etcd watcher with previous values included in updates

main.go

package main

import (
	"context"
	"log"
	"time"

	"github.com/google/uuid"
	etcd "go.etcd.io/etcd/client/v3"
)

func main() {
	client, err := etcd.New(etcd.Config{
		Endpoints:   []string{"127.0.0.1:2379"},
		DialTimeout: 5 * time.Second,
	})
	if err != nil {
		log.Fatal(err)
	}

	key := uuid.NewString()
	val := uuid.NewString()
	v, err := client.Put(context.Background(), key, val)
	if err != nil {
		log.Fatalf("unable to put: %s", err)
	}

	w := client.Watch(context.Background(), key)

	go func() {
		for v := range w {
			log.Printf("new value: %s", v.Events[0].Kv.Value)
		}
	}()

	// v, err := client.Get(context.Background(), key)
	// if err != nil {
	// 	log.Fatalf("unable to get: %s", err)
	// }
	// log.Printf("v: version: %d; value: %s", v.Kvs[0].Version, v.Kvs[0].Value)

	log.Printf("tx: %+v", v.OpResponse())

	newVal := uuid.NewString()
	tx, err := client.Txn(context.Background()).
		If(etcd.Compare(etcd.Value(key), "!=", newVal)).
		Then(etcd.OpPut(key, newVal, etcd.WithPrevKV())).
		Else(etcd.OpGet(key)).
		Commit()
	if err != nil {
		log.Fatalf("unable to commit: %s", err)
	}

	log.Printf("old: %s; new: %s", tx.Responses[0].GetResponsePut().PrevKv.Value, newVal)

	tx, err = client.Txn(context.Background()).
		If(etcd.Compare(etcd.Value(key), "!=", newVal)).
		Then(etcd.OpPut(key, newVal, etcd.WithPrevKV())).
		Else(etcd.OpGet(key, etcd.WithFirstKey()...)).
		Commit()
	if err != nil {
		log.Fatalf("unable to commit: %s", err)
	}

	log.Printf("should be same: %s", tx.Responses[0].GetResponseRange().Kvs[0].Value)

	// if _, err := client.Put(context.Background(), key, "foo"); err != nil {
	// 	log.Fatalf("unable to put: %s", err)
	// }

	time.Sleep(time.Second * 5)
}