Verifies PostgreSQL version is supported (+9.2) before spawning server [fixes #157]

src/PostgREST/Main.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE QuasiQuotes, ScopedTypeVariables #-}
 module Main where
 
 import Paths_postgrest (version)
@@ -17,12 +18,18 @@ import Network.Wai.Middleware.Static (staticPolicy, only)
 import Network.Wai.Middleware.RequestLogger (logStdout)
 import Data.List (intercalate)
 import Data.Version (versionBranch)
+import Data.Functor.Identity
+import Data.Text(Text)
 import qualified Hasql as H
 import qualified Hasql.Postgres as P
 import Options.Applicative hiding (columns)
 
 import PostgREST.Config (AppConfig(..), argParser, corsPolicy)
 
+isServerVersionSupported = do
+  Identity (row :: Text) <- H.tx Nothing $ H.singleEx $ [H.stmt|SHOW server_version_num|]
+  return $ read (cs row) >= 90200
+
 main :: IO ()
 main = do
   let opts = info (helper <*> argParser) $
@@ -61,6 +68,9 @@ main = do
   pool :: H.Pool P.Postgres
           <- H.acquirePool pgSettings poolSettings
 
+  resOrError <- H.session pool isServerVersionSupported
+  either (fail . show) (\supported -> unless supported $ fail "Cannot run in this PostgreSQL version, PostgREST needs at least 9.2.0") resOrError
+
   runSettings appSettings $ middle $ \req respond -> do
     body <- strictRequestBody req
     resOrError <- liftIO $ H.session pool $ H.tx Nothing $