API for serializing / deserializing delegations

[Gozala]

As per #173 (comment) there seems to be a desire for an API that can serialize / de-serialize delegations

[Gozala]

@alanshaw this has came up in the past with @hugomrdias and my answer was, we can't have fromJSON because:

1. It's unclear what JSON representation of DAG would look like or how would it deduplicate.
2. I also worry that one could craft JSON that is invalid delegation and could deceive system into thinking it's valid unless verified.

All in all fromJSON sounds error prone that I don't believe it's worth it.

What we do have instead is

ucanto/packages/core/src/delegation.js

Lines 215 to 225 in e97bd8e

	const exportDAG = function* (root, blocks) {
	for (const link of decode(root).proofs) {
	// Check if block is included in this delegation
	const root = /** @type {UCAN.Block} */ (blocks.get(link.toString()))
	if (root) {
	yield* exportDAG(root, blocks)
	}
	}
	yield root
	}

Which is used by transport to serialize delegation into a CAR which can represent DAGs

ucanto/packages/transport/src/car.js

Lines 25 to 30 in e97bd8e

	for (const block of delegation.export()) {
	blocks.set(block.cid.toString(), block)
	}
	blocks.delete(delegation.root.cid.toString())
	}
	const body = CAR.encode({ roots, blocks })

Only reason there was never toCAR / fromCAR is because I wrote sync car encoder but have not got around to writing sync decoder. However sounds like @hugomrdias got around to doing it, so perhaps he'd be game to integrate it here and add those methods ?

I know CAR isn't a string, but but we have base codec to deal with that.

If we really want a JSON version than I think we need to define CAR like structure in DAG JSON in which case it would become plausible.

[hugomrdias]

yes its this file https://github.com/web3-storage/w3protocol/blob/6abe8c2dcc72a888ce998c6f5d126f6ba3f81c4c/packages/access-client/src/encoding.js

I used base64url for the string encoding.
We should move those to ucanto directly.

Is this enough for your needs @alanshaw ?

if it is we should add this task to the current phase