@polkadot/util/hex/toU8aBuffer.js

A collection of useful utilities for @polkadot

// Copyright 2017-2022 @polkadot/util authors & contributors
// SPDX-License-Identifier: Apache-2.0
import { hexStripPrefix } from "./stripPrefix.js";
/**
 * @name hexToU8a
 * @summary Creates a Uint8Array object from a hex string.
 * @description
 * `null` inputs returns an empty `Uint8Array` result. Hex input values return the actual bytes value converted to a Uint8Array. Anything that is not a hex string (including the `0x` prefix) throws an error.
 * @example
 * <BR>
 *
 * ```javascript
 * import { hexToU8a } from '@polkadot/util';
 *
 * hexToU8a('0x80001f'); // Uint8Array([0x80, 0x00, 0x1f])
 * hexToU8a('0x80001f', 32); // Uint8Array([0x00, 0x80, 0x00, 0x1f])
 * ```
 */

export function hexToU8a(_value, bitLength = -1) {
  if (!_value) {
    return new Uint8Array();
  }

  const value = hexStripPrefix(_value);
  const buf = Buffer.from(value, 'hex');
  const valLength = value.length / 2;
  const resultLength = Math.ceil(bitLength === -1 ? valLength : bitLength / 8);

  if (resultLength === valLength) {
    return Uint8Array.from(buf);
  }

  const offset = resultLength > valLength ? resultLength - valLength : 0;

  if (offset) {
    const u8a = new Uint8Array(resultLength);
    u8a.set(buf, offset);
    return u8a;
  }

  return Uint8Array.from(buf.slice(0, resultLength));
}