Use js-ipld for DAG API

[vmx]

Basic support for the DAG API landed with #534.

Though not all formats are supported and you can't traverse through different types of formats. I.e. you couldn't follow a link from a dag-cbor node to a dag-pb node.

The solution is to use js-ipld instead of hard-coding the formats (currently dag-cbor and dag-pb).

Using js-ipld is not straight forward. The problem is that js-ipld needs a Block Service which in turn needs a Repository to work. But js-htt-api doesn't have the blocks available in the JS environment, but receives them manually over the HTTP API.

So I guess you would need a Block Service (or Repository) that uses the HTTP API to retrieve the blocks. But I leave the details to whoever will implement this.

[alanshaw]

If no-one else is working on this I'd like to have a stab at it. We need the DAG API to work properly for the IPLD Explorers to work with JS-IPFS.

I'm thinking create an IPLDResolver with a block service that uses an "API exchange" (a bitswap exchange that just uses the block API to retrieve blocks it doesn't have).

At least, from reading the commentary on #534 that seems to be the idea.

Any objections?

[alanshaw]

Is it as simple as this? I added IPLD to js-ipfs-api and it now dag.get git dags 😮

[vmx]

No objections. If it's easy that's even better :)

[daviddias]

Woot! Great work @alanshaw ❤️ Let's finish this feat convo up on #755