ddrescue_extract.go

// Binary ddrescue_extract reads finished blocks from a ddrescue-produced image.
package main

import (
	"bufio"
	"fmt"
	"io"
	"log"
	"os"
)

func main() {
	args := os.Args
	if len(args) != 3 {
		usage()
	}
	imageFilename := args[1]
	imageFile, err := os.Open(imageFilename)
	if err != nil {
		log.Fatalf("Can't open image file: %s", err)
	}
	defer imageFile.Close()

	mapFilename := args[2]
	mapFile, err := os.Open(mapFilename)
	if err != nil {
		log.Fatalf("Can't open mapfile: %s", err)
	}
	defer mapFile.Close()

	b := bufio.NewReader(mapFile)

	// skip status line
	readLine(b)

	for {
		line, err := readLine(b)
		if err == io.EOF {
			break
		}
		if err != nil {
			log.Fatalf("Error reading from mapfile %s: %v", mapFilename, err)
		}

		var start, nbytes uint64
		var status byte

		if n, err := fmt.Sscanf(line, "0x%x 0x%x %c", &start, &nbytes, &status); err != nil {
			log.Fatalf("Error scanning line %q: %v\nScanned items: %d", line, err, n)
		}

		if status != '+' {
			continue
		}

		log.Printf("Reading %d bytes at offset %d; status=%c\n", nbytes, start, status)

		imageFile.Seek(int64(start), os.SEEK_SET)
		if _, err := io.CopyN(os.Stdout, imageFile, int64(nbytes)); err != nil {
			log.Fatalf("Error copying block at %d: %v", start, err)
		}
	}
}

// readLine returns next line from the reader that isn't a comment (doesn't start with "#").
func readLine(b *bufio.Reader) (string, error) {
	for {
		line, err := b.ReadString('\n')
		if err != nil {
			return "", err
		}
		if line[0] != '#' {
			return line, nil
		}
	}
}

func usage() {
	fmt.Fprintln(os.Stderr, "Usage: ddrescue_extract <imagefile> <mapfile>")
	os.Exit(1)
}