snapshot of https://github.com/ThreeDotsLabs/watermill.git (master, 2026-09-15; blobs > 131072B omitted)

_examples/real-world-examples/exactly-once-delivery-counter/run.go

@@ -0,0 +1,173 @@
+package main
+
+import (
+	stdSQL "database/sql"
+	"fmt"
+	"net/http"
+	"os/exec"
+	"sync"
+	"time"
+
+	"github.com/cheggaaa/pb/v3"
+	"github.com/go-sql-driver/mysql"
+	"github.com/google/uuid"
+)
+
+const messagesCount = 5000
+
+// at these messages we will restart MySQL
+var restartMySQLAt = map[int]struct{}{
+	50:   {},
+	1000: {},
+	1500: {},
+	3000: {},
+}
+
+// at these messages we will restart counter worker
+var restartWorkerAt = map[int]struct{}{
+	100:  {},
+	1500: {},
+	1600: {},
+	3000: {},
+}
+
+const senderGoroutines = 5
+
+func main() {
+	db := createDB()
+	counterUUID := uuid.New().String()
+
+	wg := &sync.WaitGroup{}
+	wg.Add(messagesCount)
+
+	bar := pb.StartNew(messagesCount)
+
+	// sending value to sendCounter counter HTTP call
+	sendCounter := make(chan struct{}, 0)
+	go func() {
+		for i := 0; i < messagesCount; i++ {
+			sendCounter <- struct{}{}
+
+			// let's challenge exactly-once delivery a bit
+			// normally it should trigger re-delivery of the message
+			if _, ok := restartMySQLAt[i]; ok {
+				restartMySQL()
+			}
+			if _, ok := restartWorkerAt[i]; ok {
+				restartWorker()
+			}
+		}
+		close(sendCounter)
+	}()
+
+	for i := 0; i < senderGoroutines; i++ {
+		go func() {
+			for range sendCounter {
+				sendCountRequest(counterUUID)
+				wg.Done()
+				bar.Increment()
+			}
+		}()
+	}
+
+	wg.Wait()
+	bar.Finish()
+
+	timeout := time.Now().Add(time.Second * 30)
+
+	fmt.Println("checking counter with DB, expected count:", messagesCount)
+
+	matchedOnce := true
+
+	for {
+		if time.Now().After(timeout) {
+			fmt.Println("timeout")
+			break
+		}
+
+		dbCounterValue, err := getDbCounterValue(db, counterUUID)
+		if err != nil {
+			fmt.Println("err:", err)
+			continue
+		}
+
+		fmt.Println("db counter value", dbCounterValue)
+		if dbCounterValue == messagesCount {
+			if !matchedOnce {
+				// let's ensure that nothing new will arrive
+				matchedOnce = true
+				time.Sleep(time.Second * 2)
+				continue
+			} else {
+				fmt.Println("expected counter value is matching DB value")
+				break
+			}
+		}
+
+		time.Sleep(time.Second)
+	}
+}
+
+func getDbCounterValue(db *stdSQL.DB, counterUUID string) (int, error) {
+	var dbCounterValue int
+	row := db.QueryRow("SELECT value from counter WHERE id = ?", counterUUID)
+
+	if err := row.Scan(&dbCounterValue); err != nil {
+		return 0, err
+	}
+
+	return dbCounterValue, nil
+}
+
+func restartWorker() {
+	fmt.Println("restarting worker")
+	err := exec.Command("docker-compose", "restart", "worker").Run()
+	if err != nil {
+		fmt.Println("restarting worker failed", err)
+	}
+}
+
+func restartMySQL() {
+	fmt.Println("restarting mysql")
+	err := exec.Command("docker-compose", "restart", "mysql").Run()
+	if err != nil {
+		fmt.Println("restarting mysql failed", err)
+	}
+}
+
+func sendCountRequest(counterUUID string) {
+    for {
+        resp, err := http.Post("http://localhost:8080/count/"+counterUUID, "", nil)
+        if err != nil {
+            time.Sleep(100 * time.Millisecond)
+            continue
+        }
+        resp.Body.Close()
+
+        if resp.StatusCode == http.StatusNoContent {
+            break
+        }
+
+        time.Sleep(100 * time.Millisecond)
+    }
+}
+
+func createDB() *stdSQL.DB {
+	conf := mysql.NewConfig()
+	conf.Net = "tcp"
+	conf.User = "root"
+	conf.Addr = "localhost"
+	conf.DBName = "example"
+
+	db, err := stdSQL.Open("mysql", conf.FormatDSN())
+	if err != nil {
+		panic(err)
+	}
+
+	err = db.Ping()
+	if err != nil {
+		panic(err)
+	}
+
+	return db
+}