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✏️ header.js

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'use strict'
// parse a 512-byte header block to a data object, or vice-versa
// encode returns `true` if a pax extended header is needed, because
// the data could not be faithfully encoded in a simple header.
// (Also, check header.needPax to see if it needs a pax header.)

const Buffer = require('./buffer.js')
const types = require('./types.js')
const pathModule = require('path').posix
const large = require('./large-numbers.js')

const SLURP = Symbol('slurp')
const TYPE = Symbol('type')

class Header {
  constructor (data, off, ex, gex) {
    this.cksumValid = false
    this.needPax = false
    this.nullBlock = false

this.block = null
    this.path = null
    this.mode = null
    this.uid = null
    this.gid = null
    this.size = null
    this.mtime = null
    this.cksum = null
    this[TYPE] = '0'
    this.linkpath = null
    this.uname = null
    this.gname = null
    this.devmaj = 0
    this.devmin = 0
    this.atime = null
    this.ctime = null

if (Buffer.isBuffer(data))
      this.decode(data, off || 0, ex, gex)
    else if (data)
      this.set(data)
  }

decode (buf, off, ex, gex) {
    if (!off)
      off = 0

if (!buf || !(buf.length >= off + 512))
      throw new Error('need 512 bytes for header')

this.path = decString(buf, off, 100)
    this.mode = decNumber(buf, off + 100, 8)
    this.uid = decNumber(buf, off + 108, 8)
    this.gid = decNumber(buf, off + 116, 8)
    this.size = decNumber(buf, off + 124, 12)
    this.mtime = decDate(buf, off + 136, 12)
    this.cksum = decNumber(buf, off + 148, 12)

// if we have extended or global extended headers, apply them now
    // See https://github.com/npm/node-tar/pull/187
    this[SLURP](ex)
    this[SLURP](gex, true)

// old tar versions marked dirs as a file with a trailing /
    this[TYPE] = decString(buf, off + 156, 1)
    if (this[TYPE] === '')
      this[TYPE] = '0'
    if (this[TYPE] === '0' && this.path.substr(-1) === '/')
      this[TYPE] = '5'

// tar implementations sometimes incorrectly put the stat(dir).size
    // as the size in the tarball, even though Directory entries are
    // not able to have any body at all.  In the very rare chance that
    // it actually DOES have a body, we weren't going to do anything with
    // it anyway, and it'll just be a warning about an invalid header.
    if (this[TYPE] === '5')
      this.size = 0

this.linkpath = decString(buf, off + 157, 100)
    if (buf.slice(off + 257, off + 265).toString() === 'ustar\u000000') {
      this.uname = decString(buf, off + 265, 32)
      this.gname = decString(buf, off + 297, 32)
      this.devmaj = decNumber(buf, off + 329, 8)
      this.devmin = decNumber(buf, off + 337, 8)
      if (buf[off + 475] !== 0) {
        // definitely a prefix, definitely >130 chars.
        const prefix = decString(buf, off + 345, 155)
        this.path = prefix + '/' + this.path
      } else {
        const prefix = decString(buf, off + 345, 130)
        if (prefix)
          this.path = prefix + '/' + this.path
        this.atime = decDate(buf, off + 476, 12)
        this.ctime = decDate(buf, off + 488, 12)
      }
    }

let sum = 8 * 0x20
    for (let i = off; i < off + 148; i++) {
      sum += buf[i]
    }
    for (let i = off + 156; i < off + 512; i++) {
      sum += buf[i]
    }
    this.cksumValid = sum === this.cksum
    if (this.cksum === null && sum === 8 * 0x20)
      this.nullBlock = true
  }

[SLURP] (ex, global) {
    for (let k in ex) {
      // we slurp in everything except for the path attribute in
      // a global extended header, because that's weird.
      if (ex[k] !== null && ex[k] !== undefined &&
          !(global && k === 'path'))
        this[k] = ex[k]
    }
  }

encode (buf, off) {
    if (!buf) {
      buf = this.block = Buffer.alloc(512)
      off = 0
    }

if (!off)
      off = 0

if (!(buf.length >= off + 512))
      throw new Error('need 512 bytes for header')

const prefixSize = this.ctime || this.atime ? 130 : 155
    const split = splitPrefix(this.path || '', prefixSize)
    const path = split[0]
    const prefix = split[1]
    this.needPax = split[2]

this.needPax = encString(buf, off, 100, path) || this.needPax
    this.needPax = encNumber(buf, off + 100, 8, this.mode) || this.needPax
    this.needPax = encNumber(buf, off + 108, 8, this.uid) || this.needPax
    this.needPax = encNumber(buf, off + 116, 8, this.gid) || this.needPax
    this.needPax = encNumber(buf, off + 124, 12, this.size) || this.needPax
    this.needPax = encDate(buf, off + 136, 12, this.mtime) || this.needPax
    buf[off + 156] = this[TYPE].charCodeAt(0)
    this.needPax = encString(buf, off + 157, 100, this.linkpath) || this.needPax
    buf.write('ustar\u000000', off + 257, 8)
    this.needPax = encString(buf, off + 265, 32, this.uname) || this.needPax
    this.needPax = encString(buf, off + 297, 32, this.gname) || this.needPax
    this.needPax = encNumber(buf, off + 329, 8, this.devmaj) || this.needPax
    this.needPax = encNumber(buf, off + 337, 8, this.devmin) || this.needPax
    this.needPax = encString(buf, off + 345, prefixSize, prefix) || this.needPax
    if (buf[off + 475] !== 0)
      this.needPax = encString(buf, off + 345, 155, prefix) || this.needPax
    else {
      this.needPax = encString(buf, off + 345, 130, prefix) || this.needPax
      this.needPax = encDate(buf, off + 476, 12, this.atime) || this.needPax
      this.needPax = encDate(buf, off + 488, 12, this.ctime) || this.needPax
    }

let sum = 8 * 0x20
    for (let i = off; i < off + 148; i++) {
      sum += buf[i]
    }
    for (let i = off + 156; i < off + 512; i++) {
      sum += buf[i]
    }
    this.cksum = sum
    encNumber(buf, off + 148, 8, this.cksum)
    this.cksumValid = true

return this.needPax
  }

set (data) {
    for (let i in data) {
      if (data[i] !== null && data[i] !== undefined)
        this[i] = data[i]
    }
  }

get type () {
    return types.name.get(this[TYPE]) || this[TYPE]
  }

get typeKey () {
    return this[TYPE]
  }

set type (type) {
    if (types.code.has(type))
      this[TYPE] = types.code.get(type)
    else
      this[TYPE] = type
  }
}

const splitPrefix = (p, prefixSize) => {
  const pathSize = 100
  let pp = p
  let prefix = ''
  let ret
  const root = pathModule.parse(p).root || '.'

if (Buffer.byteLength(pp) < pathSize)
    ret = [pp, prefix, false]
  else {
    // first set prefix to the dir, and path to the base
    prefix = pathModule.dirname(pp)
    pp = pathModule.basename(pp)

do {
      // both fit!
      if (Buffer.byteLength(pp) <= pathSize &&
          Buffer.byteLength(prefix) <= prefixSize)
        ret = [pp, prefix, false]

// prefix fits in prefix, but path doesn't fit in path
      else if (Buffer.byteLength(pp) > pathSize &&
          Buffer.byteLength(prefix) <= prefixSize)
        ret = [pp.substr(0, pathSize - 1), prefix, true]

else {
        // make path take a bit from prefix
        pp = pathModule.join(pathModule.basename(prefix), pp)
        prefix = pathModule.dirname(prefix)
      }
    } while (prefix !== root && !ret)

// at this point, found no resolution, just truncate
    if (!ret)
      ret = [p.substr(0, pathSize - 1), '', true]
  }
  return ret
}

const decString = (buf, off, size) =>
  buf.slice(off, off + size).toString('utf8').replace(/\0.*/, '')

const decDate = (buf, off, size) =>
  numToDate(decNumber(buf, off, size))

const numToDate = num => num === null ? null : new Date(num * 1000)

const decNumber = (buf, off, size) =>
  buf[off] & 0x80 ? large.parse(buf.slice(off, off + size))
    : decSmallNumber(buf, off, size)

const nanNull = value => isNaN(value) ? null : value

const decSmallNumber = (buf, off, size) =>
  nanNull(parseInt(
    buf.slice(off, off + size)
      .toString('utf8').replace(/\0.*$/, '').trim(), 8))

// the maximum encodable as a null-terminated octal, by field size
const MAXNUM = {
  12: 0o77777777777,
  8 : 0o7777777
}

const encNumber = (buf, off, size, number) =>
  number === null ? false :
  number > MAXNUM[size] || number < 0
    ? (large.encode(number, buf.slice(off, off + size)), true)
    : (encSmallNumber(buf, off, size, number), false)

const encSmallNumber = (buf, off, size, number) =>
  buf.write(octalString(number, size), off, size, 'ascii')

const octalString = (number, size) =>
  padOctal(Math.floor(number).toString(8), size)

const padOctal = (string, size) =>
  (string.length === size - 1 ? string
  : new Array(size - string.length - 1).join('0') + string + ' ') + '\0'

const encDate = (buf, off, size, date) =>
  date === null ? false :
  encNumber(buf, off, size, date.getTime() / 1000)

// enough to fill the longest string we've got
const NULLS = new Array(156).join('\0')
// pad with nulls, return true if it's longer or non-ascii
const encString = (buf, off, size, string) =>
  string === null ? false :
  (buf.write(string + NULLS, off, size, 'utf8'),
   string.length !== Buffer.byteLength(string) || string.length > size)

module.exports = Header

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✏️ header.js