My understanding is that additionalProperties should only be true for maps in Go, Go objects do not make it possible to dynamically add fields to them. Maybe we should instead always set it to false except for maps (which is already taken into consideration)? The specification says:

Consistent with JSON Schema, additionalProperties defaults to true.

So it does seem like we should always generate it and set it to false except for maps.

Sorry, I didn't explain it enough. This function was supposed to set additionalProperties: false on an object.

In this case, bar is sent even though it is not defined in the OpenAPI schema, but that is OK because additionalProperties is considered true by default.

OpenAPI schema

Payload:
    title: Payload
    type: object
    properties:
        foo:
            type: string

Incoming request

{"foo":"1","bar":"2"}

If additionalProperties: false is specified, this will be considered an invalid request and will cause OpenAPI validation errors in many libraries.

All of this is about OpenAPI and has nothing to do with the actual server implementation. In terms of Go encoding/json, if the unmarshal target contains undefined fields, they are simply ignored.

Ah great, that makes sense! Thank you for the explanation.