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|
package encoding
import (
"errors"
"reflect"
"runtime"
"sync"
)
var byteSliceType = reflect.TypeOf([]byte(nil))
type decoderFunc func(dv reflect.Value, sv reflect.Value) error
// Decode decodes map[string]interface{} into a struct. The first parameter
// must be a pointer.
func Decode(dst interface{}, src interface{}) (err error) {
return decode(dst, src, true)
}
func Merge(dst interface{}, src interface{}) (err error) {
return decode(dst, src, false)
}
func decode(dst interface{}, src interface{}, blank bool) (err error) {
defer func() {
if r := recover(); r != nil {
if _, ok := r.(runtime.Error); ok {
panic(r)
}
if v, ok := r.(string); ok {
err = errors.New(v)
} else {
err = r.(error)
}
}
}()
dv := reflect.ValueOf(dst)
sv := reflect.ValueOf(src)
if dv.Kind() != reflect.Ptr {
return &DecodeTypeError{
DestType: dv.Type(),
SrcType: sv.Type(),
Reason: "must be a pointer",
}
}
dv = dv.Elem()
if !dv.CanAddr() {
return &DecodeTypeError{
DestType: dv.Type(),
SrcType: sv.Type(),
Reason: "must be addressable",
}
}
return decodeValue(dv, sv, blank)
}
// decodeValue decodes the source value into the destination value
func decodeValue(dv, sv reflect.Value, blank bool) error {
return valueDecoder(dv, sv, blank)(dv, sv)
}
type decoderCacheKey struct {
dt, st reflect.Type
}
var decoderCache struct {
sync.RWMutex
m map[decoderCacheKey]decoderFunc
}
func valueDecoder(dv, sv reflect.Value, blank bool) decoderFunc {
if !sv.IsValid() {
return invalidValueDecoder
}
if dv.IsValid() {
dv = indirect(dv, false)
if sv.Kind() == reflect.Ptr {
sv = indirect(sv, false)
dv.Set(sv)
} else if blank {
dv.Set(reflect.Zero(dv.Type()))
}
}
return typeDecoder(dv.Type(), sv.Type(), blank)
}
func typeDecoder(dt, st reflect.Type, blank bool) decoderFunc {
decoderCache.RLock()
f := decoderCache.m[decoderCacheKey{dt, st}]
decoderCache.RUnlock()
if f != nil {
return f
}
// To deal with recursive types, populate the map with an
// indirect func before we build it. This type waits on the
// real func (f) to be ready and then calls it. This indirect
// func is only used for recursive types.
decoderCache.Lock()
var wg sync.WaitGroup
wg.Add(1)
decoderCache.m[decoderCacheKey{dt, st}] = func(dv, sv reflect.Value) error {
wg.Wait()
return f(dv, sv)
}
decoderCache.Unlock()
// Compute fields without lock.
// Might duplicate effort but won't hold other computations back.
f = newTypeDecoder(dt, st, blank)
wg.Done()
decoderCache.Lock()
decoderCache.m[decoderCacheKey{dt, st}] = f
decoderCache.Unlock()
return f
}
// indirect walks down v allocating pointers as needed,
// until it gets to a non-pointer.
func indirect(v reflect.Value, decodeNull bool) reflect.Value {
// If v is a named type and is addressable,
// start with its address, so that if the type has pointer methods,
// we find them.
if v.Kind() != reflect.Ptr && v.Type().Name() != "" && v.CanAddr() {
v = v.Addr()
}
for {
// Load value from interface, but only if the result will be
// usefully addressable.
if v.Kind() == reflect.Interface && !v.IsNil() {
e := v.Elem()
if e.Kind() == reflect.Ptr && !e.IsNil() && (!decodeNull || e.Elem().Kind() == reflect.Ptr) {
v = e
continue
}
}
if v.Kind() != reflect.Ptr {
break
}
if v.IsNil() {
v.Set(reflect.New(v.Type().Elem()))
}
v = v.Elem()
}
return v
}
|
