internal/util.go

package internal

import (
	"reflect"
)

// RemainingKeys will inspect a struct and compare it to a map. Any key that
// is not defined in a JSON tag of the struct will be added to the extras map
// and returned.
//
// This is useful for determining the extra fields returned in response bodies
// for resources that can contain an arbitrary or dynamic number of fields.
func RemainingKeys(s interface{}, m map[string]interface{}) (extras map[string]interface{}) {
	extras = make(map[string]interface{})
	valueOf := reflect.ValueOf(s)
	typeOf := reflect.TypeOf(s)
	for i := 0; i < valueOf.NumField(); i++ {
		field := typeOf.Field(i)
		tagValue := field.Tag.Get("json")
		if _, ok := m[tagValue]; !ok {
			extras[tagValue] = m[tagValue]
		}
	}

	return
}