Support GET as well as POST

[simonw]

GraphiQL desktop app provides this as an option.

[simonw]

https://graphql.org/learn/serving-over-http/#http-methods-headers-and-body

Your GraphQL HTTP server should handle the HTTP GET and POST methods.

GET request

When receiving an HTTP GET request, the GraphQL query should be specified in the "query" query string. For example, if we wanted to execute the following GraphQL query:

{
  me {
    name
  }
}

This request could be sent via an HTTP GET like so:

http://myapi/graphql?query={me{name}}

Query variables can be sent as a JSON-encoded string in an additional query parameter called variables. If the query contains several named operations, an operationName query parameter can be used to control which one should be executed.

[simonw]

I'm serving GraphiQL from on GET to /graphql at the moment if there is now POST body.

https://github.com/simonw/datasette-graphql/blob/c06b5e3566a05a9ddfedd8f5f3cfb7ef6f988c2c/datasette_graphql/__init__.py#L24-L39

To support GET I can change this logic to include a check to see if ?query= was passed.

[simonw]

I'm going to imitate Starlette here: they do this:

        if request.method in ("GET", "HEAD"):
            if "text/html" in request.headers.get("Accept", ""):
                if not self.graphiql:
                    return PlainTextResponse(
                        "Not Found", status_code=status.HTTP_404_NOT_FOUND
                    )
                return await self.handle_graphiql(request)

Where handle_graphiql(request) returns the GraphiQL interface.

One difference: I'm going to set Vary: accept on the GraphiQL response to ensure things can be cached correctly.