main.go

package main

import (
	"database/sql"
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"strconv"
	"time"

	"github.com/go-sql-driver/mysql"
)

var (
	username, password, host, port string
	timeout                        int
)

func init() {
	username = getenv("USERNAME", "root")
	password = getenv("PASSWORD", "")
	host = getenv("HOST", "mysql")
	port = getenv("PORT", "3306")

	var err error
	timeout, err = strconv.Atoi(getenv("TIMEOUT", "60"))
	if err != nil {
		timeout = 60
	}

	mysql.SetLogger(log.New(ioutil.Discard, "[mysql] ", log.Ldate|log.Ltime|log.Lshortfile))
}

func main() {
	db, err := sql.Open("mysql", fmt.Sprintf("%s:%s@tcp(%s:%s)/", username, password, host, port))
	if err != nil {
		fmt.Printf("Unexpected error: %s\n", err)
		os.Exit(1)
	}
	defer db.Close()

	t := 1
	for t < timeout {
		t += 1

		err = db.Ping()
		if err != nil {
			switch err.(type) {
			case *mysql.MySQLError:
			default:
				fmt.Print(".")
				time.Sleep(1 * time.Second)
				continue
			}
		}
		fmt.Printf("Connected.\n")
		os.Exit(0)
	}

	fmt.Printf("\nOperation timed out in %d seconds.\n", timeout)
	os.Exit(1)
}

func getenv(key, fallback string) string {
	value := os.Getenv(key)
	if len(value) == 0 {
		return fallback
	}
	return value
}