um-react/src/decrypt-worker/decipher/XiamiMusic.ts

import { DecipherInstance, DecipherOK, DecipherResult, Status } from '~/decrypt-worker/Deciphers.ts';
import { Xiami } from '@unlock-music/crypto';
import { chunkBuffer } from '~/decrypt-worker/util/buffer.ts';

export class XiamiDecipher implements DecipherInstance {
  cipherName = 'Xiami (XM)';

  async decrypt(buffer: Uint8Array): Promise<DecipherResult | DecipherOK> {
    const xm = Xiami.from_header(buffer.subarray(0, 0x10));
    const { copyPlainLength } = xm;
    const audioBuffer = buffer.slice(0x10);

    for (const [block] of chunkBuffer(audioBuffer.subarray(copyPlainLength))) {
      xm.decrypt(block);
    }
    xm.free();

    return {
      cipherName: this.cipherName,
      status: Status.OK,
      data: audioBuffer,
    };
  }

  public static make() {
    return new XiamiDecipher();
  }
}