How to query a Cardano node for an NFT's owner?

Question

Is there a way to use cardano-cli (or another tool) to query a Cardano node for an NFT's current owner (wallet address holding the NFT)? The parameters for such a query would likely be the Policy ID & Asset Name of the NFT.

Since, from a blockchain perspective, there is no difference between native tokens for which an arbitrary amount of tokens exist and those where there is only a single one (NFTs), I guess a query like the one I'm looking for is not something that fits into the grand scheme of things; but maybe I'm missing something?

If there is no tool readily available, how could I use cardano-cli (or another tool) to look through all transactions (starting with the most recent and going backwards in time) until I find the most recent transaction containing the NFT in question?

Answer 1

There is no way to find that information without syncing the whole blockchain into a database with a tool such as cardano-db-sync.

This takes a lot of time and resources, so you might want to use an API like blockfrost.io to query the addresses owning a specific token.

$ curl  -s -H "Project_id: $BLOCKFROST_PROJECT_ID" https://cardano-mainnet.blockfrost.io/api/v0/assets/00000002df633853f6a47465c9496721d2d5b1291b8398016c0e87ae6e7574636f696e/addresses | jq
  [
   {
    "address": "addr1qxlmfhfcjck5pctuvlpww3kuxvqjucz40qusgeqgmyqq4utntgjccmteyrsldd67rxv2yq6ew2a7t48q34p9j7nf0kjqskku78",
    "quantity": "1"
   }
  ]

Answer 2

As suggested by Marek, blockfrost.io seems to be a great way to jump right in.
For an alternative do-it-yourself way other tools can be used.

Using cardano-db-sync the blockchain data acquired by a Cardano node will be fed into a PostgreSQL database, allowing to query the data through SQL.

Querying that database looks like this (this is just a random query taken from the example queries, it does not answer the original question):

select tx_out.* from tx_out
inner join tx_in on tx_out.tx_id = tx_in.tx_out_id
inner join tx on tx.id = tx_in.tx_in_id and tx_in.tx_out_index = tx_out.index
where tx.hash = '\xf9c0997afc8159dbe0568eadf0823112e0cc29cd097c8dc939ff44c372388bc0' ;

   id    | tx_id  | index |        address          |    value     |        address_raw        | payment_cred
---------+--------+-------+-------------------------+--------------+---------------------------+--------------
 2195714 | 996126 |     4 | DdzFFzCqrh...dtq1FQQSCN | 158685237964 | \x82d8185842...1a330b42df |

Building on that, one could further set up cardano-graphql to provide a GraphQL API for cardano-db-sync. This is what the Cardano Explorer is built upon.

Using cardano-graphql, a query to find the current owner of a given token could look like this:

query TokenOwner($policy_id : Hash28Hex, $asset_name : String) {
  utxos (where: {tokens: {_and: {asset: {policyId: {_eq: $policy_id} assetName: {_eq: $asset_name}}}}})
  { 
    txHash
    address
    value
    tokens {asset {policyId assetName} quantity}
  }
}

Where the arguments denoting the NFT are its policy id and asset name, for example:

{
  "policy_id": "d5e6bf0500378d4f0da4e8dde6becec7621cd8cbf5cbb9b87013d4cc",
  "asset_name": "537061636542756433373430"
}

Note that asset_name is provided in hex format.

For this example, a random SpaceBud (SpaceBud759) with no other tokens in the UTXO was selected, resulting in the following output (on 2021-05-02) where the address field denotes the current owner:

{
  "data": {
    "utxos": [
      {
        "txHash": "4fcf200a8b18f866bd4e9324600ffe636b081d79a9bb06b748fa41947f3a6a5e",
        "address": "addr1qxjtqaxmv44u2zx02v7658wrlt87tv9yp7knzwh6hana3ra5ay9tjpf6e0d3p2t7s6gnnqtwmva02lx4p0dlx8a7x8uqrw46dy",
        "value": "1500000",
        "tokens": [
          {
            "asset": {
              "policyId": "d5e6bf0500378d4f0da4e8dde6becec7621cd8cbf5cbb9b87013d4cc",
              "assetName": "5370616365427564373539"
            },
            "quantity": "1"
          }
        ]
      }
    ]
  }
}

As of writing, using the policy id in queries like shown above seems to be non-functional, as described in this github issue.

Further example queries can found here, one might also check out this graphical representation of the API.