TypeError while opening Links/

[lidel]

Explorer returns an error while traversing some DAGs.

Steps to reproduce:

1. Open QmWYmE8fzNRYg48E5PaDhMfHqfbPjyQVmUjGQfgAsa4NYq
2. Click on Links/0, you will be moved to QmY4HSz1oVGdUzb8poVYPLsoqBZjH6LZrtgnme9wWn2Qko
3. Then click on Links/0 again, you will see error looking similar to this:

   

Demo: https://webui.ipfs.io/#/explore/QmWYmE8fzNRYg48E5PaDhMfHqfbPjyQVmUjGQfgAsa4NYq/Links/0

Additional notes:

• afaik this happens only when trying to open leaf nodes that are not raw leaves (dag-pb without any children) – perhaps something in IPLD APIs changed and we now need to check if Links array is present?

[lidel]

I have no bandwidth to dig into this, but if someone wants to pick this up, comments by @rvagg in ipld/specs#297 sound relevant.

I suspect the current JS implementation expects [] but gets undefined instead, and that causes the error in IPLD Explorer.

[rvagg]

I'm trying to understand this but finding I don't have nearly enough background in how all of these components work. I'm poking around in js-ipfs to no avail but maybe I'm not even looking in the right place.

The work in the specs repo are for a newer implementation of dag-pb that this shouldn't impact. I don't believe there's been any major changes that should impact this in a while, this was probably the biggest thing (aside from Buffer -> Uint8Array): ipld/js-ipld-dag-pb#184

I'm pretty sure that there will always be a Links array in the current ipld-dag-pb, regardless of what's in the protobuf (this will likely change for the new version - it'll either have elements or not be there at all, although Eric was hinting today that he might prefer an empty array to be the no-links case, we'll discuss further). That terminal without links comes out like this when running in the repl:

> ipldDagPb.util.deserialize(fs.readFileSync('./QmRk1rduJvo5DfEYAaLobS2za9tDszk35hzaNSDCJ74DA7'))
DAGNode {
  Data: <Buffer 08 02 12 80 80 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ... 262104 more bytes>,
  Links: []
}

(there is no Links in the raw pb, but it's created anyway).

Can you tell me how /Links/0/Links/0 is supposed to work? According to the data model form that we put out from ipld-dag-pb it should be /Links/0/Hash/Links/0/Hash and I can run this on the js-ipfs CLI and have it work: js-ipfs dag get QmWYmE8fzNRYg48E5PaDhMfHqfbPjyQVmUjGQfgAsa4NYq/Links/0/Hash/Links/0/Hash. I don't think we have a way to transparently resolve a Link to a CID, it has to go through Hash, but maybe there was a historical time when this worked? It doesn't work in go-ipfs which has its own pathing mechanism for DAG-PB (one of the things that I'm trying to get properly unified for the new JS and Go implementations). Maybe there's some hard-wiring of this Links array that needs to be undone so that they display the contents of each Link element instead?

[rvagg]

Ah, I think I have it!

https://github.com/ipfs-shipyard/ipld-explorer-components/blob/07dc1837ee8ff6f791db312ad00f4a2aef1441d6/src/lib/normalise-dag-node.js#L63

extracting { name, size, cid } from a DAGLink object to support this pathing. That was changed in ipld/js-ipld-dag-pb#127

It should now be { Name, Tsize, Hash }, which will map to what you need. The set of links displayed should probably look like these and be navigable by /Links/x/Hash/... rather than the /Links/x/... magic. I don't know how painful that would be to change but it'll be the "correct" and future-proof version for DAG-PB.

[rvagg]

oh, and this: path: name || `Links/${index}`, maybe could change too - this magic named link stuff is going away too. Only go-ipfs supports this method, it doesn't work in JS and it's being removed in the newer JS & Go libraries entirely. So it's just pure: { Data: Uint8Array, Links: [ { Hash: CID, Name: string, Tsize: number }, ... ] } (where most of the properties can be omitted, but we're making Hash mandatory for links, but an entirely empty block is still possible).