108 lines
2.8 KiB
Go
108 lines
2.8 KiB
Go
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// GoToSocial
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// Copyright (C) GoToSocial Authors admin@gotosocial.org
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// SPDX-License-Identifier: AGPL-3.0-or-later
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Affero General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Affero General Public License for more details.
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//
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// You should have received a copy of the GNU Affero General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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package model
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import (
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"bytes"
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"encoding/json"
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"errors"
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)
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// Nullable is a generic type, which implements a field that can be one of three states:
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//
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// - field is not set in the request
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// - field is explicitly set to `null` in the request
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// - field is explicitly set to a valid value in the request
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//
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// Nullable is intended to be used with JSON unmarshalling.
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//
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// Adapted from https://github.com/oapi-codegen/nullable/blob/main/nullable.go
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type Nullable[T any] struct {
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state nullableState
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value T
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}
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type nullableState uint8
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const (
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nullableStateUnspecified nullableState = 0
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nullableStateNull nullableState = 1
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nullableStateSet nullableState = 2
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)
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// Get retrieves the underlying value, if present,
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// and returns an error if the value was not present.
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func (t Nullable[T]) Get() (T, error) {
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var empty T
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if t.IsNull() {
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return empty, errors.New("value is null")
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}
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if !t.IsSpecified() {
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return empty, errors.New("value is not specified")
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}
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return t.value, nil
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}
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// IsNull indicates whether the field
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// was sent, and had a value of `null`
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func (t Nullable[T]) IsNull() bool {
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return t.state == nullableStateNull
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}
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// IsSpecified indicates whether the field
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// was sent either as a value or as `null`.
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func (t Nullable[T]) IsSpecified() bool {
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return t.state != nullableStateUnspecified
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}
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// If field is unspecified,
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// UnmarshalJSON won't be called.
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func (t *Nullable[T]) UnmarshalJSON(data []byte) error {
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// If field is specified as `null`.
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if bytes.Equal(data, []byte("null")) {
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t.setNull()
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return nil
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}
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// Otherwise, we have an
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// actual value, so parse it.
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var v T
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if err := json.Unmarshal(data, &v); err != nil {
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return err
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}
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t.set(v)
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return nil
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}
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// setNull indicates that the field
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// was sent, and had a value of `null`
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func (t *Nullable[T]) setNull() {
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*t = Nullable[T]{state: nullableStateNull}
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}
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// set the underlying value to given value.
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func (t *Nullable[T]) set(value T) {
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*t = Nullable[T]{
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state: nullableStateSet,
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value: value,
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}
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}
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