Warp: Binding to Unix Domain Sockets

Question

The example code listed here shows how to make warp listen only on specific hosts.

Furtheremore, this post shows some basics on how to use unix domain sockets in Haskell.

How can I combine those two approaches in order to make warp listen on (i.e. bind to) a specific unix domain socket (say, warp.sock)?

Note: This question intentionally shows no research effort as it was answered Q&A-Style.

Answer 1

You can use runSettingsSocket with a AF_UNIX socket:

{-# LANGUAGE OverloadedStrings #-}

import Network.Wai (responseLBS)
import Network.Wai.Handler.Warp
import Network.Socket
import Network.HTTP.Types (status200)
import Network.HTTP.Types.Header (hContentType)

main = do
    let port = 3000
    -- Open the socket
    sock <- socket AF_UNIX Stream 0
    bind sock $ SockAddrUnix "warp.sock"
    listen sock maxListenQueue
    -- Run the server
    let settings = defaultSettings { settingsPort = port }
    runSettingsSocket settings sock app
    -- Cleanup: Close socket
    close sock

app req f = f $
    responseLBS status200 [(hContentType, "text/plain")] "Hello world!"

Note that this will obviously only work on unixoid platforms.

Answer 2

FWIW: If one wants to use http-client to use that UNIX socket:

{-# LANGUAGE OverloadedStrings #-}

import Network.HTTP.Client
import Network.HTTP.Client.Internal (Connection, openSocketConnection, makeConnection)
import Network.Socket.ByteString (sendAll, recv)

import qualified Control.Exception as E
import qualified Network.Socket as NS

main :: IO ()
main = do
    mgr <- newManager defaultManagerSettings {
        managerRawConnection = createUnixConnection
    }
    -- This changes in http-client-0.5, use parseUrlThrow
    req <- parseUrl "http://localhost/whatever"
    res <- httpLbs req mgr
    print (responseBody res)

createUnixConnection :: IO (Maybe NS.HostAddress -> String -> Int -> IO Connection)
createUnixConnection = return $ \_ _ _ -> openUnixConnection "warp.sock"

openUnixConnection :: String -> IO Connection
openUnixConnection addr = E.bracketOnError
    (NS.socket NS.AF_UNIX NS.Stream NS.defaultProtocol)
    (NS.close)
    $ \sock -> do
        NS.connect sock sockAddr
        socketConnection sock chunksize
  where
    sockAddr = NS.SockAddrUnix addr
    chunksize = 8192

-------------------------------------------------------------------------------
-- Copied from http-client
-------------------------------------------------------------------------------

socketConnection :: NS.Socket -> Int -> IO Connection
socketConnection socket chunksize = makeConnection
    (recv socket chunksize)
    (sendAll socket)
    (NS.close socket)