Detect subscription successfully started

[Amerehei]

When we use Observable, using error we can detect that subscription is failed to star, But there is no way to detect that it's successfully started

How can I detect that the server response of subscription is received?

[enisdenjo]

Since there is no confirmation message on the protocol level, you can provide an initial subscription event that is sent as soon as the client subscribes.

[Amerehei]

@enisdenjo I know that your answer is correct. I faced a problem. I can get connection_ack. My problem is, when I send subscribe to the server there is either an error in case of error or no reply for the subscribe request in case of success.

Is it a server bug? You previously mentioned "here is no confirmation message on the protocol level" so how message.type === MessageType.Subscribe can work?

[enisdenjo]

Is it a server bug?

Not a bug, connection_ack is for acknowledging the connection; meaning, the connection_init is valid and correct.

You previously mentioned "here is no confirmation message on the protocol level" so how message.type === MessageType.Subscribe can work?

As I said here, if the WebSocket message is sent and the connection did not error out - you can be sure that the server has received the event.

So, if you send a subscribe message and the server does not reply with an error - you're good to go. Furthermore, even if the server is late to send the error message (because validation took too long or whatever) - you still show the error screen when you get the error, so you're good in that case too.

[Amerehei]

@enisdenjo This is not only a loading UI. I would like to resolve/reject a promise and I cannot resolve it immediately. If an error occurs in this case I cannot reject the promise. So there is no way to resolve the promise.

Is it a server bug?
My question was not about the connection_ack. I asked I only get an acknowledging the connection. For the subscription there is no response so message.type === MessageType.Subscribe would never satisfy

I asked if we have MessageType.Subscribe and there is no confirmation message on the protocol level for subscription, How does it work?

[enisdenjo]

I asked if we have MessageType.Subscribe and there is no confirmation message on the protocol level for subscription, How does it work?

There is no confirmation message for subscriptions, only for connections.

I just remembered, there is actually a way to acknowledge subscription - through pings. See the recipe here. You will need to change the server though...

[Amerehei]

@enisdenjo Thanks a lot for sharing your knowledge