use UUID to generate a unique SessionID

1 files changed, 16 insertions, 3 deletions

diff --git a/SessionID.hs b/SessionID.hs
index 71f2150..3827e1d 100644
--- a/SessionID.hs
+++ b/SessionID.hs
@@ -13,10 +13,13 @@ import Serialization
 import System.FilePath
 import Data.Text
 import System.IO
+import System.Directory
 import Network.Wai.Handler.Warp (Port)
 import Network.WebSockets hiding (Message)
 import qualified Data.Aeson
 import Data.Maybe
+import Data.UUID
+import Data.UUID.V4
 
 -- | A SessionID is the base name of the log file to use,
 -- and may not contain any path information.
@@ -48,11 +51,21 @@ sessionLogFile :: FilePath -> SessionID -> FilePath
 sessionLogFile dir (SessionID f) = dir </> "debug-me." ++ f ++ ".log"
 
 -- | Allocate a new SessionID and return an open Handle to its log file.
+--
+-- A UUID is used, to avoid ever generating a SessionID that has been used
+-- before.
 withSessionID :: FilePath -> ((Handle, SessionID) -> IO a) -> IO a
 withSessionID dir a = do
-	-- TODO find an unused log file and open it
-	let sid = SessionID "1"
-	withFile "debug-me-server.log" WriteMode $ \h -> a (h, sid)
+	createDirectoryIfMissing False dir
+	sid <- SessionID . toString <$> nextRandom
+	let f = sessionLogFile dir sid
+	-- File should not already exist, but just in case we get
+	-- spectacularly unlucky (or the RNG is broken..),
+	-- avoid overwriting a log, and try again.
+	exists <- doesFileExist f
+	if exists
+		then withSessionID dir a
+		else withFile f WriteMode $ \h -> a (h, sid)
 
 type UrlString = String