github.com/kstenerud/go-qrcode

go-qrcode

Package qrcode implements a QR Code encoder.

A QR Code is a matrix (two-dimensional) barcode. Arbitrary content may be encoded, with URLs being a popular choice :)

Each QR Code contains error recovery information to aid reading damaged or obscured codes. There are four levels of error recovery: Low, medium, high and highest. QR Codes with a higher recovery level are more robust to damage, at the cost of being physically larger.

Install

go get -u github.com/kstenerud/go-qrcode/...

A command-line tool qrcode will be built into $GOPATH/bin/.

Usage

import qrcode "github.com/kstenerud/go-qrcode"

• Create a 256x256 PNG image:

    var png []byte
    png, err := qrcode.Encode([]byte("https://example.org"), qrcode.Medium, 256)
  

• Create a 256x256 PNG image and write to a file:

    err := qrcode.WriteFile([]byte("https://example.org"), qrcode.Medium, 256, "qr.png")
  

• Create a 256x256 PNG image with custom colors and write to file:

    err := qrcode.WriteColorFile([]byte("https://example.org"), qrcode.Medium, 256, color.Black, color.White, "qr.png")
  

All examples use the qrcode.Medium error Recovery Level and create a fixed 256x256px size QR Code. The last function creates a white on black instead of black on white QR Code.

Important!

QR codes are only meant to support ISO 8859-1 text and a special kanji encoding! If you pass in UTF-8 text, it may not be decoded properly by a QR code scanner. Characters from the ASCII range (0x20-0x7e) will always work.

Documentation

Demoapp

http://go-qrcode.appspot.com

CLI

A command-line tool qrcode will be built into $GOPATH/bin/.

qrcode -- QR Code encoder in Go

Flags:
  -b int
        QR Code border size (default 4)
  -e int
        error recovery level: 0=lowest, 3=highest (default 3)
  -i    invert black and white
  -o string
        out PNG file prefix, empty for stdout
  -s int
        image size (pixel) (default 256)
  -t    print as text-art on stdout

Usage:
  1. Data is read from STDIN and used to generate the QR code.
     Default output is STDOUT.

     echo "hello world" | qrcode > out.png

  2. Pipe to imagemagick command "display" to display on any X server.

     echo "hello world" | qrcode | display

Maximum capacity

The maximum capacity of a QR Code varies according to the content encoded and the error recovery level. The maximum capacity is 2,953 bytes, 4,296 alphanumeric characters, 7,089 numeric digits, or a combination of these.

Borderless QR Codes

To aid QR Code reading software, QR codes have a built in whitespace border. To disable it completely, set the border size to 0.

Links

• http://en.wikipedia.org/wiki/QR_code
• ISO/IEC 18004:2006 - Main QR Code specification (approx CHF 198,00)
  
• https://github.com/qpliu/qrencode-go/ - alternative Go QR encoding library based on ZXing