BitTorrent protocol implementation: Not receiving "Piece" messages

Question

I've implemented most of the BitTorrent protocol in Java. The problem is that for some reason none of the peers are sending me any of the pieces I request. (After 3 hours I received only 2 piece-messages)

My handshaking is as follows:

send 19
send "BitTorrent protocol"
send 8 zero'd reserved bytes
send info_hash (20 bytes)
send peer_id (20 bytes)

read 19
read "BitTorrent protocol"
read 8 reserved bytes
read info_hash. Compare with own info_hash
read peer_id

send unchoke

start listening for messages

I listen for messages in another thread as follows:

while(true)
    read length (4 bytes)
    read id (1 byte)
    if length == 0: continue //keep-alive message
    if id == 1: Stop all requests to this peer
    if id == 2: Continue all requests to this peer
    if id == 4: Read index from have-message and request piece if we don't have it
    if id == 5: If we have not already received bitfield. Read and store it. Request any pieces that we don't have yet
    if id == 7: Read index, begin and length. Read and store piece. Send have-message if a piece was fully downloaded

Can you see any problem with this approach? I've tried doing periodic keep-alive messages every minute, but that doesn't help. What's weird is that I'm receiving tons of bitfield-messages and maintaining 30+ active connections.

daxnitro daxnitro · Accepted Answer · 2013-05-10T21:35:00

This answer is pretty late, but I got linked to it so maybe this'll still be useful.

I think you have your ids mixed up. 0 is "choke" and 1 is "unchoke" (not 1 and 2). Also you might need to make sure you're triggering requests when you get unchoked too just in case you get the "have" message before that.

BitTorrent protocol implementation: Not receiving "Piece" messages

1 Answers