06.middlewares.md

Middleware

From Hotchocolate documentation:

Hot Chocolate has three kinds of middleware. The query middleware which allows to extend or rewrite the processing of a query request, the field middleware which allows to extend or rewrite the processing of field resolvers and the directive middleware which allows basically to add a field middleware to fields that are annotated with a specific directive.

To test the middleware I tried to introduce a new directive that can return the Base64 decoding of the ids decoded by the introduction of the Global Object Identifier.

The process is simple:

    public class DecodeBase64DirectiveType : DirectiveType
    {
        protected override void Configure(IDirectiveTypeDescriptor descriptor)
        {
            descriptor.Name("decodeBase64");
            descriptor.Location(DirectiveLocation.Field);
            descriptor.Use(next => async context =>
            {
                await next.Invoke(context);

                if (context.Result is string s)
                {
                    byte[] data = Convert.FromBase64String(s);
                    context.Result = Encoding.UTF8.GetString(data);
                }
            });
        }

    }

Register it

builder.Services.AddDirectiveType<DecodeBase64DirectiveType>()

et voilà. Now it is possible to make queries that decode the single returned field:

query {
  authorById(id: "2d2cbbee-5a3a-4102-bc41-04679bfa2968") {
    id @decodeBase64
    firstName
  }
}

the result now is this:

{
  "data": {
    "authorById": {
      "id": "Author\nd2d2cbbee-5a3a-4102-bc41-04679bfa2968",
      "firstName": "Faustina"
    }
  }
}