I'm trying to implement a bittorent client and I got stuck at the part were I succesfully connected to a peer but I don't know how to communicate with the peer.
I managed to decode the torrent metadata file, I succesfully got all the info from there, I connected to a peer with TCP, I send the handshake message, I receive the handshake message back from the peer, but after that I don't receive any message from the peer (I was expecting the have messages). I tried sending an unchoke message to the peer and I started receiving some data but I don't know how to understand that data.
This is what I have until now:
s.connect((ip, port))
print "Connected"
message = "%s%s%s%s%s" % (chr(19), "BitTorrent protocol", 8 * chr(0),
handshake_params["info_hash"],
handshake_params["peer_id"]
s.send(message)
handshake_data = s.recv(4096)
# unchoke
m = struct.pack(">IB", 1, 1)
s.send(m)
data = s.recv(4096)
print handshake_data
print struct.unpack("B" * len(data), data)
And this is the output:
BitTorrent protocolp p�I0a��9"x`��-UT3450-��kP+�BG ���������
(255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 253, 231, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 127, 255, 251, 255, 255, 255, 255, 255, 255, 223, 255, 255, 255, 239, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 239, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 191, 255, 255, 255, 255, 255, 127, 255, 221, 255, 255, 255, 255, 255, 191, 191, 255, 255, 127, 255, 255, 255, 255, 191, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 191, 255, 255, 255, 255, 255, 255, 247, 255, 255, 255, 255, 255, 255, 255, 255, 255, 239, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 191, 255, 255, 255, 255, 255, 255, 255, 255, 251, 255, 255, 251, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 252, 0, 0, 0, 5, 4, 0, 0, 4, 191, 0, 0, 0, 5, 4, 0, 0, 1, 123, 0, 0, 0, 5, 4, 0, 0, 2, 122, 0, 0, 0, 5, 4, 0, 0, 2, 126, 0, 0, 0, 5, 4, 0, 0, 2, 177, 0, 0, 0, 5, 4, 0, 0, 2, 104, 0, 0, 0, 5, 4, 0, 0, 1, 37, 0, 0, 0, 5, 4, 0, 0, 0, 174, 0, 0, 0, 5, 4, 0, 0, 4, 157, 0, 0, 0, 5, 4, 0, 0, 0, 4, 0, 0, 0, 5, 4, 0, 0, 3, 172, 0, 0, 0, 5, 4, 0, 0, 2, 241, 0, 0, 0, 5, 4, 0, 0, 1, 90, 0, 0, 0, 5, 4, 0, 0, 3, 251, 0, 0, 0, 5, 4, 0, 0, 2, 200, 0, 0, 0, 5, 4, 0, 0, 0, 179, 0, 0, 0, 5, 4, 0, 0, 0, 180, 0, 0, 0, 5, 4, 0, 0, 3, 113, 0, 0, 0, 5, 4, 0, 0, 4, 181, 0, 0, 0, 5, 4, 0, 0, 1, 16, 0, 0, 0, 5, 4, 0, 0, 2, 169, 0, 0, 0, 5, 4, 0, 0, 4, 81, 0, 0, 0, 5, 4, 0, 0, 2, 57, 0, 0, 0, 5, 4, 0, 0, 1, 219)
The handshake data looks ok. What I can't figure out is why I get so many 255 bytes there. I was trying to decode the message using the length_prefix, message_id, payload format, but since I get so many 255 bytes at the beginning it results in the message having a huge length and I don't have a message that big.
Is there any kind of noise I should try and filter out? If you scroll right a lot you will see that at some point the bytes start being decent but I don't know what to do with the beginning of the message.
s.recv(4096)
You're just reading an block of data of some unspecified length, presumably whatever is in the TCP buffer.
Bittorrent is message-based. TCP is a stream of bytes, which means it does not nicely chop the data sent by the remote peer into messages, you will have to do that yourself.
来源：https://stackoverflow.com/questions/33461878/bittorrent-protocol-tcp-communication-example