					Payload: reqPayload.Bytes(),
				}
				fmt.Println("send:", peerMsg.Bytes())
				_, err = conn.Write(peerMsg.Bytes())
				if err != nil {
					return err
				}
				fmt.Println("writed")
				peerMsg.Read(conn)
				fmt.Println("recv[", block, "]:", len(peerMsg.Bytes()))
				copy(allPiece[block*BlockSize:block*BlockSize+length], peerMsg.Bytes())
				if peerMsg.Length != 0 {
					break
				}
			}

These are the auxiliar functions.

func (p *PeerMessage) Read(conn net.Conn) error {
	header := make([]byte, 4)
	_, err := io.ReadFull(conn, header)
	if err != nil {
		return err
	}

	length := binary.BigEndian.Uint32(header)
	p.Length = length

	if length == 0 {
		p.Id = 0
		p.Payload = nil
		return nil
	}

	body := make([]byte, length)
	_, err = io.ReadFull(conn, body)
	if err != nil {
		return err
	}

	p.Id = body[0]
	p.Payload = body[1:]

	return nil
}

func (p *PeerMessage) Bytes() []byte {
	var peerMsg bytes.Buffer

	buff := make([]byte, 4)
	binary.BigEndian.PutUint32(buff, p.Length)

	peerMsg.Write(buff)
	peerMsg.WriteByte(p.Id)
	peerMsg.Write(p.Payload)

	return peerMsg.Bytes()
}

func (p *PieceRequest) New(index int, offset uint, length uint) {
	p.Index = uint32(index)
	p.Begin = uint32(offset)
	p.Length = uint32(length)
}

func (p *PieceRequest) Bytes() []byte {
	buf := make([]byte, 12)

	binary.BigEndian.PutUint32(buf[0:4], p.Index)
	binary.BigEndian.PutUint32(buf[4:8], p.Begin)
	binary.BigEndian.PutUint32(buf[8:12], p.Length)

	return buf
}
6

@adecora It’s a bit tricky to debug a partial code snippet. :sweat_smile:

We have access to your submissions, but the latest one is from five days ago.

image
image2118×352 65.1 KB

If you could push your most recent code, that’d make it much easier to debug. I’ll be able to run it directly and help more effectively. :handshake:

7

Sorry :see_no_evil_monkey: I’m already push a commit with the buggy download_piece implementation.

1 Like