Utilities.hs: Implemented `IO [Int]' function for reconnection waiting

source/Network/Xmpp/Utilities.hs

@@ -28,6 +28,7 @@ import           Prelude
 import           System.IO.Unsafe(unsafePerformIO)
 import qualified Text.XML.Stream.Render as TXSR
 import           Text.XML.Unresolved as TXU
+import           System.Random
 
 -- | Apply f with the content of tv as state, restoring the original value when an
 -- exception occurs
@@ -92,3 +93,13 @@ hostnameP = do
                 if Text.length label + 1 + Text.length r > 255
                     then fail "Hostname too long."
                     else return $ Text.concat [label, Text.pack ".", r]
+
+-- The number of seconds to wait before reconnection attempts in accordance with
+-- the truncated binary exponential backoff algorithm.
+waitingTimes :: IO [Int]
+waitingTimes = do
+    wait <- randomRIO (1, 59)
+    waits <- Prelude.mapM (\n -> randomRIO (0, wait * n)) slotTimes
+    return (wait:waits)
+  where
+    slotTimes = [1, 3, 8, 15, 24, 35, 48, 63, 80, 99, 99, 99, 99, 99, 99]