Monitor Network Traffic Mac

I'm wondering how to go about monitoring network traffic on my Mac. Like the way activity monitor does it, showing the bytes /开发者_JAVA百科 packets in and out.

I know it's a bit vague, but I'm unsure of the best place to start.

EDIT: I'm wanting to do this in code, not use an existing piece of software.

I just found the open source project, MenuMeters. It's got exactly what I'm looking for.

You may want to look into programming with pcap. That's the library which drives tcpdump.

Use tcpdump for quick-n-dirty low-level command-line monitoring, and wireshark for the kitchen sink.

OTOH, if you just want to know the number of bytes/packets (as opposed to their contents), try Net Monitor, which is commercial, unfortunately.

There are lot of paid & freeware applications. But if you a command line person like me, Try this:

nettop //displays network usage per application with lot of details
nettop (press h) //displays help menu
nettop (press c) //collapse and display brief info on network usage