I'm trying to write a program whose network behaviour is analogous to a web proxy. A client connects to my server and gives me some data, my server connects to an upstream server and gives data to it, my server gets data from upstream, and gives data to the client. I'd like to write this using the enumerator library, since it seems like it should be possible to do that cleanly. Now, the guts of an echo server are pretty easy: runIteratee $ enumSocket cs sock $$ iterSocket sock That's just plain pretty. You can even put interesting data tranformations (Enumeratees) in there to make it behave a bit differently. What I'd like to do is have an Enumeratee that connects to the upstream server, forwards the request, and then uses one of the Data.Enumerator.List functions to generate a response that is the response from the upstream server. It doesn't look like this is possible though, since Enumeratees are pretty much one output per input. Is my basic model broken here? It's occurred to me that what I actually want to do is tie the enumSocket clientSock to an iterSocket upstreamSock, do the reverse, and then do two runIteratee calls (one in a forkIO, I guess?). That seems uglier, I'm not sure if there would be complications in making sure both Iteratees stop running correctly. Is that the right way to do, or am I just missing some capability that Enumeratees have?