mirror of
https://github.com/openwrt/openwrt.git
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72 lines
2.1 KiB
Bash
72 lines
2.1 KiB
Bash
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# SPDX-License-Identifier: GPL-2.0-or-later OR MIT
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# Example usage:
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#
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# {
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# tar_print_member "date.txt" "It's $(date +"%Y")"
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# tar_print_trailer
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# } > test.tar
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__tar_print_padding() {
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dd if=/dev/zero bs=1 count=$1 2>/dev/null
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}
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tar_print_member() {
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local name="$1"
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local content="$2"
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local mtime="${3:-$(date +%s)}"
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local mode=644
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local uid=0
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local gid=0
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local size=${#content}
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local type=0
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local link=""
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local username="root"
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local groupname="root"
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# 100 byte of padding bytes, using 0x01 since the shell does not tolerate null bytes in strings
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local pad=$'\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1\1'
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# validate name (strip leading slash if present)
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name=${name#/}
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# truncate string header values to their maximum length
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name=${name:0:100}
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link=${link:0:100}
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username=${username:0:32}
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groupname=${groupname:0:32}
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# construct header part before checksum field
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local header1="${name}${pad:0:$((100 - ${#name}))}"
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header1="${header1}$(printf '%07d\1' $mode)"
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header1="${header1}$(printf '%07o\1' $uid)"
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header1="${header1}$(printf '%07o\1' $gid)"
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header1="${header1}$(printf '%011o\1' $size)"
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header1="${header1}$(printf '%011o\1' $mtime)"
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# construct header part after checksum field
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local header2="$(printf '%d' $type)"
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header2="${header2}${link}${pad:0:$((100 - ${#link}))}"
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header2="${header2}ustar ${pad:0:1}"
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header2="${header2}${username}${pad:0:$((32 - ${#username}))}"
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header2="${header2}${groupname}${pad:0:$((32 - ${#groupname}))}"
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# calculate checksum over header fields
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local checksum=0
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for byte in $(printf '%s%8s%s' "$header1" "" "$header2" | tr '\1' '\0' | hexdump -ve '1/1 "%u "'); do
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checksum=$((checksum + byte))
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done
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# print member header, padded to 512 byte
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printf '%s%06o\0 %s' "$header1" $checksum "$header2" | tr '\1' '\0'
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__tar_print_padding 183
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# print content data, padded to multiple of 512 byte
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printf "%s" "$content"
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__tar_print_padding $((512 - (size % 512)))
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}
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tar_print_trailer() {
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__tar_print_padding 1024
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}
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