Should relays send back a CLOSED message after the client sends CLOSE?

[alexgleason]

• Client: ["REQ", "123", ...]
• Relay: ["EVENT", "a", ...], ["EVENT", "b", ...], etc...
• Relay: ["EOSE", "123"]
• Client: ["CLOSE", "123"]
• Relay: ["CLOSED", "123"] (maybe? this is the question)

When writing the code, the relay naturally wanted to send a CLOSED message after the client sent CLOSE. I did extra work to prevent it from sending the extra CLOSED message, by checking whether it was a client-initiated or relay-initiated close.

But maybe it should send CLOSED? It's redundant. Or maybe it's useful information to know that the relay respected the close.

[staab]

CLOSE indicates that the client isn't listening any more, regardless of what subsequent messages the relay sends. I think CLOSED is redundant. If clients want to monitor whether relays respect CLOSE they can listen for more messages on a dead subscription, no need to rely on CLOSED.

[mikedilger]

I think clients shouldn't rely on getting a CLOSED, but relays should probably send one anyways for those clients who for some reason are. Just to play it safe.

[fiatjaf]

the relay naturally wanted

AGI achieved.

[fiatjaf]

Just to play it safe.

this is Postel law's breaking protocols again. Every time you "play it safe" you create more people that depends on that and the spec becomes the "safe" version and now everybody has to update.

It's better if a new client notices early that they are wrong so they can fix themselves without disruption.

[fiatjaf]

I propose that, after receiving a CLOSED, clients send a CLOSED-RECEIVED message.
And relays, upon receiving that, should send a CLOSED-RECEIVED-ACK.

[staab]

Don't forget CLOSED-RECEIVED-ACK-ACK and CLOSED-RECEIVED-ACK-REJECTED

[mikedilger]

Ok then, so relays should not send CLOSED unless they are initiating the closure.

I notice a comment in chorus source code: "Don't send a CLOSED because there is no valid prefix for this kind of message, and clients just presume it was closed." So chorus already does it like this.