Establishing a Connection

In order to contact the API server, we need to open a socket connection to an endpoint.

note

We are using the endpoint deisgnated for live accounts and JSON messaging. We are also running our program endlessly using an infinite loop.

JavaScript

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

// util functions
const { log } = console;
const sleep = (secs) => new Promise((r) => setTimeout(r, secs * 1000));

ws.onopen = function () {
  log('connected to server');
};

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

(async () => {
  while (true) await sleep(0.25);
})();

Python

note

Install the websockets package with pip install websockets.

import asyncio as aio
import websockets
from websockets.asyncio.client import connect

async def main():
  async with connect('wss://echo.websocket.org') as ws:
    print('connected to server')

    while True:
      await aio.sleep(0)

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

aio.run(main())

Why Connection Closes Automatically

If you ran previous code examples, you'll notice that the script runs sucessfully and prints the following:

connected to server
connection closed

So it seems that the connection is opened at first, but then after some time passes, it gets closed automatically.

Let's adjust the code to measure the time between the events happening. We want to measure the time taken between following events:

• from when script is first run, until connection is opened
• from when connection is opened, until it's closed

JavaScript

// util functions
const round = (n, dp) => +n.toFixed(dp);

let t = Date.now();

ws.onopen = function () {
  // ...
  log(
    'it took',
    round((Date.now() - t) / 1000, 1),
    'secs to open the connection',
  );
  t = Date.now();
};

ws.onclose = function () {
  // ...
  const secsPassed = round((Date.now() - t) / 1000, 1);
  log('connection stayed open for', secsPassed, 'seconds before it was closed');
};

Python

from timeit import default_timer as timer

async def main():
  t = timer()

  async with connect('wss://live.ctraderapi.com:5036') as ws:
    # ...

    secs_passed = round(timer() - t, 1)
    print('it took', secs_passed, 'seconds to open the connection')
    t = timer()

    while True:
      await aio.sleep(0)

      if ws.state != websockets.State.OPEN:
        # ...
        secs_passed = round(timer() - t, 1)
        print('connection stayed open for', secs_passed,
          'seconds before it was closed')
        break

Results from running the code:

connected to server
it took 0.8 seconds to open the connection
connection closed
connection stayed open for 29.8 seconds before it was closed

As the results show, the connection gets closed after being open for 30 seconds. It is actually the server that closes the connection.

When the server notices that a client that was previously connected, hasn't been sending any messages for awhile, it decides to close the connection to that client. The time a client spends being connected to the server, but not sending any messages to it, is also called the idle time. One of the reasons for this server's behaviour is to save its resources.

Later, when we learn about Exchanging Messages with the server, we will see how the server counts the idle time of a connected client from the last message that the client sent to it.

We will also learn a special way of preventing this from happening in Keeping Connection Open.