Support data URLs

[fulldecent]

As written, ERC-721 expects the tokenURI to return:

A distinct Uniform Resource Identifier (URI) for a given asset. ... URIs are defined in RFC 3986.

And it IS possible to encode a JSON file in a RFC 3986 URI using Data URLs (RFC 2397).

All you need to do is prepend this string to the JSON:

data:application/json,

[bmeredith]

I really appreciate you checking this out @fulldecent

In regards to the data URLs - although generating metadata for ERC-721 was the driving use-case behind this library, it was made as a general-purpose library.

Part of the reasoning for this is:

1. There may be other applications or smart contracts that would be able to utilize this library to generate JSON.
2. There has been a rise in popularity of building JSON metadata within an ERC-721 smart contract, but then base64 encoding the resulting JSON or base64 encoding the tokenURI itself.

For these reasons, I have left it up to the client to decide how they will use the resulting JSON. I would love to hear your thoughts, though.

[fulldecent]

Great, it's really nice to have general support. Perhaps something that might be in-scope for this project then is just to add an implementation note for people wanting to use this for ERC-721 metadata.

If your metadata does not contain any RFC3986 reserved characters, simply prepend data:application/json,.

If you may have reserved characters, here is the more general approach...

Here is a basic example NFT contract that implements tokenURI entirely on-chain...

Because I want to recommend this project and just don't want to see people make rookie mistakes on production contracts.

[bmeredith]

That's a great idea.

I can probably get something in there about that within the next week or so. Otherwise I'm happy to accept a PR as well.

[bmeredith]

@fulldecent I've gone ahead and created a PR for this issue. If you have time to check it out, I would really appreciate your thoughts on it before merging in.

[fulldecent]

For number 2:

If the metadata does contain reserved characters, prepend data:application/json;base64, then encode the produced JSON as base64.

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P.S. if you have a preferred base64 approach you can mention that here.

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P.S. OnChain Monkey uses this approach for ERC-721 JSON unchain with Base64 encoding.

[bmeredith]

Thanks for the feedback. I've gone ahead and pushed a change to the PR recommending the use of base64 encoding instead.

I'm currently holding off on mentioning a recommended library for the time being as I am waiting on the base64 library to get added to the official OpenZeppelin utils library. Once that is in place, I'll be adding a note regarding it, though.

OpenZeppelin/openzeppelin-contracts#2884

[fulldecent]

Cool thank you