Copy spans from memory store, fixes #2719

Copying allows spans to be freely modified by adjusters and any other code
without accidentally altering what is stored in the in-memory store itself.

plugin/storage/memory/memory.go

@@ -170,11 +170,37 @@ func (m *Store) GetTrace(ctx context.Context, traceID model.TraceID) (*model.Tra
 // Spans may still be added to traces after they are returned to user code, so make copies.
 func (m *Store) copyTrace(trace *model.Trace) *model.Trace {
 	return &model.Trace{
-		Spans:    append([]*model.Span(nil), trace.Spans...),
+		Spans:    m.copySpans(trace),
 		Warnings: append([]string(nil), trace.Warnings...),
 	}
 }
 
+func (m *Store) copySpans(trace *model.Trace) []*model.Span {
+	spans := make([]*model.Span, len(trace.Spans))
+	for i := range trace.Spans {
+		spans[i] = m.copySpan(trace.Spans[i])
+	}
+	return spans
+}
+
+// Copy static span attributes and discard the ones that can be altered outside of the store.
+func (m *Store) copySpan(span *model.Span) *model.Span {
+	return &model.Span{
+		TraceID:       span.TraceID,
+		SpanID:        span.SpanID,
+		OperationName: span.OperationName,
+		References:    span.References,
+		Flags:         span.Flags,
+		StartTime:     span.StartTime,
+		Duration:      span.Duration,
+		Tags:          span.Tags,
+		Logs:          span.Logs,
+		Process:       span.Process,
+		ProcessID:     span.ProcessID,
+		Warnings:      []string(nil),
+	}
+}
+
 // GetServices returns a list of all known services
 func (m *Store) GetServices(ctx context.Context) ([]string, error) {
 	m.RLock()

plugin/storage/memory/memory_test.go

@@ -210,6 +210,24 @@ func TestStoreGetTraceSuccess(t *testing.T) {
 	})
 }
 
+func TestStoreGetAndMutateTrace(t *testing.T) {
+	withPopulatedMemoryStore(func(store *Store) {
+		trace, err := store.GetTrace(context.Background(), testingSpan.TraceID)
+		assert.NoError(t, err)
+		assert.Len(t, trace.Spans, 1)
+		assert.Equal(t, testingSpan, trace.Spans[0])
+		assert.Len(t, trace.Spans[0].Warnings, 0)
+
+		trace.Spans[0].Warnings = append(trace.Spans[0].Warnings, "the end is near")
+
+		trace, err = store.GetTrace(context.Background(), testingSpan.TraceID)
+		assert.NoError(t, err)
+		assert.Len(t, trace.Spans, 1)
+		assert.Equal(t, testingSpan, trace.Spans[0])
+		assert.Len(t, trace.Spans[0].Warnings, 0)
+	})
+}
+
 func TestStoreGetTraceFailure(t *testing.T) {
 	withPopulatedMemoryStore(func(store *Store) {
 		trace, err := store.GetTrace(context.Background(), model.TraceID{})