[Question] Why does AspNetCore instrumentation documentation suggests adding custom attributes through Enrich hook instead of directly updating activity in middleware?

[jundayin]

Component

OpenTelemetry.Instrumentation.AspNetCore

Question details

In the documentation we were told to add custom attributes through enrich hook in the following format

services.AddOpenTelemetry()
    .WithTracing(builder => builder
        .AddAspNetCoreInstrumentation(o =>
        {
            o.EnrichWithHttpRequest = (activity, httpRequest) =>
            {
                activity.SetTag("requestProtocol", httpRequest.Protocol);
            };
            o.EnrichWithHttpResponse = (activity, httpResponse) =>
            {
                activity.SetTag("responseLength", httpResponse.ContentLength);
            };
            o.EnrichWithException = (activity, exception) =>
            {
                if (exception.Source != null)
                {
                    activity.SetTag("exception.source", exception.Source);
                }
            };
        }));

In my code I need to read the request body and set one of the fields as part of the custom attributes. Basically I do something like

o.EnrichWithHttpRequest = (activity, httpRequest) =>
{
    httpRequest.EnableBuffering();
    try
    {
        var buffer = new byte[Convert.ToInt32(httpRequest.ContentLength)];
        httpRequest.Body.ReadAsync(buffer, 0, buffer.Length);
        var requestContent = Encoding.UTF8.GetString(buffer);
        var policyRequest = JsonConvert.DeserializeObject<PolicyRequest>(requestContent);
        string policyNamespace = policyRequest.Namespace;
        activity.SetTag(TelemetryConstants.PolicyNamespaceKey, policyNamespace);
    }
    catch (Exception e)
    {
        Console.WriteLine($"Failed to process policy namespace. Exception: {e.Message}");
    }
    finally
    {
        httpRequest.Body.Position = 0;
    }
};

This is not a thread-safe approach and apparently it breaks a lot of inbound requests. Later I realize since we only need to update the acitivity tag directly, maybe I can get the Acitivity directly in the middleware

public class TestMiddleware
{
    public async Task InvokeAsync(HttpContext httpContext) 
    {
        --- get the namespace from request body ---
        Activity.Current?.AddTag(TelemetryConstants.PolicyNamespaceKey, policyNamespace);
}

Although it works, I don't know if this has any issue that I'm not aware. That makes me curious why the documentation only mentions the hook approach