refactor: move socket creation and management to App module

Right now listening sockets initialization, management and usage is split between App, AppState and Admin modules: they are created in AppState.init and remembered in AppState but used only in App and Admin.

It has several negative consequences:
- sockets are initialized even if not needed (eg. command line invocations like dump-config or dump-schema)
- it is impossible to start listening on a socket after initial schema cache load because it requires AppState

This change decouples listen socket management from AppState. Sockets are created only when needed (ie. not in command line tools invocation) and passed to admin application and to Warp by the App module.

src/PostgREST/App.hs

@@ -60,10 +60,15 @@ import PostgREST.SchemaCache          (SchemaCache (..))
 import PostgREST.TimeIt               (timeItT)
 import PostgREST.Version              (docsVersion, prettyVersion)
 
-import qualified Data.ByteString.Char8 as BS
-import qualified Data.List             as L
-import qualified Network.HTTP.Types    as HTTP
-import           Protolude             hiding (Handler)
+import qualified Data.ByteString.Char8  as BS
+import qualified Data.List              as L
+import           Data.Streaming.Network (bindPortTCP,
+                                         bindRandomPortTCP)
+import qualified Data.Text              as T
+import qualified Network.HTTP.Types     as HTTP
+import qualified Network.Socket         as NS
+import           PostgREST.Unix         (createAndBindDomainSocket)
+import           Protolude              hiding (Handler)
 
 type Handler = ExceptT Error
 
@@ -72,19 +77,21 @@ run appState = do
   conf@AppConfig{..} <- AppState.getConfig appState
 
   AppState.schemaCacheLoader appState -- Loads the initial SchemaCache
+  (mainSocket, adminSocket) <- initSockets conf
+
   Unix.installSignalHandlers observer (AppState.getMainThreadId appState) (AppState.schemaCacheLoader appState) (AppState.readInDbConfig False appState)
 
   Listener.runListener appState
 
-  Admin.runAdmin appState (serverSettings conf)
+  Admin.runAdmin appState adminSocket mainSocket (serverSettings conf)
 
   let app = postgrest configLogLevel appState (AppState.schemaCacheLoader appState)
 
   do
-    address <- resolveSocketToAddress (AppState.getSocketREST appState)
+    address <- resolveSocketToAddress mainSocket
     observer $ AppServerAddressObs address
 
-  Warp.runSettingsSocket (serverSettings conf & setOnException onWarpException) (AppState.getSocketREST appState) app
+  Warp.runSettingsSocket (serverSettings conf & setOnException onWarpException) mainSocket app
   where
     observer = AppState.getObserver appState
 
@@ -228,3 +235,40 @@ addRetryHint delay response = do
 
 isServiceUnavailable :: Wai.Response -> Bool
 isServiceUnavailable response = Wai.responseStatus response == HTTP.status503
+
+type AppSockets = (NS.Socket, Maybe NS.Socket)
+
+initSockets :: AppConfig -> IO AppSockets
+initSockets AppConfig{..} = do
+  let
+    cfg'usp = configServerUnixSocket
+    cfg'uspm = configServerUnixSocketMode
+    cfg'host = configServerHost
+    cfg'port = configServerPort
+    cfg'adminHost = configAdminServerHost
+    cfg'adminPort = configAdminServerPort
+
+  sock <- case cfg'usp of
+    -- I'm not using `streaming-commons`' bindPath function here because it's not defined for Windows,
+    -- but we need to have runtime error if we try to use it in Windows, not compile time error
+    Just path -> createAndBindDomainSocket path cfg'uspm
+    Nothing -> do
+      (_, sock) <-
+        if cfg'port /= 0
+          then do
+            sock <- bindPortTCP cfg'port (fromString $ T.unpack cfg'host)
+            pure (cfg'port, sock)
+          else do
+            -- explicitly bind to a random port, returning bound port number
+            (num, sock) <- bindRandomPortTCP (fromString $ T.unpack cfg'host)
+            pure (num, sock)
+      pure sock
+
+  adminSock <- case cfg'adminPort of
+    Just adminPort -> do
+      adminSock <- bindPortTCP adminPort (fromString $ T.unpack cfg'adminHost)
+      pure $ Just adminSock
+    Nothing -> pure Nothing
+
+  pure (sock, adminSock)
+