Use env interpolation in config (#826)

src/PostgREST/Config.hs

@@ -1,3 +1,4 @@
+{-# OPTIONS_GHC -fno-warn-type-defaults #-}
 {-|
 Module      : PostgREST.Config
 Description : Manages PostgREST configuration options.
@@ -27,9 +28,11 @@ import qualified Data.ByteString             as B
 import qualified Data.ByteString.Char8       as BS
 import qualified Data.CaseInsensitive        as CI
 import qualified Data.Configurator           as C
-import qualified Data.Configurator.Types     as C
+import qualified Data.Configurator.Parser    as C
+import           Data.Configurator.Types     (Value(..))
 import           Data.List                   (lookup)
 import           Data.Monoid
+import           Data.Scientific             (floatingOrInteger)
 import           Data.Text                   (strip, intercalate, lines)
 import           Data.Text.Encoding          (encodeUtf8)
 import           Data.Text.IO                (hPutStrLn)
@@ -38,6 +41,7 @@ import           Network.Wai
 import           Network.Wai.Middleware.Cors (CorsResourcePolicy (..))
 import           Options.Applicative hiding  (str)
 import           Paths_postgrest             (version)
+import           System.IO                   (hPrint)
 import           Text.Heredoc
 import           Text.PrettyPrint.ANSI.Leijen hiding ((<>), (<$>))
 import qualified Text.PrettyPrint.ANSI.Leijen as L
@@ -95,30 +99,37 @@ readOptions = do
   cfgPath <- customExecParser parserPrefs opts
   -- Now read the actual config file
   conf <- catch
-    (C.load [C.Required cfgPath])
+    (C.readConfig =<< C.load [C.Required cfgPath])
     configNotfoundHint
 
-  handle missingKeyHint $ do
-    -- db ----------------
-    cDbUri    <- C.require conf "db-uri"
-    cDbSchema <- C.require conf "db-schema"
-    cDbAnon   <- C.require conf "db-anon-role"
-    cPool     <- C.lookupDefault 10 conf "db-pool"
-    -- server ------------
-    cHost     <- C.lookupDefault "*4" conf "server-host"
-    cPort     <- C.lookupDefault 3000 conf "server-port"
-    cProxy    <- C.lookup conf "server-proxy-uri"
-    -- jwt ---------------
-    cJwtSec   <- C.lookup conf "jwt-secret"
-    cJwtB64   <- C.lookupDefault False conf "secret-is-base64"
-    -- safety ------------
-    cMaxRows  <- C.lookup conf "max-rows"
-    cReqCheck <- C.lookup conf "pre-request"
+  let (mAppConf, errs) = flip C.runParserA conf $
+        AppConfig <$>
+            C.key "db-uri"
+          <*> C.key "db-anon-role"
+          <*> C.key "server-proxy-uri"
+          <*> C.key "db-schema"
+          <*> (fromMaybe "*4" <$> C.key "server-host")
+          <*> (fromMaybe 3000 . join . fmap coerceInt <$> C.key "server-port")
+          <*> (fmap encodeUtf8 . mfilter (/= "") <$> C.key "jwt-secret")
+          <*> (fromMaybe False <$> C.key "secret-is-base64")
+          <*> (fromMaybe 10 . join . fmap coerceInt <$> C.key "db-pool")
+          <*> (join . fmap coerceInt <$> C.key "max-rows")
+          <*> C.key "pre-request"
+          <*> pure False
 
-    return $ AppConfig cDbUri cDbAnon cProxy cDbSchema cHost cPort
-          (encodeUtf8 <$> cJwtSec) cJwtB64 cPool cMaxRows cReqCheck False
+  case mAppConf of
+    Nothing -> do
+      forM_ errs $ hPrint stderr
+      exitFailure
+    Just appConf ->
+      return appConf
 
  where
+  coerceInt :: (Read i, Integral i) => Value -> Maybe i
+  coerceInt (Number x) = rightToMaybe $ floatingOrInteger x
+  coerceInt (String x) = readMaybe $ toS x
+  coerceInt _ = Nothing
+
   opts = info (helper <*> pathParser) $
            fullDesc
            <> progDesc (
@@ -139,15 +150,6 @@ readOptions = do
       "Cannot open config file:\n\t" <> show e
     exitFailure
 
-  missingKeyHint :: C.KeyError -> IO a
-  missingKeyHint (C.KeyError n) = do
-    hPutStrLn stderr $
-      "Required config parameter \"" <> n <> "\" is missing or of wrong type.\n" <>
-      "Documentation for configuration options available at\n" <>
-      "\thttp://postgrest.com/en/v0.4/admin.html#configuration\n\n" <>
-      "Try the --example-config option to see how to configure PostgREST."
-    exitFailure
-
   exampleCfg :: Doc
   exampleCfg = vsep . map (text . toS) . lines $
     [str|db-uri = "postgres://user:pass@localhost:5432/dbname"
@@ -173,7 +175,6 @@ readOptions = do
         |# pre-request = "stored_proc_name"
         |]
 
-
 pathParser :: Parser FilePath
 pathParser =
   strArgument $