NATS - Haskell client

Haskell API for NATS messaging system (see https://github.com/derekcollison/nats).

• Network failures/reconnections are handled automatically in the background, however subscribe and request functions can still return a network exception.
• It should correctly combine with System.Timeout, therefore there is no API for timeouts as in other language API.
• There is no automatic unsubscribe after certain number of messages as this is easily handled by other means.
• The functions unsubscribe and publish will not fail. They may take up to 1 second if there is a problem with network connection. They will not block and not throw an exception if the client is disconnected from the server. (NATS does not guarantee delivery anyway)
• Clustered NATS is supported. NATS servers can be specified by overriding defaultSettings. Upon failure, the background thread automatically reconnects to the next available server. Rejected connections and unresponsive servers are handled by closing current connection and trying next server (the timeout is 1 second).

Example use:

{-# LANGUAGE OverloadedStrings #-}
importqualifiedData.ByteString.LazyasBLimportNetwork.NatsimportControl.Concurrentmain::IO()
main =do-- Connect to the NATS server
nats <- connect "nats://user:password@localhost:4222"-- Subscribe to channel "news", we do not use any queue group
sid <- subscribe nats "news"Nothing$\_ _ msg _ ->-- The parameters are (sid, subject, message, reply_subject)putStrLn$show msg
-- Publish a message (the message parameter is a lazy ByteString)
publish nats "news""I got news for you"-- Wait so that we can receive the message from the server
threadDelay 1000000-- Unsubscribe from the channel
unsubscribe nats sid
-- Subscribe to a "gift" channel
subscribe nats "gift"Nothing$\_ _ msg mreply ->doputStrLn$show msg
case mreply of-- If the sender used a 'request' call, use this subject to send message backNothing->return()Just reply -> publish nats reply "I've got a gift for you."-- Request/response communication with a "gift" channel
reply <- request nats "gift""Do you have anything for me?"putStrLn$show reply