How to share mysql connection between http goroutines?

I'm a Go noob and can't find any complete examples of opening a mysql connection in Go and then sharing it among http handlers. Here is my code so far, how would I use the db connection that I opened in main() in my HomeHandler?

package main

import (
  "database/sql"
  "fmt"
  _ "github.com/go-sql-driver/mysql"
  "github.com/gorilla/mux"
  "log"
  "net/http"
)

func main() {

  fmt.Println("starting up")

  db, err := sql.Open("mysql", "root:@/mydb?charset=utf8")
  if err != nil {
  	log.Fatalf("Error opening database: %v", err)
  }

  db.SetMaxIdleConns(100)

  r := mux.NewRouter()
  r.HandleFunc("/", HomeHandler)

  http.Handle("/", r)
  http.ListenAndServe(":8080", nil)

}

func HomeHandler(w http.ResponseWriter, r *http.Request) {

  fmt.Fprintf(w, "home")

}

The database/sql package manages the connection pooling automatically for you.

sql.Open(..) returns a handle which represents a connection pool, not a single connection. The database/sql package automatically opens a new connection if all connections in the pool are busy.

Applied to your code this means, that you just need to share the db-handle and use it in the HTTP handlers:

package main

import (
	"database/sql"
	"fmt"
	"github.com/gorilla/mux"
	_ "github.com/go-sql-driver/mysql"
	"log"
	"net/http"
)

var db *sql.DB // global variable to share it between main and the HTTP handler

func main() {
	fmt.Println("starting up")

	var err error
	db, err = sql.Open("mysql", "root@unix(/tmp/mysql.sock)/mydb") // this does not really open a new connection
	if err != nil {
		log.Fatalf("Error on initializing database connection: %s", err.Error())
	}

	db.SetMaxIdleConns(100)

	err = db.Ping() // This DOES open a connection if necessary. This makes sure the database is accessible
	if err != nil {
		log.Fatalf("Error on opening database connection: %s", err.Error())
	}

	r := mux.NewRouter()
	r.HandleFunc("/", HomeHandler)

	http.Handle("/", r)
	http.ListenAndServe(":8080", nil)
}

func HomeHandler(w http.ResponseWriter, r *http.Request) {
	var msg string
	err := db.QueryRow("SELECT msg FROM hello WHERE page=?", "home").Scan(&msg)
	if err != nil {
		fmt.Fprintf(w, "Database Error!")
	} else {
		fmt.Fprintf(w, msg)
	}
}