One thing I haven't been able to with tcpdump is just dump the data stream (payload) without any protocol bits. I presume it's possible with the right command

One thing I haven't been able to with tcpdump is just dump the data stream (payload) without any protocol bits. I presume it's possible with the right command line option incantation. Instead, for this purpose, I have used tcpflow. This is useful for listening in on data streams, potentially piping a binary message stream to a decoder for human-readable output.