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value.go
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value.go
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package jsong
import (
"fmt"
"reflect"
"strings"
)
var (
booleanType = reflect.TypeOf(boolean(false))
numType = reflect.TypeOf(num(0))
strType = reflect.TypeOf(str(""))
stringType = reflect.TypeOf(string(""))
)
// ValueOf creates the jsong value of the input v.
//
// It performs an operation similar to, but more
// efficient than:
//
// data, _ := json.Marshal(x)
// v := new(any)
// json.Unmarshal(data, v)
//
// ValueOf panics if v contains any cycles.
func ValueOf(v any) any {
if _, ok := v.(valueInterface); ok {
// No need to re-encode valueInterface.
return v
}
return new(encoder).encode(reflect.ValueOf(v))
}
type encoder struct {
// Avoid cycles.
// See pkg.go.dev/encoding/json#encodeState for details.
ptrLevel uint
ptrSeen map[any]struct{}
}
const startDetectingCyclesAfter = 100
func (e *encoder) encode(v reflect.Value) valueInterface {
switch v.Kind() {
case reflect.Bool:
return v.Convert(booleanType).Interface().(boolean)
case reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Int,
reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uint,
reflect.Float32, reflect.Float64:
return v.Convert(numType).Interface().(valueInterface)
case reflect.String:
return v.Convert(strType).Interface().(valueInterface)
case reflect.Array:
return e.encodeArray(v)
case reflect.Slice:
return e.encodeArray(v)
case reflect.Map:
return e.encodeMap(v)
case reflect.Struct:
return e.encodeStruct(v)
case reflect.Interface:
return e.encodeInterface(v)
case reflect.Pointer:
return e.encodePointer(v)
case reflect.Invalid:
return null{}
default:
panic(fmt.Errorf("ValueOf: unsupported Kind: %q", v.Kind()))
}
}
func (e *encoder) encodeInterface(v reflect.Value) valueInterface {
if v.IsNil() {
return nil
}
return e.encode(v.Elem())
}
func (e *encoder) encodePointer(v reflect.Value) valueInterface {
if v.IsNil() {
return nil
}
if e.ptrLevel++; e.ptrLevel > startDetectingCyclesAfter {
ptr := v.Interface()
if _, ok := e.ptrSeen[ptr]; ok {
panic(fmt.Errorf("ValueOf: encountered a cycle via %s", v.Type()))
}
if e.ptrSeen == nil {
e.ptrSeen = make(map[any]struct{})
}
e.ptrSeen[ptr] = struct{}{}
defer func() { e.ptrLevel--; delete(e.ptrSeen, ptr) }()
}
return e.encode(v.Elem())
}
func (e *encoder) encodeArray(v reflect.Value) valueInterface {
if v.IsNil() {
return array(nil)
}
if v.Kind() == reflect.Slice && v.Type().Elem().Kind() == reflect.Uint8 {
// Special case for []byte.
return v.Convert(strType).Interface().(valueInterface)
}
if e.ptrLevel++; e.ptrLevel > startDetectingCyclesAfter {
ptr := struct {
ptr interface{}
len int
}{v.UnsafePointer(), v.Len()}
if _, ok := e.ptrSeen[ptr]; ok {
panic(fmt.Errorf("ValueOf: encountered a cycle via %s", v.Type()))
}
if e.ptrSeen == nil {
e.ptrSeen = make(map[any]struct{})
}
e.ptrSeen[ptr] = struct{}{}
defer func() { e.ptrLevel--; delete(e.ptrSeen, ptr) }()
}
res := make(array, v.Len())
for i := 0; i < v.Len(); i++ {
res[i] = e.encode(v.Index(i))
}
return res
}
func (e *encoder) encodeMap(v reflect.Value) valueInterface {
if v.IsNil() {
return object(nil)
}
if !v.Type().Key().ConvertibleTo(stringType) {
panic(fmt.Errorf("ValueOf: map keys must be convertable to string"))
}
if e.ptrLevel++; e.ptrLevel > startDetectingCyclesAfter {
ptr := v.UnsafePointer()
if _, ok := e.ptrSeen[ptr]; ok {
panic(fmt.Errorf("ValueOf: encountered a cycle via %s", v.Type()))
}
if e.ptrSeen == nil {
e.ptrSeen = make(map[any]struct{})
}
e.ptrSeen[ptr] = struct{}{}
defer func() { e.ptrLevel--; delete(e.ptrSeen, ptr) }()
}
iter := v.MapRange()
res := make(object, v.Len())
for iter.Next() {
k := iter.Key().Convert(stringType).Interface().(string)
res[k] = e.encode(iter.Value())
}
return res
}
func (d *encoder) encodeStruct(rv reflect.Value) valueInterface {
t := rv.Type()
res := make(object, t.NumField())
for i := 0; i < t.NumField(); i++ {
f := t.Field(i)
name := f.Name
var omitEmpty bool
if jsonTag, ok := f.Tag.Lookup("json"); ok {
omitEmpty = strings.HasSuffix(jsonTag, ",omitempty")
name = strings.TrimSuffix(jsonTag, ",omitempty")
}
if name == "-" {
continue // Skip no JSON.
}
v := d.encode(rv.Field(i))
if name == "" && f.Anonymous {
vm := v.(object)
// Embed resulting values into the map directly
// While avoiding collisions.
var toDeleteKeys []string
for k, v := range vm {
if _, ok := res[k]; !ok {
res[k] = v
toDeleteKeys = append(toDeleteKeys, k)
}
}
for _, k := range toDeleteKeys {
delete(vm, k)
}
if len(vm) > 0 {
// Any collision keys are stored in the original place.
res[f.Name] = vm
}
continue
}
if !omitEmpty || !reflect.ValueOf(v).IsZero() {
res[name] = v
}
}
return res
}