refactor: make sure proper sockets cleanup is performed in App.run

[mkleczek]

Right now code in App.run does not properly use bracket/finally to close sockets and clean-up mainSocketRef. This is not a big problem at the moment because the application is going to exit enyway but introducting proper resource handling will make future refactorings safer.

[steve-chavez]

So on #5045, we added a socket close here:

postgrest/src/PostgREST/Admin.hs

Lines 41 to 43 in 9f3dc46

	onError adminSock ex = do
	observer $ AdminServerCrashedObs ex
	NS.close adminSock -- we close the socket so request doesn't hang

Which makes me wonder, should we move

postgrest/src/PostgREST/Admin.hs

Lines 26 to 27 in 9f3dc46

	runAdmin :: AppState -> Maybe NS.Socket -> IO (Maybe NS.Socket) -> Warp.Settings -> IO ()
	runAdmin appState maybeAdminSocket getSocketREST settings = do

To App.hs so we can have all the logic about opening/closing sockets centralized and visible?

[mkleczek]

Which makes me wonder, should we move

postgrest/src/PostgREST/Admin.hs

Lines 26 to 27 in 9f3dc46

	runAdmin :: AppState -> Maybe NS.Socket -> IO (Maybe NS.Socket) -> Warp.Settings -> IO ()
	runAdmin appState maybeAdminSocket getSocketREST settings = do

To App.hs so we can have all the logic about opening/closing sockets centralized and visible?

That would make Admin module really unnecessary, I'd say.

Not opposing this but I'd say this should be a separate refactoring PR.

I also think we should go even further and "pull up" main thread id from AppState - but, again, in a separate PR.

[taimoorzaeem]

That would make Admin module really unnecessary, I'd say.

Not opposing this but I'd say this should be a separate refactoring PR.

Agreed.

[mkleczek]

Which makes me wonder, should we move

postgrest/src/PostgREST/Admin.hs

Lines 26 to 27 in 9f3dc46

	runAdmin :: AppState -> Maybe NS.Socket -> IO (Maybe NS.Socket) -> Warp.Settings -> IO ()
	runAdmin appState maybeAdminSocket getSocketREST settings = do

To App.hs so we can have all the logic about opening/closing sockets centralized and visible?

See #5076

That would make Admin module really unnecessary, I'd say.

Not opposing this but I'd say this should be a separate refactoring PR.

I also think we should go even further and "pull up" main thread id from AppState - but, again, in a separate PR.

See #5056

@steve-chavez @taimoorzaeem