use alternate port for CPython example

[tedder]

Follows up on #76, specifically @FoamyGuy's note that sudo is required.

[FoamyGuy]

Thank you @tedder

This version does run without sudo.

One other thing I noticed now is that after running the script and then stopping it, if I attempt to run it again this exception is raised:

❯ python httpserver_cpython.py 
Traceback (most recent call last):
  File "/home/timc/repos/circuitpython/Adafruit_CircuitPython_HTTPServer/examples/httpserver_cpython.py", line 23, in <module>
    server.serve_forever("127.0.0.1", 5000)
  File "/home/timc/.local/lib/python3.10/site-packages/adafruit_httpserver/server.py", line 185, in serve_forever
    self.start(host, port)
  File "/home/timc/.local/lib/python3.10/site-packages/adafruit_httpserver/server.py", line 213, in start
    self._sock.bind((host, port))
OSError: [Errno 98] Address already in use

In this case I had changed "0.0.0.0" to "127.0.0.1" after "using up" a few ports on "0.0.0.0" in order to see if they'd also be blocked with the 127 address. I was able to re-use the same port once on the 127 address, but then if I stopped and started again it would be in use error.

It seems that each pairing of IP + Port is getting held onto by something and is ineligible for re-use.

I'm not sure if it will help, but it might be worth trying the polling method rather than serve_forever(), perhaps that will be be better able to free the resources associated with the IP+Port.

[FoamyGuy]

It appears that the resources do get freed after a few minutes. I tried again after 2-3 minutes and it was able to run, but after stopping it goes back to having the error of address in use if you run again without waiting for 2-3 minutes.

If there is any way to modify the example code and/or library code to make it so these get freed whenever the script is stopped with KeyboardInterrupt I would be in favor of that.

[michalpokusa]

In theory, that is what should be happening.
https://github.com/adafruit/Adafruit_CircuitPython_HTTPServer/blob/main/adafruit_httpserver/server.py#L191

The login in Server.stop() should be able to do just that by calling self._sock.close(), maybe there is something missing there.

[michalpokusa]

https://docs.python.org/3/library/socket.html#socket.socket.close

close() releases the resource associated with a connection but does not necessarily close the connection immediately. If you want to close the connection in a timely fashion, call shutdown() before close().

Maybe there should be a .shutdown() before .close()? I canot test right now but seems like this might be the issue.

[michalpokusa]

I managed to test my first idea, turned out that it was not it, but this version might be the the solution:
https://github.com/michalpokusa/Adafruit_CircuitPython_HTTPServer/tree/cpython-fix

Works correctly on my machine, additional tests would be appreciated.

[FoamyGuy]

This looks good to me, and it is independent from the address in use thing which can be addressed in a future PR. Thanks again for this change @tedder.

@michalpokusa the branch you linked does seem to resolve the issue on my end as well. Go ahead and make a PR from that branch when you have a moment. Thank you for looking into it!