Asp.Net MVC Unique id per request

Question

In our MVC 5 site, no session, we need to get/generate a unique ID per request. THhis will be used as an ID for logging all activity in the request.

Is there a way to as

Answer 1

Here's some extension methods that I created for this purpose:

public static Guid GetId(this HttpContext ctx) => new HttpContextWrapper(ctx).GetId();

public static Guid GetId(this HttpContextBase ctx)
{
    const string key = "tq8OuyxHpDgkRg54klfpqg== (Request Id Key)";

    if (ctx.Items.Contains(key))
        return (Guid) ctx.Items[key];

    var mutex = string.Intern($"{key}:{ctx.GetHashCode()}");
    lock (mutex)
    {
        if (!ctx.Items.Contains(key))
            ctx.Items[key] = Guid.NewGuid();

        return (Guid) ctx.Items[key];
    }
}

Update

@Luiso made a comment about interned strings not being garbage collected. This is a good point. In a very busy web app that doesn't recycle app pools frequently enough (or ever) this would be a serious issue.

Thankfully, recent versions of .NET have ephemeron support via the ConditionalWeakTable class. Which gives a convenient and memory safe way of tackling this problem:

private static readonly ConditionalWeakTable>
Ephemerons = new ConditionalWeakTable>();

public static Guid GetId(this HttpContext ctx) => new HttpContextWrapper(ctx).GetId();

public static Guid GetId(this HttpContextBase ctx)
{
    var dict = Ephemerons.GetOrCreateValue(ctx);
    var id = (Guid)dict.GetOrAdd(
        "c53fd485-b6b6-4da9-9e9d-bf30500d510b",
        _ => Guid.NewGuid());
    return id;
}

My Overby.Extensions.Attachments package has an extension method that simplify things.

/// 

/// Unique identifier for the object reference.
/// 
public static Guid GetReferenceId(this object obj) =>
    obj.GetOrSetAttached(() => Guid.NewGuid(), RefIdKey);

Using that extension method, you would just call httpContext.GetReferenceId().