Haskell Control.Proxy.TCP Producer

Question

我一直在玩Control.Proxy.TCP庫，並希望從網絡源創建一個Producer。

producer :: Proxy p => HostName -> ServiceName ->() -> Producer p BS.ByteString IO() 
producer h p() = runIdentityP $ 
    lift $ connect h p $ \(s, r) -> 
     runProxy $ nsocketReadS s >-> pxy >-> socketWriteD s 
    where 
     pxy() = runIdentityP $ do 
      respond "resource-id" -- ask for "resource-id" 
      bs <- request 1024 -- fetch up to 1024 bytes 
      lift $ respond bs  -- and produce them from the outer proxy 
      return() 

上面的代碼不鍵入檢查：

Couldn't match type `p0 a'0 a1 a0 BS.ByteString m0' with `IO' 
Expected type:() 
       -> ProxyFast Int BS.ByteString() BS.ByteString IO() 
    Actual type:() 
       -> ProxyFast 
        Int 
        BS.ByteString 
        () 
        BS.ByteString 
        (p0 a'0 a1 a0 BS.ByteString m0) 
        () 
In the second argument of `(>->)', namely `pxy' 
In the first argument of `(>->)', namely `nsocketReadS s >-> pxy' 
In the second argument of `($)', namely 
    `nsocketReadS s >-> pxy >-> socketWriteD s' 

我看到，基單子爲nsocketReadS和socketWriteD是IO而我需要不同的類型。我該如何糾正這個問題？

Answer 1

如果你想在管道中分配一個插座，你需要使用Control.Proxy.TCP.Safe模塊，其中有connect的替代版本，您正在尋找：

connect 
    :: (Proxy p, Monad m) 
    => (forall x. SafeIO x -> m x) 
    -> HostName 
    -> ServiceName 
    -> ((Socket, SockAddr) -> ExceptionP p a' a b' b m r) 
    -> ExceptionP p a' a b' b m r 

這使用pipes-safe管理資源分配在管道內。如果您之前沒有使用過pipes-safe，那麼最好的地方是pipes-safe tutorial。

編輯：更新在評論中回答你的問題。您需要hoist套接字讀取器和寫入器，因爲它們的基本monad是周邊代理，而不是SafeIO。

producer 
    :: (Proxy p) 
    => HostName -> ServiceName 
    ->() -> Producer (ExceptionP p) BS.ByteString SafeIO() 
producer h p() = connect id h p $ \(s, r) -> 
    runProxy $ hoist lift . nsocketReadS s >-> pxy >-> hoist lift . socketWriteD s 
    where 
    pxy() = do 
     respond "resource-id" -- ask for "resource-id" 
     bs <- request 1024 -- fetch up to 1024 bytes 
     lift $ respond bs  -- and produce them from the outer proxy 
     return()