Query, Mutation and Subscriptions [ALL] over websockets

[paulm17]

Similar to this question: https://spectrum.chat/apollo/general/query-mutation-subscriptions-over-one-websocket-connection~a324fef0-d1b1-45f7-a784-449ddf71ab08

I'm currently investigating graphql for a possible migration of an existing development using centrifugo, which is a websocket server writting in golang.

Will we ever see the ability to do queries and mutations using websockets, instead of http?

I can understand initial requests before websockets have bootstrapped, but once the connection is in play. Websockets have a much lower overhead.

Thanks

[JoviDeCroock]

It is already possible, here is an example repo leveraging the enableAllOperations property of our subscriptionExchange

[paulm17]

I changed the websocket implementation to subscriptions-transport-ws and I don't get any issues.

[JoviDeCroock]

hmm yeah, I've heard this before where graphql-ws is incompatible with the backend version of subscriptions-transport-ws 😅

[tornqvist]

I'm having trouble with his approach, getting the error Expected operation of type "subscription" but found "query".

It appears that a check in createRequestOperation introduced in #1829 will throw if trying to send a query or mutation over WebSockets before ever getting to the enableAllOperations-check. Is this intended behavior?

Ironically it does work in production since the check is only done in development.

[kitten]

@tornqvist: That error is specifically related to mismatching operations and APIs, e.g. passing a query to useSubscription / client.executeSubscription.

The operation kind and API used must always match.

[tornqvist]

Oh, that makes sense. So that means I should still use client.executeQuery (or createQuery, as I'm using svelte) and just not have a fetchExchange in there to have the subscriptionExchange handle the query?

Unfortunately, I need to have fetchExchange since it's only certain queries I want to execute over WebSocket. I've tried to implement an intermediate exchange to determine whether to use fetchExchange or forward to subscriptionExchange but am getting a forward() must only be called once in each Exchange. error, just like #3559

How would one go about doing this?

function maybeFetchExchange(params) {
  const fetch = fetchExchange(params)
  return (operations$) => {
    const toWebSocket = pipe(
      operations$,
      filter((operation) => operation.context.useWebSocket),
      params.forward
    )

    const toFetch = pipe(
      operations$,
      filter((operation) => !operation.context.useWebSocket),
      fetch
    )

    return merge([toFetch, toWebSocket])
  }
}