Turn a net socket into an observable - node.js

Question

I have a net tcp socket node.js section of code that I would like to convert from using a callback to rx.
I looks like this in feed.js module:
var net = require('net');
var server = net.createServer(function(socket) {
...
// Handle incoming messages from clients.
socket.on('data', function (data) {
broadcast(data, socket);
});
...
}
function broadcast(message, sender)
{
...
onChangeHandler(stock.symbol, 'stock', stock);
}
}
function start(onChange) {
onChangeHandler = onChange;
}
exports.start = start;
server.listen(....);
Then the client of the above call registers a callback:
feed.start(function(room, type, message) {
//...Do something with the message
});
I would like to convert this to use an Rx Observable/Observer. I see that there is a way to make an observable stream from the web socket (although it uses a bidirectional Subject which I don't need):
fromWebSocket(address, protocol) {
var ws = new WebSocket(address, protocol);
// Handle the data
var osbervable = Rx.Observable.create (function (obs) {
// Handle messages
ws.onmessage = obs.onNext.bind(obs);
ws.onerror = obs.onError.bind(obs);
ws.onclose = obs.onCompleted.bind(obs);
// Return way to unsubscribe
return ws.close.bind(ws);
});
var observer = Rx.Observer.create(function (data) {
if (ws.readyState === WebSocket.OPEN) { ws.send(data); }
});
return Rx.Subject.create(observer, observable);
}
var socketSubject = fromWebSocket('ws://localhost:9999', 'sampleProtocol');
// Receive data
socketSubject.subscribe(
function (data) {
// Do something with the data
},
function (error) {
// Do something with the error
},
function () {
// Do something on completion
});
// Send data
socketSubject.onNext(42);
What is the equivalent for a net socket? If there is a standard library to use that is ok.
My initial attempt is thus, but I don't know how to tie Rx and and the socket functions together into an onnext:
var net = require('net');
fromNetSocket(address, protocol) {
var ns = net.createServer(function(socket) {
socket.on('disconnect', function () { // This seems like it maps to onclose
console.log('User disconnected. %s. Socket id %s', socket.id);
});
// Handle incoming messages from clients.
socket.on('data', function (data) { //this should map to onnext
});
// Handle the data
var osbervable = Rx.Observable.create (function (obs) {
// Handle messages
ns.onmessage = obs.onNext.bind(obs);
ns.onerror = obs.onError.bind(obs);
ns.onclose = obs.onCompleted.bind(obs);
// Return way to unsubscribe
return ns.close.bind(ns);
});
});
};

Answer 1

Try the following
const createSubject = () => {
return Rx.Observable.create((observer) => {
const socket = net.connect({port: 1705}, () => {
log.i('Connected to Server!');
let socketObservable = Rx.Observable.create((observer) => {
socket.on('data', (data) => observer.next(JSON.parse(data)));
socket.on('error', (err) => observer.error(err));
socket.on('close', () => observer.complete());
});
let socketObserver = {
next: (data) => {
if (!socket.destroyed) {
socket.write(`${JSON.stringify(data)}\r\n`);
}
}
};
const subject = Rx.Subject.create(socketObserver, socketObservable);
observer.next(subject);
observer.complete();
});
});
};
Then you can use the subject like this
createSubject().subscribe((con) => {
con.subscribe((data) => console.log(data));
con.next({
id: utils.UUID(),
jsonrpc: '2.0',
method: 'Server.GetRPCVersion'
});
});