Ignore closed FastCGI stream.

With Apache Benchmark, it is possible to elicit an exception:

    ab -n 5000 -c 100 -t 60 'http://...'

Would result in:

    user error (FCGX_PutStr failed with error code: -1)

I have experienced this merely with a lighttpd and nginx FastCGI web site not even under particularly heavy load.

So it's a problem that this isn't handled. FCGX_PutStr returns an error if you try to write to a closed stream.

So we now handle that case by discontinuing the response as there is nothing to respond to, and going about our business.

Network/FastCGI.hsc

@@ -224,7 +224,9 @@ peekEnvp = (#peek FCGX_Request, envp)
 
 sPutStr :: StreamPtr -> Lazy.ByteString -> IO ()
 sPutStr h str =
-    mapM_ (flip BSB.unsafeUseAsCStringLen (fcgxPutCStringLen h)) (Lazy.toChunks str)
+  mapM_ (flip BSB.unsafeUseAsCStringLen (fcgxPutCStringLen h))
+        (Lazy.toChunks str)
+  `catch` \(_ :: IOException) -> return ()
 
 fcgxPutCStringLen :: StreamPtr -> CStringLen -> IO ()
 fcgxPutCStringLen h (cs,len) =