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#!/bin/sh
# img-lib.sh: utilities for dealing with archives and filesystem images.
#
# TODO: identify/unpack rpm, deb, maybe others?
# super-simple "file" that only identifies archives.
# works with stdin if $1 is not set.
det_archive() {
# NOTE: internal echo -e works in ash and bash, but not dash
local bz xz gz zs
local headerblock
bz="BZh"
# shellcheck disable=SC3037
xz="$(/bin/echo -e '\xfd7zXZ')"
# shellcheck disable=SC3037
gz="$(/bin/echo -e '\x1f\x8b')"
# shellcheck disable=SC3037
zs="$(/bin/echo -e '\x28\xB5\x2F\xFD')"
headerblock="$(dd ${1:+if=$1} bs=262 count=1 2> /dev/null | tr -d '\0')"
case "$headerblock" in
$xz*) echo "xz" ;;
$gz*) echo "gzip" ;;
$bz*) echo "bzip2" ;;
$zs*) echo "zstd" ;;
07070*) echo "cpio" ;;
*ustar) echo "tar" ;;
esac
}
# determine filesystem type for a filesystem image
det_fs_img() {
local dev
dev=$(losetup --find --show "$1") rv=""
det_fs "$dev"
rv=$?
losetup -d "$dev"
return $rv
}
# unpack_archive ARCHIVE OUTDIR
# unpack a (possibly compressed) cpio/tar archive
unpack_archive() {
local img="$1" outdir="$2" archiver="" decompr=""
local ft
ft="$(det_archive "$img")"
case "$ft" in
xz | gzip | bzip2 | zstd) decompr="$ft -dc" ;;
cpio | tar) decompr="cat" ;;
*) return 1 ;;
esac
ft="$($decompr "$img" | det_archive)"
case "$ft" in
cpio) archiver="cpio -iumd" ;;
tar) archiver="tar -xf -" ;;
*) return 2 ;;
esac
mkdir -p "$outdir"
(
cd "$outdir" || exit
$decompr | $archiver 2> /dev/null
) < "$img"
}
# unpack_fs FSIMAGE OUTDIR
# unpack a filesystem image
unpack_fs() {
local img="$1" outdir="$2"
local mnt
mnt="$(mkuniqdir /tmp unpack_fs.)"
mount -o loop "$img" "$mnt" || {
rmdir "$mnt"
return 1
}
mkdir -p "$outdir"
outdir="$(
cd "$outdir" || exit
pwd
)"
copytree "$mnt" "$outdir"
umount "$mnt"
rmdir "$mnt"
}
# unpack an image file - compressed/uncompressed cpio/tar, filesystem, whatever
# unpack_img IMAGEFILE OUTDIR
unpack_img() {
local img="$1" outdir="$2"
[ -r "$img" ] || {
warn "can't read img!"
return 1
}
[ -n "$outdir" ] || {
warn "unpack_img: no output dir given"
return 1
}
if [ "$(det_archive "$img")" ]; then
unpack_archive "$@" || {
warn "can't unpack archive file!"
return 1
}
else
unpack_fs "$@" || {
warn "can't unpack filesystem image!"
return 1
}
fi
}
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