metamask-extension/app/scripts/lib/ens-ipfs/resolver.js

const namehash = require('eth-ens-namehash')
const multihash = require('multihashes')
const Eth = require('ethjs-query')
const EthContract = require('ethjs-contract')
const registrarAbi = require('./contracts/registrar')
const resolverAbi = require('./contracts/resolver')

module.exports = resolveEnsToIpfsContentId


async function resolveEnsToIpfsContentId ({ provider, name }) {
  const eth = new Eth(provider)
  const hash = namehash.hash(name)
  const contract = new EthContract(eth)
  // lookup registrar
  const chainId = Number.parseInt(await eth.net_version(), 10)
  const registrarAddress = getRegistrarForChainId(chainId)
  if (!registrarAddress) {
    throw new Error(`EnsIpfsResolver - no known ens-ipfs registrar for chainId "${chainId}"`)
  }
  const Registrar = contract(registrarAbi).at(registrarAddress)
  // lookup resolver
  const resolverLookupResult = await Registrar.resolver(hash)
  const resolverAddress = resolverLookupResult[0]
  if (hexValueIsEmpty(resolverAddress)) {
    throw new Error(`EnsIpfsResolver - no resolver found for name "${name}"`)
  }
  const Resolver = contract(resolverAbi).at(resolverAddress)
  // lookup content id
  const contentLookupResult = await Resolver.content(hash)
  const contentHash = contentLookupResult[0]
  if (hexValueIsEmpty(contentHash)) {
    throw new Error(`EnsIpfsResolver - no content ID found for name "${name}"`)
  }
  const nonPrefixedHex = contentHash.slice(2)
  const buffer = multihash.fromHexString(nonPrefixedHex)
  const contentId = multihash.toB58String(multihash.encode(buffer, 'sha2-256'))
  return contentId
}

function hexValueIsEmpty(value) {
  return [undefined, null, '0x', '0x0', '0x0000000000000000000000000000000000000000000000000000000000000000'].includes(value)
}

function getRegistrarForChainId (chainId) {
  switch (chainId) {
    // mainnet
    case 1:
      return '0x314159265dd8dbb310642f98f50c066173c1259b'
    // ropsten
    case 3:
      return '0x112234455c3a32fd11230c42e7bccd4a84e02010'
  }
}