**parseTraceFlag erroneously marks non‑“1” values as sampled, causing over‑sampling**

[PhilemonBrain]

Description

parseTraceFlag sets the sampled bit for any value whose length ≠ 1, even when the flag is invalid (e.g. Sampled=maybe).

func parseTraceFlag(xraySampledFlag string) trace.TraceFlags {
    if len(xraySampledFlag) == 1 && xraySampledFlag != "1" {
        return traceFlagNone        // ok: explicit “0”
    }
    return trace.FlagsSampled       // ← bug: treats “maybe”, “foo”, “”, etc. as sampled
}

According to AWS X‑Ray header spec the only value that should map to trace.FlagsSampled is "1". Any other value (including "0" or garbage) must clear the flag.

Because of this, downstream OpenTelemetry SDKs mark spans as sampled when they should be drop‑eligible, inflating trace volume and potentially incurring unexpected cost.

---

Environment

• OS: any (confirmed on macOS 14 & Ubuntu 22.04)
• Architecture: amd64 & arm64
• Go version: 1.22.2
• Module: go.opentelemetry.io/contrib/propagators/aws/xray
• Version / commit: v0.47.0 ( 2e1b0bb )

---

Steps To Reproduce

1. Create an inbound carrier with an invalid sampled flag:

   carrier := propagation.MapCarrier{
       "X-Amzn-Trace-Id": "Root=1-abcdef12-1234567890abcdef12345678;" +
                          "Parent=1234567890abcdef;" +
                          "Sampled=maybe",
   }
   ctx := xray.Propagator{}.Extract(context.Background(), carrier)
   sc  := trace.SpanContextFromContext(ctx)

2. Check the flag:

   fmt.Println(sc.IsValid(), sc.IsSampled())   // → true, **true**

3. Observe that IsSampled() is true, even though "maybe" is not legal.

---

Expected Behavior

parseTraceFlag("maybe") (or any value other than "1") should return traceFlagNone, so the extracted SpanContext is not sampled.

Proposed fix:

func parseTraceFlag(xraySampledFlag string) trace.TraceFlags {
	if xraySampledFlag == isSampled {
		return trace.FlagsSampled
	}
	return traceFlagNone
}

This change:

• Honors the X‑Ray spec
• Prevents accidental over‑sampling
• Aligns with Otel propagator behavior for W3C traceparent

Happy to submit a PR if this approach is acceptable.

[PhilemonBrain]

@akats7 @dmathieu Here is the issue for the bug. Please kindly assign to me

[MrAlias]

Can you add the quote for the part of the specification that states only 1 is a valid sample state?

It seems odd they would not use bit masks like the W3C.

[seankhliao]

Can't find a spec for xray, but given their use of Sampled=? as in
go: https://github.com/aws/aws-xray-sdk-go/blob/v1.8.5/header/header.go#L50C32-L50C41
node: aws/aws-xray-sdk-node#291
java: https://github.com/aws/aws-xray-sdk-java/blob/3e0b21c5bafec8d0577768cdfc31f4139c4fbecc/aws-xray-recorder-sdk-core/src/main/java/com/amazonaws/xray/entities/TraceHeader.java#L17-L18
(also can't find any docs for this...), I'd say they do treat it as a literal string rather than a bit mask.