CAIP-19: Add block number tag

[TimDaub]

• In today's CASA call we discussed this change and it was suggested that I e.g. use the "#" separator to indicate the block number.
• Some writing about uri hierarchy: https://datatracker.ietf.org/doc/html/rfc3986#section-1.2.3
• I also checked DID ethr and it doesn't use block numbers: https://github.com/decentralized-identity/ethr-did-resolver/blob/master/doc/did-method-spec.md
• I'm not sure if I'm specifying the ABNF correctly. Happy to have someone correct me.
• We should probably indicate that the + "#" + block_number_tag section is optional. How would I do that in ABNF?

Survey

Did a survey on which chains use ascending block number heights. All that I checked use the concept except for Hedera

ethereum: https://etherscan.io/block/15051057
bitcoin: https://blockchair.com/bitcoin/block/743020
cosmos: https://www.mintscan.io/cosmos/blocks/11082723
litecoin: https://blockchair.com/litecoin/block/2289502
lisk: https://legacy-explorer.lisk.com/block/11289477821881538126
eos: https://eosauthority.com/block/254866414?network=eos
polkadot: https://explorer.polkascan.io/polkadot/block/10964158
filecoin: https://explorer.bitquery.io/filecoin/height/1943190
handshake: https://e.hnsfans.com/block/126736
tezos: https://tzstats.com/2494326
stellar: https://stellarchain.io/ledger/41553526
solana: https://explorer.solana.com/block/139663191
hedera: doesn't use block tags

[qizhou]

Do we want to be HTTP compatible (e.g., can be used by an HTTP gateway with translated HTTP URL)? If so, I would suggest using a character other than "#" as "#" will be treated as a hashtag in HTTP.

[TimDaub]

not sure if I understand this. Wouldn't slashes and colons also interfere? I understand that if you wanted to use CAIP19 as an ID in an URL you'd be running into trouble.

Actually, I've also called this out in an issue but there is someone missing who is making the problematic abundantly clear IMO: #81

[qizhou]

The issue with hashtag # is that in modern browsers, the fragment after hashtag will not be passed to the webservers, i.e., if the webservers need to process the fragment part, it will never find it in the request if the link is visited by a browser (e.g., visited by gateway_link + CAIP19_link).

For slashes and colons, I think they are fine as long as they are passed to the server (e.g., https://web3q.io/vitalikca.eth:4/ works for ERC-4804-translated URL).

[TimDaub]

Great point, but then I think the block number tag should come after the chainId and it'll break existing CAIP-19

[qizhou]

Have ever tried a query with blockNumber attribute? This may become

asset_type: chain_id + "/" + asset_namespace + ":" + asset_reference + "&" + query

query = ("blockNumber" | "n") "=" blockNumber

[TimDaub]

great suggestion, feel free to submit this directly as a PR superseeding/updating mine. I'll be a week on Holiday so I won't make the change sooon

[qizhou]

See #125