fixes issue where placeholder spans were not technically valid and so weren't showing in some backends (#5)

Thanks @davidlee992 for the contribution

Author: jamesmoessis

internal/ptraceutil/go.mod

@@ -1,6 +1,6 @@
 module github.com/atlassian-labs/atlassian-sampling-processor/internal/ptraceutil
 
-go 1.23.5
+go 1.23.6
 
 require (
 	github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatatest v0.115.0

pkg/processor/atlassiansamplingprocessor/go.mod

@@ -1,6 +1,6 @@
 module github.com/atlassian-labs/atlassian-sampling-processor/pkg/processor/atlassiansamplingprocessor
 
-go 1.23.5
+go 1.23.6
 
 require (
 	github.com/atlassian-labs/atlassian-sampling-processor/internal/ptraceutil v0.7.6

pkg/processor/atlassiansamplingprocessor/processor.go

@@ -2,6 +2,7 @@ package atlassiansamplingprocessor // import "github.com/atlassian-labs/atlassia
 
 import (
 	"context"
+	"crypto/rand"
 	"encoding/hex"
 	"fmt"
 	"sync"
@@ -416,9 +417,11 @@ func (asp *atlassianSamplingProcessor) releaseNotSampledTrace(ctx context.Contex
 		// Create a placeholder trace with a single span containing the decision policy name
 		notSampledTrace := ptrace.NewTraces()
 		rs := notSampledTrace.ResourceSpans().AppendEmpty()
+		rs.Resource().Attributes().PutStr("service.name", "not-sampled-dummy-service")
 		ss := rs.ScopeSpans().AppendEmpty()
 		span := ss.Spans().AppendEmpty()
 		span.SetTraceID(id)
+		span.SetSpanID(generateRandomSpanID())
 		span.SetName("TRACE NOT SAMPLED")
 		span.SetStartTimestamp(pcommon.NewTimestampFromTime(time.Now().Add(-time.Second)))
 		span.SetEndTimestamp(pcommon.NewTimestampFromTime(time.Now()))
@@ -572,3 +575,13 @@ func (asp *atlassianSamplingProcessor) reportTraceDataErr(ctx context.Context, e
 	asp.log.Error("failed to perform operation on TraceData", fields...)
 	asp.telemetry.ProcessorAtlassianSamplingInternalErrorDroppedSpans.Add(ctx, spanCount)
 }
+
+// To generate a random span ID for the placeholder trace
+func generateRandomSpanID() pcommon.SpanID {
+	var id [8]byte
+	_, err := rand.Read(id[:])
+	if err != nil {
+		panic("failed to generate random span ID: " + err.Error())
+	}
+	return id
+}

pkg/processor/atlassiansamplingprocessor/processor_test.go

@@ -1005,9 +1005,12 @@ func TestReleaseNotSampledTrace_EmitSingleSpan(t *testing.T) {
 	assert.Equal(t, 1, sink.SpanCount())
 	consumed := sink.AllTraces()
 	assert.Len(t, consumed, 1)
+	serviceName, _ := consumed[0].ResourceSpans().At(0).Resource().Attributes().Get("service.name")
 	consumedSpan := consumed[0].ResourceSpans().At(0).ScopeSpans().At(0).Spans().At(0)
+	assert.Equal(t, serviceName.Str(), "not-sampled-dummy-service")
 	assert.Equal(t, testTraceID, consumedSpan.TraceID())
 	assert.Equal(t, "TRACE NOT SAMPLED", consumedSpan.Name())
+	assert.NotEmpty(t, consumedSpan.SpanID())
 	pn, found := consumedSpan.Attributes().Get("sampling.policy")
 	assert.True(t, found)
 	assert.Equal(t, "test-policy", pn.Str())