SSE Keep-Alive

[demius]

Product

Hot Chocolate

Is your feature request related to a problem?

Subscriptions over SSE work really well, but a problem we have is that there's no keep-alive mechanism. This manifests itself when using something like Azure Application Gateway which closes idle connections after a pre-configured timeout. There's an open discussion regarding this topic in the Web Hypertext Application Technology Working Group repository.

The solution you'd like

SSE support should be more explicit and allow a configurable keep-alive message to be dispatched to all connected clients. Alternatively, is there an injectable interface which allows us to get all connected subscribers and manually issue keep-alives in a background service?

[michaelstaib]

Hey @enisdenjo I saw similar things with other gateways ... is that something that can be added to the protocol ... to send a keep alive message?

[enisdenjo]

graphql-sse itself pings clients every 12 seconds.

Legacy proxy servers are known to, in certain cases, drop HTTP connections after a short timeout. To protect against such proxy servers, authors can include a comment line (one starting with a ':' character) every 15 seconds or so.

SSE spec "Authoring notes" section

Essentially, issuing an empty comment message (:\n\n) is considered a keep-alive ping. The graphql-sse client ignores these empty messages, and so does the browser native EventSource.

[demius]

Thanks @enisdenjo, but how can I submit this empty message to all connected/subscribed clients? What I was thinking of was having some kind of background service which sends a keep-alive payload to all connected subscribers (regardless of topic), but I've been digging around in the transport code and I can't find an injectable service I can use for this purpose. Does such a service exist, or would I need to create a separate subscription just for this?

[enisdenjo]

Sorry but I am not familiar with this library. I'd say @michaelstaib is the better person to ask.

[demius]

Any suggestions on this topic @michaelstaib?

[michaelstaib]

We will implement that with 13.1 .... thanks @enisdenjo for the feedback