1 files changed, 108 insertions, 0 deletions
diff --git a/modules.d/99img-lib/img-lib.sh b/modules.d/99img-lib/img-lib.sh
new file mode 100755
index 0000000..4700832
--- /dev/null
+++ b/modules.d/99img-lib/img-lib.sh
@@ -0,0 +1,108 @@
+#!/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
+}