A description of the TDCC protocol, for all you aspiring IRC client authors:

Send the victim -- er, receiver -- a CTCP "DCC TSEND <filename> <encoded-ip> <port> <filesize>". Surround the filename with quotes if it contains spaces. Open a listening socket on the given port. When the receiver connects, send the data as fast as your TCP/IP stack will allow -- don't wait for acknowledgements, as TDCC doesn't use them. The receiver will close the connection after it has received the entire file.