smp server: expire subscribed clients too, with 3x TTL

src/Simplex/Messaging/Server.hs

@@ -744,11 +744,14 @@
   where
     loop = do
       threadDelay' $ checkInterval expCfg * 1000000
-      ifM noSubscriptions checkExpired loop
-    checkExpired = do
-      old <- expireBeforeEpoch expCfg
+      ifM noSubscriptions (checkExpired expCfg) (checkExpired expCfg')
+    checkExpired cfg = do
+      old <- expireBeforeEpoch cfg
       ts <- max <$> readTVarIO rcvActiveAt <*> readTVarIO sndActiveAt
       if systemSeconds ts < old then closeConnection connection else loop
+    expCfg' =
+      let ExpirationConfig {ttl} = expCfg
+       in expCfg {ttl = 3 * ttl}
 
 data VerificationResult = VRVerified (Maybe QueueRec) | VRFailed
 
@@ -807,7 +810,7 @@
 
 -- These dummy keys are used with `dummyVerify` function to mitigate timing attacks
 -- by having the same time of the response whether a queue exists or nor, for all valid key/signature sizes
 dummySignKey :: C.SignatureAlgorithm a => C.SAlgorithm a -> C.PublicKey a
 dummySignKey = \case
   C.SEd25519 -> dummyKeyEd25519
   C.SEd448 -> dummyKeyEd448