Add response middlewares to the network queryers

[cideM]

Problem

NetworkMiddleware lets callers see every outgoing request, there's no equivalent for inspecting the response. We ran into this when we were trying to implement support for extensions in our GraphQL gateway (which is based on nautilus/gateway).

More specifically, SingleRequestQueryer.Query and MultiOpQueryer.Query parse the response and then decode only data into the receiver, so everything else is dropped, including extensions.

Solution

Add a ResponseMiddleware, similar to NetworkMiddleware:

type ResponseMiddleware func(ctx context.Context, response map[string]interface{}) error

type QueryerWithResponseMiddlewares interface {
    WithResponseMiddlewares(wares []ResponseMiddleware) Queryer
}

Both network queryers implement it through WithResponseMiddlewares, mirroring WithMiddlewares. The middlewares run after the response is parsed and before data is decoded. Returning an error aborts the query with that error, like a NetworkMiddleware does on the request side.

In MultiOpQueryer the middlewares run once per bundled query, with that query's own context and its own entry of the batched response.

With no middlewares configured the queryers behave exactly as before.

Tests

queryerResponseMiddleware_test.go covers the single request queryer (JSON and multipart responses, error propagation) and the multi-op queryer (each bundled query sees its own entry and context).