Question

Using snap-server’s httpServe method, I can setPort 0 to instruct the server to connect on the next free port. Unfortunately, once I have started the http server, I can’t find any way to determine which port it actually started on. As an example, my first try started on port 2679 – is there any way to determine that number?

Answer 1

I wrote this patch, included with snap-server 0.9 and above, using which you can write:

let hook dat = print $ socketPort $ head $ getStartupSockets dat
let config = setStartupHook hook $ setPort 0 mempty
httpServer config ...

Now hook will be called after the server is ready, and will print the port it started on.