skim
skim records the sizes of packets passing through an interface so you can monitor network usage. it sorts this information by transport type, tcp/udp, and port number.

skim exposes an interface for retrieving statistics on tcp port 6666. first send a u32, big endian, and then json data with the ports you want. the json should look like this:
{ "tcp": [80, 443], "udp": [53] }

you'll get a response back in a similar format. the first four bytes will be the length of the response, big endian, and then the json data. the data'll look like this:

{
    "tcp":[{"port":80,"tx":0,"rx":0},{"port":443,"tx":56260,"rx":4195}],
    "udp":[{"port":53,"tx":210,"rx":173}]
}

skim records network traffic assuming the host system is acting as a server.