[Rest Api Compatibility] Licence accept_enterprise and response changes

[pgomulka]

in #50067 for _license the accept_enterprise = false was no longer supported. This
commit allows it under rest compatibility and is showing enterprise licenses as platinum
The same change had to be applied to _xpack endpoint #58217

in #50735 max_resource_units was introduced to be more accurate. For v7 requests, which do not know about enterprise license we will return max_node which will be set from max_resource_units (it assumes that one resource unit is 32GB - which corresponds to 1 node)

relates #51816

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[elasticmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)

[elasticmachine]

Pinging @elastic/es-security (Team:Security)

[pgomulka]

we also no longer parse hide_enterprise but it was present in 7.x?

[tvernum]

I find this compatibility change to be a bit weird. We're going out of our way to accept a parameter value so that we can ignore it and not do the thing that the client asked for.
I haven't kept up to date with the objectives of the compatibility project, but this one really puzzles me. The client is explicitly saying "don't show me an enterprise licenses" and our response is "yes, we hear you, and that's fine, but we're going to show you one anyway". I don't understand why that's helpful.

On this one I really think we should go all the way and hide enterprise licenses from 7.x clients, or reject the parameter. Accepting it but refusing to honor it doesn't make sense to me.

we also no longer parse hide_enterprise but it was present in 7.x?

We never supported hide_enterprise in the Rest API. It was only used as an override parameter to the XContent generation of the license body.
We'd only need to add it back if we want to continue to support hiding enterprise licenses.

[pgomulka]

I might have prematurely hit ready for review when this was meant to be a draft helping me to ask a question offline.
thank you for explanation @tvernum I did not notice at first that the change to allow enterprise was only in 7.x.
And I agree, I think we should honor the parameter and only show enterprise licenses to a 7.x client when he asked for this.

[ywangd]

The existing (7.x) behaviours of accept_enterprise seem inconsistent to me between GetLicense and GetXPackInfo APIs. For this review, I assume we are not trying to fix the inconsistency and just to ensure 8.x behaves the same as 7.x when rest compat is requested. Happy to chat if you need clarification for any of the comments.

[ywangd]

Maybe I don't fully understand the intended behaviour for hideEnterprise. In GetLicense 7.x, it seems that it is only honored if version < VERSION_ENTERPRISE. But this is already inconsistent with RestXPackInfo 7.x which always hide enterprise if requested.

Anyway, if we just want to keep whatever 7.x have as is and be compatible, I think we can just copy the code from 7.x, i.e.:

if (version >= VERSION_ENTERPRISE) {
    builder.field(Fields.MAX_NODES, maxNodes == -1 ? null : maxNodes);
    builder.field(Fields.MAX_RESOURCE_UNITS, maxResourceUnits == -1 ? null : maxResourceUnits);
} else if (hideEnterprise && maxNodes == -1) {
    builder.field(Fields.MAX_NODES, maxResourceUnits);
} else {
    builder.field(Fields.MAX_NODES, maxNodes);
}

The value of hideEnterprise is already a result of checking rest compat, so I don't think we need check it again here.

[ywangd]

We discussed lively and realised that 7.x sets the license version is set to before enterprise when accept_enterprise=false. So it does always hide it similar to RestGetXPackInfo.
We also decided that the V7 compat should just behave the same way as 7.x (by mostly adding relevant code from 7.x).

[ywangd]

LGTM

[pgomulka]

@elasticmachine update branch