Incorrect tracestate key validation in W3CPropagator (.NET 10 RC1)

[gjuttla]

Description

It appears that the W3CPropagator incorrectly detects digits in the tracestate keys as invalid characters and therefore skips calling the setter delegate for the tracestate header.
Based on the TraceContext spec tracestate keys can contain digits [1].

Digits missing in

runtime/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/W3CPropagator.cs

Line 429 in cbfd526

private const string TraceStateKeyValidChars = "*-/@_abcdefghijklmnopqrstuvwxyz";

key = simple-key / multi-tenant-key
simple-key = lcalpha 0*255( lcalpha / DIGIT / "_" / "-"/ "*" / "/" )
multi-tenant-key = tenant-id "@" system-id
tenant-id = ( lcalpha / DIGIT ) 0*240( lcalpha / DIGIT / "_" / "-"/ "*" / "/" )
system-id = lcalpha 0*13( lcalpha / DIGIT / "_" / "-"/ "*" / "/" )
lcalpha    = %x61-7A ; a-z

[1] https://www.w3.org/TR/trace-context/#key

cc @tarekgh

Reproduction Steps

app.cs

using System.Diagnostics;

using var listener = new ActivityListener
{
    ShouldListenTo = _ => true,
    Sample = (ref ActivityCreationOptions<ActivityContext> _) => ActivitySamplingResult.AllDataAndRecorded,
    ActivityStarted = activity => { }
};

ActivitySource.AddActivityListener(listener);

var activitySource = new ActivitySource("myapp");

using (var activity = activitySource.StartActivity("myactivity"))
{
    activity!.TraceStateString = "f0o=b4r";
    DistributedContextPropagator.CreatePreW3CPropagator().Inject(activity, null, HeaderSetter);
    Console.WriteLine("----");
    DistributedContextPropagator.CreateW3CPropagator().Inject(activity, null, HeaderSetter);
}

void HeaderSetter(object? carrier, string fieldName, string fieldValue)
{
    Console.WriteLine($"{fieldName} = {fieldValue}");
}

traceparent = 00-6be559b2c9a18d5161ab496103927731-86bc8f6b5595b4af-01
tracestate = f0o=b4r
----
traceparent = 00-6be559b2c9a18d5161ab496103927731-86bc8f6b5595b4af-01

Expected behavior

Setter delegate being called for tracestate header when using the W3CPropagator.

Actual behavior

Setter delegate not called for tracestate header when using the W3CPropagator.

Regression?

Yes, works with the LegacyPropagator.

Known Workarounds

Using the LegacyPropagator.

DistributedContextPropagator.Current = DistributedContextPropagator.CreatePreW3CPropagator();

Configuration

.NET 10.0.0-rc.1.25451.107

Other information

No response

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[tarekgh]

@gjuttla thanks for your report. This is now fixed applying https://www.w3.org/TR/trace-context-2/#key.

[gjuttla]

Thanks for the quick resolution.