How can I build a wrapper to wait for listening on a port?

Question

Hi,

I am looking for a way of programmatically testing a script written with the asyncore Python module. My test consists of launching the script in question -- if a TCP listen socket is opened, the test passes. Otherwise, if the script dies before getting to that point, the test fails.

The purpose of this is knowing if a nightly build works (at least up to a point) or not.

I was thinking the best way to test would be to launch the script in some kind of sandbox wrapper which waits for a socket request. I don't care about actually listening for anything on that port, just intercepting the request and using that as an indication that my test passed.

I think it would be preferable to intercept the open socket request, rather than polling at set intervals (I hate polling!). But I'm a bit out of my depths as far as how exactly to do this.

Can I do this with a shell script? Or perhaps I need to override the asyncore module at the Python level?

Thanks in advance,
- B

Answer 1

This felt like code-golf:

#!/bin/sh
# iamwaiting: run a command for a specified time then kill it
# returns the status of cmd on normal termination


opath=$PATH
PATH=/bin:/usr:/bin

SIGNAL=
case $1 in
    -*) SIGNAL=$1; shift;;
esac

case $# in
    0|1) echo 'usage iamwaiting [-signal] wait cmd [args]' 1>&2; exit 2;;
esac

wait=$1 ; shift

PATH=$opath "$@" &
child=$!

# unfortunately, this script takes at least wait seconds to run
sleep $wait

if kill ${SIGNAL:--2} $child 2> /dev/null ; then
    echo "iamwaiting timeout after $wait seconds: $@" 1>&2
    exit 1
else
    wait $child
    exit $?
fi

runs thusly:

$ iamwaiting  5 dd if=/dev/zero of=/dev/null count=5
5+0 records in
5+0 records out
2560 bytes (2.6 kB) copied, 2.0973e-05 s, 122 MB/s
$ echo $?
0
$ iamwaiting -9 5 dd if=/dev/zero of=/dev/null 
iamwaiting timeout after 5 seconds: dd if=/dev/zero of=/dev/null
$ echo $?
1
$ iamwaiting 1 cat /dev/does-not-exist
cat: /dev/does-not-exist: No such file or directory
$ echo $?
1

I'd be wary of testing asyncore programs with asynchore routines, but I'm superstitious that way.

Answer 2

Another option is to mock the socket module before importing the asyncore module. Of course, then you have to make sure that the mock works properly first.