Rearrange etw packages

pkg/etw/eventmetadata.go

@@ -0,0 +1,51 @@
+package etw
+
+import (
+	"bytes"
+	"encoding/binary"
+)
+
+// InType indicates the type of data contained in the ETW event.
+type InType byte
+
+// Various InType definitions for TraceLogging.
+const (
+	InTypeNull InType = iota
+	InTypeUnicodeString
+	InTypeAnsiString
+	InTypeInt8
+	InTypeUint8
+	InTypeInt16
+	InTypeUint16
+	InTypeInt32
+	InTypeUint32
+	InTypeInt64
+	InTypeUint64
+	InTypeFloat
+	InTypeDouble
+	InTypeBool32
+)
+
+// EventMetadata maintains a buffer which builds up the metadatadata for an ETW
+// event. It needs to be paired with EventData which describes the event.
+type EventMetadata struct {
+	buffer bytes.Buffer
+}
+
+// NewEventMetadata returns a new EventMetadata with event name and initial
+// metadata written to the buffer.
+func NewEventMetadata(name string) *EventMetadata {
+	em := EventMetadata{}
+	binary.Write(&em.buffer, binary.LittleEndian, uint16(0))    // Length placeholder
+	binary.Write(&em.buffer, binary.LittleEndian, byte(0))      // Tags
+	binary.Write(&em.buffer, binary.LittleEndian, []byte(name)) // Event name
+	binary.Write(&em.buffer, binary.LittleEndian, byte(0))      // Null terminator for name
+	return &em
+}
+
+// AddField appends a single field to the end of the event metadata buffer.
+func (em *EventMetadata) AddField(name string, inType InType) {
+	binary.Write(&em.buffer, binary.LittleEndian, []byte(name)) // Field name
+	binary.Write(&em.buffer, binary.LittleEndian, byte(0))      // Null terminator for name
+	binary.Write(&em.buffer, binary.LittleEndian, byte(inType)) // In type
+}