contrib/slog: clone record before calling Add

contrib/log/slog/slog.go

@@ -42,6 +42,7 @@ type handler struct {
 func (h *handler) Handle(ctx context.Context, rec slog.Record) error {
  span, ok := tracer.SpanFromContext(ctx)
  if ok {
+ rec = rec.Clone()
  rec.Add(
  slog.Uint64(ext.LogKeyTraceID, span.Context().TraceID()),
  slog.Uint64(ext.LogKeySpanID, span.Context().SpanID()),

contrib/log/slog/slog_test.go

@@ -9,6 +9,7 @@ import (
  "bytes"
  "context"
  "encoding/json"
+ "io"
  "log/slog"
  "strings"
  "testing"
@@ -74,3 +75,47 @@ func TestWrapHandler(t *testing.T) {
  return WrapHandler(slog.NewJSONHandler(b, nil))
  })
 }
+
+// TestRecordClone is a regression test for https://github.com/DataDog/dd-trace-go/issues/2918.
+func TestRecordClone(t *testing.T) {
+ // start a new span
+ span, ctx := tracer.StartSpanFromContext(context.Background(), "test")
+ defer span.Finish()
+
+ r := slog.Record{}
+ gate := func() {
+ // Calling Handle below should not overwrite this value
+ r.Add("sentinel-key", "sentinel-value")
+ }
+ h := handlerGate{gate, WrapHandler(slog.NewJSONHandler(io.Discard, nil))}
+ // Up to slog.nAttrsInline (5) attributes are stored in the front array of
+ // the record. Make sure to add more records than that to trigger the bug.
+ for i := 0; i < 5*10; i++ {
+ r.Add("i", i)
+ }
+ h.Handle(ctx, r)
+
+ var foundSentinel bool
+ r.Attrs(func(a slog.Attr) bool {
+ if a.Key == "sentinel-key" {
+ foundSentinel = true
+ return false
+ }
+ return true
+ })
+ assert.True(t, foundSentinel)
+}
+
+// handlerGate calls a gate function before calling the underlying handler. This
+// allows simulating a concurrent modification of the record that happens after
+// Handle is called (and the record has been copied), but before the back array
+// of the Record is written to.
+type handlerGate struct {
+ gate func()
+ slog.Handler
+}
+
+func (h handlerGate) Handle(ctx context.Context, r slog.Record) {
+ h.gate()
+ h.Handler.Handle(ctx, r)
+}