Implement DagJSON

[vmx]

There should be a DagJSON implementation using the Ipld enum specified in the ipld-core crate.

It doesn't necessarily need to use Serde (like DagCBOR is doing), I'd actually be happy if it wouldn't use Serde as it currently is an unnecessary intermediate step. So it would do the JSON encoding straight from an Ipld enum.

[Gozala]

I would like to work on this (I have no way of assigning it to myself so just commenting instead)

[Gozala]

I'd actually be happy if it wouldn't use Serde as it currently is an unnecessary intermediate step. So it would do the JSON encoding straight from an Ipld enum.

What about decoder though ? It seems like using established library serde for parsing might be better than writing a JSON parser doesn't it ?

[Gozala]

@vmx, @mikeal what the expected dag-json encoding for the following:

rust-ipld/dag-cbor/tests/lib.rs

Lines 9 to 15 in a508ee6

	// Contact { name: "Hello World", details: CID }
	let mut map = BTreeMap::new();
	map.insert("name".to_string(), Ipld::String("Hello World!".to_string()));
	map.insert("details".to_string(), Ipld::Link(vec![7, 8, 9]));
	let contact = Ipld::Map(map);
	let contact_encoded = ipld_dag_cbor::encode(&contact).unwrap();

Looking at the JS implementation I'm under impression that it should be:

{
 "details":{"/":"BwgJ"}, // Base64 encoded bytes 7, 8, 9
 "name":"Hello World!"
}

Which in turns makes me wonder if invalid CIDs should even be allowed.

[vmx]

What about decoder though ? It seems like using established library serde for parsing might be better than writing a JSON parser doesn't it ?

I would've hoped that there would also be any other JSON parsers. I won't reject a PR which is using Serde, but it might not be worth the effort getting it working.

[vmx]

Which in turns makes me wonder if invalid CIDs should even be allowed.

Invialid CIDs probably shouldn't be accepted. It's early days for this lib still, hence such things are not taken into account yet. Those are the things that need to be worked on :)

[Gozala]

@vmx #2 implements dag-json using serde under the hood. I could go and reimplement it from scratch to not use it serde, but would think that maybe getting other codecs implemented first would be a better option as that experience might inform design.

#2 also makes an assumption outlined in #1 (comment)

Invialid CIDs probably shouldn't be accepted. It's early days for this lib still, hence such things are not taken into account yet. Those are the things that need to be worked on :)

I'm happy to take on that next. However I am still not exactly sure how to distinguish between incorrectly encoded CID vs some other data in some encodings. In dag-cbor it's clear due to a tag however in JSON encoding { "/": "...." } could be either invalid link or some valid JSON object that happens to look similar.

[Gozala]

Oh it is also worth mentioning that it appears ipfs-rust/dag-cbor does not make use of serde and implements own macros similar to it.