Make etw package internal

internal/etw/eventdata.go

@@ -0,0 +1,22 @@
+package etw
+
+import (
+	"bytes"
+)
+
+// EventData maintains a buffer which builds up the data for an ETW event. It
+// needs to be paired with EventMetadata which describes the event.
+type EventData struct {
+	buffer bytes.Buffer
+}
+
+// NewEventData returns a new EventData with an empty buffer.
+func NewEventData() *EventData {
+	return &EventData{}
+}
+
+// AddString appends the data for a string to the end of the buffer.
+func (ed *EventData) AddString(data string) {
+	ed.buffer.Write([]byte(data))
+	ed.buffer.WriteByte(0)
+}