How to get socat exit code when piping stdin to it?

I am executing commands against a docker container using socat and I want to get the exit code of the code executed in the container. This is what I've tried:

$ docker run --rm -itd --name test123 ubuntu
$ echo "ls" | socat EXEC:"docker attach test123",pty - &> /dev/null
$ echo $?
0
$ echo "foobar" | socat EXEC:"docker attach test123",pty - &> /dev/null
$ echo $?
0

as you can see this is not working properly because the exit code for the foobar command should obviously be non-zero.

$ socat -V
socat version 1.8.0.1 on 
   running on Darwin version