Node stream pipeline stops prematurely - node.js

Question

Think of this piece of code as a relay between a NAT-ted service (input) and an external service (output) that wants to communicate with the input.
This relay is on a public server and opens two ports in order to relay:
port 4040 where input connects and forwards the TCP traffic from target service
port 4041 where some external client connects to the relay
The relay should pipe what it receives from input on port 4040 to the external client on port 4041.
I can see both services connecting to the relay but the data flow just stops after, what I suspect the output socket closing. In the following example I used a stream.pipeline but I also tried with simple .pipe directly on the sockets with same results
import net from "net"
import stream from "stream";
export default () => {
const inputServer = net.createServer();
const outputServer = net.createServer();
inputServer.listen(4040, "0.0.0.0", () => {
console.log('TCP Server is running on port ' + 4040 + '.');
});
outputServer.listen(4041, "0.0.0.0", () => {
console.log('TCP Server is running on port ' + 4041 + '.');
});
let inSocket = null;
inputServer.on('connection', (sock) => {
inSocket = sock;
});
outputServer.on('connection', (sock) => {
if (inSocket) {
stream.pipeline(inSocket, sock, (err) => {
if (err) {
console.error('Pipeline failed.', err);
} else {
console.log('Pipeline succeeded.');
}
})
stream.pipeline(sock, inSocket, (err) => {
if (err) {
console.error('Pipeline failed.', err);
} else {
console.log('Pipeline succeeded.');
}
})
}
});
}
My goal is to keep an open socket to the input service and relay with any output will connect.

Answer 1

data flow just stops after, what I suspect the output socket closing
pipeline or .pipe() will automatically close the output stream when the input stream ends so it won't keep your input stream open for successive input stream connections.
Using .pipe(), you can override that behavior by passing an option:
inSocket.pipe(sock, {end: false});
and
sock.pipe(inSocket, {end: false});
You will then need some separate error handling for each stream as .pipe() doesn't do as complete error handling as pipeline() does.
In this way, you let each stream close itself when the client chooses rather than having the server close it when a given streaming operation is complete.
I don't see a similar option for pipeline().
I'm also curious how you plan to use this. Do you intend for there to be one long connected inSocket and many separate connections to the outputServer? Do you intend or need more than one outputServer connection at once? Or just one at at time. Since you're not auto destroying, I wonder if you need to do some manual cleanup (unpiping, for example) when any socket disconnects? .pipe() is also famous for not unwinding all its event listeners which can sometimes lead to GC issues if you don't manually clean up things properly.