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The Fname registry server is hosted at https://fnames.farcaster.xyz It’s a simple HTTP service that’s responsible for issuing and tracking fnames. All Fname changes are recorded as a transfer. Registering an fname is a transfer from FID 0 to the user’s fid. Transferring an fname is a transfer from the user’s fid to another fid. Unregistering an fname is a transfer from the user’s fid to fid 0.
Registering an fname - When registering a new fname, calling this api is not sufficient. This only reserves the name to your fid. You must also submit a UserDataAdd message to the hub to set this name as your username.

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Get Transfer History

To get a history of all transfers, make a GET request to /transfers 
curl https://fnames.farcaster.xyz/transfers | jq
It also accepts the following query parameters:
  • from_id - The transfer id to start from for pagination
  • name - The fname to filter by
  • fid - The fid (either from or to) to filter by
  • from_ts - The timestamp (in seconds) to start from for pagination

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Get current fname or fid

To get the most recent transfer event for an fid or fname, make a GET request to /transfers/current e.g. To determine the fid of @farcaster, make the following call and use the value from the to field in the return value 
curl https://fnames.farcaster.xyz/transfers?name=farcaster | jq
To determine the fname of fid 1, make the following call and use the value from the username field in the return value 
curl https://fnames.farcaster.xyz/transfers?fid=1 | jq
Both will return the same transfers object: 
{
  "transfers": [
    {
      "id": 1,
      "timestamp": 1628882891,
      "username": "farcaster",
      "owner": "0x8773442740c17c9d0f0b87022c722f9a136206ed",
      "from": 0,
      "to": 1,
      "user_signature": "0xa6fdd2a69deab5633636f32a30a54b21b27dff123e6481532746eadca18cd84048488a98ca4aaf90f4d29b7e181c4540b360ba0721b928e50ffcd495734ef8471b",
      "server_signature": "0xb7181760f14eda0028e0b647ff15f45235526ced3b4ae07fcce06141b73d32960d3253776e62f761363fb8137087192047763f4af838950a96f3885f3c2289c41b"
    }
  ]
}

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Register or transfer an fname

To register a new fname, e.g. farcaster, first make sure the fname is not already registered. Then make a POST request to /transfers with the following body: 
{
  "name": "farcaster", // Name to register
  "from": 0,  // Fid to transfer from (0 for a new registration)
  "to": 123, // Fid to transfer to (0 to unregister)
  "fid": 123, // Fid making the request (must match from or to)
  "owner": "0x...", // Custody address of fid making the request
  "timestamp": 1641234567,  // Current timestamp in seconds
  "signature": "0x..."  // EIP-712 signature signed by the custody address of the fid
}
To generate the EIP-712 signature, use the following code: 
import { makeUserNameProofClaim, EIP712Signer } from '@farcaster/hub-nodejs';

const accountKey: EIP712Signer = undefined; // Account key for the custody address (use appropriate subclass from hub-nodejs for ethers or viem)

const claim = makeUserNameProofClaim({
  name: 'farcaster',
  owner: '0x...',
  timestamp: Math.floor(Date.now() / 1000),
});
const signature = (
  await accountKey.signUserNameProofClaim(claim)
)._unsafeUnwrap();
This is the exact same kind of signature used in the ENS UsernameProofs provided to hubs to prove ownership of an ENS name. e.g. 
curl -X POST https://fnames.farcaster.xyz/transfers \
  -H "Content-Type: application/json" \
  -d \
'{"name": "farcaster", "owner": "0x...", "signature": "0x...", "from": 0, "to": 1000, "timestamp": 1641234567, "fid": 1000}'
Once a name is registered, it still needs a UserData message to be sent to the hub in order to actually set the username for the user. See examples in the hub-nodejs repo.