patterns-0.1.1: Common patterns in message-oriented applications

Safe HaskellNone



Client side of Client/Server



data Client Source

Client data type

withClient :: Context -> Service -> String -> LinkType -> (Client -> IO a) -> IO aSource

Create a client with name Service, linking to address String, connecting or binding the address according to LinkType and finally entering the action, in whose scope the client lives.

request :: Client -> Timeout -> Source -> SinkR (Maybe r) -> IO (Maybe r)Source

Request a service:

  • Client - The client, through which the service is requested
  • Timeout - Timeout in microseconds, -1 to wait eternally. With timeout = 0, the function returns immediately with Nothing. When the timeout expires, request is abandoned. In this case, the result of the request is Nothing.
  • Source - The source of the request stream; the format of the request will probably comply with some communication protocol, as, for instance, in the majordomo pattern.
  • SinkR - The sink receiving the reply. The result of the sink is returned as the request's overall result. Note that the sink may perform different actions on the segments of the resulting stream, e.g. storing data in a database, and return the number of records received.

A 'hello world' Example:

  import qualified Data.Conduit          as C
  import qualified Data.ByteString.Char8 as B
  import           Network.Mom.Patterns.Basic.Client
  import           Network.Mom.Patterns.Types
  main :: IO ()
  main = withContext 1 $ \ctx -> 
           withClient ctx "test" 
               "tcp://localhost:5555" Connect $ \c -> do
             mbX <- request c (-1) src snk
             case mbX of
               Nothing -> putStrLn "No Result"
               Just x  -> putStrLn $ "Result: " ++ x
    where src = C.yield (B.pack "hello world")
          snk = do mbX <- C.await 
                   case mbX of
                     Nothing -> return Nothing
                     Just x  -> return $ Just $ B.unpack x

checkResult :: Client -> Timeout -> SinkR (Maybe r) -> IO (Maybe r)Source

Check for a of a previously requested result; use case: request with timout 0, do some work and check for a result later. Do not use this function without having requested the service previously. The parameters equal those of request, but do not include a Source.