Utilities for creating and waiting on ports https://github.com/jfischoff/port-utils#readme

Version on this page:
LTS Haskell 13.25:
Stackage Nightly 2019-06-12:
Latest on Hackage:

See all snapshots port-utils appears in

BSD-3-Clause licensed by Jonathan Fischoff
Maintained by jonathangfischoff@gmail.com

Module documentation for



This is another version of warp’s openFreePort function. This function has fewer dependencies than the warp version.

openFreePort returns a socket on a random port and the port it has been bound to.

openFreePort :: IO (Int, Socket)


wait will attempt to connect to a host and port until it is successful. Between each unsuccessful attempt, it sleeps for 10 ms.

Here is an example of the primary function:

import Network.Socket.Wait (wait)

void $ forkIO $ Warp.run 7000 app
-- Wait for the server to start listening on the socket
wait "" 7000
-- Communicate with the server

In bash one could write:

while ! nc -z localhost 7000 ; do sleep 0.01 ; done

The bash script above was copied from this stackoverflow answer https://stackoverflow.com/a/50008755


Changelog for wait-on-port

  • First version

  • Rework internals and change EventHandlers to EventHandlers m. Fix bug if host could not be found. It would loop forever and now throws.

Depends on 2 packages:
Used by 2 packages:
comments powered byDisqus