// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build goexperiment.jsonv2
package json
import (
"errors"
"fmt"
"reflect"
"sync"
"encoding/json/internal"
"encoding/json/internal/jsonflags"
"encoding/json/internal/jsonopts"
"encoding/json/jsontext"
)
// SkipFunc may be returned by [MarshalToFunc] and [UnmarshalFromFunc] functions.
//
// Any function that returns SkipFunc must not cause observable side effects
// on the provided [jsontext.Encoder] or [jsontext.Decoder].
// For example, it is permissible to call [jsontext.Decoder.PeekKind],
// but not permissible to call [jsontext.Decoder.ReadToken] or
// [jsontext.Encoder.WriteToken] since such methods mutate the state.
var SkipFunc = errors.New("json: skip function")
var errSkipMutation = errors.New("must not read or write any tokens when skipping")
var errNonSingularValue = errors.New("must read or write exactly one value")
// Marshalers is a list of functions that may override the marshal behavior
// of specific types. Populate [WithMarshalers] to use it with
// [Marshal], [MarshalWrite], or [MarshalEncode].
// A nil *Marshalers is equivalent to an empty list.
// There are no exported fields or methods on Marshalers.
type Marshalers = typedMarshalers
// JoinMarshalers constructs a flattened list of marshal functions.
// If multiple functions in the list are applicable for a value of a given type,
// then those earlier in the list take precedence over those that come later.
// If a function returns [SkipFunc], then the next applicable function is called,
// otherwise the default marshaling behavior is used.
//
// For example:
//
// m1 := JoinMarshalers(f1, f2)
// m2 := JoinMarshalers(f0, m1, f3) // equivalent to m3
// m3 := JoinMarshalers(f0, f1, f2, f3) // equivalent to m2
func JoinMarshalers(ms ...*Marshalers) *Marshalers {
return newMarshalers(ms...)
}
// Unmarshalers is a list of functions that may override the unmarshal behavior
// of specific types. Populate [WithUnmarshalers] to use it with
// [Unmarshal], [UnmarshalRead], or [UnmarshalDecode].
// A nil *Unmarshalers is equivalent to an empty list.
// There are no exported fields or methods on Unmarshalers.
type Unmarshalers = typedUnmarshalers
// JoinUnmarshalers constructs a flattened list of unmarshal functions.
// If multiple functions in the list are applicable for a value of a given type,
// then those earlier in the list take precedence over those that come later.
// If a function returns [SkipFunc], then the next applicable function is called,
// otherwise the default unmarshaling behavior is used.
//
// For example:
//
// u1 := JoinUnmarshalers(f1, f2)
// u2 := JoinUnmarshalers(f0, u1, f3) // equivalent to u3
// u3 := JoinUnmarshalers(f0, f1, f2, f3) // equivalent to u2
func JoinUnmarshalers(us ...*Unmarshalers) *Unmarshalers {
return newUnmarshalers(us...)
}
type typedMarshalers = typedArshalers[jsontext.Encoder]
type typedUnmarshalers = typedArshalers[jsontext.Decoder]
type typedArshalers[Coder any] struct {
nonComparable
fncVals []typedArshaler[Coder]
fncCache sync.Map // map[reflect.Type]arshaler
// fromAny reports whether any of Go types used to represent arbitrary JSON
// (i.e., any, bool, string, float64, map[string]any, or []any) matches
// any of the provided type-specific arshalers.
//
// This bit of information is needed in arshal_default.go to determine
// whether to use the specialized logic in arshal_any.go to handle
// the any interface type. The logic in arshal_any.go does not support
// type-specific arshal functions, so we must avoid using that logic
// if this is true.
fromAny bool
}
type typedMarshaler = typedArshaler[jsontext.Encoder]
type typedUnmarshaler = typedArshaler[jsontext.Decoder]
type typedArshaler[Coder any] struct {
typ reflect.Type
fnc func(*Coder, addressableValue, *jsonopts.Struct) error
maySkip bool
}
func newMarshalers(ms ...*Marshalers) *Marshalers { return newTypedArshalers(ms...) }
func newUnmarshalers(us ...*Unmarshalers) *Unmarshalers { return newTypedArshalers(us...) }
func newTypedArshalers[Coder any](as ...*typedArshalers[Coder]) *typedArshalers[Coder] {
var a typedArshalers[Coder]
for _, a2 := range as {
if a2 != nil {
a.fncVals = append(a.fncVals, a2.fncVals...)
a.fromAny = a.fromAny || a2.fromAny
}
}
if len(a.fncVals) == 0 {
return nil
}
return &a
}
func (a *typedArshalers[Coder]) lookup(fnc func(*Coder, addressableValue, *jsonopts.Struct) error, t reflect.Type) (func(*Coder, addressableValue, *jsonopts.Struct) error, bool) {
if a == nil {
return fnc, false
}
if v, ok := a.fncCache.Load(t); ok {
if v == nil {
return fnc, false
}
return v.(func(*Coder, addressableValue, *jsonopts.Struct) error), true
}
// Collect a list of arshalers that can be called for this type.
// This list may be longer than 1 since some arshalers can be skipped.
var fncs []func(*Coder, addressableValue, *jsonopts.Struct) error
for _, fncVal := range a.fncVals {
if !castableTo(t, fncVal.typ) {
continue
}
fncs = append(fncs, fncVal.fnc)
if !fncVal.maySkip {
break // subsequent arshalers will never be called
}
}
if len(fncs) == 0 {
a.fncCache.Store(t, nil) // nil to indicate that no funcs found
return fnc, false
}
// Construct an arshaler that may call every applicable arshaler.
fncDefault := fnc
fnc = func(c *Coder, v addressableValue, o *jsonopts.Struct) error {
for _, fnc := range fncs {
if err := fnc(c, v, o); err != SkipFunc {
return err // may be nil or non-nil
}
}
return fncDefault(c, v, o)
}
// Use the first stored so duplicate work can be garbage collected.
v, _ := a.fncCache.LoadOrStore(t, fnc)
return v.(func(*Coder, addressableValue, *jsonopts.Struct) error), true
}
// MarshalFunc constructs a type-specific marshaler that
// specifies how to marshal values of type T.
// T can be any type except a named pointer.
// The function is always provided with a non-nil pointer value
// if T is an interface or pointer type.
//
// The function must marshal exactly one JSON value.
// The value of T must not be retained outside the function call.
// It may not return [SkipFunc].
func MarshalFunc[T any](fn func(T) ([]byte, error)) *Marshalers {
t := reflect.TypeFor[T]()
assertCastableTo(t, true)
typFnc := typedMarshaler{
typ: t,
fnc: func(enc *jsontext.Encoder, va addressableValue, mo *jsonopts.Struct) error {
val, err := fn(va.castTo(t).Interface().(T))
if err != nil {
err = wrapSkipFunc(err, "marshal function of type func(T) ([]byte, error)")
if mo.Flags.Get(jsonflags.ReportErrorsWithLegacySemantics) {
return internal.NewMarshalerError(va.Addr().Interface(), err, "MarshalFunc") // unlike unmarshal, always wrapped
}
err = newMarshalErrorBefore(enc, t, err)
return collapseSemanticErrors(err)
}
if err := enc.WriteValue(val); err != nil {
if mo.Flags.Get(jsonflags.ReportErrorsWithLegacySemantics) {
return internal.NewMarshalerError(va.Addr().Interface(), err, "MarshalFunc") // unlike unmarshal, always wrapped
}
if isSyntacticError(err) {
err = newMarshalErrorBefore(enc, t, err)
}
return err
}
return nil
},
}
return &Marshalers{fncVals: []typedMarshaler{typFnc}, fromAny: castableToFromAny(t)}
}
// MarshalToFunc constructs a type-specific marshaler that
// specifies how to marshal values of type T.
// T can be any type except a named pointer.
// The function is always provided with a non-nil pointer value
// if T is an interface or pointer type.
//
// The function must marshal exactly one JSON value by calling write methods
// on the provided encoder. It may return [SkipFunc] such that marshaling can
// move on to the next marshal function. However, no mutable method calls may
// be called on the encoder if [SkipFunc] is returned.
// The pointer to [jsontext.Encoder] and the value of T
// must not be retained outside the function call.
func MarshalToFunc[T any](fn func(*jsontext.Encoder, T) error) *Marshalers {
t := reflect.TypeFor[T]()
assertCastableTo(t, true)
typFnc := typedMarshaler{
typ: t,
fnc: func(enc *jsontext.Encoder, va addressableValue, mo *jsonopts.Struct) error {
xe := export.Encoder(enc)
prevDepth, prevLength := xe.Tokens.DepthLength()
xe.Flags.Set(jsonflags.WithinArshalCall | 1)
err := fn(enc, va.castTo(t).Interface().(T))
xe.Flags.Set(jsonflags.WithinArshalCall | 0)
currDepth, currLength := xe.Tokens.DepthLength()
if err == nil && (prevDepth != currDepth || prevLength+1 != currLength) {
err = errNonSingularValue
}
if err != nil {
if err == SkipFunc {
if prevDepth == currDepth && prevLength == currLength {
return SkipFunc
}
err = errSkipMutation
}
if mo.Flags.Get(jsonflags.ReportErrorsWithLegacySemantics) {
return internal.NewMarshalerError(va.Addr().Interface(), err, "MarshalToFunc") // unlike unmarshal, always wrapped
}
if !export.IsIOError(err) {
err = newSemanticErrorWithPosition(enc, t, prevDepth, prevLength, err)
}
return err
}
return nil
},
maySkip: true,
}
return &Marshalers{fncVals: []typedMarshaler{typFnc}, fromAny: castableToFromAny(t)}
}
// UnmarshalFunc constructs a type-specific unmarshaler that
// specifies how to unmarshal values of type T.
// T must be an unnamed pointer or an interface type.
// The function is always provided with a non-nil pointer value.
//
// The function must unmarshal exactly one JSON value.
// The input []byte must not be mutated.
// The input []byte and value T must not be retained outside the function call.
// It may not return [SkipFunc].
func UnmarshalFunc[T any](fn func([]byte, T) error) *Unmarshalers {
t := reflect.TypeFor[T]()
assertCastableTo(t, false)
typFnc := typedUnmarshaler{
typ: t,
fnc: func(dec *jsontext.Decoder, va addressableValue, uo *jsonopts.Struct) error {
val, err := dec.ReadValue()
if err != nil {
return err // must be a syntactic or I/O error
}
err = fn(val, va.castTo(t).Interface().(T))
if err != nil {
err = wrapSkipFunc(err, "unmarshal function of type func([]byte, T) error")
if uo.Flags.Get(jsonflags.ReportErrorsWithLegacySemantics) {
return err // unlike marshal, never wrapped
}
err = newUnmarshalErrorAfter(dec, t, err)
return collapseSemanticErrors(err)
}
return nil
},
}
return &Unmarshalers{fncVals: []typedUnmarshaler{typFnc}, fromAny: castableToFromAny(t)}
}
// UnmarshalFromFunc constructs a type-specific unmarshaler that
// specifies how to unmarshal values of type T.
// T must be an unnamed pointer or an interface type.
// The function is always provided with a non-nil pointer value.
//
// The function must unmarshal exactly one JSON value by calling read methods
// on the provided decoder. It may return [SkipFunc] such that unmarshaling can
// move on to the next unmarshal function. However, no mutable method calls may
// be called on the decoder if [SkipFunc] is returned.
// The pointer to [jsontext.Decoder] and the value of T
// must not be retained outside the function call.
func UnmarshalFromFunc[T any](fn func(*jsontext.Decoder, T) error) *Unmarshalers {
t := reflect.TypeFor[T]()
assertCastableTo(t, false)
typFnc := typedUnmarshaler{
typ: t,
fnc: func(dec *jsontext.Decoder, va addressableValue, uo *jsonopts.Struct) error {
xd := export.Decoder(dec)
prevDepth, prevLength := xd.Tokens.DepthLength()
xd.Flags.Set(jsonflags.WithinArshalCall | 1)
err := fn(dec, va.castTo(t).Interface().(T))
xd.Flags.Set(jsonflags.WithinArshalCall | 0)
currDepth, currLength := xd.Tokens.DepthLength()
if err == nil && (prevDepth != currDepth || prevLength+1 != currLength) {
err = errNonSingularValue
}
if err != nil {
if err == SkipFunc {
if prevDepth == currDepth && prevLength == currLength {
return SkipFunc
}
err = errSkipMutation
}
if uo.Flags.Get(jsonflags.ReportErrorsWithLegacySemantics) {
if err2 := xd.SkipUntil(prevDepth, prevLength+1); err2 != nil {
return err2
}
return err // unlike marshal, never wrapped
}
if !isSyntacticError(err) && !export.IsIOError(err) {
err = newSemanticErrorWithPosition(dec, t, prevDepth, prevLength, err)
}
return err
}
return nil
},
maySkip: true,
}
return &Unmarshalers{fncVals: []typedUnmarshaler{typFnc}, fromAny: castableToFromAny(t)}
}
// assertCastableTo asserts that "to" is a valid type to be casted to.
// These are the Go types that type-specific arshalers may operate upon.
//
// Let AllTypes be the universal set of all possible Go types.
// This function generally asserts that:
//
// len([from for from in AllTypes if castableTo(from, to)]) > 0
//
// otherwise it panics.
//
// As a special-case if marshal is false, then we forbid any non-pointer or
// non-interface type since it is almost always a bug trying to unmarshal
// into something where the end-user caller did not pass in an addressable value
// since they will not observe the mutations.
func assertCastableTo(to reflect.Type, marshal bool) {
switch to.Kind() {
case reflect.Interface:
return
case reflect.Pointer:
// Only allow unnamed pointers to be consistent with the fact that
// taking the address of a value produces an unnamed pointer type.
if to.Name() == "" {
return
}
default:
// Technically, non-pointer types are permissible for unmarshal.
// However, they are often a bug since the receiver would be immutable.
// Thus, only allow them for marshaling.
if marshal {
return
}
}
if marshal {
panic(fmt.Sprintf("input type %v must be an interface type, an unnamed pointer type, or a non-pointer type", to))
} else {
panic(fmt.Sprintf("input type %v must be an interface type or an unnamed pointer type", to))
}
}
// castableTo checks whether values of type "from" can be casted to type "to".
// Nil pointer or interface "from" values are never considered castable.
//
// This function must be kept in sync with addressableValue.castTo.
func castableTo(from, to reflect.Type) bool {
switch to.Kind() {
case reflect.Interface:
// TODO: This breaks when ordinary interfaces can have type sets
// since interfaces now exist where only the value form of a type (T)
// implements the interface, but not the pointer variant (*T).
// See https://go.dev/issue/45346.
return reflect.PointerTo(from).Implements(to)
case reflect.Pointer:
// Common case for unmarshaling.
// From must be a concrete or interface type.
return reflect.PointerTo(from) == to
default:
// Common case for marshaling.
// From must be a concrete type.
return from == to
}
}
// castTo casts va to the specified type.
// If the type is an interface, then the underlying type will always
// be a non-nil pointer to a concrete type.
//
// Requirement: castableTo(va.Type(), to) must hold.
func (va addressableValue) castTo(to reflect.Type) reflect.Value {
switch to.Kind() {
case reflect.Interface:
return va.Addr().Convert(to)
case reflect.Pointer:
return va.Addr()
default:
return va.Value
}
}
// castableToFromAny reports whether "to" can be casted to from any
// of the dynamic types used to represent arbitrary JSON.
func castableToFromAny(to reflect.Type) bool {
for _, from := range []reflect.Type{anyType, boolType, stringType, float64Type, mapStringAnyType, sliceAnyType} {
if castableTo(from, to) {
return true
}
}
return false
}
func wrapSkipFunc(err error, what string) error {
if err == SkipFunc {
return errors.New(what + " cannot be skipped")
}
return err
}
