Peer not responding to Handshake Message in BitTorrent Protocol

Question

I am sending a handshake to a peer. This is what the handshake looks like:

b'\x13BitTorrent Protocol\x00\x00\x00\x00\x00\x00\x00\x00\x08O\xae=J2\xc5g\x98Y\xafK\x9e\x8d\xbb\x7f`qcG\x08O\xff=J2\xc5g\x98Y\xafK\x9e\x8d\xbb\x7f`qcG'

However, I get an empty b'' in response. I have set timeout to 10. Here's my code:

            clientsocket=socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            clientsocket.settimeout(5)
            print("trying")
            try:
                clientsocket.connect((ip,port))
            except:
                continue
            print('connected')
            #print(req)
            clientsocket.send(req)
            clientsocket.settimeout(10)
            try:
                buffer = clientsocket.recv(1048)
            except:
                continue

Any idea what my mistake is?

Answer 1

There are a few issues with your sample code. The core issue is the header in your handshake mistakenly capitalizes "Protocol", most BitTorrent implementations will drop the TCP connection if this header isn't byte-for-byte correct.

The following is a slightly cleaned up version of the code that works:

# IP and Port, obviously change these to match where the server is
ip, port = "127.0.0.1", 6881

import socket

# Broken up the BitTorrent header to multiple lines just to make it easier to read

# The main header, note the lower "p" in protocol, that's important
req = b'\x13'
req += b'BitTorrent protocol'

# The optional bits, note that normally some of these are set by most clients
req += b'\x00\x00\x00\x00\x00\x00\x00\x00'
# The Infohash we're interested in.  Let python convert the human readable
# version to a byte array just to make it easier to read
req += bytearray.fromhex("5fff0e1c8ac414860310bcc1cb76ac28e960efbe")
# Our client ID.  Just a random blob of bytes, note that most clients
# use the first bytes of this to mark which client they are
req += bytearray.fromhex("5b76c604def8aa17e0b0304cf9ac9caab516c692")

# Open the socket
clientsocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
clientsocket.settimeout(5)
print("Trying")
clientsocket.connect((ip,port))
print('Connected')
# Note: Use sendall, in case the handshake doesn't make it one packet for
# whatever reason
clientsocket.sendall(req)
# And see what the server sends back. Note that really you should keep reading
# till one of two things happens:
#  - Nothing is returned, likely meaning the server "hung up" on us, probably
#    because it doesn't care about the infohash we're talking about
#  - We get 68 bytes in the handshake response, so we have a full handshake
buffer = clientsocket.recv(1048)
print(buffer)