@polkadot/types/metadata/Metadata.js

// Copyright 2017-2022 @polkadot/types authors & contributors
// SPDX-License-Identifier: Apache-2.0
import { isString, isU8a, u8aToU8a } from '@polkadot/util';
import { MetadataVersioned } from "./MetadataVersioned.js"; // magic u32 preceding the version id

const VERSION_IDX = 4; // magic + lowest supported version

const EMPTY_METADATA = new Uint8Array([0x6d, 0x65, 0x74, 0x61, 9]);

function decodeU8a(registry, value) {
  const u8a = value.length === 0 ? EMPTY_METADATA : value; // This is an f-ing hack as a follow-up to another ugly hack
  // https://github.com/polkadot-js/api/commit/a9211690be6b68ad6c6dad7852f1665cadcfa5b2
  // when we fail on V9, try to re-parse it as v10...

  if (u8a[VERSION_IDX] === 9) {
    try {
      return new MetadataVersioned(registry, u8a);
    } catch (error) {
      u8a[VERSION_IDX] = 10;
      return u8a;
    }
  }

  return u8a;
}
/**
 * @name Metadata
 * @description
 * The versioned runtime metadata as a decoded structure
 */


export class Metadata extends MetadataVersioned {
  constructor(registry, value) {
    // console.time('Metadata')
    super(registry, isU8a(value) || isString(value) ? decodeU8a(registry, u8aToU8a(value)) : value); // console.timeEnd('Metadata')
  }

}