Wrap callbacks in newtype to make wrong usage harder

src/Kafka/Callbacks.hs

@@ -2,12 +2,13 @@ module Kafka.Callbacks
 ( errorCallback
 , logCallback
 , statsCallback
+, Callback
 )
 where
 
 import Data.ByteString (ByteString)
 import Kafka.Internal.RdKafka (rdKafkaConfSetErrorCb, rdKafkaConfSetLogCb, rdKafkaConfSetStatsCb)
-import Kafka.Internal.Setup (HasKafkaConf(..), getRdKafkaConf)
+import Kafka.Internal.Setup (HasKafkaConf(..), getRdKafkaConf, Callback(..))
 import Kafka.Types (KafkaError(..), KafkaLogLevel(..))
 
 -- | Add a callback for errors.
@@ -20,10 +21,10 @@ import Kafka.Types (KafkaError(..), KafkaLogLevel(..))
 -- >
 -- > myErrorCallback :: 'KafkaError' -> String -> IO ()
 -- > myErrorCallback kafkaError message = print $ show kafkaError <> "|" <> message
-errorCallback :: HasKafkaConf k => (KafkaError -> String -> IO ()) -> k -> IO ()
-errorCallback callback k =
+errorCallback :: (KafkaError -> String -> IO ()) -> Callback
+errorCallback callback =
   let realCb _ err = callback (KafkaResponseError err)
-  in rdKafkaConfSetErrorCb (getRdKafkaConf k) realCb
+  in Callback $ \k -> rdKafkaConfSetErrorCb (getRdKafkaConf k) realCb
 
 -- | Add a callback for logs.
 --
@@ -35,10 +36,10 @@ errorCallback callback k =
 -- >
 -- > myLogCallback :: 'KafkaLogLevel' -> String -> String -> IO ()
 -- > myLogCallback level facility message = print $ show level <> "|" <> facility <> "|" <> message
-logCallback :: HasKafkaConf k => (KafkaLogLevel -> String -> String -> IO ()) -> k -> IO ()
-logCallback callback k =
+logCallback :: (KafkaLogLevel -> String -> String -> IO ()) -> Callback
+logCallback callback =
   let realCb _ = callback . toEnum
-  in rdKafkaConfSetLogCb (getRdKafkaConf k) realCb
+  in Callback $ \k -> rdKafkaConfSetLogCb (getRdKafkaConf k) realCb
 
 -- | Add a callback for stats. The passed ByteString contains an UTF-8 encoded JSON document and can e.g. be parsed using Data.Aeson.decodeStrict. For more information about the content of the JSON document see <https://github.com/edenhill/librdkafka/blob/master/STATISTICS.md>.
 --
@@ -50,7 +51,7 @@ logCallback callback k =
 -- >
 -- > myStatsCallback :: String -> IO ()
 -- > myStatsCallback stats = print $ show stats
-statsCallback :: HasKafkaConf k => (ByteString -> IO ()) -> k -> IO ()
-statsCallback callback k =
+statsCallback :: (ByteString -> IO ()) -> Callback
+statsCallback callback =
   let realCb _ = callback
-  in rdKafkaConfSetStatsCb (getRdKafkaConf k) realCb
+  in Callback $ \k -> rdKafkaConfSetStatsCb (getRdKafkaConf k) realCb

src/Kafka/Consumer.hs

@@ -85,7 +85,7 @@ import           Foreign                    hiding (void)
 import           Kafka.Consumer.Convert     (fromMessagePtr, fromNativeTopicPartitionList'', offsetCommitToBool, offsetToInt64, toMap, toNativeTopicPartitionList, toNativeTopicPartitionList', toNativeTopicPartitionListNoDispose, topicPartitionFromMessageForCommit)
 import           Kafka.Consumer.Types       (KafkaConsumer (..))
 import           Kafka.Internal.RdKafka     (RdKafkaRespErrT (..), RdKafkaTopicPartitionListTPtr, RdKafkaTypeT (..), newRdKafkaT, newRdKafkaTopicPartitionListT, newRdKafkaTopicT, rdKafkaAssign, rdKafkaAssignment, rdKafkaCommit, rdKafkaCommitted, rdKafkaConfSetDefaultTopicConf, rdKafkaConsumeBatchQueue, rdKafkaConsumeQueue, rdKafkaConsumerClose, rdKafkaConsumerPoll, rdKafkaOffsetsStore, rdKafkaPausePartitions, rdKafkaPollSetConsumer, rdKafkaPosition, rdKafkaQueueDestroy, rdKafkaQueueNew, rdKafkaResumePartitions, rdKafkaSeek, rdKafkaSetLogLevel, rdKafkaSubscribe, rdKafkaSubscription, rdKafkaTopicConfDup, rdKafkaTopicPartitionListAdd)
-import           Kafka.Internal.Setup       (CallbackPollStatus (..), Kafka (..), KafkaConf (..), KafkaProps (..), TopicConf (..), TopicProps (..), getKafkaConf, getRdKafka, kafkaConf, topicConf)
+import           Kafka.Internal.Setup       (CallbackPollStatus (..), Kafka (..), KafkaConf (..), KafkaProps (..), TopicConf (..), TopicProps (..), getKafkaConf, getRdKafka, kafkaConf, topicConf, Callback(..))
 import           Kafka.Internal.Shared      (kafkaErrorToMaybe, maybeToLeft, rdKafkaErrorToEither)
 
 import Kafka.Consumer.ConsumerProperties as X
@@ -327,7 +327,7 @@ closeConsumer (KafkaConsumer (Kafka k) (KafkaConf _ qr statusVar)) = liftIO $
 newConsumerConf :: ConsumerProperties -> IO KafkaConf
 newConsumerConf ConsumerProperties {cpProps = m, cpCallbacks = cbs} = do
   conf <- kafkaConf (KafkaProps m)
-  forM_ cbs (\setCb -> setCb conf)
+  forM_ cbs (\(Callback setCb) -> setCb conf)
   return conf
 
 -- | Subscribes to a given list of topics.

src/Kafka/Consumer/Callbacks.hs

@@ -14,16 +14,17 @@ import Kafka.Callbacks        as X
 import Kafka.Consumer.Convert (fromNativeTopicPartitionList', fromNativeTopicPartitionList'')
 import Kafka.Consumer.Types   (KafkaConsumer (..), RebalanceEvent (..), TopicPartition (..))
 import Kafka.Internal.RdKafka
-import Kafka.Internal.Setup   (HasKafka (..), HasKafkaConf (..), Kafka (..), KafkaConf (..), getRdMsgQueue)
+import Kafka.Internal.Setup   (HasKafka (..), HasKafkaConf (..), Kafka (..), KafkaConf (..), getRdMsgQueue, Callback (..))
 import Kafka.Types            (KafkaError (..), PartitionId (..), TopicName (..))
 
 import qualified Data.Text as Text
 
 -- | Sets a callback that is called when rebalance is needed.
-rebalanceCallback :: (KafkaConsumer -> RebalanceEvent -> IO ()) -> KafkaConf -> IO ()
-rebalanceCallback callback kc@(KafkaConf conf _ _) = rdKafkaConfSetRebalanceCb conf realCb
+rebalanceCallback :: (KafkaConsumer -> RebalanceEvent -> IO ()) -> Callback
+rebalanceCallback callback =
+  Callback $ \kc@(KafkaConf con _ _) -> rdKafkaConfSetRebalanceCb con (realCb kc)
   where
-    realCb k err pl = do
+    realCb kc k err pl = do
       k' <- newForeignPtr_ k
       pls <- newForeignPtr_ pl
       setRebalanceCallback callback (KafkaConsumer (Kafka k') kc) (KafkaResponseError err) pls
@@ -36,10 +37,11 @@ rebalanceCallback callback kc@(KafkaConf conf _ _) = rdKafkaConfSetRebalanceCb c
 -- If no partitions had valid offsets to commit this callback will be called
 -- with 'KafkaResponseError' 'RdKafkaRespErrNoOffset' which is not to be considered
 -- an error.
-offsetCommitCallback :: (KafkaConsumer -> KafkaError -> [TopicPartition] -> IO ()) -> KafkaConf -> IO ()
-offsetCommitCallback callback kc@(KafkaConf conf _ _) = rdKafkaConfSetOffsetCommitCb conf realCb
+offsetCommitCallback :: (KafkaConsumer -> KafkaError -> [TopicPartition] -> IO ()) -> Callback
+offsetCommitCallback callback =
+  Callback $ \kc@(KafkaConf conf _ _) -> rdKafkaConfSetOffsetCommitCb conf (realCb kc)
   where
-    realCb k err pl = do
+    realCb kc k err pl = do
       k' <- newForeignPtr_ k
       pls <- fromNativeTopicPartitionList' pl
       callback (KafkaConsumer (Kafka k') kc) (KafkaResponseError err) pls

src/Kafka/Consumer/ConsumerProperties.hs

@@ -34,7 +34,7 @@ import           Data.Semigroup       as Sem
 import           Data.Text            (Text)
 import qualified Data.Text            as Text
 import           Kafka.Consumer.Types (ConsumerGroupId (..))
-import           Kafka.Internal.Setup (KafkaConf (..))
+import           Kafka.Internal.Setup (KafkaConf (..), Callback(..))
 import           Kafka.Types          (BrokerAddress (..), ClientId (..), KafkaCompressionCodec (..), KafkaDebug (..), KafkaLogLevel (..), Millis (..), kafkaCompressionCodecToText, kafkaDebugToText)
 
 import Kafka.Consumer.Callbacks as X
@@ -53,7 +53,7 @@ data CallbackPollMode =
 data ConsumerProperties = ConsumerProperties
   { cpProps            :: Map Text Text
   , cpLogLevel         :: Maybe KafkaLogLevel
-  , cpCallbacks        :: [KafkaConf -> IO ()]
+  , cpCallbacks        :: [Callback]
   , cpCallbackPollMode :: CallbackPollMode
   }
 
@@ -117,7 +117,7 @@ clientId (ClientId cid) =
 -- * 'errorCallback'
 -- * 'logCallback'
 -- * 'statsCallback'
-setCallback :: (KafkaConf -> IO ()) -> ConsumerProperties
+setCallback :: Callback -> ConsumerProperties
 setCallback cb = mempty { cpCallbacks = [cb] }
 
 -- | Set the logging level.

src/Kafka/Internal/Setup.hs

@@ -7,6 +7,7 @@ module Kafka.Internal.Setup
 , HasKafka(..)
 , HasKafkaConf(..)
 , HasTopicConf(..)
+, Callback(..)
 , CallbackPollStatus(..)
 , getRdKafka
 , getRdKafkaConf
@@ -46,6 +47,11 @@ newtype TopicProps = TopicProps (Map Text Text) deriving (Show, Eq)
 newtype Kafka      = Kafka RdKafkaTPtr deriving Show
 newtype TopicConf  = TopicConf RdKafkaTopicConfTPtr deriving Show
 
+-- | Callbacks allow retrieving various information like error occurences, statistics
+-- and log messages.
+-- See `Kafka.Consumer.setCallback` (Consumer) and `Kafka.Producer.setCallback` (Producer) for more details.
+newtype Callback = Callback (KafkaConf -> IO ())
+
 data CallbackPollStatus = CallbackPollEnabled | CallbackPollDisabled deriving (Show, Eq)
 
 data KafkaConf         = KafkaConf

src/Kafka/Producer.hs

@@ -82,7 +82,7 @@ import           Foreign.Ptr              (Ptr, nullPtr, plusPtr)
 import           Foreign.Storable         (Storable (..))
 import           Foreign.StablePtr        (newStablePtr, castStablePtrToPtr)
 import           Kafka.Internal.RdKafka   (RdKafkaMessageT (..), RdKafkaRespErrT (..), RdKafkaTypeT (..), destroyUnmanagedRdKafkaTopic, newRdKafkaT, newUnmanagedRdKafkaTopicT, rdKafkaOutqLen, rdKafkaProduce, rdKafkaProduceBatch, rdKafkaSetLogLevel)
-import           Kafka.Internal.Setup     (Kafka (..), KafkaConf (..), KafkaProps (..), TopicConf (..), TopicProps (..), kafkaConf, topicConf)
+import           Kafka.Internal.Setup     (Kafka (..), KafkaConf (..), KafkaProps (..), TopicConf (..), TopicProps (..), kafkaConf, topicConf, Callback(..))
 import           Kafka.Internal.Shared    (pollEvents)
 import           Kafka.Producer.Convert   (copyMsgFlags, handleProduceErr', producePartitionCInt, producePartitionInt)
 import           Kafka.Producer.Types     (KafkaProducer (..), ImmediateError(..))
@@ -120,7 +120,7 @@ newProducer pps = liftIO $ do
   deliveryCallback (const mempty) kc
 
   -- set callbacks
-  forM_ (ppCallbacks pps) (\setCb -> setCb kc)
+  forM_ (ppCallbacks pps) (\(Callback setCb) -> setCb kc)
 
   mbKafka <- newRdKafkaT RdKafkaProducer kc'
   case mbKafka of

src/Kafka/Producer/ProducerProperties.hs

@@ -27,7 +27,7 @@ import           Control.Monad            (MonadPlus(mplus))
 import           Data.Map                 (Map)
 import qualified Data.Map                 as M
 import           Data.Semigroup           as Sem
-import           Kafka.Internal.Setup     (KafkaConf(..))
+import           Kafka.Internal.Setup     (KafkaConf(..), Callback(..))
 import           Kafka.Types              (KafkaDebug(..), Timeout(..), KafkaCompressionCodec(..), KafkaLogLevel(..), BrokerAddress(..), kafkaDebugToText, kafkaCompressionCodecToText, Millis(..))
 
 import           Kafka.Producer.Callbacks
@@ -37,7 +37,7 @@ data ProducerProperties = ProducerProperties
   { ppKafkaProps :: Map Text Text
   , ppTopicProps :: Map Text Text
   , ppLogLevel   :: Maybe KafkaLogLevel
-  , ppCallbacks  :: [KafkaConf -> IO ()]
+  , ppCallbacks  :: [Callback]
   }
 
 instance Sem.Semigroup ProducerProperties where
@@ -70,7 +70,7 @@ brokersList bs =
 -- * 'errorCallback'
 -- * 'logCallback'
 -- * 'statsCallback'
-setCallback :: (KafkaConf -> IO ()) -> ProducerProperties
+setCallback :: Callback -> ProducerProperties
 setCallback cb = mempty { ppCallbacks = [cb] }
 
 -- | Sets the logging level.