Keeping Connection Open

As mentioned earlier, connection does not stay open forever, and in order to keep it open, we have to do some extra work.

Let's adjust the code so that our program runs endlessly. This way we have an opportunity to check program state at specific intervals like 5 second for example.

JavaScript

const ws = new WebSocket('wss://live.ctraderapi.com:5036');

// util functions
const sleep = (secs) => new Promise((r) => setTimeout(r, secs * 1000));
const round = (n, dp) => +n.toFixed(dp);
const fmt = (n) => round(n / 1000, 1);

const CHECK_INTERVAL_SECS = 5;
let timeWhenOpened = 0;

ws.onopen = function () {
  timeWhenOpened = Date.now();
  console.log('connected to server');
};

ws.onclose = function () {
  console.log('connection closed');
};

(async () => {
  while (true) {
    await sleep(0); // neccessary in "async infinite loops"
    if (ws.readyState !== WebSocket.OPEN) continue;

    const timeBeenOpen = Date.now() - timeWhenOpened;
    console.log('connection is been open for', fmt(timeBeenOpen), 'seconds');

    await sleep(CHECK_INTERVAL_SECS);
  }
})();

Python

import asyncio as aio
import websockets
from websockets.asyncio.client import connect
from timeit import default_timer as timer

CHECK_INTERVAL_SECS = 5
time_when_opened = 0

async def main():

  async with connect('wss://live.ctraderapi.com:5036') as ws:
    print('connected to server')
    time_when_opened = timer()

    while True:
      await aio.sleep(0)

      if ws.state != websockets.State.OPEN:
        print('connection closed')
        break

      time_been_open = round(timer() - time_when_opened, 1)
      print('connection is been open for', time_been_open, 'seconds')

      await aio.sleep(CHECK_INTERVAL_SECS)

aio.run(main())

Results from running the code:

connected to server
connection is been open for 0 seconds
connection is been open for 5 seconds
connection is been open for 10.1 seconds
connection is been open for 15.1 seconds
connection is been open for 20.1 seconds
connection is been open for 25.1 seconds
connection closed

As we learned here , the connection gets closed by the server after being idle for about 30 seconds.

Now that we have the ability to detect how long our connection has been open, we can prevent the connection from being closed by repeatedly sending a special message to the server at intervals that are under 30 seconds. Let's add below parts to our previous code and run it again:

let timeOfLastAction = 0;

ws.onopen = function () {
  timeOfLastAction = Date.now();
  // ...
};

(async () => {
  while (true) {
    // ...
    const idleTime = fmt(Date.now() - timeOfLastAction);
    if (idleTime >= 25) {
      ws.send(JSON.stringify({ payloadType: 51 }));
      timeOfLastAction = Date.now();
      console.log('we just sent heartbeat');
    }
    // ...
  }
})();

Results from running the code:

connected to server
connection is been open for 0 seconds
connection is been open for 5 seconds
connection is been open for 10.1 seconds
connection is been open for 15.1 seconds
connection is been open for 20.1 seconds
just sent heartbeat
connection is been open for 25.1 seconds
connection closed: { code: 1000, reason: 'Bye', wasClean: true }

As you see from the results, connection did not stay open and it got closed by server again after idle time reached around 30 seconds. So why our heartbeat sending didn't have any effects? It's because we did not authenticate first. You can think about it this way, imagine you're the server, and every one that connects to you consumes a little bit of your resources, so you let anyone connect for 30 seconds and you don't say anything because you're a nice server, but if clients want to stay for longer than 30 seconds, they have to show some ID, so at least server knows it's not wasting its resources on a stranger.

So let's add the showing our ID part to our previous code and run it again:

const { clientId, clientSecret } = require('./credentials.json');

ws.onopen = function () {
  // ...
  ws.send(
    JSON.stringify({ payloadType: 2100, payload: { clientId, clientSecret } }),
  );
};

Results from running the code:

connected to server
connection is been open for 0 seconds
server sent: {"payloadType":2101}
connection is been open for 5 seconds
connection is been open for 10.1 seconds
connection is been open for 15.1 seconds
connection is been open for 20.1 seconds
we just sent heartbeat
connection is been open for 25.1 seconds
server sent: {"payloadType":51}
connection is been open for 30.2 seconds
connection is been open for 35.2 seconds
connection is been open for 40.2 seconds
we just sent heartbeat
connection is been open for 45.3 seconds
connection is been open for 50.3 seconds
connection is been open for 55.3 seconds
server sent: {"payloadType":51}
connection is been open for 60.4 seconds
we just sent heartbeat
connection is been open for 65.4 seconds
connection is been open for 70.4 seconds

As you see from the results, we succeeded in keeping the connection open for longer than 30 seconds. You might have also noticed that not only we're sending the heartbeat, but the server is also sending us a heartbeat.