Expire terminal mutation identities by configured epoch

src/Nuthatch/Config.hs

@@ -50,6 +50,7 @@ data Config = Config
   , cfgListCacheTtlSec     :: Integer
   , cfgSearchMaxKeys       :: Int
   , cfgRecoveryGraceSec    :: Integer
+  , cfgIdempotencyWindowSec :: Integer
   }
 
 loadConfig :: IO Config
@@ -112,6 +113,9 @@ loadConfig = do
   listTtl <- envInteger "NUTHATCH_LIST_CACHE_TTL_SEC" 30
   searchMax <- fromInteger <$> envInteger "NUTHATCH_SEARCH_MAX_KEYS" 500
   recoveryGrace <- envInteger "NUTHATCH_RECOVERY_GRACE_SEC" 90
+  idempotencyWindow <- envInteger "NUTHATCH_IDEMPOTENCY_WINDOW_SEC" 86400
+  when (idempotencyWindow <= 0) $
+    fail "NUTHATCH_IDEMPOTENCY_WINDOW_SEC must be positive"
   pure Config
     { cfgListenHost = host
     , cfgListenPort = port
@@ -148,6 +152,7 @@ loadConfig = do
     , cfgListCacheTtlSec = listTtl
     , cfgSearchMaxKeys = searchMax
     , cfgRecoveryGraceSec = recoveryGrace
+    , cfgIdempotencyWindowSec = idempotencyWindow
     }
 
 luaExactIntegerMax :: Integer