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().

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.