Might also need changes in Buildx client: https://github.com/docker/buildx/blob/23cabd67fb1c5e7ba2e3765e91bd5cc0f0311337/build/utils.go#L41-L56

Ah, yes, see docker/cli#2337

Although, I'm wondering if we should perform validation at all on the client side (basically; perhaps it should always be delegated to the API server to consider if options are valid or not)

Although, I'm wondering if we should perform validation at all on the client side (basically; perhaps it should always be delegated to the API server to consider if options are valid or not)

Yes I think it would be better, we already validate extra hosts on BuildKit: https://github.com/moby/buildkit/blob/7804e2c7fc09b4a536934f5607698bc3255cf0ed/frontend/dockerfile/builder/build.go#L751-L775

Not sure if they can factored since there is currently no way for buildx to retrieve the host-gateway-ip setting from the daemon (not even exposed in /info).

I think this feature would currently only apply to the docker builder, unless BuildKit itself (running as container-builder) would implement a configuration for this, in which case it would (should?) also do the conversion on the daemon side.

As mentioned in an earlier comment, I think we should remove validation from the client side altogether (other than splitting key/value where needed), and leave it to the daemon to return an error if the value is valid or not.

As mentioned in an earlier comment, I think we should remove validation from the client side altogether (other than splitting key/value where needed), and leave it to the daemon to return an error if the value is valid or not.

I discussed about this with @tonistiigi yesterday and the validation client-side avoid sending extra build request.

Edit: opened follow-up on buildx repo: docker/buildx#1446