git ssb

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var alloc = Buffer.alloc
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var ZEROS = '0000000000000000000'
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var SEVENS = '7777777777777777777'
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var ZERO_OFFSET = '0'.charCodeAt(0)
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var USTAR = 'ustar\x0000'
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var MASK = parseInt('7777', 8)
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var clamp = function (index, len, defaultValue) {
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  if (typeof index !== 'number') return defaultValue
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  index = ~~index // Coerce to integer.
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  if (index >= len) return len
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  if (index >= 0) return index
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  index += len
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  if (index >= 0) return index
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  return 0
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}
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var toType = function (flag) {
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  switch (flag) {
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    case 0:
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      return 'file'
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    case 1:
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      return 'link'
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    case 2:
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      return 'symlink'
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    case 3:
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      return 'character-device'
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    case 4:
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      return 'block-device'
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    case 5:
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      return 'directory'
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    case 6:
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      return 'fifo'
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    case 7:
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      return 'contiguous-file'
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    case 72:
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      return 'pax-header'
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    case 55:
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      return 'pax-global-header'
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    case 27:
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      return 'gnu-long-link-path'
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    case 28:
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    case 30:
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      return 'gnu-long-path'
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  }
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  return null
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}
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var toTypeflag = function (flag) {
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  switch (flag) {
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    case 'file':
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      return 0
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    case 'link':
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      return 1
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    case 'symlink':
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      return 2
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    case 'character-device':
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      return 3
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    case 'block-device':
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      return 4
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    case 'directory':
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      return 5
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    case 'fifo':
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      return 6
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    case 'contiguous-file':
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      return 7
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    case 'pax-header':
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      return 72
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  }
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  return 0
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}
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var indexOf = function (block, num, offset, end) {
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  for (; offset < end; offset++) {
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    if (block[offset] === num) return offset
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  }
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  return end
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}
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var cksum = function (block) {
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  var sum = 8 * 32
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  for (var i = 0; i < 148; i++) sum += block[i]
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  for (var j = 156; j < 512; j++) sum += block[j]
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  return sum
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}
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var encodeOct = function (val, n) {
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  val = val.toString(8)
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  if (val.length > n) return SEVENS.slice(0, n) + ' '
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  else return ZEROS.slice(0, n - val.length) + val + ' '
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}
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/* Copied from the node-tar repo and modified to meet
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 * tar-stream coding standard.
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 *
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 * Source: https://github.com/npm/node-tar/blob/51b6627a1f357d2eb433e7378e5f05e83b7aa6cd/lib/header.js#L349
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 */
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function parse256 (buf) {
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  // first byte MUST be either 80 or FF
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  // 80 for positive, FF for 2's comp
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  var positive
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  if (buf[0] === 0x80) positive = true
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  else if (buf[0] === 0xFF) positive = false
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  else return null
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  // build up a base-256 tuple from the least sig to the highest
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  var zero = false
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  var tuple = []
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  for (var i = buf.length - 1; i > 0; i--) {
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    var byte = buf[i]
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    if (positive) tuple.push(byte)
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    else if (zero && byte === 0) tuple.push(0)
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    else if (zero) {
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      zero = false
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      tuple.push(0x100 - byte)
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    } else tuple.push(0xFF - byte)
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  }
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  var sum = 0
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  var l = tuple.length
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  for (i = 0; i < l; i++) {
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    sum += tuple[i] * Math.pow(256, i)
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  }
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  return positive ? sum : -1 * sum
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}
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var decodeOct = function (val, offset, length) {
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  val = val.slice(offset, offset + length)
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  offset = 0
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  // If prefixed with 0x80 then parse as a base-256 integer
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  if (val[offset] & 0x80) {
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    return parse256(val)
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  } else {
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    // Older versions of tar can prefix with spaces
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    while (offset < val.length && val[offset] === 32) offset++
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    var end = clamp(indexOf(val, 32, offset, val.length), val.length, val.length)
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    while (offset < end && val[offset] === 0) offset++
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    if (end === offset) return 0
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    return parseInt(val.slice(offset, end).toString(), 8)
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  }
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}
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var decodeStr = function (val, offset, length, encoding) {
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  return val.slice(offset, indexOf(val, 0, offset, offset + length)).toString(encoding)
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}
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var addLength = function (str) {
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  var len = Buffer.byteLength(str)
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  var digits = Math.floor(Math.log(len) / Math.log(10)) + 1
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  if (len + digits >= Math.pow(10, digits)) digits++
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  return (len + digits) + str
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}
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exports.decodeLongPath = function (buf, encoding) {
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  return decodeStr(buf, 0, buf.length, encoding)
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}
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exports.encodePax = function (opts) { // TODO: encode more stuff in pax
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  var result = ''
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  if (opts.name) result += addLength(' path=' + opts.name + '\n')
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  if (opts.linkname) result += addLength(' linkpath=' + opts.linkname + '\n')
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  var pax = opts.pax
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  if (pax) {
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    for (var key in pax) {
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      result += addLength(' ' + key + '=' + pax[key] + '\n')
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    }
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  }
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  return Buffer.from(result)
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}
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exports.decodePax = function (buf) {
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  var result = {}
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  while (buf.length) {
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    var i = 0
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    while (i < buf.length && buf[i] !== 32) i++
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    var len = parseInt(buf.slice(0, i).toString(), 10)
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    if (!len) return result
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    var b = buf.slice(i + 1, len - 1).toString()
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    var keyIndex = b.indexOf('=')
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    if (keyIndex === -1) return result
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    result[b.slice(0, keyIndex)] = b.slice(keyIndex + 1)
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    buf = buf.slice(len)
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  }
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  return result
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}
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exports.encode = function (opts) {
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  var buf = alloc(512)
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  var name = opts.name
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  var prefix = ''
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  if (opts.typeflag === 5 && name[name.length - 1] !== '/') name += '/'
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  if (Buffer.byteLength(name) !== name.length) return null // utf-8
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  while (Buffer.byteLength(name) > 100) {
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    var i = name.indexOf('/')
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    if (i === -1) return null
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    prefix += prefix ? '/' + name.slice(0, i) : name.slice(0, i)
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    name = name.slice(i + 1)
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  }
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  if (Buffer.byteLength(name) > 100 || Buffer.byteLength(prefix) > 155) return null
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  if (opts.linkname && Buffer.byteLength(opts.linkname) > 100) return null
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  buf.write(name)
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  buf.write(encodeOct(opts.mode & MASK, 6), 100)
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  buf.write(encodeOct(opts.uid, 6), 108)
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  buf.write(encodeOct(opts.gid, 6), 116)
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  buf.write(encodeOct(opts.size, 11), 124)
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  buf.write(encodeOct((opts.mtime.getTime() / 1000) | 0, 11), 136)
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  buf[156] = ZERO_OFFSET + toTypeflag(opts.type)
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  if (opts.linkname) buf.write(opts.linkname, 157)
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  buf.write(USTAR, 257)
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  if (opts.uname) buf.write(opts.uname, 265)
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  if (opts.gname) buf.write(opts.gname, 297)
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  buf.write(encodeOct(opts.devmajor || 0, 6), 329)
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  buf.write(encodeOct(opts.devminor || 0, 6), 337)
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  if (prefix) buf.write(prefix, 345)
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  buf.write(encodeOct(cksum(buf), 6), 148)
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  return buf
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}
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exports.decode = function (buf, filenameEncoding) {
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  var typeflag = buf[156] === 0 ? 0 : buf[156] - ZERO_OFFSET
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  var name = decodeStr(buf, 0, 100, filenameEncoding)
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  var mode = decodeOct(buf, 100, 8)
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  var uid = decodeOct(buf, 108, 8)
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  var gid = decodeOct(buf, 116, 8)
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  var size = decodeOct(buf, 124, 12)
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  var mtime = decodeOct(buf, 136, 12)
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  var type = toType(typeflag)
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  var linkname = buf[157] === 0 ? null : decodeStr(buf, 157, 100, filenameEncoding)
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  var uname = decodeStr(buf, 265, 32)
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  var gname = decodeStr(buf, 297, 32)
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  var devmajor = decodeOct(buf, 329, 8)
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  var devminor = decodeOct(buf, 337, 8)
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  if (buf[345]) name = decodeStr(buf, 345, 155, filenameEncoding) + '/' + name
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  // to support old tar versions that use trailing / to indicate dirs
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  if (typeflag === 0 && name && name[name.length - 1] === '/') typeflag = 5
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  var c = cksum(buf)
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  // checksum is still initial value if header was null.
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  if (c === 8 * 32) return null
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  // valid checksum
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  if (c !== decodeOct(buf, 148, 8)) throw new Error('Invalid tar header. Maybe the tar is corrupted or it needs to be gunzipped?')
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  return {
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    name: name,
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    mode: mode,
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    uid: uid,
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    gid: gid,
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    size: size,
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    mtime: new Date(1000 * mtime),
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    type: type,
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    linkname: linkname,
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    uname: uname,
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    gname: gname,
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    devmajor: devmajor,
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    devminor: devminor
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  }
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}
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