Node Stream to emulate duplex socket - node.js

Question

I'm using node with the mqtt-connection and aedes mqtt libraries. I am using aedes to run a mqtt server, and I wish to connect to the mqtt server from within node using a stream, rather than open a tcp socket. Both libraries will accept a Duplex stream.
Why does something like this work:
const mqttCon = require('mqtt-connection');
const duplex = require('net').createConnection(1883);
const client = mqttCon(duplex, {
protocolVersion: 3
});
While something like this fails (closes the stream)after the first data exchange?
const mqttCon = require('mqtt-connection');
const duplex = new stream.Transform();
duplex._transform = (chunk, encoding, callback) => {
duplex.push(chunk);
console.log(chunk);
callback();
};
const client = mqttCon(duplex, {
protocolVersion: 3
});
aedes.handle(duplex);
I feel like I must have some fundamental misconception about how streams are supposed to work. Basically I want to create something that acts like a TCP socket, allowing these two "processes" to communicate internal to node.
Typical use of aedes to create a mqtt server would looking this this:
const aedes = require('aedes')(
{
concurrency: 500,
maxClientsIdLength: 100
}
);
const server = require('net').createServer(aedes.handle);
Edit: More details about the failure.
Then client feeds data to the stream, then as soon as aedes finishes responding, duplex.on('close') fires. There are no error messages, and no indication from either side that there has been an error, the stream just closes so each side then closes gracefully. I'm guessing that one side or the other sees an "end" to the stream so it closes.

Answer 1

The problem is that "duplex" is a single stream, where it really needs two streams bridged. Here is what works:
const duplexAedes = new stream.Duplex({
write: function (chunk, encoding, next) {
setImmediate(function () {
duplexClient.push(chunk);
});
next();
},
read: function (size) {
// Placeholder
}
});
const duplexClient = new stream.Duplex({
write: function (chunk, encoding, next) {
setImmediate(function () {
duplexAedes.push(chunk);
});
next();
},
read: function (size) {
// Placeholder
}
});
duplexAedes.authentication = clientId;
const client = mqttCon(duplexClient, {
protocolVersion: 3
});
aedes_handle(duplexAedes);