find png in dump

find_png_in_dump.go

package main

import (
	"bufio"
	"flag"
	"fmt"
	"image/png"
	"io"
	"os"
	"strconv"
)

var fileName = flag.String("f", "", "filename")

var pngHeader = []byte{0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a}

func main() {
	flag.Parse()

	file, err := os.Open(*fileName)
	if err != nil {
		panic(err)
	}
	defer file.Close()

	r := bufio.NewReader(file)

	var fileCount int64 = 0

	for true {
		bval, err := r.ReadByte()
		if err == io.EOF {
			break
		}
		check(err)

		if bval == pngHeader[0] {
			// unread last byte and read full header bytes
			r.UnreadByte()
			nextBytes, _ := r.Peek(len(pngHeader))

			if !isPngHeader(nextBytes) {
				// not a png header ?
				// read byte again to continue
				r.ReadByte()
				continue
			}

			// ok we found a header, try to decode it.
			fmt.Println("Found png header, try to decode.")
			img, err := png.Decode(r)

			if err != nil {
				// can't decode, skip it.
				// the png.Decode reads some bytes
				// so we already p
				continue
			}

			fw, err := os.Create("test" + strconv.FormatInt(fileCount, 10) + ".png")
			// can't create new file ? theres something wrong. panic!
			check(err)
			defer fw.Close()
			png.Encode(fw, img)
			fileCount += 1
		}
	}

	fmt.Printf("done")
}

func isPngHeader(header []byte) bool {
	// easy header check for png
	return testEq(header, pngHeader)
}

func testEq(a, b []byte) bool {
	if len(a) != len(b) {
		return false
	}

	for i := range a {
		if a[i] != b[i] {
			return false
		}
	}

	return true
}

func check(err error) {
	if err != nil {
		panic(err)
	}
}