Module to produce messages to Kafka topics.

Here's an example of code to produce messages to a topic:

import Control.Exception (bracket)
import Control.Monad (forM_)
import Data.ByteString (ByteString)
import Kafka.Producer

-- Global producer properties
producerProps :: ProducerProperties
producerProps = brokersList ["localhost:9092"]
             <> logLevel KafkaLogDebug

-- Topic to send messages to
targetTopic :: TopicName
targetTopic = TopicName "kafka-client-example-topic"

-- Run an example
runProducerExample :: IO ()
runProducerExample =
    bracket mkProducer clProducer runHandler >>= print
    where
      mkProducer = newProducer producerProps
      clProducer (Left _)     = pure ()
      clProducer (Right prod) = closeProducer prod
      runHandler (Left err)   = pure $ Left err
      runHandler (Right prod) = sendMessages prod

-- Example sending 2 messages and printing the response from Kafka
sendMessages :: KafkaProducer -> IO (Either KafkaError ())
sendMessages prod = do
  err1 <- produceMessage prod (mkMessage Nothing (Just "test from producer") )
  forM_ err1 print

  err2 <- produceMessage prod (mkMessage (Just "key") (Just "test from producer (with key)"))
  forM_ err2 print

  pure $ Right ()

mkMessage :: Maybe ByteString -> Maybe ByteString -> ProducerRecord
mkMessage k v = ProducerRecord
                  { prTopic = targetTopic
                  , prPartition = UnassignedPartition
                  , prKey = k
                  , prValue = v
                  }