Auth0 Go SDK unmarshal polymorphic structs using discriminator

json.go

package management

import (
	"encoding/json"
	"reflect"
)

type S struct {

	// The discriminator used to undertsand which concrete type of Option we
	// should use to unmarshal into. Can be either [foo, bar].
	Strategy *string `json:"strategy,omitempty"`

	RawOptions json.RawMessage `json:"options,omitempty"`

	*FooOptions `json:"-"`
	*BarOptions `json:"-"`
}

func (s *S) MarshalJSON() ([]byte, error) {

	type aS S

	v := reflect.ValueOf(s).Elem()

	for _, name := range []string{
		"FooOptions",
		"BarOptions",
	} {
		f := v.FieldByName(name)
		if !f.IsNil() {
			b, err := json.Marshal(f.Interface())
			if err != nil {
				return nil, err
			}
			s.RawOptions = b
		}
	}

	return json.Marshal((*aS)(s))
}

func (s *S) UnmarshalJSON(b []byte) error {

	type aS S

	err := json.Unmarshal(b, (*aS)(s))
	if err != nil {
		return err
	}

	if s.Strategy != nil {

		var v interface{}

		switch *s.Strategy {
		case "foo":
			v = &s.FooOptions
		case "bar":
			v = &s.BarOptions
		default:
			return nil
		}

		err := json.Unmarshal(s.RawOptions, v)
		if err != nil {
			return err
		}
	}

	return nil
}

type FooOptions struct {
	ClientID      *string       `json:"client_id,omitempty"`
	ClientSecret  *string       `json:"client_secret,omitempty"`
	Domain        *string       `json:"domain,omitempty"`
	TenantDomain  *string       `json:"tenant_domain,omitempty"`
	DomainAliases []interface{} `json:"domain_aliases,omitempty"`
}

type BarOptions struct {
	ClientID               *string `json:"client_id,omitempty"`
	ClientSecret           *string `json:"client_secret,omitempty"`
	Contacts               *bool   `json:"contacts,omitempty"`
	Calendar               *bool   `json:"calendar,omitempty"`
	GooglePlus             *bool   `json:"google_plus,omitempty"`
	PicasaWeb              *bool   `json:"picasa_web,omitempty"`
	Youtube                *bool   `json:"youtube,omitempty"`
	GoogleAffiliateNetwork *bool   `json:"google_affiliate_network,omitempty"`
	GoogleBooks            *bool   `json:"google_books,omitempty"`
	Email                  *bool   `json:"email,omitempty"`
	Profile                *bool   `json:"profile,omitempty"`
}

json_test.go

package management

import (
	"encoding/json"
	"testing"

	"gopkg.in/auth0.v3"
)

func TestJSONUnmarshal(t *testing.T) {
	for _, j := range []string{
		`{"strategy": "foo", "options": {"domain": "example.com"}}`,
		`{"strategy": "bar", "options": {"email": true, "profile": true}}`,
		`{"options": {"baz": "true"}}`,
	} {
		var s S
		err := json.Unmarshal([]byte(j), &s)
		if err != nil {
			t.Error(err)
		}
		if s.Strategy != nil {
			switch *s.Strategy {
			case "foo":
				t.Logf("%s %s %s", *s.Strategy, *s.FooOptions.Domain, s.RawOptions)
			case "bar":
				t.Logf("%s %t %t %s", *s.Strategy, *s.BarOptions.Email, *s.BarOptions.Profile, s.RawOptions)
			}
		} else {
			t.Logf("%s", s.RawOptions)
		}
	}
}

func TestJSONMarshal(t *testing.T) {
	for _, s := range []S{
		{
			Strategy: auth0.String("foo"),
			FooOptions: &FooOptions{
				Domain: auth0.String("example.com"),
			},
		},
		{
			Strategy: auth0.String("bar"),
			BarOptions: &BarOptions{
				Email:   auth0.Bool(true),
				Profile: auth0.Bool(true),
			},
		},
	} {
		b, err := json.Marshal(&s)
		if err != nil {
			t.Error(err)
		}
		t.Logf("%s\n", b)
	}
}