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Feat: Have SpanContext support the new W3C random flag. #7834

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Feat: Have SpanContext support the new W3C random flag. #7834

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c26986d
chore: primary implementation
nikhilmantri0902 Jan 24, 2026
4bb34cf
chore: added changelog
nikhilmantri0902 Jan 24, 2026
6356e89
chore: formatting improved
nikhilmantri0902 Jan 24, 2026
b679bd9
Merge branch 'main' into feat/support_w3c_random_flag
nikhilmantri0902 Jan 24, 2026
0778d30
chore: added test
nikhilmantri0902 Jan 29, 2026
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
- Fix bad log message when key-value pairs are dropped because of key duplication in `go.opentelemetry.io/otel/sdk/log`. (#7662)
- Fix `DroppedAttributes` on `Record` in `go.opentelemetry.io/otel/sdk/log` to not count the non-attribute key-value pairs dropped because of key duplication. (#7662)
- Fix `SetAttributes` on `Record` in `go.opentelemetry.io/otel/sdk/log` to not log that attributes are dropped when they are actually not dropped. (#7662)
- Preserve W3C TraceFlags bitmask (including the random Trace ID flag) during trace context extraction and injection in `go.opentelemetry.io/otel/propagation`. (#7635)
- `WithHostID` detector in `go.opentelemetry.io/otel/sdk/resource` to use full path for `ioreg` command on Darwin (macOS). (#7818)
- Fix missing `request.GetBody` in `go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp` to correctly handle HTTP2 GOAWAY frame. (#7794)

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9 changes: 3 additions & 6 deletions propagation/trace_context.go
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Expand Up @@ -46,8 +46,7 @@ func (TraceContext) Inject(ctx context.Context, carrier TextMapCarrier) {
carrier.Set(tracestateHeader, ts)
}

// Clear all flags other than the trace-context supported sampling bit.
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@dashpole dashpole Jan 29, 2026

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Seems like we were doing this intentionally before. I'm hesitant to remove this behavior without understanding why it was added in the first place.

flags := sc.TraceFlags() & trace.FlagsSampled
flags := sc.TraceFlags()

var sb strings.Builder
sb.Grow(2 + 32 + 16 + 2 + 3)
Expand Down Expand Up @@ -104,14 +103,12 @@ func (TraceContext) extract(carrier TextMapCarrier) trace.SpanContext {
if !extractPart(opts[:], &h, 2) {
return trace.SpanContext{}
}
if version == 0 && (h != "" || opts[0] > 2) {
if version == 0 && h != "" {
// version 0 not allow extra
// version 0 not allow other flag
return trace.SpanContext{}
}

// Clear all flags other than the trace-context supported sampling bit.
scc.TraceFlags = trace.TraceFlags(opts[0]) & trace.FlagsSampled // nolint:gosec // slice size already checked.
scc.TraceFlags = trace.TraceFlags(opts[0]) // nolint:gosec // slice size already checked.

// Ignore the error returned here. Failure to parse tracestate MUST NOT
// affect the parsing of traceparent according to the W3C tracecontext
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83 changes: 72 additions & 11 deletions propagation/trace_context_test.go
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Expand Up @@ -56,6 +56,42 @@ func TestExtractValidTraceContext(t *testing.T) {
Remote: true,
}),
},
{
name: "random",
header: http.Header{
traceparent: []string{"00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-02"},
},
sc: trace.NewSpanContext(trace.SpanContextConfig{
TraceID: traceID,
SpanID: spanID,
TraceFlags: trace.TraceFlags(0x02),
Remote: true,
}),
},
{
name: "sampled and random",
header: http.Header{
traceparent: []string{"00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-03"},
},
sc: trace.NewSpanContext(trace.SpanContextConfig{
TraceID: traceID,
SpanID: spanID,
TraceFlags: trace.TraceFlags(0x03),
Remote: true,
}),
},
{
name: "additional flag bits preserved",
header: http.Header{
traceparent: []string{"00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-09"},
},
sc: trace.NewSpanContext(trace.SpanContextConfig{
TraceID: traceID,
SpanID: spanID,
TraceFlags: trace.TraceFlags(0x09),
Remote: true,
}),
},
{
name: "valid tracestate",
header: http.Header{
Expand Down Expand Up @@ -112,7 +148,7 @@ func TestExtractValidTraceContext(t *testing.T) {
sc: trace.NewSpanContext(trace.SpanContextConfig{
TraceID: traceID,
SpanID: spanID,
TraceFlags: trace.FlagsSampled,
TraceFlags: trace.TraceFlags(0x09),
Remote: true,
}),
},
Expand All @@ -122,9 +158,10 @@ func TestExtractValidTraceContext(t *testing.T) {
traceparent: []string{"02-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-08"},
},
sc: trace.NewSpanContext(trace.SpanContextConfig{
TraceID: traceID,
SpanID: spanID,
Remote: true,
TraceID: traceID,
SpanID: spanID,
TraceFlags: trace.TraceFlags(0x08),
Remote: true,
}),
},
{
Expand Down Expand Up @@ -228,10 +265,6 @@ func TestExtractInvalidTraceContextFromHTTPReq(t *testing.T) {
name: "zero trace ID and span ID",
header: "00-00000000000000000000000000000000-0000000000000000-01",
},
{
name: "trace-flag unused bits set",
header: "00-ab000000000000000000000000000000-cd00000000000000-09",
},
{
name: "missing options",
header: "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7",
Expand All @@ -240,6 +273,10 @@ func TestExtractInvalidTraceContextFromHTTPReq(t *testing.T) {
name: "empty options",
header: "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-",
},
{
name: "version 0 with extra content",
header: "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01-extra",
},
}

empty := trace.SpanContext{}
Expand Down Expand Up @@ -287,14 +324,38 @@ func TestInjectValidTraceContext(t *testing.T) {
}),
},
{
name: "unsupported trace flag bits dropped",
name: "trace flag bits preserved",
header: http.Header{
traceparent: []string{"00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01"},
traceparent: []string{"00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-ff"},
},
sc: trace.NewSpanContext(trace.SpanContextConfig{
TraceID: traceID,
SpanID: spanID,
TraceFlags: trace.TraceFlags(0xff),
Remote: true,
}),
},
{
name: "random",
header: http.Header{
traceparent: []string{"00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-02"},
},
sc: trace.NewSpanContext(trace.SpanContextConfig{
TraceID: traceID,
SpanID: spanID,
TraceFlags: trace.TraceFlags(0x02),
Remote: true,
}),
},
{
name: "sampled and random",
header: http.Header{
traceparent: []string{"00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-03"},
},
sc: trace.NewSpanContext(trace.SpanContextConfig{
TraceID: traceID,
SpanID: spanID,
TraceFlags: 0xff,
TraceFlags: trace.TraceFlags(0x03),
Remote: true,
}),
},
Expand Down