Looking up Ethereum addresses

The simplest and most frequently used function in ENS is resolving a name. Names can have many types of data associated with them; the most common is an Ethereum address. Resolving a name to an Ethereum address using a library is simple:

var address = await ens.name('resolver.eth').getAddress();

var address = ens.getAddress('alice.eth');

var address = await ens.lookup('alice.eth');

var address = await provider.resolveName('alice.eth');

var balance = await provider.getBalance('alice.eth');

const abi = [
  "function getValue() view returns (string value)",
  "function setValue(string value)"
];
const contract = new ethers.Contract('contract.alice.eth', abi, provider);

address, err := ens.Resolve(client, "alice.eth")

address = ns.address('alice.eth')

String address = ens.resolve("alice.eth");

YourSmartContract contract = YourSmartContract.load(
        "contract.alice.eth", web3j, credentials, GAS_PRICE, GAS_LIMIT);

Resolution without a library is a three step process:

1. Normalise and hash the name - see name processing for details.

2. Call resolver() on the ENS registry, passing in the output of step 1. This returns the address of the resolver responsible for the name.

3. Using the resolver interface, call addr() on the resolver address returned in step 2, passing in the hashed name calculated in step 1.

Multicoin address resolution support is implemented with an additional overload on addr(). To resolve a multicoin address, supply both the namehash and the SLIP44 chain ID of the cryptocurrency whose address you want to resolve. For example, to resolve a Bitcoin address, you would call addr(hash, 0). Note that the returned address will be in binary representation, and so will need decoding to a text-format address; for details, see EIP 2304.

Looking up other resources

ENS supports many types of resources besides Ethereum addresses, including other cryptocurrency addresses, content hashes for data stored in Swarm or IPFS, contract interfaces (ABIs), and text-based metadata. The process for looking these up varies from library to library; for specific details see your chosen library's documentation.

Resolving these content types without a library follows the same 3-step process detailed above; simply call the relevant method on the resolver in step 3 instead of addr().

// Getting contenthash
await ens.name('abittooawesome.eth').getContent()
// Setting contenthash
await ens.name('abittooawesome.eth').setContenthash(contentHash)
​
// Getting other coins
await ens.name('brantly.eth').getAddress('BTC')
// Setting other coins
await ens.name('superawesome.eth').setAddress('ETC', '0x0000000000000000000000000000000000012345')
// Getting text
await ens.name('resolver.eth').getText('url')
// Setting text
await ens.name('superawesome.eth').setText('url', 'http://google.com')

// Getting contenthash
web3.eth.ens.getContenthash('ethereum.eth').then(function (result) {
    console.log(result);
});
// Setting contenthash
web3.eth.ens.setContenthash('ethereum.eth', hash);

Not supported.

  const contentHash = await resolver.getContentHash();
  const btcAddress = await resolver.getAddress(0);
  const dogeAddress = await resolver.getAddress(3);
  const email = await resolver.getText("email");

// Encoding
bin, err := ens.StringToContenthash("/ipfs/QmayQq2DWCkY3d4x3xKh4suohuRPEXe2fBqMBam5xtDj3t")
// Setting contenthash
resolver.SetContenthash(opts, data)
// Getting contenthash
resolver.Contenthash()
// Decoding
repr, err := ens.ContenthashToString(bin)
​
// Getting Multicoin
btcAddress, err := resolver.MultiAddress(0)
// Setting Multicoin
resolver.SetMultiAddress(opts, address)
​
// Setting text
resolver.SetText(opts, name, value)
// Getting text
resolver.Text(name)

Not supported.

Not supported.

Encoding and decoding contenthash

contenthash is used to store IPFSand Swarm content hashes, which permit resolving ENS addresses to distributed content (eg, websites) hosted on these distributed networks. content-hash javascript library provides a convenient way to encode/decode these hashes.

 const contentHash = require('content-hash')
const encoded = 'e3010170122029f2d17be6139079dc48696d1f582a8530eb9805b561eda517e22a892c7e3f1f'
const content = contentHash.decode(encoded)
// 'QmRAQB6YaCyidP37UdDnjFY5vQuiBrcqdyoW1CuDgwxkD4'
​
const onion = 'zqktlwi4fecvo6ri'
contentHash.encode('onion', onion);
// 'bc037a716b746c776934666563766f367269'
​
const encoded = 'e40101701b20d1de9994b4d039f6548d191eb26786769f580809256b4685ef316805265ea162'
​
const codec = contentHash.getCodec(encoded) // 'swarm-ns'
codec === 'ipfs-ns' // false

Note for ipns: For security reasons, the encoding of ipns is only allowed for libp2p-key codec. Decoding with other formats will show a deprecation warning. Please read here for more detail.

Coin type and encoding/decoding

While some libraries allow you to query multicoin address via symbol (e.g.: BTC), others do not have the built-in support, and you have to call via each coin id (e.g.: 0 for BTC, 16 for `ETH). For Javascript/Typescript, we have @ensdomains/address-encoder library that allows you to convert

import { formatsByName, formatsByCoinType } from '@ensdomains/address-encoder';
​
formatsByName['BTC']
// {
//   coinType: 0,
//   decoder: [Function (anonymous)],
//   encoder: [Function (anonymous)],
//   name: 'BTC'
// }

To save storage space as well as prevent users from setting wrong token address, the library has encoder and decoder

const data = formatsByName['BTC'].decoder('1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa');
console.log(data.toString('hex')); // 76a91462e907b15cbf27d5425399ebf6f0fb50ebb88f1888ac
const addr = formatsByCoinType[0].encoder(data);
console.log(addr); // 1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa

Listing multicoins and text records

For multicoins and text record, you need to know the coin type or key names to get the value. If you want to list down all the multicoins and text records the user has set, you have to either retrieve the information from Event or query via ENS subgraph.

For example

{
  domains(where:{name:"vitalik.eth"}) {
    id
    name
    resolver{
      texts
      coinTypes
    }
  }
}

will return the following result

{
  "data": {
    "domains": [
      {
        "id": "0xee6c4522aab0003e8d14cd40a6af439055fd2577951148c14b6cea9a53475835",
        "name": "vitalik.eth",
        "resolver": {
          "coinTypes": [
            60
          ],
          "texts": [
            "url"
          ]
        }
      }
    ]
  }
}

Reverse Resolution

While 'regular' resolution involves mapping from a name to an address, reverse resolution maps from an address back to a name - or other metadata. ENS supports reverse resolution to allow applications to display ENS names in place of hexadecimal addresses.

Reverse resolution is accomplished via the special purpose domain addr.reverse and the resolver function name(). addr.reverse is owned by a special purpose registrar contract that allocates subdomains to the owner of the matching address - for instance, the address 0x314159265dd8dbb310642f98f50c066173c1259b may claim the name 314159265dd8dbb310642f98f50c066173c1259b.addr.reverse, and configure a resolver and records on it. The resolver in turn supports the name() function, which returns the name associated with that address.

Most libraries provide functionality for doing reverse resolution:

const address = '0x1234...';
var name = await ens.getName(address)
// Check to be sure the reverse record is correct.
if(address != await ens.name(name).getAddress()) {
  name = null;
}

var address = '0x1234...';
var name = await ens.reverse(address);
// Check to be sure the reverse record is correct.
if(address != await ens.lookup(name)) {
  name = null;
}

var address = '0x1234...';
var name = await provider.lookupAddress(address);
// ethers.js automatically checks that the forward resolution matches.

name, err := ens.ReverseResolve(client, common.HexToAddress("0x1234...")

address = '0x1234...'
name = ns.reverse(address)
# Check to be sure the reverse record is correct.
if address != ns.address(name):
  name = None

String address = "0x1234...";
String name = ens.reverseResolve(address);
// Check to be sure the reverse record is correct.
if(address != ens.resolve(name)) {
  name = null;
}

Reverse resolution without a library follows the same pattern as forward resolution: Get the resolver for 1234....addr.reverse(where 1234... is the address you want to reverse-resolve), and call the name() function on that resolver. Then, perform a forward resolution to verify the record is accurate.

If you need to process many addresses (eg: showing reverse record of transaction histories), resolving both reverse and forward resolution for each item may not be practical. We have a seperate smartcontract called ReverseRecords which allows you to lookup multiple names in one function call.

const namehash = require('eth-ens-namehash');
const allnames = await ReverseRecords.getNames(['0x123','0x124'])
const validNames = allnames.filter((n) => namehash.normalize(n) === n )

Make sure to compare that the returned names match with the normalised names to prevent from homograph attack as well as people simply using capital letters.