[Haskell-beginners] Haskell network sample

[Bob Ippolito]

I don't have a GHC installation that old, but I think that a bug in that
version of GHC is the only reasonable explanation for this. I highly
recommend that you upgrade to GHC 7.8.x or at least 7.6.x.

Lazy IO is a bit unsafe and error-prone in some scenarios. hGetContents
doesn't really do any reading from the handle until the input is demanded,
which is why you can print "read from handle done" but not the contents of
bs.


On Tue, May 20, 2014 at 11:10 PM, yang.zhao <hckjsnzf at gmail.com> wrote:

> Here's my new code:
>
> $ cat serv.hs
>
> import Control.Concurrent
> import System.IO
> import Network
>
> port :: Int
> port = 1234
>
> main :: IO ()
> main = withSocketsDo $ do
>     s <- listenOn $ PortNumber $ fromIntegral port
>     putStrLn "Listening..."
>
>     (h, _, _) <- accept s
>     putStrLn "After accept"
>     sline <- hGetLine h
>     putStrLn "get line from handle"
>
>     hPutStrLn h sline
>     putStrLn $ "send "++sline
>     threadDelay 1000000
>
>     hClose h
>     sClose s
>
> --------
> $ cat clie.hs
>
> import System.IO
> import Network
>
> port :: Int
> port = 1234
>
> main :: IO ()
> main = withSocketsDo $ do
>     h <- connectTo "127.0.0.1" $ PortNumber $ fromIntegral port
>     putStrLn "After connect"
>     hPutStrLn h "hello"
>     putStrLn "put hello to handle done"
>     bs <- hGetContents h
>     putStrLn "read from handle done"
>     putStrLn bs
>     hClose h
>
>
> ===
> one terminal, run ./serv, then run ./clie in another terminal. Output is :
>
> $ ./serv
> Listening...
> After accept
>
> $ ./clie
> After connect
> put hello to handle done
> read from handle done
>
>
> it seems that client has read from then handle, but donesn't read
> anything, then block.
> and server donesn't receive anything, still wait for something...
>
> ghc version is 7.4.1, because of this?..
>
>
> 2014-05-21 13:57 GMT+08:00 Bob Ippolito <bob at redivi.com>:
>
> Not sure why you're having issues, I just tried it on GHC 7.6.3 on Fedora
>> 20 and it worked fine there as well (both with runhaskell or compiled with
>> -O).
>>
>> I might start adding putStrLn statements to the code to see where it's
>> unexpectedly blocking, or perhaps use 127.0.0.1 instead of "localhost" in
>> case the issue is a DNS misconfiguration.
>>
>>
>>
>> On Tue, May 20, 2014 at 10:51 PM, yang.zhao <hckjsnzf at gmail.com> wrote:
>>
>>> thanks for your replay.
>>> i run the two program in two different teriminal for sure.
>>>
>>> it works for you?
>>> but why can't run well on my computer.
>>>
>>> make me creazy....
>>>
>>>
>>> 2014-05-21 13:47 GMT+08:00 Bob Ippolito <bob at redivi.com>:
>>>
>>> How precisely are you trying to run the client? Are you typing it in to
>>>> the same terminal? If so, then the client is never actually started,
>>>> because when you type ./cli the input is going to ./serv and not the shell.
>>>> Try running the client in a separate terminal.
>>>>
>>>> It works for me here on Mac OS X 10.9.2 with GHC 7.8.2.
>>>>
>>>>
>>>> On Tue, May 20, 2014 at 10:42 PM, yang.zhao <hckjsnzf at gmail.com> wrote:
>>>>
>>>>> hi guys,
>>>>> I'm newbie, just begin to learn Haskell.
>>>>> now i write a very simple server and client .
>>>>>
>>>>> Server:
>>>>> import Control.Concurrent
>>>>> import System.IO
>>>>> import Network
>>>>>
>>>>> port :: Int
>>>>> port = 1234
>>>>>
>>>>> main :: IO ()
>>>>> main = withSocketsDo $ do
>>>>>     s <- listenOn $ PortNumber $ fromIntegral port
>>>>>     (h, _, _) <- accept s
>>>>>
>>>>>     sline <- hGetLine h
>>>>>     hPutStrLn h sline
>>>>>     putStrLn $ "send "++sline
>>>>>     threadDelay 1000000
>>>>>
>>>>>     hClose h
>>>>>     sClose s
>>>>>
>>>>> Client :
>>>>> import System.IO
>>>>> import Network
>>>>>
>>>>> port :: Int
>>>>> port = 1234
>>>>>
>>>>> main :: IO ()
>>>>> main = withSocketsDo $ do
>>>>>     h <- connectTo "localhost" $ PortNumber $ fromIntegral port
>>>>>     hPutStrLn h "hello"
>>>>>     bs <- hGetContents h
>>>>>     putStrLn bs
>>>>>     hClose h
>>>>>
>>>>>
>>>>> And, it doesn't work now . I run ./serv , then run ./cli , they will
>>>>> block all the time.
>>>>> but,  when i run ./serv, and telnet localhost 1234 in another
>>>>> terminal, it works fine.
>>>>> so i don't know what's the wrong with my code.
>>>>> anybody can tell me about my problem?
>>>>>
>>>>> os is Debian 7,  haskell-platform  2012.2.0.0
>>>>>
>>>>> thanks a lot!!!
>>>>> --
>>>>> K.I.S.S.
>>>>>
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>>>>> Beginners mailing list
>>>>> Beginners at haskell.org
>>>>> http://www.haskell.org/mailman/listinfo/beginners
>>>>>
>>>>>
>>>>
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>>
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>
>
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>
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