From 19dbaff8dd051688c0acf1b6605bf13a7fe019bd Mon Sep 17 00:00:00 2001
From: Alexey Gladkov <gladkov.alexey@gmail.com>
Date: Fri, 9 Sep 2016 15:03:41 +0200
Subject: [PATCH] rpm2cpio.sh: refactoring to reduce extra dependencies

rpm2cpio.sh was refactored to minimize the use of external tools.

* after refactoring the utility requires to work: dd, printf, and unarchivers;
* add check that file passed as argument is a rpm-file;
* fix signatures of compressed data.

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
 scripts/rpm2cpio.sh | 92 ++++++++++++++++++++++++++++++-----------------------
 1 file changed, 52 insertions(+), 40 deletions(-)

diff --git a/scripts/rpm2cpio.sh b/scripts/rpm2cpio.sh
index cb93ead..f7d50fd 100755
--- a/scripts/rpm2cpio.sh
+++ b/scripts/rpm2cpio.sh
@@ -1,41 +1,53 @@
-#!/bin/sh
-
-# Prevent gawk >= 4.0.x from getting funny ideas wrt UTF in printf()
-LANG=C
-
-pkg=$1
-if [ "$pkg" = "" -o ! -e "$pkg" ]; then
-    echo "no package supplied" 1>&2
-   exit 1
-fi
-
-leadsize=96
-o=`expr $leadsize + 8`
-set `od -j $o -N 8 -t u1 $pkg`
-il=`expr 256 \* \( 256 \* \( 256 \* $2 + $3 \) + $4 \) + $5`
-dl=`expr 256 \* \( 256 \* \( 256 \* $6 + $7 \) + $8 \) + $9`
-# echo "sig il: $il dl: $dl"
-
-sigsize=`expr 8 + 16 \* $il + $dl`
-o=`expr $o + $sigsize + \( 8 - \( $sigsize \% 8 \) \) \% 8 + 8`
-set `od -j $o -N 8 -t u1 $pkg`
-il=`expr 256 \* \( 256 \* \( 256 \* $2 + $3 \) + $4 \) + $5`
-dl=`expr 256 \* \( 256 \* \( 256 \* $6 + $7 \) + $8 \) + $9`
-# echo "hdr il: $il dl: $dl"
-
-hdrsize=`expr 8 + 16 \* $il + $dl`
-o=`expr $o + $hdrsize`
-
-comp=`dd if="$pkg" ibs=$o skip=1 count=1 2>/dev/null \
-      | dd bs=3 count=1 2>/dev/null`
-
-gz="`echo . | awk '{ printf("%c%c", 0x1f, 0x8b); }'`"
-lzma="`echo . | awk '{ printf("%cLZ", 0xff); }'`"
-xz="`echo . | awk '{ printf("%c7z", 0xfd); }'`"
-case "$comp" in
-    BZh)      dd if="$pkg" ibs=$o skip=1 2>/dev/null | bunzip2 ;;
-    "$gz"*)   dd if="$pkg" ibs=$o skip=1 2>/dev/null | gunzip ;;
-    "$xz"*)   dd if="$pkg" ibs=$o skip=1 2>/dev/null | xzcat ;;
-    "$lzma"*) dd if="$pkg" ibs=$o skip=1 2>/dev/null | unlzma ;;
-    *)        echo "Unrecognized rpm file: $pkg"; exit 1 ;;
+#!/bin/sh -efu
+
+fatal() {
+	echo "$*" >&2
+	exit 1
+}
+
+pkg="$1"
+[ -n "$pkg" -a -e "$pkg" ] ||
+	fatal "No package supplied"
+
+_dd() {
+	local o="$1"; shift
+	dd if="$pkg" skip="$o" iflag=skip_bytes status=none $*
+}
+
+calcsize() {
+	offset=$(($1 + 8))
+
+	local i b b0 b1 b2 b3 b4 b5 b6 b7
+
+	i=0
+	while [ $i -lt 8 ]; do
+		b="$(_dd $(($offset + $i)) bs=1 count=1)"
+		[ -z "$b" ] &&
+			b="0" ||
+			b="$(exec printf '%u\n' "'$b")"
+		eval "b$i=\$b"
+		i=$(($i + 1))
+	done
+
+	rsize=$((8 + ((($b0 << 24) + ($b1 << 16) + ($b2 << 8) + $b3) << 4) + ($b4 << 24) + ($b5 << 16) + ($b6 << 8) + $b7))
+	offset=$(($offset + $rsize))
+}
+
+case "$(_dd 0 bs=8 count=1)" in
+	"$(printf '\355\253\356\333')"*) ;; # '\xed\xab\xee\xdb'
+	*) fatal "File doesn't look like rpm: $pkg" ;;
+esac
+
+calcsize 96
+sigsize=$rsize
+
+calcsize $(($offset + (8 - ($sigsize % 8)) % 8))
+hdrsize=$rsize
+
+case "$(_dd $offset bs=3 count=1)" in
+	"$(printf '\102\132')"*) _dd $offset | bunzip2 ;; # '\x42\x5a'
+	"$(printf '\037\213')"*) _dd $offset | gunzip  ;; # '\x1f\x8b'
+	"$(printf '\375\067')"*) _dd $offset | xzcat   ;; # '\xfd\x37'
+	"$(printf '\135\000')"*) _dd $offset | unlzma  ;; # '\x5d\x00'
+	*) fatal "Unrecognized rpm file: $pkg" ;;
 esac
-- 
2.10.1