Allow Arbitrary Data in Transaction Extra Nonce via Wallet-API

[brandonlehmann]

This allows for the addition of arbitrary hexadecimal data to be added to a transaction nonce via wallet-api.

The additional body parameter extra has been added to support this.

Once supplied, the data is encoded behind a special nonce tag (127) and appended to the nonce such that:

Example: https://explorer.turtlecoin.lol/transaction.html?hash=5591fc3bb7384d304341066b214635687c615c860b17024d8cdb593e23aae017

Note: This does not remove the 1,024 byte limit for the TX_EXTRA so that limit still applies.

This matches how I handled this in turtlecoin-utils

[zpalmtree]

This parsing code looks pretty good to me, but have you tested it with slightly too short/too long lengths? It's very easy to get off by one errors in code like this.

[brandonlehmann]

This parsing code looks pretty good to me, but have you tested it with slightly too short/too long lengths? It's very easy to get off by one errors in code like this.

I've ran it through as many tests as I possibly can of long/short values and while it does not throw an error -- improperly constructed fields will lead to unexpected behavior.

Example: If you put the public key behind the nonce field, and you say the nonce field is 25-bytes long but only supply 24-bytes, the public key will not be read as the identifier 01 will be considered part of the nonce field. Little things like that. It's pretty much the same issue as if someone were to construct extra with garbage data at the front and the parser would find 01 and the next 32-bytes are considered the public key -- although the real public key is farther back in the array. Garbage in, garbage out.

All that being said, I've moved this to a WIP as I'd like to extend wallet-api to be able to return this information when getting transaction information; however, I haven't started on that just yet. We'll call that Phase 2 in another PR

[brandonlehmann]

Removed WIP tag. Storing and retrieving the data in wallets, as an option, will be addressed in another PR.