encode/decode binary data in bitmap

data2bmp.go

package main

import (
	"image"
	"os"
	"io/ioutil"
	"math"
	"golang.org/x/image/bmp"
	"log"
	"bytes"
	"fmt"
	"image/color"
)
func main(){
	if os.Args[1] == "e" {
		encode()
	}else{
		decode()
	}
}
func decode(){
	data,err:=ioutil.ReadFile(os.Args[2])
	if err != nil {
		panic(err)
	}
	outFile, err := os.Create("out.data")
	if err != nil {
		panic(err)
	}
	defer outFile.Close()

	img, err:=bmp.Decode(bytes.NewBuffer(data))
	if err != nil {
		panic(err)
	}
	rgba:=img.(*image.RGBA)
	wh:=img.Bounds().Max.X
	log.Println("width,height:",wh)

	bytesLen:=uint32(0)
	c:=rgba.RGBAAt(0,wh-1)
	bytesLen|=uint32(c.R)
	bytesLen|=uint32(c.G)<<8
	//log.Println(c.R,c.G)
	c=rgba.RGBAAt(1,wh-1)
	bytesLen|=uint32(c.R)<<16
	bytesLen|=uint32(c.G)<<24
	//log.Println(c.R,c.G)

	log.Println(fmt.Sprintf("bytes:0x%x",bytesLen))

	buf:=make([]byte, wh*wh*2)
	i:=0
	for y:=wh-1;y>=0;y--{
		for x:=2;x<wh;x++{
			c:=rgba.RGBAAt(x,y)
			buf[i]=c.R
			buf[i+1]=c.G
			i+=2
		}
	}
	_,err=outFile.Write(buf[:bytesLen])
	if err != nil {
		panic(err)
	}
}

func encode(){
	data,err:=ioutil.ReadFile(os.Args[2])
	if err != nil {
		panic(err)
	}
	outFile, err := os.Create("out.bmp")
	if err != nil {
		panic(err)
	}
	defer outFile.Close()

	realBytesLen := len(data)
	log.Println(fmt.Sprintf("bytes:0x%x",realBytesLen))
	dataPoints:=(realBytesLen+ 1) / 2 + 2//+1 for align +4 for length info
	sqrtF := math.Sqrt(float64(dataPoints))
	wh := int(sqrtF+1)
	log.Println("width,height:",wh, wh * wh * 2)
	data=append(data,make([]byte, wh*wh*2-realBytesLen)...)

	rgba := image.NewRGBA(image.Rect(0,0,wh,wh))
	log.Println("bmp bytes:", len(rgba.Pix))

	rgba.SetRGBA(0,wh-1,color.RGBA{
		R:uint8(realBytesLen&0xFF),
		G:uint8((realBytesLen&0xFF00)>>8),
	})
	rgba.SetRGBA(1,wh-1,color.RGBA{
		R:uint8((realBytesLen&0xFF0000)>>16),
		G:uint8((realBytesLen&0xFF000000)>>24),
	})

	i:=0
	for y:=wh-1;y>=0;y--{
		for x:=2;x<wh;x++{
			rgba.SetRGBA(x,y,color.RGBA{
				R:data[i],
				G:data[i+1],
			})
			i+=2
		}
	}

	err = bmp.Encode(outFile, rgba)
	if err != nil {
		panic(err)
	}
}