Code sample for parsing metadata for Solana NFT and updating the metadata

Question

On Solana, NFT metadata is stored in accounts which are owned by the shared contract Token Metadata Program at address metaqbxxUerdq28cj1RbAWkYQm3ybzjb6a8bt518x1s.

I need a clear, concise code example for how I can use some existing library to obtain the metadata for a particular NFT. Let's use this NFT for example: a SolStone 4itgFt6tSotypyVAaUkLJzpGQ5KXsJNhwpKBANMv49mf

The furthest I've gotten so far is copying over the metaplex library and using a call like so

 await getProgramAccounts(connection, METADATA_PROGRAM_ID, 'finalized');

however this will load the metadata for all NFTs in existence. I instead need to use some filter instead of 'finalized' as the commitment argument.

In the metaplex codebase they have an example of filtering by creator's address I believe.

filters: [
    {
        memcmp: {
            offset:
            1 + // key
            32 + // update auth
            32 + // mint
            4 + // name string length
            MAX_NAME_LENGTH + // name
            4 + // uri string length
            MAX_URI_LENGTH + // uri
            4 + // symbol string length
            MAX_SYMBOL_LENGTH + // symbol
            2 + // seller fee basis points
            1 + // whether or not there is a creators vec
            4 + // creators vec length
            i * MAX_CREATOR_LEN,
            bytes: whitelistedCreators[j].info.address,
        }
    }
]

So in theory I should be able to update this filter to instead filter by the NFT's own address, but I'm not sure how to get the bit offset correct here to make the filter accurate.

After I am able to read the nft metadata, next I need a code example for updating the metadata. Specifically the URI field.

Answer 1

You're almost there on most of this!

The address 4itgFt6tSotypyVAaUkLJzpGQ5KXsJNhwpKBANMv49mf is in fact a token mint, as seen on the explorer: https://explorer.solana.com/address/4itgFt6tSotypyVAaUkLJzpGQ5KXsJNhwpKBANMv49mf

This means that you'll use a very similar call as that example you found, but instead of filtering on the whitelistedCreators array, you'll filter on the position of the mint, which is at byte 1 + 32, assuming we can trust the comment in the code. That gives a function call of:

getProgramAccounts(connection, METADATA_PROGRAM_ID, {
  filters: [
    {
      memcmp: {
        offset:
          1 + // key
          32 // update auth
        bytes: mintAddress.toBytes(),
      },
    },
  ],
})

For updating the metadata, you'll likely want to use the UpdateMetadata instruction. It looks like the Metaplex JS library has a utility function to do just that: https://github.com/metaplex-foundation/metaplex/blob/9d5a5c6d668cd9c597cff8c63dfba00dee2f72f0/js/packages/common/src/actions/metadata.ts#L481