cyberia/research/events/client/src/shared/lib/web3/multihash.js

import bs58 from "bs58";

/**
 * @typedef {Object} Multihash
 * @property {`0x${string}`} digest The digest output of hash function in hex with prepended '0x'
 * @property {number} hashFunction The hash function code for the function used
 * @property {number} size The length of digest
 */

/**
 * Partition multihash string into object representing multihash
 *
 * @param {string} multihash A base58 encoded multihash string
 * @returns {Multihash}
 */
export function getBytes32FromMultiash(multihash) {
  const decoded = bs58.decode(multihash);

  return {
    digest: `0x${Buffer.from(decoded.slice(2)).toString("hex")}`,
    hashFunction: decoded[0],
    size: decoded[1],
  };
}

/**
 * Encode a multihash structure into base58 encoded multihash string
 *
 * @param {Multihash} multihash
 * @returns {(string|null)} base58 encoded multihash string
 */
export function getMultihashFromBytes32(multihash) {
  const { digest, hashFunction, size } = multihash;
  if (size === 0) return null;

  // cut off leading "0x"
  const hashBytes = Buffer.from(digest.slice(2), "hex");

  // prepend hashFunction and digest size
  const multihashBytes = new hashBytes.constructor(2 + hashBytes.length);
  multihashBytes[0] = hashFunction;
  multihashBytes[1] = size;
  multihashBytes.set(hashBytes, 2);

  return bs58.encode(multihashBytes);
}

/**
 * Parse Solidity response in array to a Multihash object
 *
 * @param {array} response Response array from Solidity
 * @returns {Multihash} multihash object
 */
export function parseContractResponse(response) {
  const [digest, hashFunction, size] = response;
  return {
    digest,
    hashFunction: hashFunction.toNumber(),
    size: size.toNumber(),
  };
}

/**
 * Parse Solidity response in array to a base58 encoded multihash string
 *
 * @param {array} response Response array from Solidity
 * @returns {string} base58 encoded multihash string
 */
export function getMultihashFromContractResponse(response) {
  return getMultihashFromBytes32(parseContractResponse(response));
}