rlp: rename ".." to "tail"

rlp/decode.go

@@ -63,8 +63,9 @@ 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 two struct tags, "nil" and
-// "..". The "nil" 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.
@@ -283,8 +284,8 @@ func makeListDecoder(typ reflect.Type, tag tags) (decoder, error) {
 		dec = func(s *Stream, val reflect.Value) error {
 			return decodeListArray(s, val, etypeinfo.decoder)
 		}
-	case tag.dotdot:
-		// A slice with .. tag can occur as the last field
+	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.

rlp/decode_tail_test.go

@@ -5,15 +5,15 @@ import (
 	"fmt"
 )
 
-type structWithDotDot struct {
+type structWithTail struct {
 	A, B uint
-	C    []uint `rlp:".."`
+	C    []uint `rlp:"tail"`
 }
 
-func ExampleDecode_structTagDotDot() {
-	// In this example, the ".." struct tag is used to decode lists of
+func ExampleDecode_structTagTail() {
+	// In this example, the "tail" struct tag is used to decode lists of
 	// differing length into a struct.
-	var val structWithDotDot
+	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)
@@ -29,5 +29,5 @@ func ExampleDecode_structTagDotDot() {
 	// 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.structWithDotDot"
+	// with 1 element: err="rlp: too few elements for rlp.structWithTail"
 }

rlp/decode_test.go

@@ -312,19 +312,24 @@ type recstruct struct {
 	Child *recstruct `rlp:"nil"`
 }
 
-type invalidDotDot1 struct {
-	A uint `rlp:".."`
+type invalidTail1 struct {
+	A uint `rlp:"tail"`
 	B string
 }
 
-type invalidDotDot2 struct {
+type invalidTail2 struct {
 	A uint
-	B string `rlp:".."`
+	B string `rlp:"tail"`
 }
 
-type dotdotRaw struct {
+type tailRaw struct {
 	A    uint
-	DotDot []RawValue `rlp:".."`
+	Tail []RawValue `rlp:"tail"`
+}
+
+type tailUint struct {
+	A    uint
+	Tail []uint `rlp:"tail"`
 }
 
 var (
@@ -454,20 +459,35 @@ var decodeTests = []decodeTest{
 	},
 	{
 		input: "C0",
-		ptr:   new(invalidDotDot1),
-		error: "rlp: invalid struct tag \"..\" for rlp.invalidDotDot1.A (must be on last field)",
+		ptr:   new(invalidTail1),
+		error: "rlp: invalid struct tag \"tail\" for rlp.invalidTail1.A (must be on last field)",
 	},
 	{
 		input: "C0",
-		ptr:   new(invalidDotDot2),
-		error: "rlp: invalid struct tag \"..\" for rlp.invalidDotDot2.B (field type is not slice)",
+		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 ".."
+	// struct tag "tail"
 	{
 		input: "C3010203",
-		ptr:   new(dotdotRaw),
-		value: dotdotRaw{A: 1, DotDot: []RawValue{unhex("02"), unhex("03")}},
+		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

rlp/encode.go

@@ -513,7 +513,7 @@ func makeSliceWriter(typ reflect.Type, ts tags) (writer, error) {
 		return nil, err
 	}
 	writer := func(val reflect.Value, w *encbuf) error {
-		if !ts.dotdot {
+		if !ts.tail {
 			defer w.listEnd(w.list())
 		}
 		vlen := val.Len()

rlp/encode_test.go

@@ -214,7 +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: &dotdotRaw{A: 1, DotDot: []RawValue{unhex("02"), unhex("03")}}, output: "C3010203"},
+	{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"},

rlp/typecache.go

@@ -38,10 +38,10 @@ type tags struct {
 	// rlp:"nil" controls whether empty input results in a nil pointer.
 	nilOK bool
 
-	// rlp:".." controls whether this field swallows additional list
+	// rlp:"tail" controls whether this field swallows additional list
 	// elements. It can only be set for the last field, which must be
-	// a slice type.
-	dotdot bool
+	// of slice type.
+	tail bool
 }
 
 type typekey struct {
@@ -97,14 +97,9 @@ 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"))
-			if tags.dotdot {
-				if i != typ.NumField()-1 {
-					return nil, fmt.Errorf(`rlp: invalid struct tag ".." for %v.%s (must be on last field)`, typ, f.Name)
-				}
-				if f.Type.Kind() != reflect.Slice {
-					return nil, fmt.Errorf(`rlp: invalid struct tag ".." for %v.%s (field type is not slice)`, typ, f.Name)
-				}
+			tags, err := parseStructTag(typ, i)
+			if err != nil {
+				return nil, err
 			}
 			info, err := cachedTypeInfo1(f.Type, tags)
 			if err != nil {
@@ -116,11 +111,27 @@ func structFields(typ reflect.Type) (fields []field, err error) {
 	return fields, nil
 }
 
-func parseStructTag(tag string) tags {
-	return tags{
-		nilOK:  strings.Contains(tag, "nil"),
-		dotdot: strings.Contains(tag, ".."),
+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) {