Comply with graphql-over-http specification

[spawnia]

It would be great if the standard server were compliant with the GraphQL-over-HTTP specification.

The test suite could be done in a way that is reusable by other servers: https://github.com/graphql/graphql-over-http/issues/57

[oprypkhantc]

Hey @spawnia. Someone has mentioned before that we could just use graphql-http's test suite to test for graphql-over-http spec compliance. I've made a tiny branch to run those: https://github.com/webonyx/graphql-php/compare/master...oprypkhantc:graphql-php:graphql-over-http

Could you take a look to see if this is even remotely what you had in mind? It's messy, but enough to show the idea. The test suite is in JS, so I thought simply running a real HTTP server is our best bet here.

If this looks alright to you, I can clean it up, add GH actions and, of course, work on the spec compliance. I believe I have a good understanding of the spec, plus there are 60 tests (only 20 of which pass with the current implementation) that cover just about everything.

What do you think?

[oprypkhantc]

Of course that can be moved out of graphql-php to graphql-http once the spec compliance is ready, merged and stable. They host tests for a lot of implementations already. Unit tests should be plenty to test against basic stuff.

[spawnia]

I have already attempted to add compliance automation for a GraphQL server implementation that sits on top of this library, see https://github.com/nuwave/lighthouse/pull/2359. I wanted to use Deno due to its leaner setup, but progress on it is currently blocked due to https://github.com/graphql/graphql-http/issues/65.

If you can implement something similar for this library, I am all for it. Your branch seems to be using Node, that is also fine with me.