Make it possible to skipResult() inside of `onSubscribe.onSubscribeResult.onNext` envelop plugin to avoid/skip re-send unchanged data

[Cauen]

Problem

I was recently researching the best approaches to implement real-time subscriptions sync with database and came across Hasura's approach.

https://github.com/hasura/graphql-engine/blob/master/architecture/live-queries.md#when-do-we-refetch

Instead of watching to real database events, they are syncing at every 1 second, and the justifications are quite reasonable.
Furthermore, in order to optimize resources, they avoid sending same data over the network every 1 second, they only send if it changed. Which also makes perfect sense.

Inside of Schema builder, its simple to make the resolver call every 1 second.

But getting it to avoid sending duplicate messages seems to be a challenge.

Solution

From Envelop plguins, we can create a custom functions to "rewrite" the result of each data response of subscription, but there is no API to avoid/skip sending it.

I think with a new option called skipResult It would make it possible to create a cache like Hasura's for Subscriptions
Does this make any sense?

onNext: ({ args, result, setResult, skipResult }) => {
  const alreadySent = cacheCompare(args, result);
  if (alreadySent) {
    skipResult();
  }
},

I took a good dive into the core/plugins code, did several tests/changes but always tried to avoid sending the expected data, graphql-ws threw an error

[EmrysMyrddin]

Hi @Cauen ! Thank you for this proposal 🙂 Looks like a good API, pretty coherent with other hooks API.

If you want to implement this, feel free to open a PR! They are very welcome! And we are here to support you if you need help or have any questions 🙂