Do we need to specify merkle value for `closestDescendantMerkleValue`?

[bkchr]

Reading the spec it isn't clear to me if merkle value returned by closestDescendantMerkleValue is an opaque object or we need to specify it? I mean it probably makes 100% sense to keep it opaque, but then we should mention this and also mention that this can not be compared across different implementations (not sure someone would ever do this).

[tomaka]

The "Merkle value" is what is defined in the spec: https://spec.polkadot.network/chap-state#sect-merkl-proof

It's either the node value if it's < 32 bytes or the hash of the node value if it's >= 32 bytes. (and the node value is concat(header, partial key, children bitmap, storage value, children))

I don't really see the problem with making it well defined. It's not like we're going to change this aspect of the trie any time soon. And I don't think "the substrate-trie-db code is a bit confusing" is a good argument to make it opaque.

Saying that the value is opaque instead of well-defined means that the value might change after chainHead_follow generates a stop event, which actually complicates the JSON-RPC-client-side code (maybe quite a lot) as it must make sure to clear all its caches.

[bkchr]

I'm also in for making it non opaque. That was the main reason I created this issue, to get consensus on this.

[bkchr]

But then we should still specify it. I would assume return an encoded version of a SCALE encoded enum like this:

enum MerkleValue {
     Node(Vec<u8>),
     Hash(H),
}

Does that makes sense to you?

[tomaka]

The Merkle value is:

• Equal to the node value if the node value is < 32 bytes and the node is not the root of the trie
• Equal to the hash of the node value otherwise

https://spec.polkadot.network/chap-state#defn-merkle-value

I don't see what more to specify

[bkchr]

• Equal to the node value if the node value is < 32 bytes and the node is not the root of the trie

The correct way is if the node value is <= 32 bytes. This means there is no way to distinguish if this is a node value or a hash.