How to test a remote port is reachable with socat

Question

How to test a remote port is reachable with socat?

with netcat we can

nc -zv 192.168.1.15 22

How to do that with socat?

Answer 1

As the OP requested the equivalent of -z the following socat command will ensure that it does not wait for input and just checks if the port is listening or not.

socat /dev/null TCP:remote:port

This can be used in a Docker context especially on health checks for the alpine/socat image. Here is an example that sets up a forwarder for the smtp service to a mailhog service and checks if the connection is up

services:
  smtp:
    image: alpine/socat
    command: tcp-listen:25,fork TCP:mailhog:1025
    healthcheck: socat /dev/null TCP:mailhog:1025

Answer 2

I would imagine that the first example in the man page would work

socat - TCP4:www.domain.org:80

For your example, this would be (and adding 2 second connect timeout):

socat - TCP4:192.168.1.15:22,connect-timeout=2

and the response would be the sshd connect banner (if that is what is listening)

SSH-2.0-OpenSSH_5.3

or

socat[12650] E connecting to AF=2 192.168.189.6:23: Connection timed out