Create a Mercure adapter for GraphQL subscriptions (Apollo)

[mathieutu]

Hi Kévin.

I would like to reopen #162.
I would like to use mercure instead of websocket for my graphql subscriptions, but I'm actually not understanding how to properly do that. I didn't find any resource about it, neither someone who have already done it.

Disclaimer : I'm not a graphql expert, and especially totally noob in real-time stuff.

What I've understood is there is a several part in subscription: the pubsub implementation, and the transport implementation.

The documentation tells us about pubsub, but it forgets totally the transport here: https://www.apollographql.com/docs/apollo-server/data/subscriptions

I'm reading about sse transport in graphql, but I don't fully understand how to adapt it to mercure and how to implement it.

It seems really simple when reading you:

In response to the subscription query, the GraphQL server may return a corresponding topic URL. The client can then subscribe to the Mercure's event stream corresponding to this subscription by creating a new EventSource with an URL like https://example.com/.well-known/mercure?topic=https://example.com/subscriptions/ as parameter.

Updates for the given subscription can then be sent from the GraphQL server to the clients through the Mercure hub (in the data property of the server-sent event).
Also, Mercure can easily be integrated with Apollo GraphQL by creating a dedicated transport.

Could you give us some advice on how to handle that? Maybe an example? Or would you mind giving an hand on creating a transport for mercure? It can helps adoption of the protocol in graphql community.

Thanks.
Mathieu.

[dunglas]

Hi Mathieu,

Using Mercure for GraphQL subscriptions has been implemented by @alanpoulain in API Platform: https://api-platform.com/docs/master/core/graphql/#subscriptions
The related code: https://github.com/api-platform/core/tree/master/src/GraphQl/Subscription

I hope this helps!

[xleliberty]

Hi,
@mathieutu , did you succeeded setting up an apollo transport for mercure subscriptions with help of the documentation ?
On my part, i don't have sufficient apollo knowledge to got it working.
I tried to use a SplitLink (https://www.apollographql.com/docs/link/composition/) to dedicate a transport to mercure, but link initialization fail with a 401.

If anyone can provide a working apollo code to subscribe to mercure ?

[mathieutu]

Hi @xleliberty.
Unfortunately no, I didn't succeed to have anything working with mercure, so I moved on to a standard websocket implementation which is ok for me. I may take a further look one day when I will have the time to do it.

[xleliberty]

ok thanks

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[lermontex]

Apparently, it will not be possible to completely get rid of the websocket yet. In addition, the current implementation in the api platform only supports update operations.

api-platform/core#3321
api-platform/core#4302

[tabha]

Hello there.
@mathieutu still using websocket?
I would like to use mercure for my subscription as well.

[mathieutu]

Hi @tabha.
Sorry but yep the project was done with WS, and I've switched project months ago so not a proper owner for this anymore.

Good luck!