How can I store more data on-chain in an NFT?

Question

I am creating an NFT that stores a small amount of data - less than 1KB - inside it. The data should be on-chain - not in an external JSON file - as the owner should be able to destroy the NFT easily using their wallet without external traces left over.

How can I write more data into the on-chain NFT?

I was hoping to use Metaplex (both the Metaplex JS SDK and the on-chain program) to write the data into an NFT. I overloaded the uri field (as it's a string) with the data to see if I could write the NFT there.

The program [TokenMetadataProgram] at address 
[metaqbxxUerdq28cj1RbAWkYQm3ybzjb6a8bt518x1s] raised an error of code
[13] that translates to "URI too long".

Some hunting through the metaplex on-chain program code shows pub const MAX_URI_LENGTH: usize = 200; which seems to indicate the maximum length of the URI field is 200 bytes.

What's the best way to make NFTs with more data inside?

Edit: I've also checked out Need assistance creating a custom type of NFT which may indicate there only way to do this is use SPL to mint the token, and make a PDA for the additional metadata that accepts the larger data.

Answer 1

The createMetadata() function from Candy Machine creates a metadata account using the NFT mint address.

Similarly, you can create a PDA for your own NFT metadata. The PDA account should be indicated with the NFT mintAddress. You can make the account similar to the metadata account.

const metadataAccount = (
  await findProgramAddress(
    [
      Buffer.from("metadata"),
      toPublicKey(metadataProgramId).toBuffer(),
      toPublicKey(mintAddress).toBuffer(),
    ],
    toPublicKey(metadataProgramId)
  )
)[0];

The Dapp has to build the logic to find the account and get the account data. So your Dapp should be able to see what the additional metadata are. You can't see the additional metadata in a wallet (unless you're building your own wallet).