I thought about it a bit more. The problem would actually be *very*
easy to solve if conduit exported one extra function: a connect
function that returned a Sink instead of running it. Then you could
do:
bsrc <- bufferSource src
sink2 <- (bsrc $= Cb.lines $= Cl.isolate 3) `connectReturnSink` snk
bsrc $$ sink2
That might be generally useful in other places as well, I'm not sure.
Michael
2012/2/3 Michael Snoyman <mich...@snoyman.com>:
> 2012/2/3 Ertugrul Söylemez <e...@ertes.de>:
>> Hello there,
>>
>> I'm trying to build a server for testing the conduit and network-conduit
>> packages. As a contrived example the goal is to pick the first three
>> lines from the client and send them back without the line feeds. After
>> that, I'd like to switch to a simple echo server. This is the code:
>>
>> module Main where
>>
>> import Data.Conduit
>> import Data.Conduit.Binary as Cb
>> import Data.Conduit.List as Cl
>> import Data.Conduit.Network
>>
>> handleClient :: Application
>> handleClient src snk =
>> src $$ do
>> (Cb.lines =$= Cl.isolate 3) =$ snk
>> snk
>>
>> main :: IO ()
>> main = runTCPServer (ServerSettings 4000 Nothing) handleClient
>>
>> I'm not sure whether it is correct to use the 'snk' sink multiple times,
>> and intuitively I'd say that this is wrong. What would be the proper
>> way to do this?
>>
>>
>> Greets,
>> Ertugrul
>
> In this particular case, it will work due to the implementation of
> snk. In general, however, you're correct: you should not use the same
> sink twice.
>
> I haven't thought about it much yet, but my initial recommendation
> would be to create a new Conduit using SequencedSink, which takes the
> three lines and then switches over to a passthrough conduit. The
> result looks like this:
>
>
> module Main where
>
> import Data.Conduit
> import Data.Conduit.Binary as Cb
> import Data.Conduit.List as Cl
> import Data.Conduit.Network
>
> handleClient :: Application
> handleClient src snk = src $$ myConduit =$ snk
>
> main :: IO ()
> main = runTCPServer (ServerSettings 4000 Nothing) handleClient
>
> myConduit =
> sequenceSink 3 go
> where
> go 0 = return $ StartConduit $ Cl.map id
> go count = do
> mx <- Cb.lines =$ Cl.head
> case mx of
> Nothing -> return Stop
> Just x -> return $ Emit (count - 1) [x]
>
> Michael
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