2 files changed, 49 insertions, 43 deletions
diff --git a/src/internal/trace/parser_test.go b/src/internal/trace/parser_test.go
index daad3e3ad7..d6f580aed5 100644
--- a/src/internal/trace/parser_test.go
+++ b/src/internal/trace/parser_test.go
@@ -90,52 +90,13 @@ func TestParseVersion(t *testing.T) {
 
 func TestTimestampOverflow(t *testing.T) {
 	// Test that parser correctly handles large timestamps (long tracing).
-	w := newWriter()
-	w.emit(EvBatch, 0, 0)
-	w.emit(EvFrequency, 1e9)
+	w := NewWriter()
+	w.Emit(EvBatch, 0, 0)
+	w.Emit(EvFrequency, 1e9)
 	for ts := uint64(1); ts < 1e16; ts *= 2 {
-		w.emit(EvGoCreate, ts, ts, 0, 0)
+		w.Emit(EvGoCreate, ts, ts, 0, 0)
 	}
 	if _, err := Parse(w, ""); err != nil {
 		t.Fatalf("failed to parse: %v", err)
 	}
 }
-
-type writer struct {
-	bytes.Buffer
-}
-
-func newWriter() *writer {
-	w := new(writer)
-	w.Write([]byte("go 1.7 trace\x00\x00\x00\x00"))
-	return w
-}
-
-func (w *writer) emit(typ byte, args ...uint64) {
-	nargs := byte(len(args)) - 1
-	if nargs > 3 {
-		nargs = 3
-	}
-	buf := []byte{typ | nargs<<6}
-	if nargs == 3 {
-		buf = append(buf, 0)
-	}
-	for _, a := range args {
-		buf = appendVarint(buf, a)
-	}
-	if nargs == 3 {
-		buf[1] = byte(len(buf) - 2)
-	}
-	n, err := w.Write(buf)
-	if n != len(buf) || err != nil {
-		panic("failed to write")
-	}
-}
-
-func appendVarint(buf []byte, v uint64) []byte {
-	for ; v >= 0x80; v >>= 7 {
-		buf = append(buf, 0x80|byte(v))
-	}
-	buf = append(buf, byte(v))
-	return buf
-}
diff --git a/src/internal/trace/writer.go b/src/internal/trace/writer.go
new file mode 100644
index 0000000000..a481f50a7e
--- /dev/null
+++ b/src/internal/trace/writer.go
@@ -0,0 +1,45 @@
+package trace
+
+import "bytes"
+
+// Writer is a test trace writer.
+type Writer struct {
+	bytes.Buffer
+}
+
+func NewWriter() *Writer {
+	w := new(Writer)
+	w.Write([]byte("go 1.7 trace\x00\x00\x00\x00"))
+	return w
+}
+
+// Emit writes an event record to the trace.
+// See Event types for valid types and required arguments.
+func (w *Writer) Emit(typ byte, args ...uint64) {
+	nargs := byte(len(args)) - 1
+	if nargs > 3 {
+		nargs = 3
+	}
+	buf := []byte{typ | nargs<<6}
+	if nargs == 3 {
+		buf = append(buf, 0)
+	}
+	for _, a := range args {
+		buf = appendVarint(buf, a)
+	}
+	if nargs == 3 {
+		buf[1] = byte(len(buf) - 2)
+	}
+	n, err := w.Write(buf)
+	if n != len(buf) || err != nil {
+		panic("failed to write")
+	}
+}
+
+func appendVarint(buf []byte, v uint64) []byte {
+	for ; v >= 0x80; v >>= 7 {
+		buf = append(buf, 0x80|byte(v))
+	}
+	buf = append(buf, byte(v))
+	return buf
+}