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rlp: add "tail" struct tag

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This commit is contained in:
Felix Lange 2015-12-21 21:05:20 +01:00
parent fdb936ee95
commit bb07ce3eed
6 changed files with 163 additions and 26 deletions
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51
rlp/decode.go
View File

@ -63,11 +63,12 @@ type Decoder interface {
// 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
// The decoding of struct fields honours two struct tags, "tail" and
// "nil". For an explanation of "tail", see the example.
// The "nil" 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.
// decode as a nil pointer. This tag can be useful when decoding
// recursive types.
//
// type StructWithEmptyOK struct {
// Foo *[20]byte `rlp:"nil"`
@ -190,7 +191,7 @@ func makeDecoder(typ reflect.Type, tags tags) (dec decoder, err error) {
case kind == reflect.String:
return decodeString, nil
case kind == reflect.Slice || kind == reflect.Array:
return makeListDecoder(typ)
return makeListDecoder(typ, tags)
case kind == reflect.Struct:
return makeStructDecoder(typ)
case kind == reflect.Ptr:
@ -264,7 +265,7 @@ func decodeBigInt(s *Stream, val reflect.Value) error {
return nil
}
func makeListDecoder(typ reflect.Type) (decoder, error) {
func makeListDecoder(typ reflect.Type, tag tags) (decoder, error) {
etype := typ.Elem()
if etype.Kind() == reflect.Uint8 && !reflect.PtrTo(etype).Implements(decoderInterface) {
if typ.Kind() == reflect.Array {
@ -277,15 +278,26 @@ func makeListDecoder(typ reflect.Type) (decoder, error) {
if err != nil {
return nil, err
}
isArray := typ.Kind() == reflect.Array
return func(s *Stream, val reflect.Value) error {
if isArray {
var dec decoder
switch {
case typ.Kind() == reflect.Array:
dec = func(s *Stream, val reflect.Value) error {
return decodeListArray(s, val, etypeinfo.decoder)
} else {
}
case tag.tail:
// A slice with "tail" tag can occur as the last field
// of a struct and is upposed to swallow all remaining
// list elements. The struct decoder already called s.List,
// proceed directly to decoding the elements.
dec = func(s *Stream, val reflect.Value) error {
return decodeSliceElems(s, val, etypeinfo.decoder)
}
default:
dec = func(s *Stream, val reflect.Value) error {
return decodeListSlice(s, val, etypeinfo.decoder)
}
}, nil
}
return dec, nil
}
func decodeListSlice(s *Stream, val reflect.Value, elemdec decoder) error {
@ -297,7 +309,13 @@ func decodeListSlice(s *Stream, val reflect.Value, elemdec decoder) error {
val.Set(reflect.MakeSlice(val.Type(), 0, 0))
return s.ListEnd()
}
if err := decodeSliceElems(s, val, elemdec); err != nil {
return err
}
return s.ListEnd()
}
func decodeSliceElems(s *Stream, val reflect.Value, elemdec decoder) error {
i := 0
for ; ; i++ {
// grow slice if necessary
@ -323,12 +341,11 @@ func decodeListSlice(s *Stream, val reflect.Value, elemdec decoder) error {
if i < val.Len() {
val.SetLen(i)
}
return s.ListEnd()
return nil
}
func decodeListArray(s *Stream, val reflect.Value, elemdec decoder) error {
_, err := s.List()
if err != nil {
if _, err := s.List(); err != nil {
return wrapStreamError(err, val.Type())
}
vlen := val.Len()
@ -398,11 +415,11 @@ func makeStructDecoder(typ reflect.Type) (decoder, error) {
return nil, err
}
dec := func(s *Stream, val reflect.Value) (err error) {
if _, err = s.List(); err != nil {
if _, err := s.List(); err != nil {
return wrapStreamError(err, typ)
}
for _, f := range fields {
err = f.info.decoder(s, val.Field(f.index))
err := f.info.decoder(s, val.Field(f.index))
if err == EOL {
return &decodeError{msg: "too few elements", typ: typ}
} else if err != nil {

33
rlp/decode_tail_test.go Normal file
View File

@ -0,0 +1,33 @@
package rlp
import (
"bytes"
"fmt"
)
type structWithTail struct {
A, B uint
C []uint `rlp:"tail"`
}
func ExampleDecode_structTagTail() {
// In this example, the "tail" struct tag is used to decode lists of
// differing length into a struct.
var val structWithTail
err := Decode(bytes.NewReader([]byte{0xC4, 0x01, 0x02, 0x03, 0x04}), &val)
fmt.Printf("with 4 elements: err=%v val=%v\n", err, val)
err = Decode(bytes.NewReader([]byte{0xC6, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06}), &val)
fmt.Printf("with 6 elements: err=%v val=%v\n", err, val)
// Note that at least two list elements must be present to
// fill fields A and B:
err = Decode(bytes.NewReader([]byte{0xC1, 0x01}), &val)
fmt.Printf("with 1 element: err=%q\n", err)
// Output:
// with 4 elements: err=<nil> val={1 2 [3 4]}
// with 6 elements: err=<nil> val={1 2 [3 4 5 6]}
// with 1 element: err="rlp: too few elements for rlp.structWithTail"
}

52
rlp/decode_test.go
View File

@ -312,6 +312,26 @@ type recstruct struct {
Child *recstruct `rlp:"nil"`
}
type invalidTail1 struct {
A uint `rlp:"tail"`
B string
}
type invalidTail2 struct {
A uint
B string `rlp:"tail"`
}
type tailRaw struct {
A uint
Tail []RawValue `rlp:"tail"`
}
type tailUint struct {
A uint
Tail []uint `rlp:"tail"`
}
var (
veryBigInt = big.NewInt(0).Add(
big.NewInt(0).Lsh(big.NewInt(0xFFFFFFFFFFFFFF), 16),
@ -437,6 +457,38 @@ var decodeTests = []decodeTest{
ptr: new(recstruct),
error: "rlp: expected input string or byte for uint, decoding into (rlp.recstruct).Child.I",
},
{
input: "C0",
ptr: new(invalidTail1),
error: "rlp: invalid struct tag \"tail\" for rlp.invalidTail1.A (must be on last field)",
},
{
input: "C0",
ptr: new(invalidTail2),
error: "rlp: invalid struct tag \"tail\" for rlp.invalidTail2.B (field type is not slice)",
},
{
input: "C50102C20102",
ptr: new(tailUint),
error: "rlp: expected input string or byte for uint, decoding into (rlp.tailUint).Tail[1]",
},
// struct tag "tail"
{
input: "C3010203",
ptr: new(tailRaw),
value: tailRaw{A: 1, Tail: []RawValue{unhex("02"), unhex("03")}},
},
{
input: "C20102",
ptr: new(tailRaw),
value: tailRaw{A: 1, Tail: []RawValue{unhex("02")}},
},
{
input: "C101",
ptr: new(tailRaw),
value: tailRaw{A: 1, Tail: []RawValue{}},
},
// RawValue
{input: "01", ptr: new(RawValue), value: RawValue(unhex("01"))},

11
rlp/encode.go
View File

@ -345,7 +345,7 @@ var (
)
// makeWriter creates a writer function for the given type.
func makeWriter(typ reflect.Type) (writer, error) {
func makeWriter(typ reflect.Type, ts tags) (writer, error) {
kind := typ.Kind()
switch {
case typ == rawValueType:
@ -371,7 +371,7 @@ func makeWriter(typ reflect.Type) (writer, error) {
case kind == reflect.Array && isByte(typ.Elem()):
return writeByteArray, nil
case kind == reflect.Slice || kind == reflect.Array:
return makeSliceWriter(typ)
return makeSliceWriter(typ, ts)
case kind == reflect.Struct:
return makeStructWriter(typ)
case kind == reflect.Ptr:
@ -507,20 +507,21 @@ func writeInterface(val reflect.Value, w *encbuf) error {
return ti.writer(eval, w)
}
func makeSliceWriter(typ reflect.Type) (writer, error) {
func makeSliceWriter(typ reflect.Type, ts tags) (writer, error) {
etypeinfo, err := cachedTypeInfo1(typ.Elem(), tags{})
if err != nil {
return nil, err
}
writer := func(val reflect.Value, w *encbuf) error {
lh := w.list()
if !ts.tail {
defer w.listEnd(w.list())
}
vlen := val.Len()
for i := 0; i < vlen; i++ {
if err := etypeinfo.writer(val.Index(i), w); err != nil {
return err
}
}
w.listEnd(lh)
return nil
}
return writer, nil

4
rlp/encode_test.go
View File

@ -214,6 +214,10 @@ var encTests = []encTest{
{val: simplestruct{A: 3, B: "foo"}, output: "C50383666F6F"},
{val: &recstruct{5, nil}, output: "C205C0"},
{val: &recstruct{5, &recstruct{4, &recstruct{3, nil}}}, output: "C605C404C203C0"},
{val: &tailRaw{A: 1, Tail: []RawValue{unhex("02"), unhex("03")}}, output: "C3010203"},
{val: &tailRaw{A: 1, Tail: []RawValue{unhex("02")}}, output: "C20102"},
{val: &tailRaw{A: 1, Tail: []RawValue{}}, output: "C101"},
{val: &tailRaw{A: 1, Tail: nil}, output: "C101"},
// nil
{val: (*uint)(nil), output: "80"},

38
rlp/typecache.go
View File

@ -17,7 +17,9 @@
package rlp
import (
"fmt"
"reflect"
"strings"
"sync"
)
@ -33,7 +35,13 @@ type typeinfo struct {
// represents struct tags
type tags struct {
// rlp:"nil" controls whether empty input results in a nil pointer.
nilOK bool
// rlp:"tail" controls whether this field swallows additional list
// elements. It can only be set for the last field, which must be
// of slice type.
tail bool
}
type typekey struct {
@ -89,7 +97,10 @@ type field struct {
func structFields(typ reflect.Type) (fields []field, err error) {
for i := 0; i < typ.NumField(); i++ {
if f := typ.Field(i); f.PkgPath == "" { // exported
tags := parseStructTag(f.Tag.Get("rlp"))
tags, err := parseStructTag(typ, i)
if err != nil {
return nil, err
}
info, err := cachedTypeInfo1(f.Type, tags)
if err != nil {
return nil, err
@ -100,8 +111,27 @@ func structFields(typ reflect.Type) (fields []field, err error) {
return fields, nil
}
func parseStructTag(tag string) tags {
return tags{nilOK: tag == "nil"}
func parseStructTag(typ reflect.Type, fi int) (tags, error) {
f := typ.Field(fi)
var ts tags
for _, t := range strings.Split(f.Tag.Get("rlp"), ",") {
switch t = strings.TrimSpace(t); t {
case "":
case "nil":
ts.nilOK = true
case "tail":
ts.tail = true
if fi != typ.NumField()-1 {
return ts, fmt.Errorf(`rlp: invalid struct tag "tail" for %v.%s (must be on last field)`, typ, f.Name)
}
if f.Type.Kind() != reflect.Slice {
return ts, fmt.Errorf(`rlp: invalid struct tag "tail" for %v.%s (field type is not slice)`, typ, f.Name)
}
default:
return ts, fmt.Errorf("rlp: unknown struct tag %q on %v.%s", t, typ, f.Name)
}
}
return ts, nil
}
func genTypeInfo(typ reflect.Type, tags tags) (info *typeinfo, err error) {
@ -109,7 +139,7 @@ func genTypeInfo(typ reflect.Type, tags tags) (info *typeinfo, err error) {
if info.decoder, err = makeDecoder(typ, tags); err != nil {
return nil, err
}
if info.writer, err = makeWriter(typ); err != nil {
if info.writer, err = makeWriter(typ, tags); err != nil {
return nil, err
}
return info, nil