Studio: Reclaim unavailable port after site deletion

[SiobhyB]

Fixes: 7366-gh-Automattic/dotcom-forge

Proposed Changes

• With the changes in this PR, ports are now released when a site is deleted and the Studio app will re-use them if users create more sites.
• The following main steps were necessary to achieve this:
  • Kill the processes associated with the port, so that it's fully released and not lingering in a CLOSED state following the site deletion.
  • Remove port from Studio's running list of unavailable ports.
  • Reset the default port used so that the app cycles through the newly available port.

Testing Instructions

• Create a new site in the Studio app and make a note of the port via the local URL (e.g. 8881).
• Verify the port is in use by running lsof -i :8881 in the command line (replace 8881 with your site's port).
• In Studio, navigate to the Settings tab and delete the site.
• Verify the port is now free by running lsof -i :8881 in the command line (again, replacing 8881 with your site's port).
• Create another new site in the Studio app and verify that the app uses the port associated with the deleted site (i.e. 8881 in our examples).

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[SiobhyB]

These steps are added to the finally block as there are some instances where we can have the desired outcome even if killPort fails. For example:

• User deletes site, but an error occurs when attempting to kill the port.
• The user's laptop gets put to sleep, thus causing the port to be killed by the OS.
• User returns to laptop and creates another site in the app.
• The reclaimed port is used thanks to the fact it was removed from the #unavailablePorts list and #searchPort was reset to the default.

[SiobhyB]

Before deciding to use this library, I tried a few things to try to release a CLOSED port for use, including:

• Used http.createServer to attempt to .close the port explicitly. This led to the port remaining in a CLOSED state, but not being released, which is the same as what's already happening when a site is deleted (reference).
• Experimented with explicitly setting socket.setReuseAddress(true), so as to be able to re-use the port more quickly and also detecting/destroying open sockets.

The only success I had was with manually killing the PIDs associated with a given port using a lsof command, which is only available for Unix systems. The cross-port-killer library works for all platforms and using it felt more efficient than the code that would be required.

I'm open to further thoughts or ideas here.

[wojtekn]

Thanks for explaining the reasoning behind using the library for that. It seems that the library is a wrapper and uses tools available in win32, linux, and darwin to kill the port, so it would go well with our support for Mac, Windows, and Linux in the future.

[wojtekn]

@SiobhyB I tested it on macOS and couldn't make it work so far:

1. Added the first site with 8906 port
2. Added the second site with 8907 port
3. Deleted the first site
4. I noticed the message logged:

Killed processes using port 8906

5. I waited about 15 seconds
6. Added the third site, and it used port 8908

I would expect it used 8906, assuming all ports between 8881 and 8905 are taken.

Another thing I noticed is that Studio still doesn't reuse ports that were used in the past and are free now. Those ports are used by sites I have locally:

8881
8883
8885
8886
8887
8890
8894
8900
8902
8903
8904
8905
8907
8908

Studio keeps adding ports over the 8908, and doesn't reuse the free ports. It should work that way:

1. Get a list of all ports claimed by existing sites
2. Get a first free port starting from 8881
3. If it's not claimed by existing site, use it, otherwise check the next port

Based on those, it should take 8882 in the above case. Any thoughts why it doesn't reuse those?

[SiobhyB]

@wojtekn, thank you for spotting that! I found it was because #openPort was the value needing to be reset, rather than #searchPort, as the latter is being set using the value of the former. I've gone ahead to update in f1c9f97 and it's working in my testing now. Let me know if you spot anything else missing, though.

[fluiddot]

LGTM 🎊 !

[wojtekn]

Thanks for fixing that @SiobhyB. The use case I shared works as expected now, and Studio now uses unused ports from the list I shared above.