From bb07ce3eedabb2133227ba1d7569d171d8e5b25c Mon Sep 17 00:00:00 2001
From: Felix Lange <fjl@twurst.com>
Date: Mon, 21 Dec 2015 21:05:20 +0100
Subject: [PATCH] rlp: add "tail" struct tag
---
rlp/decode.go | 51 ++++++++++++++++++++++++++--------------
rlp/decode_tail_test.go | 33 ++++++++++++++++++++++++++
rlp/decode_test.go | 52 +++++++++++++++++++++++++++++++++++++++++
rlp/encode.go | 11 +++++----
rlp/encode_test.go | 4 ++++
rlp/typecache.go | 38 ++++++++++++++++++++++++++----
6 files changed, 163 insertions(+), 26 deletions(-)
create mode 100644 rlp/decode_tail_test.go
diff --git a/rlp/decode.go b/rlp/decode.go
index c4d42c6fc..c4e5869cc 100644
--- a/rlp/decode.go
+++ b/rlp/decode.go
@@ -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 {
diff --git a/rlp/decode_tail_test.go b/rlp/decode_tail_test.go
new file mode 100644
index 000000000..885354390
--- /dev/null
+++ b/rlp/decode_tail_test.go
@@ -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"
+}
diff --git a/rlp/decode_test.go b/rlp/decode_test.go
index 408f1a5a9..2d465b74d 100644
--- a/rlp/decode_test.go
+++ b/rlp/decode_test.go
@@ -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"))},
diff --git a/rlp/encode.go b/rlp/encode.go
index d73b17c28..17cfc6b66 100644
--- a/rlp/encode.go
+++ b/rlp/encode.go
@@ -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
diff --git a/rlp/encode_test.go b/rlp/encode_test.go
index a3f30d804..6f38294e4 100644
--- a/rlp/encode_test.go
+++ b/rlp/encode_test.go
@@ -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"},
diff --git a/rlp/typecache.go b/rlp/typecache.go
index 0ab096695..a2f217c66 100644
--- a/rlp/typecache.go
+++ b/rlp/typecache.go
@@ -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
--
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