Release all db connections on ctrl-c

Fixes #268

postgrest.cabal

@@ -61,6 +61,7 @@ executable postgrest
                      , HTTP, http-types
                      , MissingH
                      , Ranged-sets
+                     , unix >= 2.7 && < 3
 
   hs-source-dirs:      src
   other-modules:       Paths_postgrest

src/PostgREST/Main.hs

@@ -10,7 +10,9 @@ import           PostgREST.Error                      (pgErrResponse, PgError)
 import           PostgREST.Middleware
 import           PostgREST.DbStructure
 
-import           Control.Monad                        (unless)
+import           Control.Concurrent                   (myThreadId)
+import           Control.Exception.Base               (throwTo, AsyncException(..))
+import           Control.Monad                        (unless, void)
 import           Control.Monad.IO.Class               (liftIO)
 import           Data.Aeson                           (encode)
 import           Data.Functor.Identity
@@ -26,6 +28,7 @@ import           Network.Wai.Middleware.RequestLogger (logStdout)
 import           System.IO                            (BufferMode (..),
                                                        hSetBuffering, stderr,
                                                        stdin, stdout)
+import           System.Posix.Signals
 import           Web.JWT                              (secret)
 
 isServerVersionSupported :: H.Session P.Postgres IO Bool
@@ -69,6 +72,13 @@ main = do
           <> show minimumPgVersion)
     ) supportedOrError
 
+  tid <- myThreadId
+  void $ installHandler keyboardSignal (Catch $ do
+      putStrLn "\nReleasing connection pool..."
+      H.releasePool pool
+      throwTo tid UserInterrupt
+    ) Nothing
+
   let txSettings = Just (H.ReadCommitted, Just True)
   dbOrError <- H.session pool $ H.tx txSettings $ getDbStructure (cs $ configSchema conf)
   dbStructure <- either hasqlError return dbOrError