Compatibility with graphql-ws keepAlive

[andreialecu]

I'm experimenting with switching from Apollo Express to Fastify and Mercurius.

I discovered something a bit weird. If I enable keepAlive in graphql-ws, it will send messages that look like {"type": "ping"} but it seems that something on the Mercurius side is not processing them correctly.

On the other hand, If I enable keepAlive in Mercurius, it sends messages like {type: "ka"}:

graphql-ws completely crashes on these messages and breaks the subscription:

My understanding is that Mercurius uses graphql-ws, so what's the deal here? 🙂

[mcollina]

I think there is a bug somewhere in Mercurius that requires the payload in https://github.com/enisdenjo/graphql-ws/blob/master/PROTOCOL.md#ping to exist.

Would you like to send a Pull Request to address this issue? Remember to add unit tests.

[andreialecu]

I'll take a look at submitting a PR for this. I believe this is also incorrect:

mercurius/lib/subscription-protocol.js

Line 29 in f25d973

GQL_CONNECTION_KEEP_ALIVE: 'ka', // Server -> Client

I don't think graphql-ws understands the ka message, based on the error in my original report.

Instead it should probably be pong.

[mcollina]

note that you should only change the graphql-transport-ws subprotocol.

[andreialecu]

Opened #852