How to set up loop in database until it connects to mysqlDB - mysql

Question

I have init funcion in my golang program. I need to make it so the connection loops until it connects to database if it cant connect it idles then try's again and again for 60 seconds if it cant connect at end then it exist out. Also, have environment variable that overrides the default 60 seconds and user can put their own time for until it connects. I have my code below im looking and theres no solid solution in web .
var override string = os.Getenv("OVERRIDE")
func dsn() string {
return fmt.Sprintf("%s:%s#tcp(%s:%s)/%s", username, password, ipdb, portdb, dbName)
func init() {
var db, err = sql.Open("mysql", dsn())
if err != nil {
fmt.Println(err.Error())
} else {
fmt.Printf("Connection established to MYSQL server\n%s\n", dsn())
}
// Checking if table exists in database
rows, table_check := db.Query("select * from " + "Url" + ";")
if table_check == nil {
fmt.Println("\nTable exists in the Database")
count := 0
for rows.Next() {
count++
}
fmt.Printf("Number of records are %d \n", count)
} else {
fmt.Printf("\nTable does not exist in Database %s", table_check)
_, status := db.Exec("CREATE TABLE Url (LongUrl varchar(255),ShortUrl varchar(32));")
if status == nil {
fmt.Println("\n New table created in the Database")
} else {
fmt.Printf("\n The table was not created %s", status)
}
}
defer db.Close()
}
func main(){
......
}

Answer 1

You could use a switch with a timer channel.
For every 500 ms the connection is attempted, and if in 60 seconds the switch has not been resolved then the timeout channel exits the loop.
For example:
func main() {
doneCh := make(chan bool)
db, err := sql.Open("mysql", dsn())
if err != nil {
fmt.Errorf("Could not open connection: %w", err)
os.Exit(1)
}
// Start polling for connection
go func() {
ticker := time.NewTicker(500 * time.Millisecond)
timeoutTimer := time.After(time.Second * 60)
for {
select {
case <-timeoutTimer:
err = errors.New("connection to db timed out")
doneCh <- true
return
case <-ticker.C:
// Simulate some strange wait ... :)
if rand.Intn(10) == 2 {
err = db.Ping()
if err == nil {
doneCh <- true
return
}
}
fmt.Println("Retrying connection ... ")
}
}
}()
// Start waiting for timeout or success
fmt.Println("Waiting for DB connection ...")
<-doneCh
if err != nil {
fmt.Printf("Could not connect to DB: %v \n", err)
os.Exit(1)
}
defer db.Close()
// Do some work
fmt.Printf("Done! Do work now. %+v", db.Stats())
}
Note
Handle your errors as necessary. The sql.Ping() may return you some specific error which will indicate to you that you should retry.
Some errors may not be worth retrying with.
For timers and channels see:
Timers
Channels
Edit: Supposedly simpler way without channels and using a while loop
func main() {
db, err := sql.Open("mysql", dsn())
if err != nil {
fmt.Errorf("Could not open connection: %w", err)
os.Exit(1)
}
defer db.Close()
timeOut := time.Second * 60
idleDuration := time.Millisecond * 500
start := time.Now()
for time.Since(start) < timeOut {
if err = db.Ping(); err == nil {
break
}
time.Sleep(idleDuration)
fmt.Println("Retrying to connect ...")
}
if time.Since(start) > timeOut {
fmt.Printf("Could not connect to DB, timeout after %s", timeOut)
os.Exit(1)
}
// Do some work
fmt.Printf("Done! \nDo work now. %+v", db.Stats())
}