rlp: add support for optional struct fields (#22832)
This adds support for a new struct tag "optional". Using this tag, structs used for RLP encoding/decoding can be extended in a backwards-compatible way, by adding new fields at the end.
This commit is contained in:
Felix Lange
GitHub
parent
8a070e8f7d
commit
700df1442d
@ -229,7 +229,7 @@ func decodeBigInt(s *Stream, val reflect.Value) error {
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i = new(big.Int)
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val.Set(reflect.ValueOf(i))
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}
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// Reject leading zero bytes
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// Reject leading zero bytes.
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if len(b) > 0 && b[0] == 0 {
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return wrapStreamError(ErrCanonInt, val.Type())
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}
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@ -394,9 +394,16 @@ func makeStructDecoder(typ reflect.Type) (decoder, error) {
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if _, err := s.List(); err != nil {
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return wrapStreamError(err, typ)
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}
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for _, f := range fields {
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for i, f := range fields {
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err := f.info.decoder(s, val.Field(f.index))
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if err == EOL {
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if f.optional {
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// The field is optional, so reaching the end of the list before
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// reaching the last field is acceptable. All remaining undecoded
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// fields are zeroed.
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zeroFields(val, fields[i:])
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break
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}
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return &decodeError{msg: "too few elements", typ: typ}
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} else if err != nil {
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return addErrorContext(err, "."+typ.Field(f.index).Name)
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@ -407,6 +414,13 @@ func makeStructDecoder(typ reflect.Type) (decoder, error) {
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return dec, nil
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}
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func zeroFields(structval reflect.Value, fields []field) {
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for _, f := range fields {
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fv := structval.Field(f.index)
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fv.Set(reflect.Zero(fv.Type()))
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}
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}
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// makePtrDecoder creates a decoder that decodes into the pointer's element type.
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func makePtrDecoder(typ reflect.Type, tag tags) (decoder, error) {
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etype := typ.Elem()
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@ -369,6 +369,39 @@ type intField struct {
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X int
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}
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type optionalFields struct {
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A uint
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B uint `rlp:"optional"`
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C uint `rlp:"optional"`
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}
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type optionalAndTailField struct {
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A uint
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B uint `rlp:"optional"`
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Tail []uint `rlp:"tail"`
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}
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type optionalBigIntField struct {
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A uint
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B *big.Int `rlp:"optional"`
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}
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type optionalPtrField struct {
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A uint
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B *[3]byte `rlp:"optional"`
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}
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type optionalPtrFieldNil struct {
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A uint
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B *[3]byte `rlp:"optional,nil"`
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}
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type ignoredField struct {
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A uint
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B uint `rlp:"-"`
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C uint
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}
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var (
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veryBigInt = big.NewInt(0).Add(
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big.NewInt(0).Lsh(big.NewInt(0xFFFFFFFFFFFFFF), 16),
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@ -376,12 +409,6 @@ var (
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)
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)
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type hasIgnoredField struct {
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A uint
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B uint `rlp:"-"`
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C uint
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}
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var decodeTests = []decodeTest{
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// booleans
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{input: "01", ptr: new(bool), value: true},
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@ -551,8 +578,8 @@ var decodeTests = []decodeTest{
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// struct tag "-"
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{
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input: "C20102",
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ptr: new(hasIgnoredField),
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value: hasIgnoredField{A: 1, C: 2},
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ptr: new(ignoredField),
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value: ignoredField{A: 1, C: 2},
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},
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// struct tag "nilList"
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@ -592,6 +619,110 @@ var decodeTests = []decodeTest{
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value: nilStringSlice{X: &[]uint{3}},
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},
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// struct tag "optional"
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{
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input: "C101",
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ptr: new(optionalFields),
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value: optionalFields{1, 0, 0},
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},
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{
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input: "C20102",
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ptr: new(optionalFields),
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value: optionalFields{1, 2, 0},
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},
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{
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input: "C3010203",
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ptr: new(optionalFields),
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value: optionalFields{1, 2, 3},
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},
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{
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input: "C401020304",
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ptr: new(optionalFields),
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error: "rlp: input list has too many elements for rlp.optionalFields",
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},
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{
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input: "C101",
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ptr: new(optionalAndTailField),
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value: optionalAndTailField{A: 1},
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},
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{
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input: "C20102",
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ptr: new(optionalAndTailField),
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value: optionalAndTailField{A: 1, B: 2, Tail: []uint{}},
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},
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{
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input: "C401020304",
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ptr: new(optionalAndTailField),
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value: optionalAndTailField{A: 1, B: 2, Tail: []uint{3, 4}},
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},
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{
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input: "C101",
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ptr: new(optionalBigIntField),
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value: optionalBigIntField{A: 1, B: nil},
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},
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{
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input: "C20102",
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ptr: new(optionalBigIntField),
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value: optionalBigIntField{A: 1, B: big.NewInt(2)},
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},
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{
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input: "C101",
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ptr: new(optionalPtrField),
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value: optionalPtrField{A: 1},
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},
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{
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input: "C20180", // not accepted because "optional" doesn't enable "nil"
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ptr: new(optionalPtrField),
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error: "rlp: input string too short for [3]uint8, decoding into (rlp.optionalPtrField).B",
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},
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{
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input: "C20102",
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ptr: new(optionalPtrField),
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error: "rlp: input string too short for [3]uint8, decoding into (rlp.optionalPtrField).B",
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},
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{
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input: "C50183010203",
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ptr: new(optionalPtrField),
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value: optionalPtrField{A: 1, B: &[3]byte{1, 2, 3}},
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},
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{
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input: "C101",
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ptr: new(optionalPtrFieldNil),
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value: optionalPtrFieldNil{A: 1},
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},
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{
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input: "C20180", // accepted because "nil" tag allows empty input
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ptr: new(optionalPtrFieldNil),
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value: optionalPtrFieldNil{A: 1},
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},
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{
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input: "C20102",
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ptr: new(optionalPtrFieldNil),
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error: "rlp: input string too short for [3]uint8, decoding into (rlp.optionalPtrFieldNil).B",
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},
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// struct tag "optional" field clearing
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{
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input: "C101",
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ptr: &optionalFields{A: 9, B: 8, C: 7},
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value: optionalFields{A: 1, B: 0, C: 0},
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},
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{
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input: "C20102",
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ptr: &optionalFields{A: 9, B: 8, C: 7},
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value: optionalFields{A: 1, B: 2, C: 0},
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},
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{
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input: "C20102",
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ptr: &optionalAndTailField{A: 9, B: 8, Tail: []uint{7, 6, 5}},
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value: optionalAndTailField{A: 1, B: 2, Tail: []uint{}},
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},
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{
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input: "C101",
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ptr: &optionalPtrField{A: 9, B: &[3]byte{8, 7, 6}},
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value: optionalPtrField{A: 1},
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},
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// RawValue
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{input: "01", ptr: new(RawValue), value: RawValue(unhex("01"))},
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{input: "82FFFF", ptr: new(RawValue), value: RawValue(unhex("82FFFF"))},
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@ -822,6 +953,40 @@ func TestDecoderFunc(t *testing.T) {
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x()
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}
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// This tests the validity checks for fields with struct tag "optional".
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func TestInvalidOptionalField(t *testing.T) {
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type (
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invalid1 struct {
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A uint `rlp:"optional"`
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B uint
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}
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invalid2 struct {
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T []uint `rlp:"tail,optional"`
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}
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invalid3 struct {
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T []uint `rlp:"optional,tail"`
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}
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)
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tests := []struct {
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v interface{}
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err string
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}{
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{v: new(invalid1), err: `rlp: struct field rlp.invalid1.B needs "optional" tag`},
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{v: new(invalid2), err: `rlp: invalid struct tag "optional" for rlp.invalid2.T (also has "tail" tag)`},
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{v: new(invalid3), err: `rlp: invalid struct tag "tail" for rlp.invalid3.T (also has "optional" tag)`},
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}
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for _, test := range tests {
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err := DecodeBytes(unhex("C20102"), test.v)
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if err == nil {
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t.Errorf("no error for %T", test.v)
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} else if err.Error() != test.err {
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t.Errorf("wrong error for %T: %v", test.v, err.Error())
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}
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}
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}
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func ExampleDecode() {
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input, _ := hex.DecodeString("C90A1486666F6F626172")
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67
rlp/doc.go
67
rlp/doc.go
@ -102,29 +102,60 @@ Signed integers, floating point numbers, maps, channels and functions cannot be
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Struct Tags
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Package rlp honours certain struct tags: "-", "tail", "nil", "nilList" and "nilString".
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As with other encoding packages, the "-" tag ignores fields.
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The "-" tag ignores fields.
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The "tail" tag, which may only be used on the last exported struct field, allows slurping
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up any excess list elements into a slice. See examples for more details.
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The "nil" tag applies to pointer-typed fields and changes the decoding rules for the field
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such that input values of size zero decode as a nil pointer. This tag can be useful when
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decoding recursive types.
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type StructWithOptionalFoo struct {
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Foo *[20]byte `rlp:"nil"`
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type StructWithIgnoredField struct{
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Ignored uint `rlp:"-"`
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Field uint
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}
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Go struct values encode/decode as RLP lists. There are two ways of influencing the mapping
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of fields to list elements. The "tail" tag, which may only be used on the last exported
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struct field, allows slurping up any excess list elements into a slice.
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type StructWithTail struct{
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Field uint
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Tail []string `rlp:"tail"`
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}
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The "optional" tag says that the field may be omitted if it is zero-valued. If this tag is
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used on a struct field, all subsequent public fields must also be declared optional.
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When encoding a struct with optional fields, the output RLP list contains all values up to
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the last non-zero optional field.
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When decoding into a struct, optional fields may be omitted from the end of the input
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list. For the example below, this means input lists of one, two, or three elements are
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accepted.
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type StructWithOptionalFields struct{
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Required uint
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Optional1 uint `rlp:"optional"`
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Optional2 uint `rlp:"optional"`
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}
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The "nil", "nilList" and "nilString" tags apply to pointer-typed fields only, and change
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the decoding rules for the field type. For regular pointer fields without the "nil" tag,
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input values must always match the required input length exactly and the decoder does not
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produce nil values. When the "nil" tag is set, input values of size zero decode as a nil
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pointer. This is especially useful for recursive types.
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type StructWithNilField struct {
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Field *[3]byte `rlp:"nil"`
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}
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In the example above, Field allows two possible input sizes. For input 0xC180 (a list
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containing an empty string) Field is set to nil after decoding. For input 0xC483000000 (a
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list containing a 3-byte string), Field is set to a non-nil array pointer.
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RLP supports two kinds of empty values: empty lists and empty strings. When using the
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"nil" tag, the kind of empty value allowed for a type is chosen automatically. A struct
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field whose Go type is a pointer to an unsigned integer, string, boolean or byte
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array/slice expects an empty RLP string. Any other pointer field type encodes/decodes as
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an empty RLP list.
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"nil" tag, the kind of empty value allowed for a type is chosen automatically. A field
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whose Go type is a pointer to an unsigned integer, string, boolean or byte array/slice
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expects an empty RLP string. Any other pointer field type encodes/decodes as an empty RLP
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list.
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The choice of null value can be made explicit with the "nilList" and "nilString" struct
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tags. Using these tags encodes/decodes a Go nil pointer value as the kind of empty
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RLP value defined by the tag.
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tags. Using these tags encodes/decodes a Go nil pointer value as the empty RLP value kind
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defined by the tag.
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*/
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package rlp
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@ -546,7 +546,12 @@ func makeStructWriter(typ reflect.Type) (writer, error) {
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return nil, structFieldError{typ, f.index, f.info.writerErr}
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}
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}
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writer := func(val reflect.Value, w *encbuf) error {
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var writer writer
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firstOptionalField := firstOptionalField(fields)
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if firstOptionalField == len(fields) {
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// This is the writer function for structs without any optional fields.
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writer = func(val reflect.Value, w *encbuf) error {
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lh := w.list()
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for _, f := range fields {
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if err := f.info.writer(val.Field(f.index), w); err != nil {
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@ -556,6 +561,26 @@ func makeStructWriter(typ reflect.Type) (writer, error) {
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w.listEnd(lh)
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return nil
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}
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} else {
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// If there are any "optional" fields, the writer needs to perform additional
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// checks to determine the output list length.
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writer = func(val reflect.Value, w *encbuf) error {
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lastField := len(fields) - 1
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for ; lastField >= firstOptionalField; lastField-- {
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if !val.Field(fields[lastField].index).IsZero() {
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break
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}
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}
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lh := w.list()
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for i := 0; i <= lastField; i++ {
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if err := fields[i].info.writer(val.Field(fields[i].index), w); err != nil {
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return err
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}
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}
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w.listEnd(lh)
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return nil
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}
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}
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return writer, nil
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}
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@ -257,12 +257,30 @@ var encTests = []encTest{
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{val: simplestruct{A: 3, B: "foo"}, output: "C50383666F6F"},
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{val: &recstruct{5, nil}, output: "C205C0"},
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{val: &recstruct{5, &recstruct{4, &recstruct{3, nil}}}, output: "C605C404C203C0"},
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{val: &intField{X: 3}, error: "rlp: type int is not RLP-serializable (struct field rlp.intField.X)"},
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// struct tag "-"
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{val: &ignoredField{A: 1, B: 2, C: 3}, output: "C20103"},
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// struct tag "tail"
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{val: &tailRaw{A: 1, Tail: []RawValue{unhex("02"), unhex("03")}}, output: "C3010203"},
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{val: &tailRaw{A: 1, Tail: []RawValue{unhex("02")}}, output: "C20102"},
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{val: &tailRaw{A: 1, Tail: []RawValue{}}, output: "C101"},
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{val: &tailRaw{A: 1, Tail: nil}, output: "C101"},
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{val: &hasIgnoredField{A: 1, B: 2, C: 3}, output: "C20103"},
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{val: &intField{X: 3}, error: "rlp: type int is not RLP-serializable (struct field rlp.intField.X)"},
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// struct tag "optional"
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{val: &optionalFields{}, output: "C180"},
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{val: &optionalFields{A: 1}, output: "C101"},
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{val: &optionalFields{A: 1, B: 2}, output: "C20102"},
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{val: &optionalFields{A: 1, B: 2, C: 3}, output: "C3010203"},
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{val: &optionalFields{A: 1, B: 0, C: 3}, output: "C3018003"},
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{val: &optionalAndTailField{A: 1}, output: "C101"},
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{val: &optionalAndTailField{A: 1, B: 2}, output: "C20102"},
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{val: &optionalAndTailField{A: 1, Tail: []uint{5, 6}}, output: "C401800506"},
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{val: &optionalAndTailField{A: 1, Tail: []uint{5, 6}}, output: "C401800506"},
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{val: &optionalBigIntField{A: 1}, output: "C101"},
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{val: &optionalPtrField{A: 1}, output: "C101"},
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{val: &optionalPtrFieldNil{A: 1}, output: "C101"},
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// nil
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{val: (*uint)(nil), output: "80"},
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@ -38,15 +38,16 @@ type typeinfo struct {
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// tags represents struct tags.
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type tags struct {
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// rlp:"nil" controls whether empty input results in a nil pointer.
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// nilKind is the kind of empty value allowed for the field.
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nilKind Kind
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nilOK bool
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// This controls whether nil pointers are encoded/decoded as empty strings
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// or empty lists.
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nilKind Kind
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// rlp:"optional" allows for a field to be missing in the input list.
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// If this is set, all subsequent fields must also be optional.
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optional bool
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// rlp:"tail" controls whether this field swallows additional list
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// elements. It can only be set for the last field, which must be
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// of slice type.
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// rlp:"tail" controls whether this field swallows additional list elements. It can
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// only be set for the last field, which must be of slice type.
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tail bool
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// rlp:"-" ignores fields.
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@ -106,26 +107,49 @@ func cachedTypeInfo1(typ reflect.Type, tags tags) *typeinfo {
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type field struct {
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index int
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info *typeinfo
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optional bool
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}
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// structFields resolves the typeinfo of all public fields in a struct type.
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func structFields(typ reflect.Type) (fields []field, err error) {
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lastPublic := lastPublicField(typ)
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var (
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lastPublic = lastPublicField(typ)
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anyOptional = false
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)
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for i := 0; i < typ.NumField(); i++ {
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if f := typ.Field(i); f.PkgPath == "" { // exported
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tags, err := parseStructTag(typ, i, lastPublic)
|
||||
if err != nil {
|
||||
return nil, err
|
||||
}
|
||||
|
||||
// Skip rlp:"-" fields.
|
||||
if tags.ignored {
|
||||
continue
|
||||
}
|
||||
// If any field has the "optional" tag, subsequent fields must also have it.
|
||||
if tags.optional || tags.tail {
|
||||
anyOptional = true
|
||||
} else if anyOptional {
|
||||
return nil, fmt.Errorf(`rlp: struct field %v.%s needs "optional" tag`, typ, f.Name)
|
||||
}
|
||||
info := cachedTypeInfo1(f.Type, tags)
|
||||
fields = append(fields, field{i, info})
|
||||
fields = append(fields, field{i, info, tags.optional})
|
||||
}
|
||||
}
|
||||
return fields, nil
|
||||
}
|
||||
|
||||
// anyOptionalFields returns the index of the first field with "optional" tag.
|
||||
func firstOptionalField(fields []field) int {
|
||||
for i, f := range fields {
|
||||
if f.optional {
|
||||
return i
|
||||
}
|
||||
}
|
||||
return len(fields)
|
||||
}
|
||||
|
||||
type structFieldError struct {
|
||||
typ reflect.Type
|
||||
field int
|
||||
@ -166,11 +190,19 @@ func parseStructTag(typ reflect.Type, fi, lastPublic int) (tags, error) {
|
||||
case "nilList":
|
||||
ts.nilKind = List
|
||||
}
|
||||
case "optional":
|
||||
ts.optional = true
|
||||
if ts.tail {
|
||||
return ts, structTagError{typ, f.Name, t, `also has "tail" tag`}
|
||||
}
|
||||
case "tail":
|
||||
ts.tail = true
|
||||
if fi != lastPublic {
|
||||
return ts, structTagError{typ, f.Name, t, "must be on last field"}
|
||||
}
|
||||
if ts.optional {
|
||||
return ts, structTagError{typ, f.Name, t, `also has "optional" tag`}
|
||||
}
|
||||
if f.Type.Kind() != reflect.Slice {
|
||||
return ts, structTagError{typ, f.Name, t, "field type is not slice"}
|
||||
}
|
||||
|
||||
Loading…
Reference in New Issue
Block a user