How to get field metadata from IHttpRequestInterceptor

[macpak]

Hi,

I am trying to implement an SLA mechanism for GraphQL queries, where we can assign an SLA value (in milliseconds) to a particular query. Then, using the SLA value, I'd like to enrich our request telemetry so that we have values to compare: actual request execution and assumed SLA.
My initial idea is to:

• Add a custom extension to IObjectFieldDescriptor which adds SLA to particular field definition. For example:

            descriptor.Field("myField")
                ...
                .UseSla(100);

            public static IObjectFieldDescriptor UseSla(
                this IObjectFieldDescriptor descriptor, 
                int milliseconds)
            {
                if(!descriptor.Extend().Definition.ContextData.ContainsKey("SLA"))
                    descriptor.Extend().Definition.ContextData.Add("SLA", milliseconds);
                
                return descriptor;
            }

• use IHttpRequestInterceptor to read the request SLA and enrich the request telemetry. Here, I've a problem, because it's hard for me to know what fields are included in the query. The only way I found is the following:

public override ValueTask OnCreateAsync(HttpContext context,
            IRequestExecutor requestExecutor, IQueryRequestBuilder requestBuilder,
            CancellationToken cancellationToken)
        {
            var request = requestBuilder.Create();
            if (request.Query is QueryDocument document)
            {
                var sla = GetSla(requestExecutor, document);
                if (sla.HasValue)
                {
                    context.AddSla(sla.Value);
                }
            }
            
            return base.OnCreateAsync(context, requestExecutor, requestBuilder,
                cancellationToken);
        }

        private static int? GetSla(IRequestExecutor requestExecutor, QueryDocument document)
        {
            foreach (var node in document.Document.GetNodes())
            {
                var name = FindFieldName(node);
                if (name != null)
                {
                    var field = requestExecutor.Schema.QueryType.Fields[name];
                    if (field.ContextData.TryGetValue("SLA", out var @value) &&
                        int.TryParse(@value?.ToString(), out var sla))
                    {
                        return sla;
                    }
                }
            }

            return null;
        }

        private static string FindFieldName(ISyntaxNode node)
        {
            if (node == null)
                return null;
            
            if (node.Kind == SyntaxKind.Field && node is FieldNode fieldNode)
                return fieldNode.Name.Value;


            foreach (var childNode in node.GetNodes())
            {
                var result = FindFieldName(childNode);
                if (!string.IsNullOrWhiteSpace(result))
                    return result;
            }

            return null;
        }

This solution seems to work but what I don't like is that I manually parse the document to find a field that has SLA applied.
Is there a better way to get metadata about the fields in the request ?