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Issuing NFTs (UDA)

RGB v0.11 line (rgb-cmd 0.11.1)

NFTs are issued as UDA contracts in v0.11. v0.12 rc.3 ships no NFT issuer: rgb-interfaces 0.12 defines NFT data types, but no issuer uses them yet. See Two RGB lines.

An RGB NFT is a contract of the UDA (Unique Digital Asset) schema. Line B used to call this "RGB21", a name it now treats as deprecated.

One token per contract​

A UDA contract holds exactly one token. In rgb-schemas 0.11.1 src/uda.rs, the tokens global and the genesis assetOwner assignment both occur Once, and the only transition is transfer. Nothing can be minted after genesis. A collection of 100 NFTs is 100 contracts. Group them in your application, for example with a shared ticker or name, or a details string.

GlobalTypeContent
specAssetSpecTicker, name, optional details, precision
termsContractTermsContract text and an optional attachment
tokensTokenDataThe token itself (see Metadata and attachments)
attachmentTypesAttachmentTypeOptional. Names an attachment slot (id: u8, name: 1–20 ASCII characters)

The owned state assetOwner is an Allocation(TokenIndex, OwnedFraction). The UDA script checks two things in genesis and in every transfer (excerpt from uda_lib()):

// the owned allocation's token index must equal the token's index
put     a8[0],ERRNO_NON_EQUAL_IN_OUT;   // errno 0
extr    s16[0],a32[0],a16[0];
lds     OS_ASSET,a16[1],s16[1];
extr    s16[1],a32[1],a16[0];
eq.n    a32[0],a32[1];
test;
// the owned fraction must be exactly 1: no fractional NFTs
put     a8[0],ERRNO_NON_FRACTIONAL;     // errno 10
put     a16[2],4;
extr    s16[1],a64[0],a16[2];
put     a64[1],1;
eq.n    a64[0],a64[1];
test;

The script doesn't check precision. Wallets usually use 0.

With rgb-lib​

issue_asset_uda in rgb-lib 0.3.0-beta.7 (src/wallet/singlesig.rs). Wallet setup is as in Issuing fungible tokens. This code wasn't run for this page.

let nft = wallet.issue_asset_uda(
    "DEMONFT".into(),                       // ticker, upper case
    "Demo NFT #1".into(),                   // name
    Some("First item of the demo set".into()), // details
    0,                                      // precision
    Some("art/1.png".into()),               // media file → TokenData.media
    vec!["art/1-hires.tiff".into()],        // up to 20 attachments → TokenData.attachments
)?;
println!("{}", nft.asset_id);
  • rgb-lib reads each file, computes its SHA-256 digest, detects its media type, and copies it to <wallet dir>/media_files/<digest>. The contract stores only the media type and digest.
  • More than 20 attachments fails (MAX_ATTACHMENTS = 20, src/wallet/offline.rs).
  • The token index is always 0. rgb-lib doesn't set preview, reserves or attachmentTypes, and it puts empty terms in genesis.
  • As with every issuance, a UTXO must be available to hold the allocation (create_utxos).
  • The RGB Lightning Node offers POST /issueassetuda. Upload files first with POST /postassetmedia and pass their digests.

rgb issue (rgb-cmd 0.11.1) can't issue a UDA, because it handles only fungible assignments. See the CLI reference (v0.11).

With the Rust builder​

To set the preview or other fields yourself, build genesis directly. This is the core of examples/uda.rs in rgb-schemas 0.11.1 (crate rgb-ops, library name rgbstd):

use rgbstd::stl::{AssetSpec, ContractTerms, EmbeddedMedia, MediaType, RicardianContract, TokenData};
use rgbstd::invoice::Precision;
use rgbstd::{Allocation, ChainNet, TokenIndex};
use schemata::UniqueDigitalAsset;

let index = TokenIndex::from_inner(0);
let token = TokenData {
    index,
    preview: Some(EmbeddedMedia { ty: MediaType::with("image/*"), data: thumbnail_blob }),
    media: Some(media_attachment), // Attachment { ty, digest }
    ..Default::default()
};

let contract = stock
    .contract_builder("ssi:anonymous", UniqueDigitalAsset::schema().schema_id(), ChainNet::BitcoinTestnet4)?
    .add_global_state("spec", AssetSpec::new("DEMONFT", "Demo NFT #1", Precision::Indivisible))?
    .add_global_state("terms", ContractTerms { text: RicardianContract::default(), media: None })?
    .add_global_state("tokens", token)?
    .add_data("assetOwner", genesis_seal, Allocation::with(index, 1))?
    .issue_contract()?;

thumbnail_blob is a SmallBlob (at most 65,535 bytes). genesis_seal and stock are set up as in the fungible example.

Back up the contract and the media

A seed phrase doesn't recover RGB assets. Back up the RGB data directory, or use rgb-lib's backup. Keep the original media files too: the contract holds only their digests, and a file that is lost can't be recreated from the digest.

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