146 lines
3.4 KiB
Go
146 lines
3.4 KiB
Go
// Copyright © 2019 Bjørn Erik Pedersen <bjorn.erik.pedersen@gmail.com>.
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//
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// Use of this source code is governed by an MIT-style
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// license that can be found in the LICENSE file.
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package tmc
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import (
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"encoding"
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"fmt"
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"math/big"
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"reflect"
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"strconv"
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"time"
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)
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// Adapter wraps a type to preserve type information when encoding and decoding
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// a map.
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//
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// The simples way to create new adapters is via the NewAdapter function.
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type Adapter interface {
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FromString(s string) (interface{}, error)
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MarshalText() (text []byte, err error)
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Type() reflect.Type
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Wrap(v interface{}) Adapter
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}
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var (
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// DefaultTypeAdapters contains the default set of type adapters.
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DefaultTypeAdapters = []Adapter{
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// Time
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NewAdapter(time.Now(), nil, nil),
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NewAdapter(
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3*time.Hour,
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func(s string) (interface{}, error) { return time.ParseDuration(s) },
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func(v interface{}) (string, error) { return v.(time.Duration).String(), nil },
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),
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// Numbers
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NewAdapter(big.NewRat(1, 2), nil, nil),
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NewAdapter(
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int(32),
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func(s string) (interface{}, error) {
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return strconv.Atoi(s)
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},
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func(v interface{}) (string, error) {
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return strconv.Itoa(v.(int)), nil
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},
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),
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}
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)
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// NewAdapter creates a new adapter that wraps the target type.
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//
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// fromString can be omitted if target implements encoding.TextUnmarshaler.
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// toString can be omitted if target implements encoding.TextMarshaler.
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//
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// It will panic if it can not be created.
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func NewAdapter(
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target interface{},
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fromString func(s string) (interface{}, error),
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toString func(v interface{}) (string, error)) Adapter {
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targetValue := reflect.ValueOf(target)
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targetType := targetValue.Type()
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wasPointer := targetType.Kind() == reflect.Ptr
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if !wasPointer {
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// Need the pointer to see the TextUnmarshaler implementation.
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v := targetValue
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targetValue = reflect.New(targetType)
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targetValue.Elem().Set(v)
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}
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if fromString == nil {
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if _, ok := targetValue.Interface().(encoding.TextUnmarshaler); ok {
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fromString = func(s string) (interface{}, error) {
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typ := targetType
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if typ.Kind() == reflect.Ptr {
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typ = typ.Elem()
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}
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v := reflect.New(typ)
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err := v.Interface().(encoding.TextUnmarshaler).UnmarshalText([]byte(s))
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if err != nil {
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return nil, err
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}
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if !wasPointer {
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v = v.Elem()
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}
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return v.Interface(), nil
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}
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} else {
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panic(fmt.Sprintf("%T can not be unmarshaled", target))
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}
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}
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var marshalText func(v interface{}) ([]byte, error)
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if toString != nil {
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marshalText = func(v interface{}) ([]byte, error) {
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s, err := toString(v)
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return []byte(s), err
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}
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} else if _, ok := target.(encoding.TextMarshaler); ok {
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marshalText = func(v interface{}) ([]byte, error) {
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return v.(encoding.TextMarshaler).MarshalText()
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}
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} else {
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panic(fmt.Sprintf("%T can not be marshaled", target))
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}
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return &adapter{
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targetType: targetType,
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fromString: fromString,
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marshalText: marshalText,
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}
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}
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var _ Adapter = (*adapter)(nil)
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type adapter struct {
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fromString func(s string) (interface{}, error)
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marshalText func(v interface{}) (text []byte, err error)
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targetType reflect.Type
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target interface{}
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}
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func (a *adapter) FromString(s string) (interface{}, error) {
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return a.fromString(s)
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}
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func (a *adapter) MarshalText() (text []byte, err error) {
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return a.marshalText(a.target)
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}
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func (a adapter) Type() reflect.Type {
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return a.targetType
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}
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func (a adapter) Wrap(v interface{}) Adapter {
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a.target = v
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return &a
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}
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