Really weird issue with ByteString socket - haskell

Question

I had a weird problem with ByteString socket programming. I have minimized the issue to the following short scripts:
-- ByteString.hs
{-# LANGUAGE OverloadedStrings #-}
import Network.Socket hiding (send, sendTo, recv, recvFrom)
import Network.Socket.ByteString
import Network.BSD
import System.IO
import qualified Data.ByteString as BS
import qualified Data.ByteString.Char8 as C8
connectMud :: HostName
-> String
-> IO Handle
connectMud hostname port = do
addrinfos <- getAddrInfo Nothing (Just hostname) (Just port)
let serveraddr = head addrinfos
sock <- socket (addrFamily serveraddr) Stream defaultProtocol
setSocketOption sock KeepAlive 1
connect sock (addrAddress serveraddr)
h <- socketToHandle sock ReadWriteMode
hSetBuffering h (BlockBuffering Nothing)
return h
main:: IO ()
main =
C8.putStrLn "connecting, please wait" >> connectMud "aardwolf.org" "4000"
>>= BS.hGetContents >>= C8.putStrLn
and
--ByteString_Lazy.hs
{-# LANGUAGE OverloadedStrings #-}
import Network.Socket hiding (send, sendTo, recv, recvFrom)
import Network.Socket.ByteString
import Network.BSD
import System.IO
import qualified Data.ByteString.Lazy as BS
import qualified Data.ByteString.Lazy.Char8 as C8
connectMud :: HostName
-> String
-> IO Handle
connectMud hostname port = do
addrinfos <- getAddrInfo Nothing (Just hostname) (Just port)
let serveraddr = head addrinfos
sock <- socket (addrFamily serveraddr) Stream defaultProtocol
setSocketOption sock KeepAlive 1
connect sock (addrAddress serveraddr)
h <- socketToHandle sock ReadWriteMode
hSetBuffering h (BlockBuffering Nothing)
return h
main:: IO ()
main =
C8.putStrLn "connecting, please wait" >> connectMud "aardwolf.org" "4000"
>>= BS.hGetContents >>= C8.putStrLn
The only difference between these two short scripts is that one is using Data.ByteString and the other one Data.ByteString.Lazy. The lazy version works fine but the strict version does not seem to receive any output at all. Any thoughts?

Answer 1

I would guess that it has to do with the differing behavior of the two hGetContents functions in question (the lazy version vs the strict version).
The strict version "reads a handle's entire contents strictly into a ByteString." But you're trying to read from a stream, so the EOF is never encountered.
Compare with the behavior of the lazy version:
Read entire handle contents lazily into a ByteString. Chunks are read on demand, using the default chunk size.
Once EOF is encountered, the Handle is closed.