Complete NFT `class` metadata support

[zone117x]

Originally posted by @zone117x in https://github.com/blockstack/stacks-blockchain-api/issues/576#issuecomment-898695717

Processing token metadata works pretty well for SIP-010 compliant FTs. Here's an example from Citycoins on testnet: http://localhost:3999/extended/v1/tokens/ST3CK642B6119EVC6CT550PW5EZZ1AJW6608HK60A.citycoin-token/ft/metadata

{
"token_uri": "https://cdn.citycoins.co/metadata/citycoin.json",
"name": "citycoins",
"description": "The CityCoin template used for testing, mine and stack to support your favorite city while earning STX yield!",
"image_uri": "https://stacks-api.imgix.net/https%3A%2F%2Fcdn.citycoins.co%2Flogos%2Fcitycoin.png?s=b30bf0315b374c32e4d9e953c46bb759",
"image_canonical_uri": "https://cdn.citycoins.co/logos/citycoin.png",
"symbol": "CYCN",
"decimals": 0,
"tx_id": "0x6c2c95a2404199a2ff0e8372d39cdf1be06f5ce1173b680a56dfdf27467ab6b2",
"sender_address": "ST3CK642B6119EVC6CT550PW5EZZ1AJW6608HK60A"
}

NFTs aren't working so well -- the code needs updated to use draft SIP-012 which defines NFT class metadata. Draft SIP-012 is still WIP, and after looking through various NFT contracts on mainnet, it looks like there's a few different ways authors have been defining metadata, examples:

https://explorer.stacks.co/txid/0x3f85e8d2a5453179438ed00e466e38b6c4acb3d2cefa579d20389b84602a12e7?chain=mainnet
(define-read-only (get-nft-meta)
  (ok {name: "Friedger Pool", uri: "https://pool.friedger.de/nft.png", mime-type: "image/png"}))
(define-read-only (get-token-uri (token-id uint))
  (ok (some "https://pool.friedger.de/nft.json")))

https://explorer.stacks.co/txid/0x7246cfb663ddd90041781919961a131938d34345879d708ed7d855039c70b84d?chain=mainnet
(define-read-only (get-nft-meta)
  (ok (some {name: "Clarity Developer OG", uri: "https://bafybeif4p2ukltj5eofwriclz4ru3p7izitprrs7a2rjhtp6qat673wagu.ipfs.dweb.link/", mime-type: "video/webm"})))

https://explorer.stacks.co/txid/0x5d1704291538dbeb201161f9f052f79281bea2a944f8c22e4ebdf67005d2b429?chain=mainnet
(define-read-only (get-nft-meta)
  (ok {name: "First Ever Hiro Hackathon Winner", uri: "https://ipfs.io/ipfs/QmXTeyFsiCGsB6st5FTbvc78RkXG8hKo5SxtCN8cv8ity3/hiro-first-hackathon.webm", mime-type: "video/webm",
        hash: "e4ce55dd89113b846c4d43f7018f66e57e7b12d6af960e2a143f91457d27e1f0"}))

https://explorer.stacks.co/txid/0xe865963227144aec75259f9c1f8e67b2d2b5764a29ba88a5794a700818659748?chain=mainnet
(define-read-only (get-nft-meta)
  {uri: "https://boom-nft-41369b66-36da-4442-be60-fff6d755b065.s3.amazonaws.com/24762181-0ba6-4c5b-9065-1c874fb334d2.svg", name: "Boomboxes", mime-type: "image/svg+xml"})

https://explorer.stacks.co/txid/0x10555a156fbd5931f2b33e843221ce73e3fd661127c64d840c3f8392dbd6887c?chain=mainnet
(define-read-only (get-nft-meta)
  (ok {name: "Friedger Pool", uri: "https://pool.friedger.de/nft.webp", mime-type: "image/webp"}))

https://explorer.stacks.co/txid/0x8f0393265a8a4102701ef6240b03022c567cf67f04e472e077709fe975424921?chain=mainnet
(define-read-only (get-nft-meta)
  (ok (some {name: "beeple", uri: "https://ipfsgateway.makersplace.com/ipfs/QmZ15eQX8FPjfrtdX3QYbrhZxJpbLpvDpsgb2p3VEH8Bqq", mime-type: "image/jpeg"})))
(define-read-only (get-token-uri (token-id uint))
  (ok (some "ipfs://ipfs/QmPAg1mjxcEQPPtqsLoEcauVedaeMH81WXDPvPx3VC5zUz")))

https://explorer.stacks.co/txid/0x8a8b1bd754664715c3280cb41fdf566c741789f200efa74681b79e4409e9800a?chain=mainnet
(define-read-only (get-nft-meta)
  (ok (some {name: "beeple", uri: "https://ipfsgateway.makersplace.com/ipfs/QmZ15eQX8FPjfrtdX3QYbrhZxJpbLpvDpsgb2p3VEH8Bqq", mime-type: "image/jpeg"})))


https://explorer.stacks.co/txid/0x5d8f968111be4556a13d8d0d25f39d998a749a982d673ae6ba7180ee7ccf1f62?chain=mainnet
(define-read-only (get-token-uri (id uint))
  (ok (some "https://cloudflare-ipfs.com/ipfs/bafkreidmfmsjiqunj4tkln57ozw2yhazufqv63j5zohhsqchwol6lznsfy")))

The NFT metadata processing code needs updated to handle the 2 or 3 common ways metadata is defined.

[unclemantis]

I am having trouble with local stacks api.

"error": "FT metadata processing is not enabled on this server"

I have the flag to allow it set to 1. What gives? I am currently synching and at block height 1854

[zone117x]

This issue is related to NFT class metadata, the error FT metadata processing is not enabled on this server is for FT class metadata.

[rafaelcr]

Replaced by #1222