[Haskell-cafe] make a server & connect to it - strange behavior

Patrick Redmond plredmond at gmail.com
Thu Nov 26 09:10:31 UTC 2015

Hi Haskell Cafe,

When I start a web server (http-server:Network.HTTP.Server.serverWith) on a
separate thread (async:Control.Concurrent.Async.withAsync) and then try to
retrieve a response from the server (HTTP:Network.Browser.*) on a threaded
runtime, I see either

   - connection refusals or
   - deadlock.

Before I sink time into reading the source of the packages in question,
does anybody see what's wrong with the code below?

Increasing the timeout to wait for the server to initialize doesn't solve
the problem. Using a bound thread doesn't solve the problem. I'm compiling
with options "-threaded -rtsopts -with-rtsopts=-N".

Thank you for taking a look.

This test project is on github.

module Lib
    ( someFunc
    ) where

import Control.Monad.IO.Class (liftIO)
import qualified Control.Concurrent as Concurrent
import qualified Control.Concurrent.Async as Async
import qualified Control.Exception as Exception
import qualified Data.Maybe as Maybe
import qualified Network.Browser as Browser
import qualified Network.HTTP as HTTP
import qualified Network.HTTP.Server as Server
import qualified Network.HTTP.Server.Logger as ServerL
import qualified Network.HTTP.Server.Response as ServerR
import qualified Network.URI as URI

someFunc :: IO (Either Exception.SomeException (URI.URI, HTTP.Response
someFunc = do
    Async.withAsync (Server.serverWith config handler) $ \_ -> do
        Concurrent.threadDelay . round $ 2e6
        Exception.try . Browser.browse . Browser.request .
Browser.defaultGETRequest $ uri
        uri = Maybe.fromJust . URI.parseURI $ "http://localhost:8080/"
        config = Server.Config ServerL.stdLogger "localhost" 8080
        handler _ url req = return (ServerR.respond ServerR.OK ::
Server.Response String)
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