usenet-indexer/lib/probe/inspect.ts

import { createHash } from 'node:crypto'
import { decodeSegment, YencCrcError, YencError, type DecodedSegment } from '#lib/yenc/index'
import { isPar2, parsePar2 } from '#lib/par2/index'
import { parseRarHeaders } from '#lib/rar/index'
import { sniffContentType, type ContentType } from '#lib/content/index'

/** What one probed article showed (REBUILD.md, part 6; stored per release and kind). */
export interface Inspection {
  /** The file name in the yEnc header. */
  yencName: string
  /** The whole file's size, from the yEnc header. */
  size: number
  type: ContentType | null
  /** Names inside: an archive's entries or a par2 set's files, the largest first, at most MAX_NAMES. */
  names?: string[]
  /** How many entries or files there are in all. */
  entries?: number
  /** An archive with encrypted entries or headers. */
  passworded?: boolean
  /**
   * MD5 of the file's first 16 KiB (hex), when this article starts the file: what a par2 set's FileDesc
   * holds per file, so a renamed file is recognised by it (the par2 merge; app/services/par2_merger.ts).
   */
  hash16k?: string
  /** A par2 body's recovery set: every file it describes (not kept in release_inspections; par2_files). */
  par2?: { setId: string; files: { fileId: string; hash16k: string; length: number; name: string }[] }
}

const HASH_BYTES = 16 * 1024

/** The inspection's version: raised when inspect() changes, so probe_cache rows of an older one are read again. */
export const PROBE_VERSION = 2

/** Names kept per inspection: the catalog wants the content's name, not every volume's. */
export const MAX_NAMES = 8
const MAX_NAME_LENGTH = 200

/** Archive volumes, par2 volumes and split parts: names of the packaging, not the content. */
const PACKAGING = /\.(rar|r\d{2,3}|s\d{2}|\d{3}|7z(\.\d+)?|zip|z\d{2}|par2|sfv|nfo|nzb)$/i

/** Decodes a body; some tools declare a size that leaves out a header, the CRC still has to match. */
function decodeBody(body: Buffer): DecodedSegment {
  try {
    return decodeSegment(body)
  } catch (error) {
    if (!(error instanceof YencError) || error instanceof YencCrcError) throw error
    return decodeSegment(body, { lenientSize: true })
  }
}

function largestFirst(items: { name: string; size: number }[]): string[] {
  return items
    .sort((a, b) => b.size - a.size)
    .slice(0, MAX_NAMES)
    .map((i) => i.name.slice(0, MAX_NAME_LENGTH))
}

/** One article's body: its yEnc header, what the first bytes are, and for par2 and RAR what's inside. Throws when it isn't yEnc. */
export function inspect(body: Buffer): Inspection {
  const segment = decodeBody(body)
  const result: Inspection = { yencName: segment.meta.begin.name.slice(0, MAX_NAME_LENGTH), size: segment.meta.begin.size, type: sniffContentType(segment.data) }
  // The file's first 16 KiB, or all of a smaller file.
  if (segment.offset === 0 && (segment.data.length >= HASH_BYTES || segment.data.length === result.size)) {
    result.hash16k = createHash('md5').update(segment.data.subarray(0, HASH_BYTES)).digest('hex')
  }
  if (isPar2(segment.data)) {
    // An index file fits one article; what a larger one cut off is skipped by the parser.
    const set = parsePar2(segment.data)
    if (set) {
      result.entries = set.files.length
      result.names = largestFirst(set.files.map((f) => ({ name: f.name, size: f.length })))
      result.par2 = {
        setId: set.recoverySetId,
        files: set.files.map((f) => ({ fileId: f.fileId, hash16k: f.md5_16k, length: f.length, name: f.name.slice(0, MAX_NAME_LENGTH) })),
      }
    }
    return result
  }
  if (result.type === 'rar4' || result.type === 'rar5') {
    const info = parseRarHeaders(segment.data)
    if (info) {
      const files = info.entries.filter((e) => !e.directory)
      result.entries = files.length
      result.names = largestFirst(files.map((e) => ({ name: e.name, size: Number(e.size ?? 0) })))
      result.passworded = info.headersEncrypted || files.some((e) => e.encrypted)
    }
  }
  return result
}

/**
 * A release's best inner name from its inspections (by probe kind): the
 * largest named entry of an archive, else the largest file of a par2 set
 * that isn't packaging, else a lone file's yEnc name. Null when none says
 * more than the release's own name.
 */
export function innerName(inspections: { kind: string; result: Inspection }[], releaseName = ''): string | null {
  const of = (kind: string) => inspections.filter((i) => i.kind === kind).map((i) => i.result)
  const content = (kind: string) => of(kind).flatMap((i) => i.names ?? []).find((n) => !PACKAGING.test(n))
  const pick = content('archive') ?? content('par2') ?? of('lone').find((i) => i.yencName && !PACKAGING.test(i.yencName))?.yencName
  const name = pick?.replace(/^.*[\\/]/, '').slice(0, 255)
  // The release's own name with an extension says nothing new (a random-named file's yEnc name is mostly its random name).
  return name && !name.toLowerCase().startsWith(releaseName.toLowerCase() || '\0') ? name : null
}