Golang : How to generate QR codes?

In this short tutorial, we will learn how to generate QR codes with the https://godoc.org/code.google.com/p/rsc/qr package. QR codes generation has many applications in the real world and the adoption is growing worldwide, especially on the online security and mobile application side. For mobile devices... beside keying data manually into the mobile phone, scanning QR code is the next most popular form of capturing text data.

Generating QR codes is pretty easy and straight forward with the https://godoc.org/code.google.com/p/rsc/qr package. Without much further ado, here is an example of generating QR code in Golang.

 package main

 import (
 "bytes"
 "code.google.com/p/rsc/qr"
 "crypto/rand"
 "fmt"
 "image"
 "image/png"
 "os"
 "runtime"
 )

 func randStr(strSize int, randType string) string {

 var dictionary string

 if randType == "alphanum" {
 dictionary = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
 }

 if randType == "alpha" {
 dictionary = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
 }

 if randType == "number" {
 dictionary = "0123456789"
 }

 var bytes = make([]byte, strSize)
 rand.Read(bytes)
 for k, v := range bytes {
 bytes[k] = dictionary[v%byte(len(dictionary))]
 }
 return string(bytes)
 }

 func main() {

 // maximize CPU usage for maximum performance
 runtime.GOMAXPROCS(runtime.NumCPU())

 // generate a random string - preferably 6 or 8 characters
 randomStr := randStr(6, "alphanum")
 fmt.Println(randomStr)

 // generate the link or any data you want to
 // encode into QR codes
 // in this example, we use an example of making purchase by QR code.
 // Replace the stuff2buy with yours.

 stuff2buy := "stuffpurchaseby?userid=" + randomStr + "&issuer=SomeBigSuperMarket"

 // Encode stuff2buy to QR codes
 // qr.H = 65% redundant level
 // see https://godoc.org/code.google.com/p/rsc/qr#Level

 code, err := qr.Encode(stuff2buy, qr.H)

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 imgByte := code.PNG()

 // convert byte to image for saving to file
 img, _, _ := image.Decode(bytes.NewReader(imgByte))

 //save the imgByte to file
 out, err := os.Create("./QRImg.png")

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 err = png.Encode(out, img)

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 // everything ok
 fmt.Println("QR code generated and saved to QRimg1.png")

 }

Sample output :

NOTE : The QR codes generated by this tutorial is not compatible with Google Authenticator. If you are looking to generate QR codes for two factors authentication purpose with Google Authenticator, you need to use follow the URI format specify in https://github.com/google/google-authenticator/wiki/Key-Uri-Format to generate the QR codes.

See : QR codes for Google Authenticator tutorial

References :

http://blog.gopheracademy.com/advent-2013/day-21-two-factor-auth/

https://godoc.org/code.google.com/p/rsc/qr