skip logfile creation if no logging (#377)

Summary:
**Motivation**
Currently the log files and the log directory for the server are always created, even if the logging is disabled. If duckling is used on OpenShift the file creation leads to errors if no volume mount is defined.

**Proposed Change**:
Only create log files / log directory if the logging is enabled.

Pull Request resolved: https://github.com/facebook/duckling/pull/377

Reviewed By: patapizza

Differential Revision: D26148878

Pulled By: chessai

fbshipit-source-id: f8e2b1a38586121d854a4826c322b4b859cc9c6b

exe/ExampleMain.hs

@@ -10,7 +10,7 @@
 
 import Control.Applicative hiding (empty)
 import Control.Arrow ((***))
-import Control.Monad (unless)
+import Control.Monad (unless, when)
 import Control.Monad.IO.Class
 import Data.Aeson
 import Data.ByteString (ByteString, empty)
@@ -43,19 +43,27 @@ createIfMissing f = do
   exists <- doesFileExist f
   unless exists $ writeFile f ""
 
-setupLogs :: IO ()
-setupLogs = do
-  createDirectoryIfMissing False "log"
-  createIfMissing "log/error.log"
-  createIfMissing "log/access.log"
+shouldLog :: Maybe ConfigLog -> Bool
+shouldLog Nothing = False
+shouldLog (Just ConfigNoLog) = False
+shouldLog _ = True
+
+setupLogs :: Config a b -> IO ()
+setupLogs conf = do
+  let shouldLogErrors = shouldLog $ getErrorLog conf
+  let shouldLogAccesses = shouldLog $ getAccessLog conf
+
+  when (shouldLogErrors || shouldLogAccesses) $ createDirectoryIfMissing False "log"
+  when shouldLogErrors $ createIfMissing "log/error.log"
+  when shouldLogAccesses $ createIfMissing "log/access.log"
 
 main :: IO ()
 main = do
-  setupLogs
   tzs <- loadTimeZoneSeries "/usr/share/zoneinfo/"
   p <- lookupEnv "PORT"
   conf <- commandLineConfig $
     maybe defaultConfig (`setPort` defaultConfig) (readMaybe =<< p)
+  setupLogs conf
   httpServe conf $
     ifTop (writeBS "quack!") <|>
     route