Merge pull request #65 from diogob/configurable-retries

Add configuration for max number of retries and exit server with an error when connection dies or fails to open

Author: diogob

CHANGELOG.md

@@ -1,5 +1,9 @@
 # CHANGELOG
 
+## 0.9.0.0
+
+- Add PGWS_RETRIES to limit the amount of times the server tries to open a database connection upon startup (defaults to 5). This breaks backward compatibility if you rely on the behaviour of the server to try infitite times.
+
 ## 0.8.0.1
 
 - Fix compilation error due to missing version upper bound for protolude.

postgres-websockets.cabal

@@ -1,5 +1,5 @@
 name:                postgres-websockets
-version:             0.8.0.1
+version:             0.9.0.0
 synopsis:            Middleware to map LISTEN/NOTIFY messages to Websockets
 description:         Please see README.md
 homepage:            https://github.com/diogob/postgres-websockets#readme

src/PostgresWebsockets/Config.hs

@@ -34,6 +34,7 @@ data AppConfig = AppConfig {
   , configJwtSecret         :: ByteString
   , configJwtSecretIsBase64 :: Bool
   , configPool              :: Int
+  , configRetries           :: Int
   }
 
 -- | User friendly version number
@@ -70,6 +71,7 @@ readOptions =
                 <*> var str "PGWS_JWT_SECRET" (help "Secret used to sign JWT tokens used to open communications channels")
                 <*> var auto "PGWS_JWT_SECRET_BASE64" (def False <> helpDef show <> help "Indicate whether the JWT secret should be decoded from a base64 encoded string")
                 <*> var auto "PGWS_POOL_SIZE" (def 10 <> helpDef show <> help "How many connection to the database should be used by the connection pool")
+                <*> var auto "PGWS_RETRIES" (def 5 <> helpDef show <> help "How many times it should try to connect to the database on startup before exiting with an error")
 
 loadSecretFile :: AppConfig -> IO AppConfig
 loadSecretFile conf = extractAndTransform secret

src/PostgresWebsockets/HasqlBroadcast.hs

@@ -23,15 +23,15 @@ import Data.Aeson              (decode, Value(..))
 import Data.HashMap.Lazy       (lookupDefault)
 import Data.Either.Combinators (mapBoth)
 import Data.Function           (id)
-import Control.Retry           (RetryStatus, retrying, capDelay, exponentialBackoff)
+import Control.Retry           (RetryStatus(..), retrying, capDelay, exponentialBackoff)
 
 import PostgresWebsockets.Broadcast
 
 {- | Returns a multiplexer from a connection URI, keeps trying to connect in case there is any error.
    This function also spawns a thread that keeps relaying the messages from the database to the multiplexer's listeners
 -}
-newHasqlBroadcaster :: IO () -> Text -> ByteString -> IO Multiplexer
-newHasqlBroadcaster onConnectionFailure ch = newHasqlBroadcasterForConnection . tryUntilConnected
+newHasqlBroadcaster :: IO () -> Text -> Int -> ByteString -> IO Multiplexer
+newHasqlBroadcaster onConnectionFailure ch maxRetries = newHasqlBroadcasterForConnection . tryUntilConnected maxRetries
   where
     newHasqlBroadcasterForConnection = newHasqlBroadcasterForChannel onConnectionFailure ch
 
@@ -44,20 +44,20 @@ newHasqlBroadcasterOrError onConnectionFailure ch =
   where
     newHasqlBroadcasterForConnection = newHasqlBroadcasterForChannel onConnectionFailure ch
 
-tryUntilConnected :: ByteString -> IO Connection
-tryUntilConnected =
+tryUntilConnected :: Int -> ByteString -> IO Connection
+tryUntilConnected maxRetries =
   fmap (either (panic "Failure on connection retry") id) . retryConnection
   where
     retryConnection conStr = retrying retryPolicy shouldRetry (const $ acquire conStr)
     maxDelayInMicroseconds = 32000000
     firstDelayInMicroseconds = 1000000
     retryPolicy = capDelay maxDelayInMicroseconds $ exponentialBackoff firstDelayInMicroseconds
     shouldRetry :: RetryStatus -> Either ConnectionError Connection -> IO Bool
-    shouldRetry _ con =
+    shouldRetry RetryStatus{..} con =
       case con of
         Left err -> do
           putErrLn $ "Error connecting notification listener to database: " <> show err
-          return True
+          pure $ rsIterNumber < maxRetries - 1
         _ -> return False
 
 {- | Returns a multiplexer from a channel and an IO Connection, listen for different database notifications on the provided channel using the connection produced.

src/PostgresWebsockets/Server.hs

@@ -25,23 +25,24 @@ import           Network.Wai.Middleware.RequestLogger (logStdout)
 
 -- | Start a stand-alone warp server using the parameters from AppConfig and a opening a database connection pool.
 serve :: AppConfig -> IO ()
-serve conf = do
+serve conf@AppConfig{..} = do
   shutdownSignal <- newEmptyMVar
-  let listenChannel = toS $ configListenChannel conf
-      pgSettings = toS (configDatabase conf)
-      waitForShutdown cl = void $ forkIO (takeMVar shutdownSignal >> cl >> die "Shutting server down...")
+  let listenChannel = toS configListenChannel
+      pgSettings = toS configDatabase
+      waitForShutdown cl = void $ forkIO (takeMVar shutdownSignal >> cl)
       appSettings = warpSettings waitForShutdown conf
 
-  putStrLn $ ("Listening on port " :: Text) <> show (configPort conf)
+  putStrLn $ ("Listening on port " :: Text) <> show configPort
 
   let shutdown = putErrLn ("Broadcaster connection is dead" :: Text) >> putMVar shutdownSignal ()
-  pool <- P.acquire (configPool conf, 10, pgSettings)
-  multi <- newHasqlBroadcaster shutdown listenChannel pgSettings
+  pool <- P.acquire (configPool, 10, pgSettings)
+  multi <- newHasqlBroadcaster shutdown listenChannel configRetries pgSettings
   getTime <- mkGetTime
 
   runSettings appSettings $
-    postgresWsMiddleware getTime listenChannel (configJwtSecret conf) pool multi $
-    logStdout $ maybe dummyApp staticApp' (configPath conf)
+    postgresWsMiddleware getTime listenChannel configJwtSecret pool multi $
+    logStdout $ maybe dummyApp staticApp' configPath
+  die "Shutting down server..."
 
   where
     mkGetTime :: IO (IO UTCTime)