feat: implement messages callbacks for channels

[SlayerDF]

Closes #2

[skryukov]

Hey @SlayerDF, thanks for the PR! ❤️

It looks like just what we need, the only thing we are missing is providing an example and docs in the readme.

Do you want to add them? If not, I will just merge this PR and add it myself.

Here is what I used to test this PR, btw:

import { check, fail, sleep } from "k6";
import cable from "k6/x/cable";

let userId = `100${__VU}`;
let userName = `Kay${userId}`;

const URL = __ENV.CABLE_URL || "ws://localhost:8080/cable";
const WORKSPACE = __ENV.WORKSPACE || "demo";

export default function () {
    let client = cable.connect(URL, {
        cookies: `uid=${userName}/${userId}`,
        receiveTimeoutMS: 30000,
    });

    if (
        !check(client, {
            "successful connection": (obj) => obj,
        })
    ) {
        fail("connection failed");
    }

    const channel = client.subscribe("ChatChannel", { id: WORKSPACE });

    if (
        !check(channel, {
            "successful subscription": (obj) => obj,
        })
    ) {
        fail("failed to subscribe");
    }

    channel.onMessage((msg) => {
        check(msg, {
            "Hello message received": (obj) => obj.message.html.includes('Hello'),
        });
    });

    channel.perform("speak", { message: "Hello" });
    channel.perform("speak", { message: "Hello" });
    // this will fail
    channel.perform("speak", { message: "Bye" });

    sleep(1);

    // Terminate the WS connection
    client.disconnect()
}

[SlayerDF]

@skryukov
I'm sorry I forgot about the docs. Nevertheless I would appreciate if you add it yourself 😌