Merge pull request #2226 from fjl/eip-8

p2p, p2p/discover: EIP-8 changes

crypto/ecies/ecies.go

@@ -192,11 +192,9 @@ func concatKDF(hash hash.Hash, z, s1 []byte, kdLen int) (k []byte, err error) {
 // messageTag computes the MAC of a message (called the tag) as per
 // SEC 1, 3.5.
 func messageTag(hash func() hash.Hash, km, msg, shared []byte) []byte {
-	if shared == nil {
-		shared = make([]byte, 0)
-	}
 	mac := hmac.New(hash, km)
 	mac.Write(msg)
+	mac.Write(shared)
 	tag := mac.Sum(nil)
 	return tag
 }
@@ -243,9 +241,11 @@ func symDecrypt(rand io.Reader, params *ECIESParams, key, ct []byte) (m []byte,
 	return
 }
 
-// Encrypt encrypts a message using ECIES as specified in SEC 1, 5.1. If
-// the shared information parameters aren't being used, they should be
-// nil.
+// Encrypt encrypts a message using ECIES as specified in SEC 1, 5.1.
+//
+// s1 and s2 contain shared information that is not part of the resulting
+// ciphertext. s1 is fed into key derivation, s2 is fed into the MAC. If the
+// shared information parameters aren't being used, they should be nil.
 func Encrypt(rand io.Reader, pub *PublicKey, m, s1, s2 []byte) (ct []byte, err error) {
 	params := pub.Params
 	if params == nil {

crypto/ecies/ecies_test.go

@@ -408,6 +408,36 @@ func TestEncryptDecrypt(t *testing.T) {
 	}
 }
 
+func TestDecryptShared2(t *testing.T) {
+	prv, err := GenerateKey(rand.Reader, DefaultCurve, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	message := []byte("Hello, world.")
+	shared2 := []byte("shared data 2")
+	ct, err := Encrypt(rand.Reader, &prv.PublicKey, message, nil, shared2)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Check that decrypting with correct shared data works.
+	pt, err := prv.Decrypt(rand.Reader, ct, nil, shared2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(pt, message) {
+		t.Fatal("ecies: plaintext doesn't match message")
+	}
+
+	// Decrypting without shared data or incorrect shared data fails.
+	if _, err = prv.Decrypt(rand.Reader, ct, nil, nil); err == nil {
+		t.Fatal("ecies: decrypting without shared data didn't fail")
+	}
+	if _, err = prv.Decrypt(rand.Reader, ct, nil, []byte("garbage")); err == nil {
+		t.Fatal("ecies: decrypting with incorrect shared data didn't fail")
+	}
+}
+
 // TestMarshalEncryption validates the encode/decode produces a valid
 // ECIES encryption key.
 func TestMarshalEncryption(t *testing.T) {

p2p/discover/udp.go

@@ -67,6 +67,8 @@ type (
 		Version    uint
 		From, To   rpcEndpoint
 		Expiration uint64
+		// Ignore additional fields (for forward compatibility).
+		Rest []rlp.RawValue `rlp:"tail"`
 	}
 
 	// pong is the reply to ping.
@@ -78,18 +80,24 @@ type (
 
 		ReplyTok   []byte // This contains the hash of the ping packet.
 		Expiration uint64 // Absolute timestamp at which the packet becomes invalid.
+		// Ignore additional fields (for forward compatibility).
+		Rest []rlp.RawValue `rlp:"tail"`
 	}
 
 	// findnode is a query for nodes close to the given target.
 	findnode struct {
 		Target     NodeID // doesn't need to be an actual public key
 		Expiration uint64
+		// Ignore additional fields (for forward compatibility).
+		Rest []rlp.RawValue `rlp:"tail"`
 	}
 
 	// reply to findnode
 	neighbors struct {
 		Nodes      []rpcNode
 		Expiration uint64
+		// Ignore additional fields (for forward compatibility).
+		Rest []rlp.RawValue `rlp:"tail"`
 	}
 
 	rpcNode struct {
@@ -522,7 +530,8 @@ func decodePacket(buf []byte) (packet, NodeID, []byte, error) {
 	default:
 		return nil, fromID, hash, fmt.Errorf("unknown type: %d", ptype)
 	}
-	err = rlp.DecodeBytes(sigdata[1:], req)
+	s := rlp.NewStream(bytes.NewReader(sigdata[1:]), 0)
+	err = s.Decode(req)
 	return req, fromID, hash, err
 }
 

p2p/discover/udp_test.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"crypto/ecdsa"
 	"encoding/binary"
+	"encoding/hex"
 	"errors"
 	"fmt"
 	"io"
@@ -33,7 +34,9 @@ import (
 	"time"
 
 	"github.com/davecgh/go-spew/spew"
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/rlp"
 )
 
 func init() {
@@ -434,6 +437,115 @@ func TestUDP_successfulPing(t *testing.T) {
 	}
 }
 
+var testPackets = []struct {
+	input      string
+	wantPacket interface{}
+}{
+	{
+		input: "71dbda3a79554728d4f94411e42ee1f8b0d561c10e1e5f5893367948c6a7d70bb87b235fa28a77070271b6c164a2dce8c7e13a5739b53b5e96f2e5acb0e458a02902f5965d55ecbeb2ebb6cabb8b2b232896a36b737666c55265ad0a68412f250001ea04cb847f000001820cfa8215a8d790000000000000000000000000000000018208ae820d058443b9a355",
+		wantPacket: &ping{
+			Version:    4,
+			From:       rpcEndpoint{net.ParseIP("127.0.0.1").To4(), 3322, 5544},
+			To:         rpcEndpoint{net.ParseIP("::1"), 2222, 3333},
+			Expiration: 1136239445,
+			Rest:       []rlp.RawValue{},
+		},
+	},
+	{
+		input: "e9614ccfd9fc3e74360018522d30e1419a143407ffcce748de3e22116b7e8dc92ff74788c0b6663aaa3d67d641936511c8f8d6ad8698b820a7cf9e1be7155e9a241f556658c55428ec0563514365799a4be2be5a685a80971ddcfa80cb422cdd0101ec04cb847f000001820cfa8215a8d790000000000000000000000000000000018208ae820d058443b9a3550102",
+		wantPacket: &ping{
+			Version:    4,
+			From:       rpcEndpoint{net.ParseIP("127.0.0.1").To4(), 3322, 5544},
+			To:         rpcEndpoint{net.ParseIP("::1"), 2222, 3333},
+			Expiration: 1136239445,
+			Rest:       []rlp.RawValue{{0x01}, {0x02}},
+		},
+	},
+	{
+		input: "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",
+		wantPacket: &ping{
+			Version:    555,
+			From:       rpcEndpoint{net.ParseIP("2001:db8:3c4d:15::abcd:ef12"), 3322, 5544},
+			To:         rpcEndpoint{net.ParseIP("2001:db8:85a3:8d3:1319:8a2e:370:7348"), 2222, 33338},
+			Expiration: 1136239445,
+			Rest:       []rlp.RawValue{{0xC5, 0x01, 0x02, 0x03, 0x04, 0x05}},
+		},
+	},
+	{
+		input: "09b2428d83348d27cdf7064ad9024f526cebc19e4958f0fdad87c15eb598dd61d08423e0bf66b2069869e1724125f820d851c136684082774f870e614d95a2855d000f05d1648b2d5945470bc187c2d2216fbe870f43ed0909009882e176a46b0102f846d79020010db885a308d313198a2e037073488208ae82823aa0fbc914b16819237dcd8801d7e53f69e9719adecb3cc0e790c57e91ca4461c9548443b9a355c6010203c2040506a0c969a58f6f9095004c0177a6b47f451530cab38966a25cca5cb58f055542124e",
+		wantPacket: &pong{
+			To:         rpcEndpoint{net.ParseIP("2001:db8:85a3:8d3:1319:8a2e:370:7348"), 2222, 33338},
+			ReplyTok:   common.Hex2Bytes("fbc914b16819237dcd8801d7e53f69e9719adecb3cc0e790c57e91ca4461c954"),
+			Expiration: 1136239445,
+			Rest:       []rlp.RawValue{{0xC6, 0x01, 0x02, 0x03, 0xC2, 0x04, 0x05}, {0x06}},
+		},
+	},
+	{
+		input: "c7c44041b9f7c7e41934417ebac9a8e1a4c6298f74553f2fcfdcae6ed6fe53163eb3d2b52e39fe91831b8a927bf4fc222c3902202027e5e9eb812195f95d20061ef5cd31d502e47ecb61183f74a504fe04c51e73df81f25c4d506b26db4517490103f84eb840ca634cae0d49acb401d8a4c6b6fe8c55b70d115bf400769cc1400f3258cd31387574077f301b421bc84df7266c44e9e6d569fc56be00812904767bf5ccd1fc7f8443b9a35582999983999999280dc62cc8255c73471e0a61da0c89acdc0e035e260add7fc0c04ad9ebf3919644c91cb247affc82b69bd2ca235c71eab8e49737c937a2c396",
+		wantPacket: &findnode{
+			Target:     MustHexID("ca634cae0d49acb401d8a4c6b6fe8c55b70d115bf400769cc1400f3258cd31387574077f301b421bc84df7266c44e9e6d569fc56be00812904767bf5ccd1fc7f"),
+			Expiration: 1136239445,
+			Rest:       []rlp.RawValue{{0x82, 0x99, 0x99}, {0x83, 0x99, 0x99, 0x99}},
+		},
+	},
+	{
+		input: "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",
+		wantPacket: &neighbors{
+			Nodes: []rpcNode{
+				{
+					ID:  MustHexID("3155e1427f85f10a5c9a7755877748041af1bcd8d474ec065eb33df57a97babf54bfd2103575fa829115d224c523596b401065a97f74010610fce76382c0bf32"),
+					IP:  net.ParseIP("99.33.22.55").To4(),
+					UDP: 4444,
+					TCP: 4445,
+				},
+				{
+					ID:  MustHexID("312c55512422cf9b8a4097e9a6ad79402e87a15ae909a4bfefa22398f03d20951933beea1e4dfa6f968212385e829f04c2d314fc2d4e255e0d3bc08792b069db"),
+					IP:  net.ParseIP("1.2.3.4").To4(),
+					UDP: 1,
+					TCP: 1,
+				},
+				{
+					ID:  MustHexID("38643200b172dcfef857492156971f0e6aa2c538d8b74010f8e140811d53b98c765dd2d96126051913f44582e8c199ad7c6d6819e9a56483f637feaac9448aac"),
+					IP:  net.ParseIP("2001:db8:3c4d:15::abcd:ef12"),
+					UDP: 3333,
+					TCP: 3333,
+				},
+				{
+					ID:  MustHexID("8dcab8618c3253b558d459da53bd8fa68935a719aff8b811197101a4b2b47dd2d47295286fc00cc081bb542d760717d1bdd6bec2c37cd72eca367d6dd3b9df73"),
+					IP:  net.ParseIP("2001:db8:85a3:8d3:1319:8a2e:370:7348"),
+					UDP: 999,
+					TCP: 1000,
+				},
+			},
+			Expiration: 1136239445,
+			Rest:       []rlp.RawValue{{0x01}, {0x02}, {0x03}},
+		},
+	},
+}
+
+func TestForwardCompatibility(t *testing.T) {
+	testkey, _ := crypto.HexToECDSA("b71c71a67e1177ad4e901695e1b4b9ee17ae16c6668d313eac2f96dbcda3f291")
+	wantNodeID := PubkeyID(&testkey.PublicKey)
+
+	for _, test := range testPackets {
+		input, err := hex.DecodeString(test.input)
+		if err != nil {
+			t.Fatalf("invalid hex: %s", test.input)
+		}
+		packet, nodeid, _, err := decodePacket(input)
+		if err != nil {
+			t.Errorf("did not accept packet %s\n%v", test.input, err)
+			continue
+		}
+		if !reflect.DeepEqual(packet, test.wantPacket) {
+			t.Errorf("got %s\nwant %s", spew.Sdump(packet), spew.Sdump(test.wantPacket))
+		}
+		if nodeid != wantNodeID {
+			t.Errorf("got id %v\nwant id %v", nodeid, wantNodeID)
+		}
+	}
+}
+
 // dgramPipe is a fake UDP socket. It queues all sent datagrams.
 type dgramPipe struct {
 	mu      *sync.Mutex

p2p/message_test.go

@@ -143,7 +143,8 @@ func TestEOFSignal(t *testing.T) {
 }
 
 func unhex(str string) []byte {
-	b, err := hex.DecodeString(strings.Replace(str, "\n", "", -1))
+	r := strings.NewReplacer("\t", "", " ", "", "\n", "")
+	b, err := hex.DecodeString(r.Replace(str))
 	if err != nil {
 		panic(fmt.Sprintf("invalid hex string: %q", str))
 	}

p2p/peer.go

@@ -56,6 +56,9 @@ type protoHandshake struct {
 	Caps       []Cap
 	ListenPort uint64
 	ID         discover.NodeID
+
+	// Ignore additional fields (for forward compatibility).
+	Rest []rlp.RawValue `rlp:"tail"`
 }
 
 // Peer represents a connected remote node.

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 {

rlp/decode_tail_test.go

+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"
+}

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"))},

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

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"},

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