README.md

nng-haskell

This is a Haskell binding for the NNG library: http://nng.nanomsg.org/.

It's based on the nanomsg bindings: https://github.com/bgamari/nanomsg-haskell.

This bindings make use of the "compatibility API" from NNG to emulate the same API nanomsg has. Thus at the moment it doesn't offer the full functionality of NNG, but it should be easy to extend over time as it's needed.

There's support for (evented) blocking send and recv, a non-blocking receive, and for all the socket types and the functions you need to wire them up and tear them down again.

Most socket options are available through accessor and mutator functions. Sockets are typed, transports are not.

Building

You would normally make sure the NNG library is on your system and then install from Hackage.

Usage

Simple pub/sub example:

Server:

module Main where

import Nanomsg
import qualified Data.ByteString.Char8 as C
import Control.Monad (mapM_)
import Control.Concurrent (threadDelay)

main :: IO ()
main =
    withSocket Pub $ \s -> do
        _ <- bind s "tcp://*:5560"
        mapM_ (\num -> sendNumber s num) (cycle [1..1000000 :: Int])
    where
        sendNumber s number = do
            threadDelay 1000        -- let's conserve some cycles
            let numAsString = show number
            send s (C.pack numAsString)

Client:

module Main where

import Nanomsg
import qualified Data.ByteString.Char8 as C
import Control.Monad (forever)

main :: IO ()
main =
    withSocket Sub $ \s -> do
        _ <- connect s "tcp://localhost:5560"
        subscribe s $ C.pack ""
        forever $ do
            msg <- recv s
            C.putStrLn msg

Nonblocking client:

module Main where

import Nanomsg
import qualified Data.ByteString.Char8 as C
import Control.Monad (forever)
import Control.Concurrent (threadDelay)

main :: IO ()
main =
    withSocket Sub $ \s -> do
        _ <- connect s "tcp://localhost:5560"
        subscribe s $ C.pack ""
        forever $ do
            threadDelay 700           -- let's conserve some cycles
            msg <- recv' s
            C.putStrLn $ case msg of
                Nothing -> C.pack "No message"
                Just m  -> m