Merge branch 'fjl-rlp-size-validation' into develop

13 files changed, 481 insertions, 233 deletions

diff --git a/cmd/rlpdump/main.go b/cmd/rlpdump/main.go
index 8567dcff8..528ccc6bd 100644
--- a/cmd/rlpdump/main.go
+++ b/cmd/rlpdump/main.go
@@ -78,7 +78,7 @@ func main() {
 		os.Exit(2)
 	}
 
-	s := rlp.NewStream(r)
+	s := rlp.NewStream(r, 0)
 	for {
 		if err := dump(s, 0); err != nil {
 			if err != io.EOF {
diff --git a/cmd/utils/cmd.go b/cmd/utils/cmd.go
index 7286f5c5e..64faf6ad1 100644
--- a/cmd/utils/cmd.go
+++ b/cmd/utils/cmd.go
@@ -154,7 +154,7 @@ func ImportChain(chainmgr *core.ChainManager, fn string) error {
 	defer fh.Close()
 
 	chainmgr.Reset()
-	stream := rlp.NewStream(fh)
+	stream := rlp.NewStream(fh, 0)
 	var i, n int
 
 	batchSize := 2500
diff --git a/core/types/transaction.go b/core/types/transaction.go
index 6646bdf29..d8dcd7424 100644
--- a/core/types/transaction.go
+++ b/core/types/transaction.go
@@ -22,7 +22,7 @@ type Transaction struct {
 	AccountNonce uint64
 	Price        *big.Int
 	GasLimit     *big.Int
-	Recipient    *common.Address // nil means contract creation
+	Recipient    *common.Address `rlp:"nil"` // nil means contract creation
 	Amount       *big.Int
 	Payload      []byte
 	V            byte
diff --git a/eth/handler.go b/eth/handler.go
index 780ec3931..5c0660d84 100644
--- a/eth/handler.go
+++ b/eth/handler.go
@@ -197,7 +197,7 @@ func (self *ProtocolManager) handleMsg(p *peer) error {
 		// returns either requested hashes or nothing (i.e. not found)
 		return p.sendBlockHashes(hashes)
 	case BlockHashesMsg:
-		msgStream := rlp.NewStream(msg.Payload)
+		msgStream := rlp.NewStream(msg.Payload, uint64(msg.Size))
 
 		var hashes []common.Hash
 		if err := msgStream.Decode(&hashes); err != nil {
@@ -209,12 +209,12 @@ func (self *ProtocolManager) handleMsg(p *peer) error {
 		}
 
 	case GetBlocksMsg:
-		msgStream := rlp.NewStream(msg.Payload)
+		var blocks []*types.Block
+
+		msgStream := rlp.NewStream(msg.Payload, uint64(msg.Size))
 		if _, err := msgStream.List(); err != nil {
 			return err
 		}
-
-		var blocks []*types.Block
 		var i int
 		for {
 			i++
@@ -236,9 +236,9 @@ func (self *ProtocolManager) handleMsg(p *peer) error {
 		}
 		return p.sendBlocks(blocks)
 	case BlocksMsg:
-		msgStream := rlp.NewStream(msg.Payload)
-
 		var blocks []*types.Block
+
+		msgStream := rlp.NewStream(msg.Payload, uint64(msg.Size))
 		if err := msgStream.Decode(&blocks); err != nil {
 			glog.V(logger.Detail).Infoln("Decode error", err)
 			blocks = nil
diff --git a/p2p/discover/udp.go b/p2p/discover/udp.go
index 61a0abed9..07a1a739c 100644
--- a/p2p/discover/udp.go
+++ b/p2p/discover/udp.go
@@ -413,7 +413,7 @@ func decodePacket(buf []byte) (packet, NodeID, []byte, error) {
 	default:
 		return nil, fromID, hash, fmt.Errorf("unknown type: %d", ptype)
 	}
-	err = rlp.Decode(bytes.NewReader(sigdata[1:]), req)
+	err = rlp.DecodeBytes(sigdata[1:], req)
 	return req, fromID, hash, err
 }
 
diff --git a/p2p/message.go b/p2p/message.go
index b42acbe3c..be6405d6f 100644
--- a/p2p/message.go
+++ b/p2p/message.go
@@ -32,7 +32,8 @@ type Msg struct {
 //
 // For the decoding rules, please see package rlp.
 func (msg Msg) Decode(val interface{}) error {
-	if err := rlp.Decode(msg.Payload, val); err != nil {
+	s := rlp.NewStream(msg.Payload, uint64(msg.Size))
+	if err := s.Decode(val); err != nil {
 		return newPeerError(errInvalidMsg, "(code %x) (size %d) %v", msg.Code, msg.Size, err)
 	}
 	return nil
diff --git a/p2p/peer_error.go b/p2p/peer_error.go
index 402131630..a912f6064 100644
--- a/p2p/peer_error.go
+++ b/p2p/peer_error.go
@@ -57,7 +57,7 @@ func (self *peerError) Error() string {
 	return self.message
 }
 
-type DiscReason byte
+type DiscReason uint
 
 const (
 	DiscRequested DiscReason = iota
diff --git a/rlp/decode.go b/rlp/decode.go
index 3b5617475..6952ecaea 100644
--- a/rlp/decode.go
+++ b/rlp/decode.go
@@ -9,6 +9,7 @@ import (
 	"io"
 	"math/big"
 	"reflect"
+	"strings"
 )
 
 var (
@@ -35,25 +36,35 @@ type Decoder interface {
 // If the type implements the Decoder interface, decode calls
 // DecodeRLP.
 //
-// To decode into a pointer, Decode will set the pointer to nil if the
-// input has size zero or the input is a single byte with value zero.
-// If the input has nonzero size, Decode will allocate a new value of
-// the type being pointed to.
+// To decode into a pointer, Decode will decode into the value pointed
+// to. If the pointer is nil, a new value of the pointer's element
+// type is allocated. If the pointer is non-nil, the existing value
+// will reused.
 //
 // To decode into a struct, Decode expects the input to be an RLP
 // list. The decoded elements of the list are assigned to each public
-// field in the order given by the struct's definition. If the input
-// list has too few elements, no error is returned and the remaining
-// fields will have the zero value.
-// Recursive struct types are supported.
+// field in the order given by the struct's definition. The input list
+// 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
+// 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.
+//
+//     type StructWithEmptyOK struct {
+//         Foo *[20]byte `rlp:"nil"`
+//     }
 //
 // To decode into a slice, the input must be a list and the resulting
-// slice will contain the input elements in order.
-// As a special case, if the slice has a byte-size element type, the input
-// can also be an RLP string.
+// slice will contain the input elements in order. For byte slices,
+// the input must be an RLP string. Array types decode similarly, with
+// the additional restriction that the number of input elements (or
+// bytes) must match the array's length.
 //
 // To decode into a Go string, the input must be an RLP string. The
-// bytes are taken as-is and will not necessarily be valid UTF-8.
+// input bytes are taken as-is and will not necessarily be valid UTF-8.
 //
 // To decode into an unsigned integer type, the input must also be an RLP
 // string. The bytes are interpreted as a big endian representation of
@@ -64,20 +75,28 @@ type Decoder interface {
 // To decode into an interface value, Decode stores one of these
 // in the value:
 //
-//	[]interface{}, for RLP lists
-//	[]byte, for RLP strings
+//	  []interface{}, for RLP lists
+//	  []byte, for RLP strings
 //
 // Non-empty interface types are not supported, nor are booleans,
 // signed integers, floating point numbers, maps, channels and
 // functions.
+//
+// Note that Decode does not set an input limit for all readers
+// and may be vulnerable to panics cause by huge value sizes. If
+// you need an input limit, use
+//
+//     NewStream(r, limit).Decode(val)
 func Decode(r io.Reader, val interface{}) error {
-	return NewStream(r).Decode(val)
+	// TODO: this could use a Stream from a pool.
+	return NewStream(r, 0).Decode(val)
 }
 
 // DecodeBytes parses RLP data from b into val.
 // Please see the documentation of Decode for the decoding rules.
 func DecodeBytes(b []byte, val interface{}) error {
-	return NewStream(bytes.NewReader(b)).Decode(val)
+	// TODO: this could use a Stream from a pool.
+	return NewStream(bytes.NewReader(b), uint64(len(b))).Decode(val)
 }
 
 type decodeError struct {
@@ -100,7 +119,9 @@ func (err *decodeError) Error() string {
 func wrapStreamError(err error, typ reflect.Type) error {
 	switch err {
 	case ErrCanonInt:
-		return &decodeError{msg: "canon int error appends zero's", typ: typ}
+		return &decodeError{msg: "non-canonical integer (leading zero bytes)", typ: typ}
+	case ErrCanonSize:
+		return &decodeError{msg: "non-canonical size information", typ: typ}
 	case ErrExpectedList:
 		return &decodeError{msg: "expected input list", typ: typ}
 	case ErrExpectedString:
@@ -125,7 +146,7 @@ var (
 	bigInt           = reflect.TypeOf(big.Int{})
 )
 
-func makeDecoder(typ reflect.Type) (dec decoder, err error) {
+func makeDecoder(typ reflect.Type, tags tags) (dec decoder, err error) {
 	kind := typ.Kind()
 	switch {
 	case typ.Implements(decoderInterface):
@@ -145,6 +166,9 @@ func makeDecoder(typ reflect.Type) (dec decoder, err error) {
 	case kind == reflect.Struct:
 		return makeStructDecoder(typ)
 	case kind == reflect.Ptr:
+		if tags.nilOK {
+			return makeOptionalPtrDecoder(typ)
+		}
 		return makePtrDecoder(typ)
 	case kind == reflect.Interface:
 		return decodeInterface, nil
@@ -186,12 +210,10 @@ func decodeBigInt(s *Stream, val reflect.Value) error {
 		i = new(big.Int)
 		val.Set(reflect.ValueOf(i))
 	}
-
-	// Reject big integers which are zero appended
+	// Reject leading zero bytes
 	if len(b) > 0 && b[0] == 0 {
 		return wrapStreamError(ErrCanonInt, val.Type())
 	}
-
 	i.SetBytes(b)
 	return nil
 }
@@ -205,7 +227,7 @@ func makeListDecoder(typ reflect.Type) (decoder, error) {
 			return decodeByteSlice, nil
 		}
 	}
-	etypeinfo, err := cachedTypeInfo1(etype)
+	etypeinfo, err := cachedTypeInfo1(etype, tags{})
 	if err != nil {
 		return nil, err
 	}
@@ -259,19 +281,10 @@ func decodeListSlice(s *Stream, val reflect.Value, elemdec decoder) error {
 }
 
 func decodeListArray(s *Stream, val reflect.Value, elemdec decoder) error {
-	size, err := s.List()
+	_, err := s.List()
 	if err != nil {
-		return err
-	}
-	if size == 0 {
-		zero(val, 0)
-		return s.ListEnd()
+		return wrapStreamError(err, val.Type())
 	}
-
-	// The approach here is stolen from package json, although we differ
-	// in the semantics for arrays. package json discards remaining
-	// elements that would not fit into the array. We generate an error in
-	// this case because we'd be losing information.
 	vlen := val.Len()
 	i := 0
 	for ; i < vlen; i++ {
@@ -282,24 +295,18 @@ func decodeListArray(s *Stream, val reflect.Value, elemdec decoder) error {
 		}
 	}
 	if i < vlen {
-		zero(val, i)
+		return &decodeError{msg: "input list has too few elements", typ: val.Type()}
 	}
 	return wrapStreamError(s.ListEnd(), val.Type())
 }
 
 func decodeByteSlice(s *Stream, val reflect.Value) error {
-	kind, _, err := s.Kind()
-	if err != nil {
-		return err
-	}
-	if kind == List {
-		return decodeListSlice(s, val, decodeUint)
-	}
 	b, err := s.Bytes()
-	if err == nil {
-		val.SetBytes(b)
+	if err != nil {
+		return wrapStreamError(err, val.Type())
 	}
-	return err
+	val.SetBytes(b)
+	return nil
 }
 
 func decodeByteArray(s *Stream, val reflect.Value) error {
@@ -307,42 +314,38 @@ func decodeByteArray(s *Stream, val reflect.Value) error {
 	if err != nil {
 		return err
 	}
+	vlen := val.Len()
 	switch kind {
 	case Byte:
-		if val.Len() == 0 {
+		if vlen == 0 {
 			return &decodeError{msg: "input string too long", typ: val.Type()}
 		}
+		if vlen > 1 {
+			return &decodeError{msg: "input string too short", typ: val.Type()}
+		}
 		bv, _ := s.Uint()
 		val.Index(0).SetUint(bv)
-		zero(val, 1)
 	case String:
-		if uint64(val.Len()) < size {
+		if uint64(vlen) < size {
 			return &decodeError{msg: "input string too long", typ: val.Type()}
 		}
-		slice := val.Slice(0, int(size)).Interface().([]byte)
+		if uint64(vlen) > size {
+			return &decodeError{msg: "input string too short", typ: val.Type()}
+		}
+		slice := val.Slice(0, vlen).Interface().([]byte)
 		if err := s.readFull(slice); err != nil {
 			return err
 		}
-		zero(val, int(size))
+		// Reject cases where single byte encoding should have been used.
+		if size == 1 && slice[0] < 56 {
+			return wrapStreamError(ErrCanonSize, val.Type())
+		}
 	case List:
-		return decodeListArray(s, val, decodeUint)
+		return wrapStreamError(ErrExpectedString, val.Type())
 	}
 	return nil
 }
 
-func zero(val reflect.Value, start int) {
-	z := reflect.Zero(val.Type().Elem())
-	end := val.Len()
-	for i := start; i < end; i++ {
-		val.Index(i).Set(z)
-	}
-}
-
-type field struct {
-	index int
-	info  *typeinfo
-}
-
 func makeStructDecoder(typ reflect.Type) (decoder, error) {
 	fields, err := structFields(typ)
 	if err != nil {
@@ -355,8 +358,7 @@ func makeStructDecoder(typ reflect.Type) (decoder, error) {
 		for _, f := range fields {
 			err = f.info.decoder(s, val.Field(f.index))
 			if err == EOL {
-				// too few elements. leave the rest at their zero value.
-				break
+				return &decodeError{msg: "too few elements", typ: typ}
 			} else if err != nil {
 				return addErrorContext(err, "."+typ.Field(f.index).Name)
 			}
@@ -366,15 +368,41 @@ func makeStructDecoder(typ reflect.Type) (decoder, error) {
 	return dec, nil
 }
 
+// makePtrDecoder creates a decoder that decodes into
+// the pointer's element type.
 func makePtrDecoder(typ reflect.Type) (decoder, error) {
 	etype := typ.Elem()
-	etypeinfo, err := cachedTypeInfo1(etype)
+	etypeinfo, err := cachedTypeInfo1(etype, tags{})
 	if err != nil {
 		return nil, err
 	}
 	dec := func(s *Stream, val reflect.Value) (err error) {
-		_, size, err := s.Kind()
-		if err != nil || size == 0 && s.byteval == 0 {
+		newval := val
+		if val.IsNil() {
+			newval = reflect.New(etype)
+		}
+		if err = etypeinfo.decoder(s, newval.Elem()); err == nil {
+			val.Set(newval)
+		}
+		return err
+	}
+	return dec, nil
+}
+
+// makeOptionalPtrDecoder creates a decoder that decodes empty values
+// as nil. Non-empty values are decoded into a value of the element type,
+// just like makePtrDecoder does.
+//
+// This decoder is used for pointer-typed struct fields with struct tag "nil".
+func makeOptionalPtrDecoder(typ reflect.Type) (decoder, error) {
+	etype := typ.Elem()
+	etypeinfo, err := cachedTypeInfo1(etype, tags{})
+	if err != nil {
+		return nil, err
+	}
+	dec := func(s *Stream, val reflect.Value) (err error) {
+		kind, size, err := s.Kind()
+		if err != nil || size == 0 && kind != Byte {
 			// rearm s.Kind. This is important because the input
 			// position must advance to the next value even though
 			// we don't read anything.
@@ -465,15 +493,18 @@ var (
 	// has been reached during streaming.
 	EOL = errors.New("rlp: end of list")
 
-	// Other errors
+	// Actual Errors
 	ErrExpectedString = errors.New("rlp: expected String or Byte")
 	ErrExpectedList   = errors.New("rlp: expected List")
-	ErrCanonInt       = errors.New("rlp: expected Int")
+	ErrCanonInt       = errors.New("rlp: non-canonical integer format")
+	ErrCanonSize      = errors.New("rlp: non-canonical size information")
 	ErrElemTooLarge   = errors.New("rlp: element is larger than containing list")
+	ErrValueTooLarge  = errors.New("rlp: value size exceeds available input length")
 
 	// internal errors
-	errNotInList = errors.New("rlp: call of ListEnd outside of any list")
-	errNotAtEOL  = errors.New("rlp: call of ListEnd not positioned at EOL")
+	errNotInList    = errors.New("rlp: call of ListEnd outside of any list")
+	errNotAtEOL     = errors.New("rlp: call of ListEnd not positioned at EOL")
+	errUintOverflow = errors.New("rlp: uint overflow")
 )
 
 // ByteReader must be implemented by any input reader for a Stream. It
@@ -496,23 +527,44 @@ type ByteReader interface {
 //
 // Stream is not safe for concurrent use.
 type Stream struct {
-	r       ByteReader
+	r ByteReader
+
+	// number of bytes remaining to be read from r.
+	remaining uint64
+	limited   bool
+
+	// auxiliary buffer for integer decoding
 	uintbuf []byte
 
 	kind    Kind   // kind of value ahead
 	size    uint64 // size of value ahead
 	byteval byte   // value of single byte in type tag
+	kinderr error  // error from last readKind
 	stack   []listpos
 }
 
 type listpos struct{ pos, size uint64 }
 
-// NewStream creates a new stream reading from r.
-// If r does not implement ByteReader, the Stream will
-// introduce its own buffering.
-func NewStream(r io.Reader) *Stream {
+// NewStream creates a new decoding stream reading from r.
+//
+// If r implements the ByteReader interface, Stream will
+// not introduce any buffering.
+//
+// For non-toplevel values, Stream returns ErrElemTooLarge
+// for values that do not fit into the enclosing list.
+//
+// Stream supports an optional input limit. If a limit is set, the
+// size of any toplevel value will be checked against the remaining
+// input length. Stream operations that encounter a value exceeding
+// the remaining input length will return ErrValueTooLarge. The limit
+// can be set by passing a non-zero value for inputLimit.
+//
+// If r is a bytes.Reader or strings.Reader, the input limit is set to
+// the length of r's underlying data unless an explicit limit is
+// provided.
+func NewStream(r io.Reader, inputLimit uint64) *Stream {
 	s := new(Stream)
-	s.Reset(r)
+	s.Reset(r, inputLimit)
 	return s
 }
 
@@ -520,7 +572,7 @@ func NewStream(r io.Reader) *Stream {
 // at an encoded list of the given length.
 func NewListStream(r io.Reader, len uint64) *Stream {
 	s := new(Stream)
-	s.Reset(r)
+	s.Reset(r, len)
 	s.kind = List
 	s.size = len
 	return s
@@ -543,6 +595,9 @@ func (s *Stream) Bytes() ([]byte, error) {
 		if err = s.readFull(b); err != nil {
 			return nil, err
 		}
+		if size == 1 && b[0] < 56 {
+			return nil, ErrCanonSize
+		}
 		return b, nil
 	default:
 		return nil, ErrExpectedString
@@ -574,8 +629,6 @@ func (s *Stream) Raw() ([]byte, error) {
 	return buf, nil
 }
 
-var errUintOverflow = errors.New("rlp: uint overflow")
-
 // Uint reads an RLP string of up to 8 bytes and returns its contents
 // as an unsigned integer. If the input does not contain an RLP string, the
 // returned error will be ErrExpectedString.
@@ -590,13 +643,27 @@ func (s *Stream) uint(maxbits int) (uint64, error) {
 	}
 	switch kind {
 	case Byte:
+		if s.byteval == 0 {
+			return 0, ErrCanonInt
+		}
 		s.kind = -1 // rearm Kind
 		return uint64(s.byteval), nil
 	case String:
 		if size > uint64(maxbits/8) {
 			return 0, errUintOverflow
 		}
-		return s.readUint(byte(size))
+		v, err := s.readUint(byte(size))
+		switch {
+		case err == ErrCanonSize:
+			// Adjust error because we're not reading a size right now.
+			return 0, ErrCanonInt
+		case err != nil:
+			return 0, err
+		case size > 0 && v < 56:
+			return 0, ErrCanonSize
+		default:
+			return v, nil
+		}
 	default:
 		return 0, ErrExpectedString
 	}
@@ -653,7 +720,7 @@ func (s *Stream) Decode(val interface{}) error {
 	if rval.IsNil() {
 		return errDecodeIntoNil
 	}
-	info, err := cachedTypeInfo(rtyp.Elem())
+	info, err := cachedTypeInfo(rtyp.Elem(), tags{})
 	if err != nil {
 		return err
 	}
@@ -667,17 +734,40 @@ func (s *Stream) Decode(val interface{}) error {
 }
 
 // Reset discards any information about the current decoding context
-// and starts reading from r. If r does not also implement ByteReader,
-// Stream will do its own buffering.
-func (s *Stream) Reset(r io.Reader) {
+// and starts reading from r. This method is meant to facilitate reuse
+// of a preallocated Stream across many decoding operations.
+//
+// If r does not also implement ByteReader, Stream will do its own
+// buffering.
+func (s *Stream) Reset(r io.Reader, inputLimit uint64) {
+	if inputLimit > 0 {
+		s.remaining = inputLimit
+		s.limited = true
+	} else {
+		// Attempt to automatically discover
+		// the limit when reading from a byte slice.
+		switch br := r.(type) {
+		case *bytes.Reader:
+			s.remaining = uint64(br.Len())
+			s.limited = true
+		case *strings.Reader:
+			s.remaining = uint64(br.Len())
+			s.limited = true
+		default:
+			s.limited = false
+		}
+	}
+	// Wrap r with a buffer if it doesn't have one.
 	bufr, ok := r.(ByteReader)
 	if !ok {
 		bufr = bufio.NewReader(r)
 	}
 	s.r = bufr
+	// Reset the decoding context.
 	s.stack = s.stack[:0]
 	s.size = 0
 	s.kind = -1
+	s.kinderr = nil
 	if s.uintbuf == nil {
 		s.uintbuf = make([]byte, 8)
 	}
@@ -700,19 +790,31 @@ func (s *Stream) Kind() (kind Kind, size uint64, err error) {
 		tos = &s.stack[len(s.stack)-1]
 	}
 	if s.kind < 0 {
+		s.kinderr = nil
+		// Don't read further if we're at the end of the
+		// innermost list.
 		if tos != nil && tos.pos == tos.size {
 			return 0, 0, EOL
 		}
-		kind, size, err = s.readKind()
-		if err != nil {
-			return 0, 0, err
+		s.kind, s.size, s.kinderr = s.readKind()
+		if s.kinderr == nil {
+			if tos == nil {
+				// At toplevel, check that the value is smaller
+				// than the remaining input length.
+				if s.limited && s.size > s.remaining {
+					s.kinderr = ErrValueTooLarge
+				}
+			} else {
+				// Inside a list, check that the value doesn't overflow the list.
+				if s.size > tos.size-tos.pos {
+					s.kinderr = ErrElemTooLarge
+				}
+			}
 		}
-		s.kind, s.size = kind, size
-	}
-	if tos != nil && tos.pos+s.size > tos.size {
-		return 0, 0, ErrElemTooLarge
 	}
-	return s.kind, s.size, nil
+	// Note: this might return a sticky error generated
+	// by an earlier call to readKind.
+	return s.kind, s.size, s.kinderr
 }
 
 func (s *Stream) readKind() (kind Kind, size uint64, err error) {
@@ -741,6 +843,9 @@ func (s *Stream) readKind() (kind Kind, size uint64, err error) {
 		// would be encoded as 0xB90400 followed by the string. The range of
 		// the first byte is thus [0xB8, 0xBF].
 		size, err = s.readUint(b - 0xB7)
+		if err == nil && size < 56 {
+			err = ErrCanonSize
+		}
 		return String, size, err
 	case b < 0xF8:
 		// If the total payload of a list
@@ -757,27 +862,46 @@ func (s *Stream) readKind() (kind Kind, size uint64, err error) {
 		// the concatenation of the RLP encodings of the items. The
 		// range of the first byte is thus [0xF8, 0xFF].
 		size, err = s.readUint(b - 0xF7)
+		if err == nil && size < 56 {
+			err = ErrCanonSize
+		}
 		return List, size, err
 	}
 }
 
 func (s *Stream) readUint(size byte) (uint64, error) {
-	if size == 1 {
+	switch size {
+	case 0:
+		s.kind = -1 // rearm Kind
+		return 0, nil
+	case 1:
 		b, err := s.readByte()
 		if err == io.EOF {
 			err = io.ErrUnexpectedEOF
 		}
 		return uint64(b), err
+	default:
+		start := int(8 - size)
+		for i := 0; i < start; i++ {
+			s.uintbuf[i] = 0
+		}
+		if err := s.readFull(s.uintbuf[start:]); err != nil {
+			return 0, err
+		}
+		if s.uintbuf[start] == 0 {
+			// Note: readUint is also used to decode integer
+			// values. The error needs to be adjusted to become
+			// ErrCanonInt in this case.
+			return 0, ErrCanonSize
+		}
+		return binary.BigEndian.Uint64(s.uintbuf), nil
 	}
-	start := int(8 - size)
-	for i := 0; i < start; i++ {
-		s.uintbuf[i] = 0
-	}
-	err := s.readFull(s.uintbuf[start:])
-	return binary.BigEndian.Uint64(s.uintbuf), err
 }
 
 func (s *Stream) readFull(buf []byte) (err error) {
+	if s.limited && s.remaining < uint64(len(buf)) {
+		return ErrValueTooLarge
+	}
 	s.willRead(uint64(len(buf)))
 	var nn, n int
 	for n < len(buf) && err == nil {
@@ -791,6 +915,9 @@ func (s *Stream) readFull(buf []byte) (err error) {
 }
 
 func (s *Stream) readByte() (byte, error) {
+	if s.limited && s.remaining == 0 {
+		return 0, io.EOF
+	}
 	s.willRead(1)
 	b, err := s.r.ReadByte()
 	if len(s.stack) > 0 && err == io.EOF {
@@ -801,6 +928,9 @@ func (s *Stream) readByte() (byte, error) {
 
 func (s *Stream) willRead(n uint64) {
 	s.kind = -1 // rearm Kind
+	if s.limited {
+		s.remaining -= n
+	}
 	if len(s.stack) > 0 {
 		s.stack[len(s.stack)-1].pos += n
 	}
diff --git a/rlp/decode_test.go b/rlp/decode_test.go
index 73a31c67f..d07520bd0 100644
--- a/rlp/decode_test.go
+++ b/rlp/decode_test.go
@@ -21,22 +21,18 @@ func TestStreamKind(t *testing.T) {
 		{"7F", Byte, 0},
 		{"80", String, 0},
 		{"B7", String, 55},
-		{"B800", String, 0},
 		{"B90400", String, 1024},
-		{"BA000400", String, 1024},
-		{"BB00000400", String, 1024},
 		{"BFFFFFFFFFFFFFFFFF", String, ^uint64(0)},
 		{"C0", List, 0},
 		{"C8", List, 8},
 		{"F7", List, 55},
-		{"F800", List, 0},
-		{"F804", List, 4},
 		{"F90400", List, 1024},
 		{"FFFFFFFFFFFFFFFFFF", List, ^uint64(0)},
 	}
 
 	for i, test := range tests {
-		s := NewStream(bytes.NewReader(unhex(test.input)))
+		// using plainReader to inhibit input limit errors.
+		s := NewStream(newPlainReader(unhex(test.input)), 0)
 		kind, len, err := s.Kind()
 		if err != nil {
 			t.Errorf("test %d: Kind returned error: %v", i, err)
@@ -70,29 +66,85 @@ func TestNewListStream(t *testing.T) {
 }
 
 func TestStreamErrors(t *testing.T) {
+	withoutInputLimit := func(b []byte) *Stream {
+		return NewStream(newPlainReader(b), 0)
+	}
+	withCustomInputLimit := func(limit uint64) func([]byte) *Stream {
+		return func(b []byte) *Stream {
+			return NewStream(bytes.NewReader(b), limit)
+		}
+	}
+
 	type calls []string
 	tests := []struct {
 		string
 		calls
-		error
+		newStream func([]byte) *Stream // uses bytes.Reader if nil
+		error     error
 	}{
-		{"", calls{"Kind"}, io.EOF},
-		{"", calls{"List"}, io.EOF},
-		{"", calls{"Uint"}, io.EOF},
-		{"C0", calls{"Bytes"}, ErrExpectedString},
-		{"C0", calls{"Uint"}, ErrExpectedString},
-		{"81", calls{"Bytes"}, io.ErrUnexpectedEOF},
-		{"81", calls{"Uint"}, io.ErrUnexpectedEOF},
-		{"BFFFFFFFFFFFFFFF", calls{"Bytes"}, io.ErrUnexpectedEOF},
-		{"89000000000000000001", calls{"Uint"}, errUintOverflow},
-		{"00", calls{"List"}, ErrExpectedList},
-		{"80", calls{"List"}, ErrExpectedList},
-		{"C0", calls{"List", "Uint"}, EOL},
-		{"C801", calls{"List", "Uint", "Uint"}, io.ErrUnexpectedEOF},
-		{"C8C9", calls{"List", "Kind"}, ErrElemTooLarge},
-		{"C3C2010201", calls{"List", "List", "Uint", "Uint", "ListEnd", "Uint"}, EOL},
-		{"00", calls{"ListEnd"}, errNotInList},
-		{"C40102", calls{"List", "Uint", "ListEnd"}, errNotAtEOL},
+		{"C0", calls{"Bytes"}, nil, ErrExpectedString},
+		{"C0", calls{"Uint"}, nil, ErrExpectedString},
+		{"89000000000000000001", calls{"Uint"}, nil, errUintOverflow},
+		{"00", calls{"List"}, nil, ErrExpectedList},
+		{"80", calls{"List"}, nil, ErrExpectedList},
+		{"C0", calls{"List", "Uint"}, nil, EOL},
+		{"C8C9010101010101010101", calls{"List", "Kind"}, nil, ErrElemTooLarge},
+		{"C3C2010201", calls{"List", "List", "Uint", "Uint", "ListEnd", "Uint"}, nil, EOL},
+		{"00", calls{"ListEnd"}, nil, errNotInList},
+		{"C401020304", calls{"List", "Uint", "ListEnd"}, nil, errNotAtEOL},
+
+		// Non-canonical integers (e.g. leading zero bytes).
+		{"00", calls{"Uint"}, nil, ErrCanonInt},
+		{"820002", calls{"Uint"}, nil, ErrCanonInt},
+		{"8133", calls{"Uint"}, nil, ErrCanonSize},
+		{"8156", calls{"Uint"}, nil, nil},
+
+		// Size tags must use the smallest possible encoding.
+		// Leading zero bytes in the size tag are also rejected.
+		{"8100", calls{"Uint"}, nil, ErrCanonSize},
+		{"8100", calls{"Bytes"}, nil, ErrCanonSize},
+		{"B800", calls{"Kind"}, withoutInputLimit, ErrCanonSize},
+		{"B90000", calls{"Kind"}, withoutInputLimit, ErrCanonSize},
+		{"B90055", calls{"Kind"}, withoutInputLimit, ErrCanonSize},
+		{"BA0002FFFF", calls{"Bytes"}, withoutInputLimit, ErrCanonSize},
+		{"F800", calls{"Kind"}, withoutInputLimit, ErrCanonSize},
+		{"F90000", calls{"Kind"}, withoutInputLimit, ErrCanonSize},
+		{"F90055", calls{"Kind"}, withoutInputLimit, ErrCanonSize},
+		{"FA0002FFFF", calls{"List"}, withoutInputLimit, ErrCanonSize},
+
+		// Expected EOF
+		{"", calls{"Kind"}, nil, io.EOF},
+		{"", calls{"Uint"}, nil, io.EOF},
+		{"", calls{"List"}, nil, io.EOF},
+		{"8158", calls{"Uint", "Uint"}, nil, io.EOF},
+		{"C0", calls{"List", "ListEnd", "List"}, nil, io.EOF},
+
+		// Input limit errors.
+		{"81", calls{"Bytes"}, nil, ErrValueTooLarge},
+		{"81", calls{"Uint"}, nil, ErrValueTooLarge},
+		{"81", calls{"Raw"}, nil, ErrValueTooLarge},
+		{"BFFFFFFFFFFFFFFFFFFF", calls{"Bytes"}, nil, ErrValueTooLarge},
+		{"C801", calls{"List"}, nil, ErrValueTooLarge},
+
+		// Test for list element size check overflow.
+		{"CD04040404FFFFFFFFFFFFFFFFFF0303", calls{"List", "Uint", "Uint", "Uint", "Uint", "List"}, nil, ErrElemTooLarge},
+
+		// Test for input limit overflow. Since we are counting the limit
+		// down toward zero in Stream.remaining, reading too far can overflow
+		// remaining to a large value, effectively disabling the limit.
+		{"C40102030401", calls{"Raw", "Uint"}, withCustomInputLimit(5), io.EOF},
+		{"C4010203048158", calls{"Raw", "Uint"}, withCustomInputLimit(6), ErrValueTooLarge},
+
+		// Check that the same calls are fine without a limit.
+		{"C40102030401", calls{"Raw", "Uint"}, withoutInputLimit, nil},
+		{"C4010203048158", calls{"Raw", "Uint"}, withoutInputLimit, nil},
+
+		// Unexpected EOF. This only happens when there is
+		// no input limit, so the reader needs to be 'dumbed down'.
+		{"81", calls{"Bytes"}, withoutInputLimit, io.ErrUnexpectedEOF},
+		{"81", calls{"Uint"}, withoutInputLimit, io.ErrUnexpectedEOF},
+		{"BFFFFFFFFFFFFFFF", calls{"Bytes"}, withoutInputLimit, io.ErrUnexpectedEOF},
+		{"C801", calls{"List", "Uint", "Uint"}, withoutInputLimit, io.ErrUnexpectedEOF},
 
 		// This test verifies that the input position is advanced
 		// correctly when calling Bytes for empty strings. Kind can be called
@@ -109,12 +161,15 @@ func TestStreamErrors(t *testing.T) {
 
 			"Bytes", // past final element
 			"Bytes", // this one should fail
-		}, EOL},
+		}, nil, EOL},
 	}
 
 testfor:
 	for i, test := range tests {
-		s := NewStream(bytes.NewReader(unhex(test.string)))
+		if test.newStream == nil {
+			test.newStream = func(b []byte) *Stream { return NewStream(bytes.NewReader(b), 0) }
+		}
+		s := test.newStream(unhex(test.string))
 		rs := reflect.ValueOf(s)
 		for j, call := range test.calls {
 			fval := rs.MethodByName(call)
@@ -124,11 +179,17 @@ testfor:
 				err = lastret.(error).Error()
 			}
 			if j == len(test.calls)-1 {
-				if err != test.error.Error() {
-					t.Errorf("test %d: last call (%s) error mismatch\ngot:  %s\nwant: %v",
+				want := "<nil>"
+				if test.error != nil {
+					want = test.error.Error()
+				}
+				if err != want {
+					t.Log(test)
+					t.Errorf("test %d: last call (%s) error mismatch\ngot:  %s\nwant: %s",
 						i, call, err, test.error)
 				}
 			} else if err != "<nil>" {
+				t.Log(test)
 				t.Errorf("test %d: call %d (%s) unexpected error: %q", i, j, call, err)
 				continue testfor
 			}
@@ -137,7 +198,7 @@ testfor:
 }
 
 func TestStreamList(t *testing.T) {
-	s := NewStream(bytes.NewReader(unhex("C80102030405060708")))
+	s := NewStream(bytes.NewReader(unhex("C80102030405060708")), 0)
 
 	len, err := s.List()
 	if err != nil {
@@ -166,7 +227,7 @@ func TestStreamList(t *testing.T) {
 }
 
 func TestStreamRaw(t *testing.T) {
-	s := NewStream(bytes.NewReader(unhex("C58401010101")))
+	s := NewStream(bytes.NewReader(unhex("C58401010101")), 0)
 	s.List()
 
 	want := unhex("8401010101")
@@ -219,7 +280,7 @@ type simplestruct struct {
 
 type recstruct struct {
 	I     uint
-	Child *recstruct
+	Child *recstruct `rlp:"nil"`
 }
 
 var (
@@ -229,78 +290,58 @@ var (
 	)
 )
 
-var (
-	sharedByteArray [5]byte
-	sharedPtr       = new(*uint)
-)
-
 var decodeTests = []decodeTest{
 	// integers
 	{input: "05", ptr: new(uint32), value: uint32(5)},
 	{input: "80", ptr: new(uint32), value: uint32(0)},
-	{input: "8105", ptr: new(uint32), value: uint32(5)},
 	{input: "820505", ptr: new(uint32), value: uint32(0x0505)},
 	{input: "83050505", ptr: new(uint32), value: uint32(0x050505)},
 	{input: "8405050505", ptr: new(uint32), value: uint32(0x05050505)},
 	{input: "850505050505", ptr: new(uint32), error: "rlp: input string too long for uint32"},
 	{input: "C0", ptr: new(uint32), error: "rlp: expected input string or byte for uint32"},
+	{input: "00", ptr: new(uint32), error: "rlp: non-canonical integer (leading zero bytes) for uint32"},
+	{input: "8105", ptr: new(uint32), error: "rlp: non-canonical size information for uint32"},
+	{input: "820004", ptr: new(uint32), error: "rlp: non-canonical integer (leading zero bytes) for uint32"},
+	{input: "B8020004", ptr: new(uint32), error: "rlp: non-canonical size information for uint32"},
 
 	// slices
 	{input: "C0", ptr: new([]uint), value: []uint{}},
 	{input: "C80102030405060708", ptr: new([]uint), value: []uint{1, 2, 3, 4, 5, 6, 7, 8}},
+	{input: "F8020004", ptr: new([]uint), error: "rlp: non-canonical size information for []uint"},
 
 	// arrays
-	{input: "C0", ptr: new([5]uint), value: [5]uint{}},
 	{input: "C50102030405", ptr: new([5]uint), value: [5]uint{1, 2, 3, 4, 5}},
+	{input: "C0", ptr: new([5]uint), error: "rlp: input list has too few elements for [5]uint"},
+	{input: "C102", ptr: new([5]uint), error: "rlp: input list has too few elements for [5]uint"},
 	{input: "C6010203040506", ptr: new([5]uint), error: "rlp: input list has too many elements for [5]uint"},
+	{input: "F8020004", ptr: new([5]uint), error: "rlp: non-canonical size information for [5]uint"},
+
+	// zero sized arrays
+	{input: "C0", ptr: new([0]uint), value: [0]uint{}},
+	{input: "C101", ptr: new([0]uint), error: "rlp: input list has too many elements for [0]uint"},
 
 	// byte slices
 	{input: "01", ptr: new([]byte), value: []byte{1}},
 	{input: "80", ptr: new([]byte), value: []byte{}},
 	{input: "8D6162636465666768696A6B6C6D", ptr: new([]byte), value: []byte("abcdefghijklm")},
-	{input: "C0", ptr: new([]byte), value: []byte{}},
-	{input: "C3010203", ptr: new([]byte), value: []byte{1, 2, 3}},
-
-	{
-		input: "C3820102",
-		ptr:   new([]byte),
-		error: "rlp: input string too long for uint8, decoding into ([]uint8)[0]",
-	},
+	{input: "C0", ptr: new([]byte), error: "rlp: expected input string or byte for []uint8"},
+	{input: "8105", ptr: new([]byte), error: "rlp: non-canonical size information for []uint8"},
 
 	// byte arrays
-	{input: "01", ptr: new([5]byte), value: [5]byte{1}},
-	{input: "80", ptr: new([5]byte), value: [5]byte{}},
+	{input: "02", ptr: new([1]byte), value: [1]byte{2}},
 	{input: "850102030405", ptr: new([5]byte), value: [5]byte{1, 2, 3, 4, 5}},
-	{input: "C0", ptr: new([5]byte), value: [5]byte{}},
-	{input: "C3010203", ptr: new([5]byte), value: [5]byte{1, 2, 3, 0, 0}},
 
-	{
-		input: "C3820102",
-		ptr:   new([5]byte),
-		error: "rlp: input string too long for uint8, decoding into ([5]uint8)[0]",
-	},
-	{
-		input: "86010203040506",
-		ptr:   new([5]byte),
-		error: "rlp: input string too long for [5]uint8",
-	},
-	{
-		input: "850101",
-		ptr:   new([5]byte),
-		error: io.ErrUnexpectedEOF.Error(),
-	},
-
-	// byte array reuse (should be zeroed)
-	{input: "850102030405", ptr: &sharedByteArray, value: [5]byte{1, 2, 3, 4, 5}},
-	{input: "8101", ptr: &sharedByteArray, value: [5]byte{1}}, // kind: String
-	{input: "850102030405", ptr: &sharedByteArray, value: [5]byte{1, 2, 3, 4, 5}},
-	{input: "01", ptr: &sharedByteArray, value: [5]byte{1}}, // kind: Byte
-	{input: "C3010203", ptr: &sharedByteArray, value: [5]byte{1, 2, 3, 0, 0}},
-	{input: "C101", ptr: &sharedByteArray, value: [5]byte{1}}, // kind: List
+	// byte array errors
+	{input: "02", ptr: new([5]byte), error: "rlp: input string too short for [5]uint8"},
+	{input: "80", ptr: new([5]byte), error: "rlp: input string too short for [5]uint8"},
+	{input: "820000", ptr: new([5]byte), error: "rlp: input string too short for [5]uint8"},
+	{input: "C0", ptr: new([5]byte), error: "rlp: expected input string or byte for [5]uint8"},
+	{input: "C3010203", ptr: new([5]byte), error: "rlp: expected input string or byte for [5]uint8"},
+	{input: "86010203040506", ptr: new([5]byte), error: "rlp: input string too long for [5]uint8"},
+	{input: "8105", ptr: new([1]byte), error: "rlp: non-canonical size information for [1]uint8"},
 
 	// zero sized byte arrays
 	{input: "80", ptr: new([0]byte), value: [0]byte{}},
-	{input: "C0", ptr: new([0]byte), value: [0]byte{}},
 	{input: "01", ptr: new([0]byte), error: "rlp: input string too long for [0]uint8"},
 	{input: "8101", ptr: new([0]byte), error: "rlp: input string too long for [0]uint8"},
 
@@ -312,20 +353,44 @@ var decodeTests = []decodeTest{
 	// big ints
 	{input: "01", ptr: new(*big.Int), value: big.NewInt(1)},
 	{input: "89FFFFFFFFFFFFFFFFFF", ptr: new(*big.Int), value: veryBigInt},
-	{input: "820001", ptr: new(big.Int), error: "rlp: canon int error appends zero's for *big.Int"},
 	{input: "10", ptr: new(big.Int), value: *big.NewInt(16)}, // non-pointer also works
 	{input: "C0", ptr: new(*big.Int), error: "rlp: expected input string or byte for *big.Int"},
+	{input: "820001", ptr: new(big.Int), error: "rlp: non-canonical integer (leading zero bytes) for *big.Int"},
+	{input: "8105", ptr: new(big.Int), error: "rlp: non-canonical size information for *big.Int"},
 
 	// structs
-	{input: "C0", ptr: new(simplestruct), value: simplestruct{0, ""}},
-	{input: "C105", ptr: new(simplestruct), value: simplestruct{5, ""}},
-	{input: "C50583343434", ptr: new(simplestruct), value: simplestruct{5, "444"}},
 	{
-		input: "C501C302C103",
+		input: "C50583343434",
+		ptr:   new(simplestruct),
+		value: simplestruct{5, "444"},
+	},
+	{
+		input: "C601C402C203C0",
 		ptr:   new(recstruct),
 		value: recstruct{1, &recstruct{2, &recstruct{3, nil}}},
 	},
 
+	// struct errors
+	{
+		input: "C0",
+		ptr:   new(simplestruct),
+		error: "rlp: too few elements for rlp.simplestruct",
+	},
+	{
+		input: "C105",
+		ptr:   new(simplestruct),
+		error: "rlp: too few elements for rlp.simplestruct",
+	},
+	{
+		input: "C7C50583343434C0",
+		ptr:   new([]*simplestruct),
+		error: "rlp: too few elements for rlp.simplestruct, decoding into ([]*rlp.simplestruct)[1]",
+	},
+	{
+		input: "83222222",
+		ptr:   new(simplestruct),
+		error: "rlp: expected input list for rlp.simplestruct",
+	},
 	{
 		input: "C3010101",
 		ptr:   new(simplestruct),
@@ -338,20 +403,16 @@ var decodeTests = []decodeTest{
 	},
 
 	// pointers
-	{input: "00", ptr: new(*uint), value: (*uint)(nil)},
-	{input: "80", ptr: new(*uint), value: (*uint)(nil)},
-	{input: "C0", ptr: new(*uint), value: (*uint)(nil)},
+	{input: "00", ptr: new(*[]byte), value: &[]byte{0}},
+	{input: "80", ptr: new(*uint), value: uintp(0)},
+	{input: "C0", ptr: new(*uint), error: "rlp: expected input string or byte for uint"},
 	{input: "07", ptr: new(*uint), value: uintp(7)},
-	{input: "8108", ptr: new(*uint), value: uintp(8)},
+	{input: "8158", ptr: new(*uint), value: uintp(0x58)},
 	{input: "C109", ptr: new(*[]uint), value: &[]uint{9}},
 	{input: "C58403030303", ptr: new(*[][]byte), value: &[][]byte{{3, 3, 3, 3}}},
 
 	// check that input position is advanced also for empty values.
-	{input: "C3808005", ptr: new([]*uint), value: []*uint{nil, nil, uintp(5)}},
-
-	// pointer should be reset to nil
-	{input: "05", ptr: sharedPtr, value: uintp(5)},
-	{input: "80", ptr: sharedPtr, value: (*uint)(nil)},
+	{input: "C3808005", ptr: new([]*uint), value: []*uint{uintp(0), uintp(0), uintp(5)}},
 
 	// interface{}
 	{input: "00", ptr: new(interface{}), value: []byte{0}},
@@ -401,11 +462,17 @@ func TestDecodeWithByteReader(t *testing.T) {
 	})
 }
 
-// dumbReader reads from a byte slice but does not
-// implement ReadByte.
-type dumbReader []byte
+// plainReader reads from a byte slice but does not
+// implement ReadByte. It is also not recognized by the
+// size validation. This is useful to test how the decoder
+// behaves on a non-buffered input stream.
+type plainReader []byte
+
+func newPlainReader(b []byte) io.Reader {
+	return (*plainReader)(&b)
+}
 
-func (r *dumbReader) Read(buf []byte) (n int, err error) {
+func (r *plainReader) Read(buf []byte) (n int, err error) {
 	if len(*r) == 0 {
 		return 0, io.EOF
 	}
@@ -416,15 +483,14 @@ func (r *dumbReader) Read(buf []byte) (n int, err error) {
 
 func TestDecodeWithNonByteReader(t *testing.T) {
 	runTests(t, func(input []byte, into interface{}) error {
-		r := dumbReader(input)
-		return Decode(&r, into)
+		return Decode(newPlainReader(input), into)
 	})
 }
 
 func TestDecodeStreamReset(t *testing.T) {
-	s := NewStream(nil)
+	s := NewStream(nil, 0)
 	runTests(t, func(input []byte, into interface{}) error {
-		s.Reset(bytes.NewReader(input))
+		s.Reset(bytes.NewReader(input), 0)
 		return s.Decode(into)
 	})
 }
@@ -516,9 +582,36 @@ func ExampleDecode() {
 	// Decoded value: rlp.example{A:0xa, B:0x14, private:0x0, String:"foobar"}
 }
 
+func ExampleDecode_structTagNil() {
+	// In this example, we'll use the "nil" struct tag to change
+	// how a pointer-typed field is decoded. The input contains an RLP
+	// list of one element, an empty string.
+	input := []byte{0xC1, 0x80}
+
+	// This type uses the normal rules.
+	// The empty input string is decoded as a pointer to an empty Go string.
+	var normalRules struct {
+		String *string
+	}
+	Decode(bytes.NewReader(input), &normalRules)
+	fmt.Printf("normal: String = %q\n", *normalRules.String)
+
+	// This type uses the struct tag.
+	// The empty input string is decoded as a nil pointer.
+	var withEmptyOK struct {
+		String *string `rlp:"nil"`
+	}
+	Decode(bytes.NewReader(input), &withEmptyOK)
+	fmt.Printf("with nil tag: String = %v\n", withEmptyOK.String)
+
+	// Output:
+	// normal: String = ""
+	// with nil tag: String = <nil>
+}
+
 func ExampleStream() {
 	input, _ := hex.DecodeString("C90A1486666F6F626172")
-	s := NewStream(bytes.NewReader(input))
+	s := NewStream(bytes.NewReader(input), 0)
 
 	// Check what kind of value lies ahead
 	kind, size, _ := s.Kind()
diff --git a/rlp/encode.go b/rlp/encode.go
index 6cf6776d6..10ff0ae79 100644
--- a/rlp/encode.go
+++ b/rlp/encode.go
@@ -194,7 +194,7 @@ func (w *encbuf) Write(b []byte) (int, error) {
 
 func (w *encbuf) encode(val interface{}) error {
 	rval := reflect.ValueOf(val)
-	ti, err := cachedTypeInfo(rval.Type())
+	ti, err := cachedTypeInfo(rval.Type(), tags{})
 	if err != nil {
 		return err
 	}
@@ -485,7 +485,7 @@ func writeInterface(val reflect.Value, w *encbuf) error {
 		return nil
 	}
 	eval := val.Elem()
-	ti, err := cachedTypeInfo(eval.Type())
+	ti, err := cachedTypeInfo(eval.Type(), tags{})
 	if err != nil {
 		return err
 	}
@@ -493,7 +493,7 @@ func writeInterface(val reflect.Value, w *encbuf) error {
 }
 
 func makeSliceWriter(typ reflect.Type) (writer, error) {
-	etypeinfo, err := cachedTypeInfo1(typ.Elem())
+	etypeinfo, err := cachedTypeInfo1(typ.Elem(), tags{})
 	if err != nil {
 		return nil, err
 	}
@@ -530,7 +530,7 @@ func makeStructWriter(typ reflect.Type) (writer, error) {
 }
 
 func makePtrWriter(typ reflect.Type) (writer, error) {
-	etypeinfo, err := cachedTypeInfo1(typ.Elem())
+	etypeinfo, err := cachedTypeInfo1(typ.Elem(), tags{})
 	if err != nil {
 		return nil, err
 	}
diff --git a/rlp/typecache.go b/rlp/typecache.go
index 398f25d90..d512012e9 100644
--- a/rlp/typecache.go
+++ b/rlp/typecache.go
@@ -7,7 +7,7 @@ import (
 
 var (
 	typeCacheMutex sync.RWMutex
-	typeCache      = make(map[reflect.Type]*typeinfo)
+	typeCache      = make(map[typekey]*typeinfo)
 )
 
 type typeinfo struct {
@@ -15,13 +15,25 @@ type typeinfo struct {
 	writer
 }
 
+// represents struct tags
+type tags struct {
+	nilOK bool
+}
+
+type typekey struct {
+	reflect.Type
+	// the key must include the struct tags because they
+	// might generate a different decoder.
+	tags
+}
+
 type decoder func(*Stream, reflect.Value) error
 
 type writer func(reflect.Value, *encbuf) error
 
-func cachedTypeInfo(typ reflect.Type) (*typeinfo, error) {
+func cachedTypeInfo(typ reflect.Type, tags tags) (*typeinfo, error) {
 	typeCacheMutex.RLock()
-	info := typeCache[typ]
+	info := typeCache[typekey{typ, tags}]
 	typeCacheMutex.RUnlock()
 	if info != nil {
 		return info, nil
@@ -29,11 +41,12 @@ func cachedTypeInfo(typ reflect.Type) (*typeinfo, error) {
 	// not in the cache, need to generate info for this type.
 	typeCacheMutex.Lock()
 	defer typeCacheMutex.Unlock()
-	return cachedTypeInfo1(typ)
+	return cachedTypeInfo1(typ, tags)
 }
 
-func cachedTypeInfo1(typ reflect.Type) (*typeinfo, error) {
-	info := typeCache[typ]
+func cachedTypeInfo1(typ reflect.Type, tags tags) (*typeinfo, error) {
+	key := typekey{typ, tags}
+	info := typeCache[key]
 	if info != nil {
 		// another goroutine got the write lock first
 		return info, nil
@@ -41,21 +54,27 @@ func cachedTypeInfo1(typ reflect.Type) (*typeinfo, error) {
 	// put a dummmy value into the cache before generating.
 	// if the generator tries to lookup itself, it will get
 	// the dummy value and won't call itself recursively.
-	typeCache[typ] = new(typeinfo)
-	info, err := genTypeInfo(typ)
+	typeCache[key] = new(typeinfo)
+	info, err := genTypeInfo(typ, tags)
 	if err != nil {
 		// remove the dummy value if the generator fails
-		delete(typeCache, typ)
+		delete(typeCache, key)
 		return nil, err
 	}
-	*typeCache[typ] = *info
-	return typeCache[typ], err
+	*typeCache[key] = *info
+	return typeCache[key], err
+}
+
+type field struct {
+	index int
+	info  *typeinfo
 }
 
 func structFields(typ reflect.Type) (fields []field, err error) {
 	for i := 0; i < typ.NumField(); i++ {
 		if f := typ.Field(i); f.PkgPath == "" { // exported
-			info, err := cachedTypeInfo1(f.Type)
+			tags := parseStructTag(f.Tag.Get("rlp"))
+			info, err := cachedTypeInfo1(f.Type, tags)
 			if err != nil {
 				return nil, err
 			}
@@ -65,9 +84,13 @@ func structFields(typ reflect.Type) (fields []field, err error) {
 	return fields, nil
 }
 
-func genTypeInfo(typ reflect.Type) (info *typeinfo, err error) {
+func parseStructTag(tag string) tags {
+	return tags{nilOK: tag == "nil"}
+}
+
+func genTypeInfo(typ reflect.Type, tags tags) (info *typeinfo, err error) {
 	info = new(typeinfo)
-	if info.decoder, err = makeDecoder(typ); err != nil {
+	if info.decoder, err = makeDecoder(typ, tags); err != nil {
 		return nil, err
 	}
 	if info.writer, err = makeWriter(typ); err != nil {
diff --git a/whisper/envelope.go b/whisper/envelope.go
index 0a817e26e..07762c300 100644
--- a/whisper/envelope.go
+++ b/whisper/envelope.go
@@ -109,16 +109,17 @@ func (self *Envelope) Hash() common.Hash {
 	return self.hash
 }
 
-// rlpenv is an Envelope but is not an rlp.Decoder.
-// It is used for decoding because we need to
-type rlpenv Envelope
-
 // DecodeRLP decodes an Envelope from an RLP data stream.
 func (self *Envelope) DecodeRLP(s *rlp.Stream) error {
 	raw, err := s.Raw()
 	if err != nil {
 		return err
 	}
+	// The decoding of Envelope uses the struct fields but also needs
+	// to compute the hash of the whole RLP-encoded envelope. This
+	// type has the same structure as Envelope but is not an
+	// rlp.Decoder so we can reuse the Envelope struct definition.
+	type rlpenv Envelope
 	if err := rlp.DecodeBytes(raw, (*rlpenv)(self)); err != nil {
 		return err
 	}
diff --git a/whisper/peer.go b/whisper/peer.go
index e4301f37c..28abf4260 100644
--- a/whisper/peer.go
+++ b/whisper/peer.go
@@ -66,7 +66,7 @@ func (self *peer) handshake() error {
 	if packet.Code != statusCode {
 		return fmt.Errorf("peer sent %x before status packet", packet.Code)
 	}
-	s := rlp.NewStream(packet.Payload)
+	s := rlp.NewStream(packet.Payload, uint64(packet.Size))
 	if _, err := s.List(); err != nil {
 		return fmt.Errorf("bad status message: %v", err)
 	}