Is it possible to resolve custom tags remotely?

[jindong-zhang-git]

Hi team.

Due to the architecture of my app, I'd like to define some remote custom tag resolvers, which should be involved when parsing YAMLs, to provide dynamic custom tag definitions.

And the communication between systems uses a JSON based RPC. So only plain datas are supported during communication.

Can I know your opinions about the possibility? Thanks.

[eemeli]

The custom tag resolvers are expected to be synchronous, as allowing asynchrony there would effectively require everything up to and including YAML.parse() to also be asynchronous.

So if your remote calls are sync, there should be no issue in writing a custom tag for handling them. OTOH, if they're async, then you're probably better off parsing the source first with YAML.parseDocument() and then using a visitor to do your remote resolution.

[eemeli]

1. Huh, good point. Yes, in that you're free to call async code from a visitor and then modify the node later. No, in that you can't return a promise from a visitor. I filed issue YAML.visit() should support async visitors #362 for this.
2. If you only need the actual data, then yes, they all have a toJSON() method.

[jindong-zhang-git]

2. If you only need the actual data, then yes, they all have a toJSON() method.

I see but its result only contains "actual data" as you said. But in this scenario, the remote resolver should return AST nodes which contains not only actual data, but also all of metadata, to construct a document as same as the one generated by local parser.

[eemeli]

Perhaps this would be easier to understand if you could provide an example of a YAML input and the remotely determined value that it should resolve to?

[suerta-git]

Hi @eemeli, this is my another account.

Perhaps this would be easier to understand if you could provide an example of a YAML input and the remotely determined value that it should resolve to?

If I parse a yaml document using YAML.parseDocument() directly, the result will be content nodes Scalar | YAMLMap | YAMLSeq which can contain "metadata" like comment, range, tag in addition to actual data.

So I expect the remote resolvers also return such content nodes, then I can insert them into parsed yaml document.

But I can't just serialize content nodes using JSON.stringify() because its result looses nodes' "metadata". Is there a simple way that I can transport those data via JSON and then restore them to Scalar | YAMLMap | YAMLSeq nodes in consumer?

[eemeli]

Then you're talking about a different operation than "tag resolution", which really should only consider the actual scalar or collection value of a node.

Again, an actual example would really help.

If you do need to transport a representation of a node to a remote processor without losing any of the metadata, then why not send it as YAML?