traceparent.go

package main

import (
	cryptorand "crypto/rand"
	"encoding/binary"
	"fmt"
	"log"
	"math/rand"
	"time"
)

type TraceID [16]byte // go.elastic.co/apm/model.TraceID
type SpanID [8]byte   // go.elastic.co/apm/model.SpanID

// https://github.com/elastic/apm-agent-go/blob/dd3e8c593580e7b80a98b57e1cc6e017e56747b4/model/marshal.go#L666-L672
func hex(t []byte) []byte {
	const hextable = "0123456789abcdef"
	var buf []byte
	for _, v := range t {
		buf = append(buf, hextable[v>>4])
		buf = append(buf, hextable[v&0x0f])
	}
	return buf
}

// go.elastic.co/apm/module/apmhttp.FormatTraceparentHeader
func FormatTraceparentHeader(t TraceID, s SpanID) string {
	var options uint8
	return fmt.Sprintf("%02x-%032x-%016x-%02x", 0, t[:], s[:], options)
}

func main() {
	rand.Seed(time.Now().Unix())
	var transactionID SpanID
	if _, err := cryptorand.Read(transactionID[:]); err != nil {
		log.Fatal(err)
	}
	var traceID TraceID
	// https://github.com/elastic/apm-agent-go/blob/dd3e8c593580e7b80a98b57e1cc6e017e56747b4/transaction.go#L91-L92
	binary.LittleEndian.PutUint64(traceID[:8], rand.Uint64())
	binary.LittleEndian.PutUint64(traceID[8:], rand.Uint64())
	fmt.Println("TraceID:", string(hex(traceID[:])))
	fmt.Println("SpanID:", string(hex(transactionID[:])))
	fmt.Println("Traceparent:", FormatTraceparentHeader(traceID, transactionID))
}