What tar standard are you aiming to adhere to?
On 2024-02-26 15:14, Rafał Miłecki wrote:
From: Jo-Philipp Wich <j...@mein.io>
This allows building uncompressed tar archives from shell scripts (and
compressing them later if needed)
Signed-off-by: Rafał Miłecki <ra...@milecki.pl>
---
package/base-files/files/lib/upgrade/tar.sh | 84 +++++++++++++++++++++
1 file changed, 84 insertions(+)
create mode 100644 package/base-files/files/lib/upgrade/tar.sh
diff --git a/package/base-files/files/lib/upgrade/tar.sh
b/package/base-files/files/lib/upgrade/tar.sh
new file mode 100644
index 0000000000..00057dd760
--- /dev/null
+++ b/package/base-files/files/lib/upgrade/tar.sh
@@ -0,0 +1,84 @@
No shebang?
+# SPDX-License-Identifier: GPL-2.0-or-later OR MIT
+
+__tar_print_padding() {
+ [ $1 -eq 0 ] || dd if=/dev/zero bs=$1 count=1 2>/dev/null
+}
+
+__tar_make_member() {
+ local name="$1"
+ local content="$2"
+ local username="$3"
+ local groupname="$4"
+ local mtime="$5"
+ local mode=644
+ local uid=0
+ local gid=0
+ local size=${#content}
+ local type=0
+ local link=""
+
recommend that they're ordered here same as struct order:
struct posix_header
{ /* byte offset */
char name[100]; /* 0 */
char mode[8]; /* 100 */
char uid[8]; /* 108 */
char gid[8]; /* 116 */
char size[12]; /* 124 */
char mtime[12]; /* 136 */
char chksum[8]; /* 148 */
char typeflag; /* 156 */
char linkname[100]; /* 157 */
char magic[6]; /* 257 */
char version[2]; /* 263 */
char uname[32]; /* 265 */
char gname[32]; /* 297 */
char devmajor[8]; /* 329 */
char devminor[8]; /* 337 */
char prefix[155]; /* 345 */
/* 500 */
};
+ # 100 byte of padding bytes, using 0x01 since the shell does not tolate
null bytes in strings
tolerate?
+ local
pad=$'\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1'
+
maybe try:
local pad=$(printf '\1%.0s' $(seq 100))
+ # validate name
+ if [ "${name:0:1}" = "/" ]; then
+ name="${name:1}"
+ fi
One liner:
name=${name#/}
+
+ # truncate string header values to their maximum length
+ name=${name:0:100}
+ link=${link:0:100}
+ username=${username:0:32}
+ groupname=${groupname:0:32}
+
+ # construct header part before checksum field
+ local header1="${name}${pad:0:$((100 - ${#name}))}"
+ header1="${header1}$(printf '%07d\1' $mode)"
+ header1="${header1}$(printf '%07o\1' $uid)"
+ header1="${header1}$(printf '%07o\1' $gid)"
+ header1="${header1}$(printf '%011o\1' $size)"
+ header1="${header1}$(printf '%011o\1' $mtime)"
+
+ # construct header part after checksum field
+ local header2="$(printf '%d' $type)"
+ header2="${header2}${link}${pad:0:$((100 - ${#link}))}"
+ header2="${header2}ustar ${pad:0:1}"
+ header2="${header2}${username}${pad:0:$((32 - ${#username}))}"
+ header2="${header2}${groupname}${pad:0:$((32 - ${#groupname}))}"
+
+ # calculate checksum over header fields
+ local checksum=0
+ for byte in $(printf '%s%8s%s' "$header1" "" "$header2" | tr '\1' '\0' | hexdump
-ve '1/1 "%u "'); do
+ checksum=$((checksum + byte))
+ done
+
+ # print member header, padded to 512 byte
+ printf '%s%06o\0 %s' "$header1" $checksum "$header2" | tr '\1' '\0'
+ __tar_print_padding 183
+
+ # print content data, padded to multiple of 512 byte
+ printf "%s" "$content"
+ __tar_print_padding $((512 - (size % 512)))
+}
+
+tar_make_member_from_file() {
+ local name="$1"
+ local username="$(ls -l "$1" | tr -s ' ' | cut -d ' ' -f 3)"
+ local groupname="$(ls -l "$1" | tr -s ' ' | cut -d ' ' -f 4)"
+
+ __tar_make_member "$name" "$(cat $name)" "$username" "$groupname" "$(date +%s -r
"$1")"
+}
+
+tar_make_member_inline() {
+ local name="$1"
+ local content="$2"
+ local username="${3:-root}"
+ local groupname="${4:-root}"
+ local mtime="${5:-$(date +%s)}"
+
+ __tar_make_member "$name" "$content" "$username" "$groupname" "$mtime"
+}
+
+tar_close() {
+ __tar_print_padding 1024
+}
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