Create UDP to TCP bridge with socat/netcat to relay control commands for vlc media-player

Question

The UDP - must listen on port. The TCP - must connect to a server.

I tried netcat and socat.

nc -v -u -l -p 3333 | nc -v 127.0.0.1 50000

socat -v UDP-LISTEN:3333,fork TCP:localhost:50000

Both work -- they delivered the message -- but the line is not ended. VLC will only take the command if I close netcat/socat.

I monitored the connection with sockettest and the messages are one after another in the same line, like this:

playpausestopexitadd

I need the line to be ended so that the message transmitted looks like this:

play
stop
exit
add

Maybe the packet is not ended?

I am wondering if nc or socat have options to send the packet/end line after a certain amount of time.

If I add \n to the output as suggested by @roaima, I get play\nstop\nplay\n on a single line.

Solution

I suspect your problem is more because whatever sends the UDP packets is not adding a newline character the commands (as in they should send "play\n" and not just "play").

In any case, if you want a new TCP connection to be created for each of the UDP packets, you should use udp-recvfrom instead of udp-listen in socat:

socat -u udp-recvfrom:3333,fork tcp:localhost:50000

Then every UDP packet should trigger one TCP connection that is only brought up to send the content of the packet and then closed.

Test by doing:

echo play | socat -u - udp-sendto:localhost:3333

(which sends a UDP packet whose payload contains the 5 bytes "play\n").