#!/bin/sh

set -eu

usage()
{
	echo "Usage: $(basename "$0") [-v] <initramfs file> <directory>"
}

# Extract a compressed cpio archive
xcpio()
{
	archive="$1"
	dir="$2"
	shift 2

	if zcat -t "$archive" >/dev/null 2>&1 ; then
		zcat "$archive"
	elif zstd -q -c -t "$archive" >/dev/null 2>&1 ; then
		zstd -q -c -d "$archive"
	elif xzcat -t "$archive" >/dev/null 2>&1 ; then
		xzcat "$archive"
	elif lz4cat -t < "$archive" >/dev/null 2>&1 ; then
		lz4cat "$archive"
	elif bzip2 -t "$archive" >/dev/null 2>&1 ; then
		bzip2 -c -d "$archive"
	elif lzop -t "$archive" >/dev/null 2>&1 ; then
		lzop -c -d "$archive"
	# Ignoring other data, which may be garbage at the end of the file
	fi | (
		if [ -n "$dir" ]; then
			mkdir -p -- "$dir"
			cd -- "$dir"
		fi
		cpio "$@"
	)
}

# Read bytes out of a file, checking that they are valid hex digits
readhex()
{
	dd < "$1" bs=1 skip="$2" count="$3" 2> /dev/null | \
		LANG=C grep -E "^[0-9A-Fa-f]{$3}\$"
}

# Check for a zero byte in a file
checkzero()
{
	dd < "$1" bs=1 skip="$2" count=1 2> /dev/null | \
		LANG=C grep -q -z '^$'
}

# Split an initramfs into archives and call xcpio on each
splitinitramfs()
{
	initramfs="$1"
	dir="$2"
	shift 2

	# There may be a prepended uncompressed archive.  cpio
	# won't tell us the true size of this so we have to
	# parse the headers and padding ourselves.  This is
	# very roughly based on linux/lib/earlycpio.c
	offset=0
	while true; do
		if checkzero "$initramfs" $offset; then
			offset=$((offset + 4))
			continue
		fi
		magic="$(readhex "$initramfs" $offset 6)" || break
		test $magic = 070701 || test $magic = 070702 || break
		namesize=0x$(readhex "$initramfs" $((offset + 94)) 8)
		filesize=0x$(readhex "$initramfs" $((offset + 54)) 8)
		offset=$(((offset + 110)))
		offset=$(((offset + $namesize + 3) & ~3))
		offset=$(((offset + $filesize + 3) & ~3))
	done

	if [ $offset -ne 0 ]; then
		# uncompressed archive
		(
			if [ -n "$dir" ]; then
				mkdir -p -- "$dir/early"
				cd -- "$dir/early"
			fi
			cpio -i "$@"
		) < "$initramfs"

		# main archive
		subarchive=$(mktemp ${TMPDIR:-/var/tmp}/unmkinitramfs_XXXXXX)
		trap "rm -f '$subarchive'" EXIT
		dd < "$initramfs" bs="$offset" skip=1 2> /dev/null \
			> $subarchive
		xcpio "$subarchive" "${dir:+$dir/main}" -i "$@"
	else
		xcpio "$initramfs" "$dir" -i "$@"
	fi
}

OPTIONS=`getopt -o hv --long help,list,verbose -n "$0" -- "$@"`
# Check for non-GNU getopt
if [ $? != 0 ] ; then echo "W: non-GNU getopt" >&2 ; exit 1 ; fi

cpio_opts="--preserve-modification-time --no-absolute-filenames --quiet"
expected_args=2
eval set -- "$OPTIONS"

while true; do
	case "$1" in
        -h|--help)
		usage
		exit 0
	;;
	--list)
		# For lsinitramfs
		cpio_opts="${cpio_opts:+${cpio_opts} --list}"
		expected_args=1
		shift
	;;
	-v|--verbose)
		cpio_opts="${cpio_opts:+${cpio_opts} --verbose}"
		shift
	;;
	--)
		shift
		break
	;;
	*)
		echo "Internal error!" >&2
		exit 1
	esac
done

if [ $# -ne $expected_args ]; then
	usage
	exit 2
fi

splitinitramfs "$1" "${2:-}" $cpio_opts
