NodeJS: How can I create a fake tcp socket for testing servers

Question

I'm trying to unit test my server code (non-http, custom protocol). I need to create a mock duplex socket that I can send messages to asynchronously and receive messages from.

I've had some marginal success creating a duplex stream from event-stream readArray and writeArray, but readArray requires having the data up front, and writeArray doesn't fire until the stream ends. I need to test over time. An ideal solution would be two duplex sockets linked together.

Are there any existing solutions for this? I'd rather not have to resort to initializing an actual server to test this.

Answer 1

Node Mitm can actually do that just fine. It can intercept and mock not only HTTP but any TCP connection.

mitm.on("connection", function(socket) { socket.write("Hello back!") })

var socket = Net.connect(22, "example.org")
socket.write("Hello!")
socket.setEncoding("utf8")
socket.read() // => "Hello back!"