116 lines
2.1 KiB
Go
116 lines
2.1 KiB
Go
// Copyright (C) 2018 Marius Schellenberger
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package main
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import (
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"errors"
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"flag"
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"fmt"
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"image"
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"image/color"
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_ "image/gif"
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_ "image/jpeg"
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"image/png"
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"os"
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)
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func unseal(p image.Image) (b []byte) {
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rect := p.Bounds()
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for i := 0; i < rect.Max.Y; i++ {
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for j := 0; j < rect.Max.X; j++ {
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pix := color.NRGBAModel.Convert(p.At(j, i)).(color.NRGBA)
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z := (pix.R << 6)
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z |= (pix.G << 6) >> 2
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z |= (pix.B << 6) >> 4
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z |= (pix.A << 6) >> 6
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if z == byte(0) {
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b = append(b, '\n')
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return
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}
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b = append(b, z)
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}
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}
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return
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}
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func seal(p image.Image, s []byte) (image.Image, error) {
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rect := p.Bounds()
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n := image.NewNRGBA(rect)
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c := 0
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max := (rect.Max.Y * rect.Max.X) - 1
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if len(s) > max {
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return nil, errors.New("not enough space in image")
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}
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for i := 0; i < rect.Max.Y; i++ {
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for j := 0; j < rect.Max.X; j++ {
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pix := color.NRGBAModel.Convert(p.At(j, i)).(color.NRGBA)
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if c < len(s) {
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r := (pix.R &^ 3) | (s[c] >> 6)
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g := (pix.G &^ 3) | (s[c]<<2)>>6
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b := (pix.B &^ 3) | (s[c]<<4)>>6
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a := (pix.A &^ 3) | (s[c]<<6)>>6
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n.Set(j, i, color.NRGBA{r, g, b, a})
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c++
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} else if c == len(s) {
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n.Set(j, i, color.NRGBA{
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pix.R &^ 3,
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pix.G &^ 3,
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pix.B &^ 3,
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pix.A &^ 3,
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})
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c++
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} else {
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n.Set(j, i, pix)
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}
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}
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}
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return n, nil
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}
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var (
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inFile string
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outFile string
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secret string
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)
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func errf(err error) {
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fmt.Fprintln(os.Stderr, err)
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os.Exit(1)
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}
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func main() {
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flag.StringVar(&inFile, "in", "-", "input file (default: stdin)")
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flag.StringVar(&outFile, "out", "-", "output file, always png (default: stdout)")
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flag.StringVar(&secret, "secret", "", "secret to hide")
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flag.Parse()
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var (
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err error
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in = os.Stdin
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out = os.Stdout
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)
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if inFile != "-" {
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in, err = os.Open(inFile)
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if err != nil {
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errf(err)
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}
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}
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p, _, err := image.Decode(in)
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if err != nil {
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errf(err)
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}
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if secret != "" {
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n, err := seal(p, []byte(secret))
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if err != nil {
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errf(err)
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}
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err = png.Encode(out, n)
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if err != nil {
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errf(err)
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}
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return
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}
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_, err = out.Write(unseal(p))
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if err != nil {
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errf(err)
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}
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}
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