New proposal: support for Google Cloud Endpoints

x-google-endpoints

extension for OpenAPI: https://cloud.google.com/endpoints/docs/openapi/openapi-extensions#x-google-endpoints

this seems doable. I'd suggest an interface like this to represent the extension:

package org.http4k.contract.openapi

interface OpenApiExtension {
    val extensionId: String
    fun <NODE> render(): Render<NODE>
}

, which will be used to produce a key/node pair that can be merged into the API JSON docs at the top level - it will also allow people to define their own extensions without importing them into http4k. The OpenAPI2 and 3 objects would need to take a list of these extensions (defaulted to an emptyList to ensure non-breaking API compatability`

Here is an example of an extension that modifies the root OpenAPI object:

the merging I was thinking of was simply that you provide a Render<MODE> and that gets kv merged into the root - but I suppose we could actually take the finished NODE and process that instead.

I suppose the main risk is a user inadvertently "merges" or overwrites something they want to keep. We could throw an error if a user attempts to over-write pre-existing JSON nodes.

I've added the following interface to cover the ability to extend/modify the JSON document:

interface OpenApiExtension {
    operator fun <NODE> invoke(node: NODE): Render<NODE>
}

. It's currently in master - take a look and let me know if that works for your purposes.

That looks perfect, thanks!