socket-test | A simple communication test interface built with Python | TCP library

You don't need the Express code because in this case the server you want to talk to is on the cryptocompare server -- not a local server. This is captured in your code when you initialize the io object in the HTML file.

Of course, you could still use Node to talk to the cryptocompare websockets API if you're more comfortable with Node. But then you wouldn't need the in-browser JavaScript. Either way, what you need is to create some kind of client in any runtime that speaks websockets and can talk to the cryptocompare websockets API.

With regard to the code being skipped over -- you're right! It is. socket.io is an event driven WebSockets framework. This means that clients register their interest in certain kinds of events/messages, and when those are triggered special functions known as callbacks are called.

If it helps, you can think of those events like channels in a chat room -- if you're not in the right room, you won't see the messages for that room. So you'll need to know what messages you should be listening for, register your interest in those, and register callback functions for each one.

Thankfully cryptocompare has provided client code examples that should help you get an idea for the kinds of messages you should be listening for. See here

.Net Framework doesn't checks whether the certificate used in WebSocket is trusted, but .Net Core does. I was unable to get how to solve from Exception, so I investigated by using PerfView.

I installed LXD's Server Certificates. Bring server.crt file(/var/lxd/server.crt) to Client PCs, then install as trusted root Certificate.
Please read how to install: Windows, Linux

When you specify a hostname or IP address​ to listen on (in this case localhost which resolves to 127.0.0.1), then your server will only listen on that IP address.

Listening on localhost isn't a problem when you are outside of a Docker container. If your server only listens on 127.0.0.1:8000, then your client can easily connect to it since the connection is also made from 127.0.0.1.

When you run your server inside a Docker container, it'll only listen on 127.0.0.1:8000 as before. The 127.0.0.1 is a local loopback address and it not accessible outside the container.

When you fire up the docker container with -p 8000:8000, it'll forward traffic heading to 127.0.0.1:8000 to the container's IP address, which in my case is 172.17.0.2.

The container gets an IP addresses within the docker0 network interface (which you can see with the ip addr ls command)

So, when your traffic gets forwarded to the container on 172.17.0.2:8000, there's nothing listening there and the connection attempt fails.

The problem is with the listen address:

You need to get this out of the db.once context:

If you want to use a TextWebSocketHandler, you could pass the auction id as part of the URL path. You'll have to copy the path to the WebSocket session during handshake (this is the only place where you'll get access to the ServerHttpRequest as the handshake is an http request) and then retrieve the attribute from your handler.

Here's the implementation: