goreplay middleware that adds a query string to a URL

gor-mw.go

package main

import (
	"bufio"
	"bytes"
	"encoding/hex"
	"log"
	"os"
	"strconv"
	"time"

	"github.com/buger/goreplay/proto"
)

func main() {
	s := bufio.NewScanner(os.Stdin)
	for s.Scan() {
		encoded := s.Bytes()
		buf := make([]byte, len(encoded)/2)
		hex.Decode(buf, encoded)

		process(buf)
	}
	if err := s.Err(); err != nil {
		log.Fatal(err)
	}
}

func process(buf []byte) {
	// First byte indicate payload type, possible values:
	//  1 - Request
	//  2 - Response
	//  3 - ReplayedResponse
	payloadtype := buf[0]
	headersize := bytes.IndexByte(buf, '\n') + 1
	payload := buf[headersize:]

	switch payloadtype {
	case '1': // Request
		// Unix timestamp is unique enough for us.
		id := strconv.FormatInt(time.Now().UnixNano(), 10)
		payload = proto.SetPathParam(payload, []byte("_from"), []byte(id))
		buf = append(buf[:headersize], payload...)
		os.Stdout.Write(encode(buf))
	case '2': // Original response
	case '3': // Replayed response
	}
}

func encode(buf []byte) []byte {
	dst := make([]byte, len(buf)*2+1)
	hex.Encode(dst, buf)
	dst[len(dst)-1] = '\n'
	return dst
}