echo server with netcat or socat
Solution 1:
Another netcat-like tool is the nmap version, ncat, that has lots of built in goodies to simplify things like this. This would work:
ncat -e /bin/cat -k -u -l 1235
-e means it executes /bin/cat (to echo back what you type)
-k means keep-alive, that it keeps listening after each connection
-u means udp
-l 1235 means that it listens on port 1235
Solution 2:
I used socat -v PIPE udp-recvfrom:5553,fork to run the server and socat - udp:localhost:5553 for clients.
This was a great help!
Solution 3:
You can also use socat (rather than using netcat) as echo server and netcat as client.
Socat echo server (listens on TCP port 1234):
socat -v tcp-l:1234,fork exec:'/bin/cat'
Netcat client (connects to serverip on TCP port 1234):
nc serverip 1234
Solution 4:
You can write a C program that forks nc -u -l -p 4321 and then uses dup(2) to connect:
- nc stdin with the parent's stdout
- nc stdout with the parent's stdin
Then in an endless loop the parent reads from stdin and writes in stdout whatever the parent reads.