usenet-indexer/tests/unit/probe/yenc.spec.ts

import { test } from '@japa/runner'
import yencode from 'yencode'
import {
  YencCrcError,
  YencError,
  crc32Hex,
  decodeSegment,
  parseYencMeta,
} from '#lib/yenc/index'

/** Builds an article body as a yEnc poster would send it. */
function article(
  data: Buffer,
  opts: { name: string; fileSize?: number; part?: number; total?: number; begin?: number; fileCrc?: string }
) {
  const fileSize = opts.fileSize ?? data.length
  const encoded = yencode.encode(data).toString('latin1')
  const lines: string[] = []
  if (opts.part) {
    lines.push(`=ybegin part=${opts.part} total=${opts.total} line=128 size=${fileSize} name=${opts.name}`)
    const begin = opts.begin ?? 1
    lines.push(`=ypart begin=${begin} end=${begin + data.length - 1}`)
    lines.push(encoded)
    const fileCrc = opts.fileCrc ? ` crc32=${opts.fileCrc}` : ''
    lines.push(`=yend size=${data.length} part=${opts.part} pcrc32=${crc32Hex(data)}${fileCrc}`)
  } else {
    lines.push(`=ybegin line=128 size=${fileSize} name=${opts.name}`)
    lines.push(encoded)
    lines.push(`=yend size=${data.length} crc32=${crc32Hex(data)}`)
  }
  return Buffer.from(lines.join('\r\n'), 'latin1')
}

function randomBytes(length: number, seed = 1) {
  const buf = Buffer.alloc(length)
  let x = seed
  for (let i = 0; i < length; i++) {
    x = (x * 1103515245 + 12345) & 0x7fffffff
    buf[i] = x & 0xff
  }
  return buf
}

test.group('yenc / parseYencMeta', () => {
  test('parses a multi-part header as seen on alt.binaries.test', ({ assert }) => {
    const body = Buffer.from(
      '=ybegin part=56 line=128 size=104857600 name=obrMkrDeLmbhaouwYO34.part08.rar\r\n' +
        '=ypart begin=21120001 end=21504000\r\n' +
        'xyz\r\n' +
        '=yend size=384000 part=56 pcrc32=B6339AFC',
      'latin1'
    )
    const meta = parseYencMeta(body)
    assert.deepEqual(meta.begin, {
      part: 56,
      total: undefined,
      line: 128,
      size: 104857600,
      name: 'obrMkrDeLmbhaouwYO34.part08.rar',
    })
    assert.deepEqual(meta.part, { begin: 21120001, end: 21504000 })
    assert.deepEqual(meta.end, { size: 384000, part: 56, pcrc32: 'b6339afc', crc32: undefined })
    assert.equal(body.subarray(meta.dataStart, meta.dataEnd).toString(), 'xyz')
  })

  test('keeps spaces and "=" in the filename', ({ assert }) => {
    const body = article(Buffer.from('hi'), { name: 'My File = v2 (final).nfo' })
    assert.equal(parseYencMeta(body).begin.name, 'My File = v2 (final).nfo')
  })

  test('ignores leading blank lines before =ybegin', ({ assert }) => {
    const body = Buffer.concat([Buffer.from('\r\n\r\n'), article(Buffer.from('hi'), { name: 'a.txt' })])
    assert.equal(parseYencMeta(body).begin.name, 'a.txt')
  })

  test('rejects bodies without yEnc markers', ({ assert }) => {
    assert.throws(() => parseYencMeta(Buffer.from('plain text\r\n')), /=ybegin/)
    assert.throws(() => parseYencMeta(Buffer.from('=ybegin line=128 size=2 name=a\r\nxx')), /=yend/)
  })
})

test.group('yenc / decodeSegment', () => {
  test('round-trips a single-part post and checks crc32', ({ assert }) => {
    const data = randomBytes(5000)
    const segment = decodeSegment(article(data, { name: 'single.bin' }))
    assert.isTrue(segment.data.equals(data))
    assert.equal(segment.offset, 0)
  })

  test('throws YencCrcError on a corrupted part', ({ assert }) => {
    const body = article(randomBytes(1000), { name: 'x.bin', part: 1, total: 1 })
    const index = body.indexOf('\r\n=ypart') + 60
    body[index] = body[index] === 0x41 ? 0x42 : 0x41
    assert.throws(() => decodeSegment(body), YencCrcError as any)
  })

  test('undoes NNTP dot-stuffing', ({ assert }) => {
    // Byte 4 encodes to "." (4 + 42 = 46). An unescaped leading "." is dot-stuffed to "..".
    const data = Buffer.from([4, 5, 6])
    const body = Buffer.from(
      `=ybegin line=128 size=3 name=dot.bin\r\n../0\r\n=yend size=3 crc32=${crc32Hex(data)}`,
      'latin1'
    )
    assert.isTrue(decodeSegment(body).data.equals(data))
    assert.throws(() => decodeSegment(body, { stripDots: false }), YencError as any)
  })
})