YouTube.js/src/core/Player.ts

import { Log, LZW, Constants } from '../utils/index.js';
import { Platform, getRandomUserAgent, getStringBetweenStrings, PlayerError } from '../utils/Utils.js';
import type { ICache, FetchFunction } from '../types/index.js';

const TAG = 'Player';

/**
 * Represents YouTube's player script. This is required to decipher signatures.
 */
export default class Player {
  nsig_sc;
  sig_sc;
  sts;
  player_id;

  constructor(signature_timestamp: number, sig_sc: string, nsig_sc: string, player_id: string) {
    this.nsig_sc = nsig_sc;
    this.sig_sc = sig_sc;
    this.sts = signature_timestamp;
    this.player_id = player_id;
  }

  static async create(cache: ICache | undefined, fetch: FetchFunction = Platform.shim.fetch): Promise<Player> {
    const url = new URL('/iframe_api', Constants.URLS.YT_BASE);
    const res = await fetch(url);

    if (res.status !== 200)
      throw new PlayerError('Failed to request player id');

    const js = await res.text();

    const player_id = getStringBetweenStrings(js, 'player\\/', '\\/');

    Log.info(TAG, `Got player id (${player_id}). Checking for cached players..`);

    if (!player_id)
      throw new PlayerError('Failed to get player id');

    // We have the player id, now we can check if we have a cached player.
    if (cache) {
      const cached_player = await Player.fromCache(cache, player_id);
      if (cached_player) {
        Log.info(TAG, 'Found up-to-date player data in cache.');
        return cached_player;
      }
    }

    const player_url = new URL(`/s/player/${player_id}/player_ias.vflset/en_US/base.js`, Constants.URLS.YT_BASE);

    Log.info(TAG, `Could not find any cached player. Will download a new player from ${player_url}.`);

    const player_res = await fetch(player_url, {
      headers: {
        'user-agent': getRandomUserAgent('desktop')
      }
    });

    if (!player_res.ok) {
      throw new PlayerError(`Failed to get player data: ${player_res.status}`);
    }

    const player_js = await player_res.text();

    const sig_timestamp = this.extractSigTimestamp(player_js);
    const sig_sc = this.extractSigSourceCode(player_js);
    const nsig_sc = this.extractNSigSourceCode(player_js);

    Log.info(TAG, `Got signature timestamp (${sig_timestamp}) and algorithms needed to decipher signatures.`);

    return await Player.fromSource(cache, sig_timestamp, sig_sc, nsig_sc, player_id);
  }

  decipher(url?: string, signature_cipher?: string, cipher?: string, this_response_nsig_cache?: Map<string, string>): string {
    url = url || signature_cipher || cipher;

    if (!url)
      throw new PlayerError('No valid URL to decipher');

    const args = new URLSearchParams(url);
    const url_components = new URL(args.get('url') || url);

    if (signature_cipher || cipher) {
      const signature = Platform.shim.eval(this.sig_sc, {
        sig: args.get('s')
      });

      Log.info(TAG, `Transformed signature from ${args.get('s')} to ${signature}.`);

      if (typeof signature !== 'string')
        throw new PlayerError('Failed to decipher signature');

      const sp = args.get('sp');

      sp ?
        url_components.searchParams.set(sp, signature) :
        url_components.searchParams.set('signature', signature);
    }

    const n = url_components.searchParams.get('n');

    if (n) {
      let nsig;

      if (this_response_nsig_cache && this_response_nsig_cache.has(n)) {
        nsig = this_response_nsig_cache.get(n) as string;
      } else {
        nsig = Platform.shim.eval(this.nsig_sc, {
          nsig: n
        });

        Log.info(TAG, `Transformed n signature from ${n} to ${nsig}.`);

        if (typeof nsig !== 'string')
          throw new PlayerError('Failed to decipher nsig');

        if (nsig.startsWith('enhanced_except_')) {
          Log.warn(TAG, 'Could not transform nsig, download may be throttled.\nChanging the InnerTube client to "ANDROID" might help!');
        } else if (this_response_nsig_cache) {
          this_response_nsig_cache.set(n, nsig);
        }
      }

      url_components.searchParams.set('n', nsig);
    }

    const client = url_components.searchParams.get('c');

    switch (client) {
      case 'WEB':
        url_components.searchParams.set('cver', Constants.CLIENTS.WEB.VERSION);
        break;
      case 'WEB_REMIX':
        url_components.searchParams.set('cver', Constants.CLIENTS.YTMUSIC.VERSION);
        break;
      case 'WEB_KIDS':
        url_components.searchParams.set('cver', Constants.CLIENTS.WEB_KIDS.VERSION);
        break;
      case 'ANDROID':
        url_components.searchParams.set('cver', Constants.CLIENTS.ANDROID.VERSION);
        break;
      case 'ANDROID_MUSIC':
        url_components.searchParams.set('cver', Constants.CLIENTS.YTMUSIC_ANDROID.VERSION);
        break;
      case 'TVHTML5_SIMPLY_EMBEDDED_PLAYER':
        url_components.searchParams.set('cver', Constants.CLIENTS.TV_EMBEDDED.VERSION);
        break;
    }

    const result = url_components.toString();

    Log.info(TAG, `Deciphered URL: ${result}`);

    return url_components.toString();
  }

  static async fromCache(cache: ICache, player_id: string): Promise<Player | null> {
    const buffer = await cache.get(player_id);

    if (!buffer)
      return null;

    const view = new DataView(buffer);
    const version = view.getUint32(0, true);

    if (version !== Player.LIBRARY_VERSION)
      return null;

    const sig_timestamp = view.getUint32(4, true);

    const sig_len = view.getUint32(8, true);
    const sig_buf = buffer.slice(12, 12 + sig_len);
    const nsig_buf = buffer.slice(12 + sig_len);

    const sig_sc = LZW.decompress(new TextDecoder().decode(sig_buf));
    const nsig_sc = LZW.decompress(new TextDecoder().decode(nsig_buf));

    return new Player(sig_timestamp, sig_sc, nsig_sc, player_id);
  }

  static async fromSource(cache: ICache | undefined, sig_timestamp: number, sig_sc: string, nsig_sc: string, player_id: string): Promise<Player> {
    const player = new Player(sig_timestamp, sig_sc, nsig_sc, player_id);
    await player.cache(cache);
    return player;
  }

  async cache(cache?: ICache): Promise<void> {
    if (!cache) return;

    const encoder = new TextEncoder();

    const sig_buf = encoder.encode(LZW.compress(this.sig_sc));
    const nsig_buf = encoder.encode(LZW.compress(this.nsig_sc));

    const buffer = new ArrayBuffer(12 + sig_buf.byteLength + nsig_buf.byteLength);
    const view = new DataView(buffer);

    view.setUint32(0, Player.LIBRARY_VERSION, true);
    view.setUint32(4, this.sts, true);
    view.setUint32(8, sig_buf.byteLength, true);

    new Uint8Array(buffer).set(sig_buf, 12);
    new Uint8Array(buffer).set(nsig_buf, 12 + sig_buf.byteLength);

    await cache.set(this.player_id, new Uint8Array(buffer));
  }

  static extractSigTimestamp(data: string): number {
    return parseInt(getStringBetweenStrings(data, 'signatureTimestamp:', ',') || '0');
  }

  static extractSigSourceCode(data: string): string {
    const calls = getStringBetweenStrings(data, 'function(a){a=a.split("")', 'return a.join("")}');
    const obj_name = calls?.split(/\.|\[/)?.[0]?.replace(';', '')?.trim();
    const functions = getStringBetweenStrings(data, `var ${obj_name}={`, '};');

    if (!functions || !calls)
      Log.warn(TAG, 'Failed to extract signature decipher algorithm.');

    return `function descramble_sig(a) { a = a.split(""); let ${obj_name}={${functions}}${calls} return a.join("") } descramble_sig(sig);`;
  }

  static extractNSigSourceCode(data: string): string {
    const sc = `function descramble_nsig(a) { let b=a.split("")${getStringBetweenStrings(data, 'b=a.split("")', '}return b.join("")}')}} return b.join(""); } descramble_nsig(nsig)`;

    if (!sc)
      Log.warn(TAG, 'Failed to extract n-token decipher algorithm');

    return sc;
  }

  get url(): string {
    return new URL(`/s/player/${this.player_id}/player_ias.vflset/en_US/base.js`, Constants.URLS.YT_BASE).toString();
  }

  static get LIBRARY_VERSION(): number {
    return 10;
  }
}