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gob: support GobEncoder for type T when the receiver is *T.

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Still to do: **T.

R=rsc
CC=golang-dev
https://golang.org/cl/4247061
This commit is contained in:
Rob Pike 2011-03-07 12:08:31 -08:00
parent 2168e6aaf1
commit 22c45c558b
4 changed files with 99 additions and 56 deletions
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18
src/pkg/gob/decode.go
View File

@ -936,8 +936,11 @@ func (dec *Decoder) decIgnoreOpFor(wireId typeId) decOp {
// GobDecoder.
func (dec *Decoder) gobDecodeOpFor(ut *userTypeInfo) (*decOp, int) {
rt := ut.user
if ut.decIndir != 0 {
errorf("gob: TODO: can't handle indirection to reach GobDecoder")
if ut.decIndir > 0 {
errorf("gob: TODO: can't handle >0 indirections to reach GobDecoder")
}
if ut.decIndir == -1 {
rt = reflect.PtrTo(rt)
}
index := -1
for i := 0; i < rt.NumMethod(); i++ {
@ -953,9 +956,16 @@ func (dec *Decoder) gobDecodeOpFor(ut *userTypeInfo) (*decOp, int) {
op = func(i *decInstr, state *decoderState, p unsafe.Pointer) {
// Allocate the underlying data, but hold on to the address we have,
// since it's known to be the receiver's address.
// TODO: fix this up when decIndir can be non-zero.
allocate(ut.base, uintptr(p), ut.indir)
v := reflect.NewValue(unsafe.Unreflect(rt, p))
var v reflect.Value
switch {
case ut.decIndir == 0:
v = reflect.NewValue(unsafe.Unreflect(rt, p))
case ut.decIndir == -1:
v = reflect.NewValue(unsafe.Unreflect(rt, unsafe.Pointer(&p)))
default:
errorf("gob: TODO: can't handle >0 indirections to reach GobDecoder")
}
state.dec.decodeGobDecoder(state, v, index)
}
return &op, int(ut.decIndir)

18
src/pkg/gob/encode.go
View File

@ -573,8 +573,11 @@ func (enc *Encoder) encOpFor(rt reflect.Type, inProgress map[reflect.Type]*encOp
// GobEncoder.
func (enc *Encoder) gobEncodeOpFor(ut *userTypeInfo) (*encOp, int) {
rt := ut.user
if ut.encIndir != 0 {
errorf("gob: TODO: can't handle indirection to reach GobEncoder")
if ut.encIndir > 0 {
errorf("gob: TODO: can't handle >0 indirections to reach GobEncoder")
}
if ut.encIndir == -1 {
rt = reflect.PtrTo(rt)
}
index := -1
for i := 0; i < rt.NumMethod(); i++ {
@ -588,8 +591,15 @@ func (enc *Encoder) gobEncodeOpFor(ut *userTypeInfo) (*encOp, int) {
}
var op encOp
op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
// TODO: this will need fixing when ut.encIndr != 0.
v := reflect.NewValue(unsafe.Unreflect(rt, p))
var v reflect.Value
switch {
case ut.encIndir == 0:
v = reflect.NewValue(unsafe.Unreflect(rt, p))
case ut.encIndir == -1:
v = reflect.NewValue(unsafe.Unreflect(rt, unsafe.Pointer(&p)))
default:
errorf("gob: TODO: can't handle >0 indirections to reach GobEncoder")
}
state.update(i)
state.enc.encodeGobEncoder(state.b, v, index)
}

26
src/pkg/gob/gobencdec_test.go
View File

@ -128,6 +128,11 @@ type GobTestIgnoreEncoder struct {
X int // guarantee we have something in common with GobTest*
}
type GobTestValueEncDec struct {
X int // guarantee we have something in common with GobTest*
G StringStruct // not a pointer.
}
func TestGobEncoderField(t *testing.T) {
b := new(bytes.Buffer)
// First a field that's a structure.
@ -162,6 +167,27 @@ func TestGobEncoderField(t *testing.T) {
}
}
// Even though the field is a value, we can still take its address
// and should be able to call the methods.
func TestGobEncoderValueField(t *testing.T) {
b := new(bytes.Buffer)
// First a field that's a structure.
enc := NewEncoder(b)
err := enc.Encode(GobTestValueEncDec{17, StringStruct{"HIJKL"}})
if err != nil {
t.Fatal("encode error:", err)
}
dec := NewDecoder(b)
x := new(GobTestValueEncDec)
err = dec.Decode(x)
if err != nil {
t.Fatal("decode error:", err)
}
if x.G.s != "HIJKL" {
t.Errorf("expected `HIJKL` got %s", x.G.s)
}
}
// As long as the fields have the same name and implement the
// interface, we can cross-connect them. Not sure it's useful
// and may even be bad but it works and it's hard to prevent

93
src/pkg/gob/type.go
View File

@ -74,14 +74,12 @@ func validUserType(rt reflect.Type) (ut *userTypeInfo, err os.Error) {
}
ut.indir++
}
ut.isGobEncoder, ut.encIndir = implementsGobEncoder(ut.user)
ut.isGobDecoder, ut.decIndir = implementsGobDecoder(ut.user)
ut.isGobEncoder, ut.encIndir = implementsInterface(ut.user, gobEncoderCheck)
ut.isGobDecoder, ut.decIndir = implementsInterface(ut.user, gobDecoderCheck)
userTypeCache[rt] = ut
if ut.encIndir != 0 || ut.decIndir != 0 {
if ut.encIndir > 0 || ut.decIndir > 0 {
// There are checks in lots of other places, but putting this here means we won't even
// attempt to encode/decode this type.
// TODO: make it possible to handle types that are indirect to the implementation,
// such as a structure field of type T when *T implements GobDecoder.
return nil, os.ErrorString("TODO: gob can't handle indirections to GobEncoder/Decoder")
}
return
@ -92,51 +90,41 @@ const (
gobDecodeMethodName = "GobDecode"
)
// implementsGobEncoder reports whether the type implements the interface. It also
// returns the number of indirections required to get to the implementation.
// TODO: when reflection makes it possible, should also be prepared to climb up
// one level if we're not on a pointer (implementation could be on *T for our T).
// That will mean that indir could be < 0, which is sure to cause problems, but
// we ignore them now as indir is always >= 0 now.
func implementsGobEncoder(rt reflect.Type) (implements bool, indir int8) {
if rt == nil {
return
// implements returns whether the type implements the interface, as encoded
// in the check function.
func implements(typ reflect.Type, check func(typ reflect.Type) bool) bool {
if typ.NumMethod() == 0 { // avoid allocations etc. unless there's some chance
return false
}
// The type might be a pointer, or it might not, and we need to keep
// dereferencing to the base type until we find an implementation.
for {
if rt.NumMethod() > 0 { // avoid allocations etc. unless there's some chance
if _, ok := reflect.MakeZero(rt).Interface().(GobEncoder); ok {
return true, indir
}
}
if p, ok := rt.(*reflect.PtrType); ok {
indir++
if indir > 100 { // insane number of indirections
return false, 0
}
rt = p.Elem()
continue
}
break
}
return false, 0
return check(typ)
}
// implementsGobDecoder reports whether the type implements the interface. It also
// returns the number of indirections required to get to the implementation.
// TODO: see comment on implementsGobEncoder.
func implementsGobDecoder(rt reflect.Type) (implements bool, indir int8) {
if rt == nil {
// gobEncoderCheck makes the type assertion a boolean function.
func gobEncoderCheck(typ reflect.Type) bool {
_, ok := reflect.MakeZero(typ).Interface().(GobEncoder)
return ok
}
// gobDecoderCheck makes the type assertion a boolean function.
func gobDecoderCheck(typ reflect.Type) bool {
_, ok := reflect.MakeZero(typ).Interface().(GobDecoder)
return ok
}
// implementsInterface reports whether the type implements the
// interface. (The actual check is done through the provided function.)
// It also returns the number of indirections required to get to the
// implementation.
func implementsInterface(typ reflect.Type, check func(typ reflect.Type) bool) (success bool, indir int8) {
if typ == nil {
return
}
// The type might be a pointer, or it might not, and we need to keep
rt := typ
// The type might be a pointer and we need to keep
// dereferencing to the base type until we find an implementation.
for {
if rt.NumMethod() > 0 { // avoid allocations etc. unless there's some chance
if _, ok := reflect.MakeZero(rt).Interface().(GobDecoder); ok {
return true, indir
}
if implements(typ, check) {
return true, indir
}
if p, ok := rt.(*reflect.PtrType); ok {
indir++
@ -148,6 +136,13 @@ func implementsGobDecoder(rt reflect.Type) (implements bool, indir int8) {
}
break
}
// No luck yet, but if this is a base type (non-pointer), the pointer might satisfy.
if _, ok := typ.(*reflect.PtrType); !ok {
// Not a pointer, but does the pointer work?
if implements(reflect.PtrTo(typ), check) {
return true, -1
}
}
return false, 0
}
@ -702,10 +697,11 @@ func mustGetTypeInfo(rt reflect.Type) *typeInfo {
// to guarantee the encoding used by a GobEncoder is stable as the
// software evolves. For instance, it might make sense for GobEncode
// to include a version number in the encoding.
//
//
// Note: At the moment, the type implementing GobEncoder must
// be exactly the type passed to Encode. For example, if *T implements
// GobEncoder, the data item must be of type *T, not T or **T.
// be more indirect than the type passed to Decode. For example, if
// if *T implements GobDecoder, the data item must be of type *T or T,
// not **T or ***T.
type GobEncoder interface {
// GobEncode returns a byte slice representing the encoding of the
// receiver for transmission to a GobDecoder, usually of the same
@ -717,8 +713,9 @@ type GobEncoder interface {
// routine for decoding transmitted values sent by a GobEncoder.
//
// Note: At the moment, the type implementing GobDecoder must
// be exactly the type passed to Decode. For example, if *T implements
// GobDecoder, the data item must be of type *T, not T or **T.
// be more indirect than the type passed to Decode. For example, if
// if *T implements GobDecoder, the data item must be of type *T or T,
// not **T or ***T.
type GobDecoder interface {
// GobDecode overwrites the receiver, which must be a pointer,
// with the value represented by the byte slice, which was written