From cad64fb911e7029bef876f16e0956b3b0b4bb4d0 Mon Sep 17 00:00:00 2001
From: Felix Lange <fjl@twurst.com>
Date: Fri, 17 Apr 2015 01:16:46 +0200
Subject: [PATCH] rlp: stricter rules for structs and pointers
The rules have changed as follows:
* When decoding into pointers, empty values no longer produce
a nil pointer. This can be overriden for struct fields using the
struct tag "nil".
* When decoding into structs, the input list must contain an element
for each field.
---
rlp/decode.go | 76 ++++++++++++++++++++++++++++++++--------------
rlp/decode_test.go | 65 +++++++++++++++++++++++++++++++--------
rlp/encode.go | 8 ++---
rlp/typecache.go | 51 ++++++++++++++++++++++---------
4 files changed, 148 insertions(+), 52 deletions(-)
diff --git a/rlp/decode.go b/rlp/decode.go
index 43dd716b5..394f83fb2 100644
--- a/rlp/decode.go
+++ b/rlp/decode.go
@@ -36,17 +36,26 @@ type Decoder interface {
// If the type implements the Decoder interface, decode calls
// DecodeRLP.
//
-// To decode into a pointer, Decode will set the pointer to nil if the
-// input has size zero. If the input has nonzero size, Decode will
-// parse the input data into a value of the type being pointed to.
-// If the pointer is non-nil, the existing value will reused.
+// To decode into a pointer, Decode will decode into the value pointed
+// to. If the pointer is nil, a new value of the pointer's element
+// type is allocated. If the pointer is non-nil, the existing value
+// will reused.
//
// To decode into a struct, Decode expects the input to be an RLP
// list. The decoded elements of the list are assigned to each public
-// field in the order given by the struct's definition. If the input
-// list has too few elements, no error is returned and the remaining
-// fields will have the zero value.
-// Recursive struct types are supported.
+// field in the order given by the struct's definition. The input list
+// must contain an element for each decoded field. Decode returns an
+// error if there are too few or too many elements.
+//
+// The decoding of struct fields honours one particular struct tag,
+// "nil". This tag applies to pointer-typed fields and changes the
+// decoding rules for the field such that input values of size zero
+// decode as a nil pointer. This tag can be useful when decoding recursive
+// types.
+//
+// type StructWithEmptyOK struct {
+// Foo *[20]byte `rlp:"nil"`
+// }
//
// To decode into a slice, the input must be a list and the resulting
// slice will contain the input elements in order.
@@ -54,7 +63,7 @@ type Decoder interface {
// can also be an RLP string.
//
// To decode into a Go string, the input must be an RLP string. The
-// bytes are taken as-is and will not necessarily be valid UTF-8.
+// input bytes are taken as-is and will not necessarily be valid UTF-8.
//
// To decode into an unsigned integer type, the input must also be an RLP
// string. The bytes are interpreted as a big endian representation of
@@ -65,8 +74,8 @@ type Decoder interface {
// To decode into an interface value, Decode stores one of these
// in the value:
//
-// []interface{}, for RLP lists
-// []byte, for RLP strings
+// []interface{}, for RLP lists
+// []byte, for RLP strings
//
// Non-empty interface types are not supported, nor are booleans,
// signed integers, floating point numbers, maps, channels and
@@ -136,7 +145,7 @@ var (
bigInt = reflect.TypeOf(big.Int{})
)
-func makeDecoder(typ reflect.Type) (dec decoder, err error) {
+func makeDecoder(typ reflect.Type, tags tags) (dec decoder, err error) {
kind := typ.Kind()
switch {
case typ.Implements(decoderInterface):
@@ -156,6 +165,9 @@ func makeDecoder(typ reflect.Type) (dec decoder, err error) {
case kind == reflect.Struct:
return makeStructDecoder(typ)
case kind == reflect.Ptr:
+ if tags.nilOK {
+ return makeOptionalPtrDecoder(typ)
+ }
return makePtrDecoder(typ)
case kind == reflect.Interface:
return decodeInterface, nil
@@ -214,7 +226,7 @@ func makeListDecoder(typ reflect.Type) (decoder, error) {
return decodeByteSlice, nil
}
}
- etypeinfo, err := cachedTypeInfo1(etype)
+ etypeinfo, err := cachedTypeInfo1(etype, tags{})
if err != nil {
return nil, err
}
@@ -352,11 +364,6 @@ func zero(val reflect.Value, start int) {
}
}
-type field struct {
- index int
- info *typeinfo
-}
-
func makeStructDecoder(typ reflect.Type) (decoder, error) {
fields, err := structFields(typ)
if err != nil {
@@ -369,8 +376,7 @@ func makeStructDecoder(typ reflect.Type) (decoder, error) {
for _, f := range fields {
err = f.info.decoder(s, val.Field(f.index))
if err == EOL {
- // too few elements. leave the rest at their zero value.
- break
+ return &decodeError{msg: "too few elements", typ: typ}
} else if err != nil {
return addErrorContext(err, "."+typ.Field(f.index).Name)
}
@@ -380,9 +386,35 @@ func makeStructDecoder(typ reflect.Type) (decoder, error) {
return dec, nil
}
+// makePtrDecoder creates a decoder that decodes into
+// the pointer's element type.
func makePtrDecoder(typ reflect.Type) (decoder, error) {
etype := typ.Elem()
- etypeinfo, err := cachedTypeInfo1(etype)
+ etypeinfo, err := cachedTypeInfo1(etype, tags{})
+ if err != nil {
+ return nil, err
+ }
+ dec := func(s *Stream, val reflect.Value) (err error) {
+ newval := val
+ if val.IsNil() {
+ newval = reflect.New(etype)
+ }
+ if err = etypeinfo.decoder(s, newval.Elem()); err == nil {
+ val.Set(newval)
+ }
+ return err
+ }
+ return dec, nil
+}
+
+// makeOptionalPtrDecoder creates a decoder that decodes empty values
+// as nil. Non-empty values are decoded into a value of the element type,
+// just like makePtrDecoder does.
+//
+// This decoder is used for pointer-typed struct fields with struct tag "nil".
+func makeOptionalPtrDecoder(typ reflect.Type) (decoder, error) {
+ etype := typ.Elem()
+ etypeinfo, err := cachedTypeInfo1(etype, tags{})
if err != nil {
return nil, err
}
@@ -706,7 +738,7 @@ func (s *Stream) Decode(val interface{}) error {
if rval.IsNil() {
return errDecodeIntoNil
}
- info, err := cachedTypeInfo(rtyp.Elem())
+ info, err := cachedTypeInfo(rtyp.Elem(), tags{})
if err != nil {
return err
}
diff --git a/rlp/decode_test.go b/rlp/decode_test.go
index 7e2ea2041..fd52bd1be 100644
--- a/rlp/decode_test.go
+++ b/rlp/decode_test.go
@@ -280,7 +280,7 @@ type simplestruct struct {
type recstruct struct {
I uint
- Child *recstruct
+ Child *recstruct `rlp:"nil"`
}
var (
@@ -390,15 +390,33 @@ var decodeTests = []decodeTest{
{input: "8105", ptr: new(big.Int), error: "rlp: non-canonical size information for *big.Int"},
// structs
- {input: "C0", ptr: new(simplestruct), value: simplestruct{0, ""}},
- {input: "C105", ptr: new(simplestruct), value: simplestruct{5, ""}},
- {input: "C50583343434", ptr: new(simplestruct), value: simplestruct{5, "444"}},
{
- input: "C501C302C103",
+ input: "C50583343434",
+ ptr: new(simplestruct),
+ value: simplestruct{5, "444"},
+ },
+ {
+ input: "C601C402C203C0",
ptr: new(recstruct),
value: recstruct{1, &recstruct{2, &recstruct{3, nil}}},
},
+ // struct errors
+ {
+ input: "C0",
+ ptr: new(simplestruct),
+ error: "rlp: too few elements for rlp.simplestruct",
+ },
+ {
+ input: "C105",
+ ptr: new(simplestruct),
+ error: "rlp: too few elements for rlp.simplestruct",
+ },
+ {
+ input: "C7C50583343434C0",
+ ptr: new([]*simplestruct),
+ error: "rlp: too few elements for rlp.simplestruct, decoding into ([]*rlp.simplestruct)[1]",
+ },
{
input: "83222222",
ptr: new(simplestruct),
@@ -417,19 +435,15 @@ var decodeTests = []decodeTest{
// pointers
{input: "00", ptr: new(*[]byte), value: &[]byte{0}},
- {input: "80", ptr: new(*uint), value: (*uint)(nil)},
- {input: "C0", ptr: new(*uint), value: (*uint)(nil)},
+ {input: "80", ptr: new(*uint), value: uintp(0)},
+ {input: "C0", ptr: new(*uint), error: "rlp: expected input string or byte for uint"},
{input: "07", ptr: new(*uint), value: uintp(7)},
{input: "8158", ptr: new(*uint), value: uintp(0x58)},
{input: "C109", ptr: new(*[]uint), value: &[]uint{9}},
{input: "C58403030303", ptr: new(*[][]byte), value: &[][]byte{{3, 3, 3, 3}}},
// check that input position is advanced also for empty values.
- {input: "C3808005", ptr: new([]*uint), value: []*uint{nil, nil, uintp(5)}},
-
- // pointer should be reset to nil
- {input: "05", ptr: sharedPtr, value: uintp(5)},
- {input: "80", ptr: sharedPtr, value: (*uint)(nil)},
+ {input: "C3808005", ptr: new([]*uint), value: []*uint{uintp(0), uintp(0), uintp(5)}},
// interface{}
{input: "00", ptr: new(interface{}), value: []byte{0}},
@@ -599,6 +613,33 @@ func ExampleDecode() {
// Decoded value: rlp.example{A:0xa, B:0x14, private:0x0, String:"foobar"}
}
+func ExampleDecode_structTagNil() {
+ // In this example, we'll use the "nil" struct tag to change
+ // how a pointer-typed field is decoded. The input contains an RLP
+ // list of one element, an empty string.
+ input := []byte{0xC1, 0x80}
+
+ // This type uses the normal rules.
+ // The empty input string is decoded as a pointer to an empty Go string.
+ var normalRules struct {
+ String *string
+ }
+ Decode(bytes.NewReader(input), &normalRules)
+ fmt.Printf("normal: String = %q\n", *normalRules.String)
+
+ // This type uses the struct tag.
+ // The empty input string is decoded as a nil pointer.
+ var withEmptyOK struct {
+ String *string `rlp:"nil"`
+ }
+ Decode(bytes.NewReader(input), &withEmptyOK)
+ fmt.Printf("with nil tag: String = %v\n", withEmptyOK.String)
+
+ // Output:
+ // normal: String = ""
+ // with nil tag: String = <nil>
+}
+
func ExampleStream() {
input, _ := hex.DecodeString("C90A1486666F6F626172")
s := NewStream(bytes.NewReader(input), 0)
diff --git a/rlp/encode.go b/rlp/encode.go
index 6cf6776d6..10ff0ae79 100644
--- a/rlp/encode.go
+++ b/rlp/encode.go
@@ -194,7 +194,7 @@ func (w *encbuf) Write(b []byte) (int, error) {
func (w *encbuf) encode(val interface{}) error {
rval := reflect.ValueOf(val)
- ti, err := cachedTypeInfo(rval.Type())
+ ti, err := cachedTypeInfo(rval.Type(), tags{})
if err != nil {
return err
}
@@ -485,7 +485,7 @@ func writeInterface(val reflect.Value, w *encbuf) error {
return nil
}
eval := val.Elem()
- ti, err := cachedTypeInfo(eval.Type())
+ ti, err := cachedTypeInfo(eval.Type(), tags{})
if err != nil {
return err
}
@@ -493,7 +493,7 @@ func writeInterface(val reflect.Value, w *encbuf) error {
}
func makeSliceWriter(typ reflect.Type) (writer, error) {
- etypeinfo, err := cachedTypeInfo1(typ.Elem())
+ etypeinfo, err := cachedTypeInfo1(typ.Elem(), tags{})
if err != nil {
return nil, err
}
@@ -530,7 +530,7 @@ func makeStructWriter(typ reflect.Type) (writer, error) {
}
func makePtrWriter(typ reflect.Type) (writer, error) {
- etypeinfo, err := cachedTypeInfo1(typ.Elem())
+ etypeinfo, err := cachedTypeInfo1(typ.Elem(), tags{})
if err != nil {
return nil, err
}
diff --git a/rlp/typecache.go b/rlp/typecache.go
index 398f25d90..d512012e9 100644
--- a/rlp/typecache.go
+++ b/rlp/typecache.go
@@ -7,7 +7,7 @@ import (
var (
typeCacheMutex sync.RWMutex
- typeCache = make(map[reflect.Type]*typeinfo)
+ typeCache = make(map[typekey]*typeinfo)
)
type typeinfo struct {
@@ -15,13 +15,25 @@ type typeinfo struct {
writer
}
+// represents struct tags
+type tags struct {
+ nilOK bool
+}
+
+type typekey struct {
+ reflect.Type
+ // the key must include the struct tags because they
+ // might generate a different decoder.
+ tags
+}
+
type decoder func(*Stream, reflect.Value) error
type writer func(reflect.Value, *encbuf) error
-func cachedTypeInfo(typ reflect.Type) (*typeinfo, error) {
+func cachedTypeInfo(typ reflect.Type, tags tags) (*typeinfo, error) {
typeCacheMutex.RLock()
- info := typeCache[typ]
+ info := typeCache[typekey{typ, tags}]
typeCacheMutex.RUnlock()
if info != nil {
return info, nil
@@ -29,11 +41,12 @@ func cachedTypeInfo(typ reflect.Type) (*typeinfo, error) {
// not in the cache, need to generate info for this type.
typeCacheMutex.Lock()
defer typeCacheMutex.Unlock()
- return cachedTypeInfo1(typ)
+ return cachedTypeInfo1(typ, tags)
}
-func cachedTypeInfo1(typ reflect.Type) (*typeinfo, error) {
- info := typeCache[typ]
+func cachedTypeInfo1(typ reflect.Type, tags tags) (*typeinfo, error) {
+ key := typekey{typ, tags}
+ info := typeCache[key]
if info != nil {
// another goroutine got the write lock first
return info, nil
@@ -41,21 +54,27 @@ func cachedTypeInfo1(typ reflect.Type) (*typeinfo, error) {
// put a dummmy value into the cache before generating.
// if the generator tries to lookup itself, it will get
// the dummy value and won't call itself recursively.
- typeCache[typ] = new(typeinfo)
- info, err := genTypeInfo(typ)
+ typeCache[key] = new(typeinfo)
+ info, err := genTypeInfo(typ, tags)
if err != nil {
// remove the dummy value if the generator fails
- delete(typeCache, typ)
+ delete(typeCache, key)
return nil, err
}
- *typeCache[typ] = *info
- return typeCache[typ], err
+ *typeCache[key] = *info
+ return typeCache[key], err
+}
+
+type field struct {
+ index int
+ info *typeinfo
}
func structFields(typ reflect.Type) (fields []field, err error) {
for i := 0; i < typ.NumField(); i++ {
if f := typ.Field(i); f.PkgPath == "" { // exported
- info, err := cachedTypeInfo1(f.Type)
+ tags := parseStructTag(f.Tag.Get("rlp"))
+ info, err := cachedTypeInfo1(f.Type, tags)
if err != nil {
return nil, err
}
@@ -65,9 +84,13 @@ func structFields(typ reflect.Type) (fields []field, err error) {
return fields, nil
}
-func genTypeInfo(typ reflect.Type) (info *typeinfo, err error) {
+func parseStructTag(tag string) tags {
+ return tags{nilOK: tag == "nil"}
+}
+
+func genTypeInfo(typ reflect.Type, tags tags) (info *typeinfo, err error) {
info = new(typeinfo)
- if info.decoder, err = makeDecoder(typ); err != nil {
+ if info.decoder, err = makeDecoder(typ, tags); err != nil {
return nil, err
}
if info.writer, err = makeWriter(typ); err != nil {
--
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