How do I run a command for each UDP packet with socat?

Question

I'm trying to print each arriving UDP packet. I'd like to use xxd to print the ascii contents as well as the raw data (as hex).

So far I've used socat - udp4-listen:11255,reuseaddr,fork | xxd

This sort of works, but xxd buffers the input until it can print a complete line of output.

I'd like socat to execute a new command for each arriving udp packet. I've tried

socat -u udp4-listen:11255,reuseaddr,fork system:"/usr/bin/xxd - /tmp/foo"

It forks a new xxd for each packet (which is good) but keeps it running instead of closing the input after passing the packet.

Is there a way to make socat close the input of the forked process after passing the UDP packet?

Answer 1

socat -u udp4-recvfrom:11255,reuseaddr,fork exec:"/usr/bin/xxd - /tmp/foo"

does it. The difference is using udp4-recvfrom instead of udp4-listen. The former seems to handle input per packet, while the latter concatenates packets into a stream.