haskakafka-0.5.0: src/Haskakafka.hs

{-# LANGUAGE DeriveDataTypeable #-}

module Haskakafka 
(  Kafka
 , KafkaConf
 , KafkaLogLevel(..)
 , KafkaMessage(..)
 , KafkaOffset(..)
 , KafkaMetadata(..)
 , KafkaBrokerMetadata(..)
 , KafkaTopicMetadata(..)
 , KafkaPartitionMetadata(..)
 , KafkaProduceMessage(..)
 , KafkaProducePartition(..)
 , KafkaTopic
 , KafkaTopicConf
 , KafkaType(..)
 , KafkaError (..)
 , rdKafkaVersionStr
 , supportedKafkaConfProperties
 , hPrintKafkaProperties
 , hPrintKafka
 , newKafkaConf
 , setKafkaConfValue
 , setKafkaTopicConfValue
 , setKafkaLogLevel
 , dumpKafkaConf
 , newKafkaTopicConf
 , newKafka
 , newKafkaTopic
 , dumpKafkaTopicConf
 , addBrokers
 , startConsuming
 , consumeMessage
 , consumeMessageBatch
 , storeOffset
 , stopConsuming
 , produceMessage
 , produceKeyedMessage
 , produceMessageBatch
 , pollEvents
 , drainOutQueue
 , getAllMetadata
 , getTopicMetadata
 , withKafkaProducer
 , withKafkaConsumer
 , dumpConfFromKafkaTopic
 , dumpConfFromKafka
 , module Haskakafka.InternalEnum
) where

import Control.Exception
import Control.Monad
import Data.Map.Strict (Map)
import Data.Typeable
import Foreign
import Foreign.C.Error
import Foreign.C.String
import Foreign.C.Types
import Haskakafka.Internal
import Haskakafka.InternalEnum
import System.IO
import System.IO.Temp (withSystemTempFile)
import qualified Data.Map.Strict as Map
import qualified Data.ByteString as BS
import qualified Data.ByteString.Internal as BSI

data KafkaLogLevel = 
  KafkaLogEmerg | KafkaLogAlert | KafkaLogCrit | KafkaLogErr | KafkaLogWarning |
  KafkaLogNotice | KafkaLogInfo | KafkaLogDebug

instance Enum KafkaLogLevel where
   toEnum 0 = KafkaLogEmerg
   toEnum 1 = KafkaLogAlert
   toEnum 2 = KafkaLogCrit
   toEnum 3 = KafkaLogErr
   toEnum 4 = KafkaLogWarning
   toEnum 5 = KafkaLogNotice
   toEnum 6 = KafkaLogInfo
   toEnum 7 = KafkaLogDebug
   toEnum _ = undefined

   fromEnum KafkaLogEmerg = 0
   fromEnum KafkaLogAlert = 1
   fromEnum KafkaLogCrit = 2
   fromEnum KafkaLogErr = 3
   fromEnum KafkaLogWarning = 4
   fromEnum KafkaLogNotice = 5
   fromEnum KafkaLogInfo = 6
   fromEnum KafkaLogDebug = 7

data KafkaError = 
    KafkaError String
  | KafkaInvalidReturnValue
  | KafkaBadSpecification String
  | KafkaResponseError RdKafkaRespErrT
  | KafkaInvalidConfigurationValue String
  | KafkaUnknownConfigurationKey String
  | KakfaBadConfiguration
    deriving (Eq, Show, Typeable)

instance Exception KafkaError

data KafkaMessage = KafkaMessage
    { messagePartition :: !Int
    , messageOffset :: !Int64
    , messagePayload :: !BS.ByteString
    , messageKey :: Maybe BS.ByteString
    }
    deriving (Eq, Show, Read, Typeable)

data KafkaProduceMessage = 
    KafkaProduceMessage 
      {-# UNPACK #-} !BS.ByteString
  | KafkaProduceKeyedMessage 
      {-# UNPACK #-} !BS.ByteString -- | Key
      {-# UNPACK #-} !BS.ByteString -- | Payload
  deriving (Eq, Show, Typeable)
      

data KafkaProducePartition = 
    KafkaSpecifiedPartition {-# UNPACK #-} !Int
  | KafkaUnassignedPartition

data KafkaOffset = KafkaOffsetBeginning
                 | KafkaOffsetEnd
                 | KafkaOffsetStored
                 | KafkaOffset Int64

data KafkaConf = KafkaConf RdKafkaConfTPtr
data KafkaTopicConf = KafkaTopicConf RdKafkaTopicConfTPtr

data KafkaType = KafkaConsumer | KafkaProducer
data Kafka = Kafka { kafkaPtr :: RdKafkaTPtr, _kafkaConf :: KafkaConf}
data KafkaTopic = KafkaTopic 
    RdKafkaTopicTPtr  
    Kafka -- Kept around to prevent garbage collection 
    KafkaTopicConf


kafkaTypeToRdKafkaType :: KafkaType -> RdKafkaTypeT
kafkaTypeToRdKafkaType KafkaConsumer = RdKafkaConsumer
kafkaTypeToRdKafkaType KafkaProducer = RdKafkaProducer

-- Because of the rdKafka API, we have to create a temp file to get properties into a string
supportedKafkaConfProperties :: IO (String)
supportedKafkaConfProperties = do 
  withSystemTempFile "haskakafka.rdkafka_properties" $ \tP tH -> do
    hPrintKafkaProperties tH
    readFile tP

hPrintKafkaProperties :: Handle -> IO ()
hPrintKafkaProperties h = handleToCFile h "w" >>= rdKafkaConfPropertiesShow

hPrintKafka :: Handle -> Kafka -> IO ()
hPrintKafka h k = handleToCFile h "w" >>= \f -> rdKafkaDump f (kafkaPtr k)

newKafkaTopicConf :: IO KafkaTopicConf
newKafkaTopicConf = newRdKafkaTopicConfT >>= return . KafkaTopicConf

newKafkaConf :: IO KafkaConf
newKafkaConf = newRdKafkaConfT >>= return . KafkaConf

checkConfSetValue :: RdKafkaConfResT -> CCharBufPointer -> IO ()
checkConfSetValue err charPtr = case err of 
    RdKafkaConfOk -> return ()
    RdKafkaConfInvalid -> do 
      str <- peekCString charPtr
      throw $ KafkaInvalidConfigurationValue str
    RdKafkaConfUnknown -> do
      str <- peekCString charPtr
      throw $ KafkaUnknownConfigurationKey str

setKafkaConfValue :: KafkaConf -> String -> String -> IO ()
setKafkaConfValue (KafkaConf confPtr) key value = do
  allocaBytes nErrorBytes $ \charPtr -> do
    err <- rdKafkaConfSet confPtr key value charPtr (fromIntegral nErrorBytes)
    checkConfSetValue err charPtr

setKafkaTopicConfValue :: KafkaTopicConf -> String -> String -> IO ()
setKafkaTopicConfValue (KafkaTopicConf confPtr) key value = do
  allocaBytes nErrorBytes $ \charPtr -> do
    err <- rdKafkaTopicConfSet confPtr key value charPtr (fromIntegral nErrorBytes)
    checkConfSetValue err charPtr

setKafkaLogLevel :: Kafka -> KafkaLogLevel -> IO ()
setKafkaLogLevel (Kafka kptr _) level = 
  rdKafkaSetLogLevel kptr (fromEnum level)

newKafka :: KafkaType -> KafkaConf -> IO Kafka
newKafka kafkaType c@(KafkaConf confPtr) = do
    et <- newRdKafkaT (kafkaTypeToRdKafkaType kafkaType) confPtr 
    case et of 
        Left e -> error e
        Right x -> return $ Kafka x c

newKafkaTopic :: Kafka -> String -> KafkaTopicConf -> IO (KafkaTopic)
newKafkaTopic k@(Kafka kPtr _) tName conf@(KafkaTopicConf confPtr) = do
    et <- newRdKafkaTopicT kPtr tName confPtr
    case et of 
        Left e -> throw $ KafkaError e
        Right x -> return $ KafkaTopic x k conf

addBrokers :: Kafka -> String -> IO ()
addBrokers (Kafka kptr _) brokerStr = do
    numBrokers <- rdKafkaBrokersAdd kptr brokerStr
    when (numBrokers == 0) 
        (throw $ KafkaBadSpecification "No valid brokers specified")

startConsuming :: KafkaTopic -> Int -> KafkaOffset -> IO ()
startConsuming (KafkaTopic topicPtr _ _) partition offset = 
    let trueOffset = case offset of
                        KafkaOffsetBeginning -> (- 2)
                        KafkaOffsetEnd -> (- 1)
                        KafkaOffsetStored -> (- 1000)
                        KafkaOffset i -> i
    in throwOnError $ rdKafkaConsumeStart topicPtr partition trueOffset


word8PtrToBS :: Int -> Word8Ptr -> IO (BS.ByteString)
word8PtrToBS len ptr = BSI.create len $ \bsptr -> 
    BSI.memcpy bsptr ptr len
    

fromMessageStorable :: RdKafkaMessageT -> IO (KafkaMessage)
fromMessageStorable s = do
    payload <- word8PtrToBS (len'RdKafkaMessageT s) (payload'RdKafkaMessageT s) 

    key <- if (key'RdKafkaMessageT s) == nullPtr then return Nothing 
           else word8PtrToBS (keyLen'RdKafkaMessageT s) (key'RdKafkaMessageT s) >>= return . Just

    return $ KafkaMessage
             (partition'RdKafkaMessageT s) 
             (offset'RdKafkaMessageT s)
             payload
             key 

consumeMessage :: KafkaTopic -> Int -> Int -> IO (Either KafkaError KafkaMessage)
consumeMessage (KafkaTopic topicPtr _ _) partition timeout = do
  ptr <- rdKafkaConsume topicPtr (fromIntegral partition) (fromIntegral timeout)
  withForeignPtr ptr $ \realPtr ->
    if realPtr == nullPtr then getErrno >>= return . Left . kafkaRespErr 
    else do
        addForeignPtrFinalizer rdKafkaMessageDestroy ptr
        s <- peek realPtr
        if (err'RdKafkaMessageT s) /= RdKafkaRespErrNoError then return $ Left $ KafkaResponseError $ err'RdKafkaMessageT s
        else do
            payload <- word8PtrToBS (len'RdKafkaMessageT s) (payload'RdKafkaMessageT s) 

            key <- if (key'RdKafkaMessageT s) == nullPtr then return Nothing 
                   else word8PtrToBS (keyLen'RdKafkaMessageT s) (key'RdKafkaMessageT s) >>= return . Just

            return $ Right $ KafkaMessage
                (partition'RdKafkaMessageT s) 
                (offset'RdKafkaMessageT s)
                payload
                key 

consumeMessageBatch :: KafkaTopic -> Int -> Int -> Int -> IO (Either KafkaError [KafkaMessage])
consumeMessageBatch (KafkaTopic topicPtr _ _) partition timeout maxMessages = 
  allocaArray maxMessages $ \outputPtr -> do
    numMessages <- rdKafkaConsumeBatch topicPtr (fromIntegral partition) timeout outputPtr (fromIntegral maxMessages)
    if numMessages < 0 then getErrno >>= return . Left . kafkaRespErr
    else do
      ms <- forM [0..(numMessages - 1)] $ \mnum -> do 
              storablePtr <- peekElemOff outputPtr (fromIntegral mnum)
              storable <- peek storablePtr
              ret <- fromMessageStorable storable
              fptr <- newForeignPtr_ storablePtr
              addForeignPtrFinalizer rdKafkaMessageDestroy fptr
              return ret
      return $ Right ms 

storeOffset :: KafkaTopic -> Int -> Int -> IO (Maybe KafkaError)
storeOffset (KafkaTopic topicPtr _ _) partition offset = do
  err <- rdKafkaOffsetStore topicPtr (fromIntegral partition) (fromIntegral offset)
  case err of 
    RdKafkaRespErrNoError -> return Nothing
    e -> return $ Just $ KafkaResponseError e

produceMessage :: KafkaTopic -> KafkaProducePartition -> KafkaProduceMessage -> IO (Maybe KafkaError)
produceMessage (KafkaTopic topicPtr _ _) partition (KafkaProduceMessage payload) = do
    let (payloadFPtr, payloadOffset, payloadLength) = BSI.toForeignPtr payload

    withForeignPtr payloadFPtr $ \payloadPtr -> do
        let passedPayload = payloadPtr `plusPtr` payloadOffset
        
        handleProduceErr =<< 
          rdKafkaProduce topicPtr (producePartitionInteger partition)
            copyMsgFlags passedPayload (fromIntegral payloadLength)
            nullPtr (CSize 0) nullPtr

produceMessage _ _ (KafkaProduceKeyedMessage _ _) = undefined

produceKeyedMessage :: KafkaTopic -> KafkaProduceMessage -> IO (Maybe KafkaError)
produceKeyedMessage _ (KafkaProduceMessage _) = undefined
produceKeyedMessage (KafkaTopic topicPtr _ _) (KafkaProduceKeyedMessage key payload) = do
    let (payloadFPtr, payloadOffset, payloadLength) = BSI.toForeignPtr payload
        (keyFPtr, keyOffset, keyLength) = BSI.toForeignPtr key

    withForeignPtr payloadFPtr $ \payloadPtr -> do
        withForeignPtr keyFPtr $ \keyPtr -> do
          let passedPayload = payloadPtr `plusPtr` payloadOffset
              passedKey = keyPtr `plusPtr` keyOffset

          handleProduceErr =<< 
            rdKafkaProduce topicPtr (producePartitionInteger KafkaUnassignedPartition)
              copyMsgFlags passedPayload (fromIntegral payloadLength)
              passedKey (fromIntegral keyLength) nullPtr

produceMessageBatch :: KafkaTopic -> KafkaProducePartition -> [KafkaProduceMessage] -> IO ([(KafkaProduceMessage, KafkaError)])
produceMessageBatch (KafkaTopic topicPtr _ _) partition pms = do
  storables <- forM pms produceMessageToMessage
  withArray storables $ \batchPtr -> do
    batchPtrF <- newForeignPtr_ batchPtr
    numRet <- rdKafkaProduceBatch topicPtr partitionInt copyMsgFlags batchPtrF (length storables)
    if numRet == (length storables) then return []
    else do 
      errs <- mapM (\i -> return . err'RdKafkaMessageT =<< peekElemOff batchPtr i) 
                   [0..((fromIntegral $ length storables) - 1)]
      return [(m, KafkaResponseError e) | (m, e) <- (zip pms errs), e /= RdKafkaRespErrNoError]
  where
    partitionInt = (producePartitionInteger partition)
    produceMessageToMessage (KafkaProduceMessage bs) =  do
        let (payloadFPtr, payloadOffset, payloadLength) = BSI.toForeignPtr bs
        withForeignPtr payloadFPtr $ \payloadPtr -> do
          let passedPayload = payloadPtr `plusPtr` payloadOffset
          return $ RdKafkaMessageT 
              { err'RdKafkaMessageT = RdKafkaRespErrNoError 
              , partition'RdKafkaMessageT = fromIntegral partitionInt
              , len'RdKafkaMessageT = payloadLength
              , payload'RdKafkaMessageT = passedPayload
              , offset'RdKafkaMessageT = 0
              , keyLen'RdKafkaMessageT = 0
              , key'RdKafkaMessageT = nullPtr
              }
    produceMessageToMessage (KafkaProduceKeyedMessage kbs bs) =  do
        let (payloadFPtr, payloadOffset, payloadLength) = BSI.toForeignPtr bs
            (keyFPtr, keyOffset, keyLength) = BSI.toForeignPtr kbs
             
        withForeignPtr payloadFPtr $ \payloadPtr -> do
          withForeignPtr keyFPtr $ \keyPtr -> do
            let passedPayload = payloadPtr `plusPtr` payloadOffset
                passedKey = keyPtr `plusPtr` keyOffset

            return $ RdKafkaMessageT 
                { err'RdKafkaMessageT = RdKafkaRespErrNoError 
                , partition'RdKafkaMessageT = fromIntegral partitionInt
                , len'RdKafkaMessageT = payloadLength
                , payload'RdKafkaMessageT = passedPayload
                , offset'RdKafkaMessageT = 0
                , keyLen'RdKafkaMessageT = keyLength
                , key'RdKafkaMessageT = passedKey
                }

type ConfigOverrides = [(String, String)]
withKafkaProducer :: ConfigOverrides -> ConfigOverrides 
                     -> String -> String 
                     -> (Kafka -> KafkaTopic -> IO a) 
                     -> IO a
withKafkaProducer configOverrides topicConfigOverrides brokerString tName cb =
  bracket 
    (do
      conf <- newKafkaConf
      mapM_ (\(k, v) -> setKafkaConfValue conf k v) configOverrides
      kafka <- newKafka KafkaProducer conf
      addBrokers kafka brokerString
      topicConf <- newKafkaTopicConf
      mapM_ (\(k, v) -> setKafkaTopicConfValue topicConf k v) topicConfigOverrides 
      topic <- newKafkaTopic kafka tName topicConf
      return (kafka, topic)
    )
    (\(kafka, _) -> drainOutQueue kafka)
    (\(k, t) -> cb k t)

withKafkaConsumer :: ConfigOverrides -> ConfigOverrides 
                     -> String -> String -> Int -> KafkaOffset 
                     -> (Kafka -> KafkaTopic -> IO a) 
                     -> IO a
withKafkaConsumer configOverrides topicConfigOverrides brokerString tName partition offset cb =
  bracket
    (do
      conf <- newKafkaConf
      mapM_ (\(k, v) -> setKafkaConfValue conf k v) configOverrides
      kafka <- newKafka KafkaConsumer conf
      addBrokers kafka brokerString
      topicConf <- newKafkaTopicConf
      mapM_ (\(k, v) -> setKafkaTopicConfValue topicConf k v) topicConfigOverrides 
      topic <- newKafkaTopic kafka tName topicConf
      startConsuming topic partition offset
      return (kafka, topic)
    )
    (\(_, topic) -> stopConsuming topic partition)
    (\(k, t) -> cb k t)

{-# INLINE copyMsgFlags  #-}
copyMsgFlags :: Int
copyMsgFlags = rdKafkaMsgFlagCopy

{-# INLINE producePartitionInteger #-}
producePartitionInteger :: KafkaProducePartition -> CInt
producePartitionInteger KafkaUnassignedPartition = -1
producePartitionInteger (KafkaSpecifiedPartition n) = fromIntegral n

{-# INLINE handleProduceErr #-}
handleProduceErr :: Int -> IO (Maybe KafkaError)
handleProduceErr (- 1) = getErrno >>= return . Just . kafkaRespErr 
handleProduceErr 0 = return $ Nothing
handleProduceErr _ = return $ Just $ KafkaInvalidReturnValue


data KafkaMetadata = KafkaMetadata
    { brokers :: [KafkaBrokerMetadata]
    , topics :: [Either KafkaError KafkaTopicMetadata]
    } deriving (Eq, Show, Typeable)

data KafkaBrokerMetadata = KafkaBrokerMetadata
    { brokerId :: Int
    , brokerHost :: String
    , brokerPort :: Int
    } deriving (Eq, Show, Typeable)

data KafkaTopicMetadata = KafkaTopicMetadata
    { topicName :: String
    , topicPartitions :: [Either KafkaError KafkaPartitionMetadata]
    } deriving (Eq, Show, Typeable)

data KafkaPartitionMetadata = KafkaPartitionMetadata
    { partitionId :: Int
    , partitionLeader :: Int
    , partitionReplicas :: [Int] 
    , partitionIsrs :: [Int]
    } deriving (Eq, Show, Typeable)


getAllMetadata :: Kafka -> Int -> IO (Either KafkaError KafkaMetadata)
getAllMetadata k timeout = getMetadata k Nothing timeout

getTopicMetadata :: Kafka -> KafkaTopic -> Int -> IO (Either KafkaError KafkaTopicMetadata)
getTopicMetadata k kt timeout = do
  err <- getMetadata k (Just kt) timeout
  case err of 
    Left e -> return $ Left $ e
    Right md -> case (topics md) of 
      [(Left e)] -> return $ Left e
      [(Right tmd)] -> return $ Right tmd
      _ -> return $ Left $ KafkaError "Incorrect number of topics returned"

getMetadata :: Kafka -> Maybe KafkaTopic -> Int -> IO (Either KafkaError KafkaMetadata)
getMetadata (Kafka kPtr _) mTopic timeout = alloca $ \mdDblPtr -> do
    err <- case mTopic of  
      Just (KafkaTopic kTopicPtr _ _) -> 
        rdKafkaMetadata kPtr False kTopicPtr mdDblPtr timeout
      Nothing -> do
        nullTopic <- newForeignPtr_ nullPtr
        rdKafkaMetadata kPtr True nullTopic mdDblPtr timeout

    case err of 
      RdKafkaRespErrNoError -> do
        mdPtr <- peek mdDblPtr
        md <- peek mdPtr
        retMd <- constructMetadata md
        rdKafkaMetadataDestroy mdPtr
        return $ Right $ retMd
      e -> return $ Left $ KafkaResponseError e

    where 
      constructMetadata md =  do
        let nBrokers = (brokerCnt'RdKafkaMetadataT md)
            brokersPtr = (brokers'RdKafkaMetadataT md)
            nTopics = (topicCnt'RdKafkaMetadataT md)
            topicsPtr = (topics'RdKafkaMetadataT md)

        brokerMds <- mapM (\i -> constructBrokerMetadata =<< peekElemOff brokersPtr i) [0..((fromIntegral nBrokers) - 1)]
        topicMds <- mapM (\i -> constructTopicMetadata =<< peekElemOff topicsPtr i) [0..((fromIntegral nTopics) - 1)]
        return $ KafkaMetadata brokerMds topicMds

      constructBrokerMetadata bmd = do
        hostStr <- peekCString (host'RdKafkaMetadataBrokerT bmd)
        return $ KafkaBrokerMetadata 
                  (id'RdKafkaMetadataBrokerT bmd)
                  (hostStr)
                  (port'RdKafkaMetadataBrokerT bmd)

      constructTopicMetadata tmd = do
        case (err'RdKafkaMetadataTopicT tmd) of
          RdKafkaRespErrNoError -> do
            let nPartitions = (partitionCnt'RdKafkaMetadataTopicT tmd)
                partitionsPtr = (partitions'RdKafkaMetadataTopicT tmd)

            topicStr <- peekCString (topic'RdKafkaMetadataTopicT tmd)
            partitionsMds <- mapM (\i -> constructPartitionMetadata =<< peekElemOff partitionsPtr i) [0..((fromIntegral nPartitions) - 1)]
            return $ Right $ KafkaTopicMetadata topicStr partitionsMds
          e -> return $ Left $ KafkaResponseError e

      constructPartitionMetadata pmd = do
        case (err'RdKafkaMetadataPartitionT pmd) of
          RdKafkaRespErrNoError -> do
            let nReplicas = (replicaCnt'RdKafkaMetadataPartitionT pmd)
                replicasPtr = (replicas'RdKafkaMetadataPartitionT pmd)
                nIsrs = (isrCnt'RdKafkaMetadataPartitionT pmd)
                isrsPtr = (isrs'RdKafkaMetadataPartitionT pmd)
            replicas <- mapM (\i -> peekElemOff replicasPtr i) [0..((fromIntegral nReplicas) - 1)]
            isrs <- mapM (\i -> peekElemOff isrsPtr i) [0..((fromIntegral nIsrs) - 1)]
            return $ Right $ KafkaPartitionMetadata 
              (id'RdKafkaMetadataPartitionT pmd)              
              (leader'RdKafkaMetadataPartitionT pmd)
              (map fromIntegral replicas)
              (map fromIntegral isrs)
          e -> return $ Left $ KafkaResponseError e

pollEvents :: Kafka -> Int -> IO ()
pollEvents (Kafka kPtr _) timeout = rdKafkaPoll kPtr timeout >> return ()

outboundQueueLength :: Kafka -> IO (Int)
outboundQueueLength (Kafka kPtr _) = rdKafkaOutqLen kPtr

drainOutQueue :: Kafka -> IO ()
drainOutQueue k = do
    pollEvents k 100
    l <- outboundQueueLength k
    if l == 0 then return ()
    else drainOutQueue k

kafkaRespErr :: Errno -> KafkaError
kafkaRespErr (Errno num) = KafkaResponseError $ rdKafkaErrno2err (fromIntegral num)

stopConsuming :: KafkaTopic -> Int -> IO ()
stopConsuming (KafkaTopic topicPtr _ _) partition = 
    throwOnError $ rdKafkaConsumeStop topicPtr partition

throwOnError :: IO (Maybe String) -> IO ()
throwOnError action = do
    m <- action
    case m of 
        Just e -> throw $ KafkaError e
        Nothing -> return ()


dumpKafkaTopicConf :: KafkaTopicConf -> IO (Map String String)
dumpKafkaTopicConf (KafkaTopicConf kptr) = 
    parseDump (\sizeptr -> rdKafkaTopicConfDump kptr sizeptr)

dumpKafkaConf :: KafkaConf -> IO (Map String String)
dumpKafkaConf (KafkaConf kptr) = do
    parseDump (\sizeptr -> rdKafkaConfDump kptr sizeptr)

dumpConfFromKafka :: Kafka -> IO (Map String String) 
dumpConfFromKafka (Kafka _ cfg) = dumpKafkaConf cfg

dumpConfFromKafkaTopic :: KafkaTopic -> IO (Map String String)
dumpConfFromKafkaTopic (KafkaTopic _ _ conf) = dumpKafkaTopicConf conf


parseDump :: (CSizePtr -> IO (Ptr CString)) -> IO (Map String String)
parseDump cstr = alloca $ \sizeptr -> do
    strPtr <- cstr sizeptr 
    size <- peek sizeptr

    keysAndValues <- mapM (\i -> peekCString =<< peekElemOff strPtr i) [0..((fromIntegral size) - 1)]

    let ret = Map.fromList $ listToTuple keysAndValues
    rdKafkaConfDumpFree strPtr size
    return ret

listToTuple :: [String] -> [(String, String)]
listToTuple [] = []
listToTuple (k:v:t) = (k, v) : listToTuple t
listToTuple _ = error "list to tuple can only be called on even length lists"