1#!/bin/sh -efu
2
3fatal() {
4	echo "$*" >&2
5	exit 1
6}
7
8pkg="$1"
9[ -n "$pkg" ] && [ -e "$pkg" ] ||
10	fatal "No package supplied"
11
12_dd() {
13	local o="$1"; shift
14	dd if="$pkg" skip="$o" iflag=skip_bytes status=none $*
15}
16
17calcsize() {
18	offset=$(($1 + 8))
19
20	local i b b0 b1 b2 b3 b4 b5 b6 b7
21
22	i=0
23	while [ $i -lt 8 ]; do
24		b="$(_dd $(($offset + $i)) bs=1 count=1)"
25		[ -z "$b" ] &&
26			b="0" ||
27			b="$(exec printf '%u\n' "'$b")"
28		eval "b$i=\$b"
29		i=$(($i + 1))
30	done
31
32	rsize=$((8 + ((($b0 << 24) + ($b1 << 16) + ($b2 << 8) + $b3) << 4) + ($b4 << 24) + ($b5 << 16) + ($b6 << 8) + $b7))
33	offset=$(($offset + $rsize))
34}
35
36case "$(_dd 0 bs=8 count=1)" in
37	"$(printf '\355\253\356\333')"*) ;; # '\xed\xab\xee\xdb'
38	*) fatal "File doesn't look like rpm: $pkg" ;;
39esac
40
41calcsize 96
42sigsize=$rsize
43
44calcsize $(($offset + (8 - ($sigsize % 8)) % 8))
45hdrsize=$rsize
46
47case "$(_dd $offset bs=3 count=1)" in
48	"$(printf '\102\132')"*) _dd $offset | bunzip2 ;; # '\x42\x5a'
49	"$(printf '\037\213')"*) _dd $offset | gunzip  ;; # '\x1f\x8b'
50	"$(printf '\375\067')"*) _dd $offset | xzcat   ;; # '\xfd\x37'
51	"$(printf '\135\000')"*) _dd $offset | unlzma  ;; # '\x5d\x00'
52	"$(printf '\050\265')"*) _dd $offset | unzstd  ;; # '\x28\xb5'
53	*) fatal "Unrecognized rpm file: $pkg" ;;
54esac
55