rlp/decode.go

@@ -518,7 +518,7 @@ func decodeDecoder(s *Stream, val reflect.Value) error {
 }
 
 // Kind represents the kind of value contained in an RLP stream.
-type Kind int
+type Kind int8
 
 const (
 	Byte Kind = iota
@@ -561,22 +561,16 @@ type ByteReader interface {
 type Stream struct {
 	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
+	remaining uint64   // number of bytes remaining to be read from r
 	size      uint64   // size of value ahead
-	byteval byte   // value of single byte in type tag
 	kinderr   error    // error from last readKind
-	stack   []listpos
+	stack     []uint64 // list sizes
+	uintbuf   [8]byte  // auxiliary buffer for integer decoding
+	kind      Kind     // kind of value ahead
+	byteval   byte     // value of single byte in type tag
+	limited   bool     // true if input limit is in effect
 }
 
-type listpos struct{ pos, size uint64 }
-
 // NewStream creates a new decoding stream reading from r.
 //
 // If r implements the ByteReader interface, Stream will
@@ -646,8 +640,8 @@ func (s *Stream) Raw() ([]byte, error) {
 		s.kind = -1 // rearm Kind
 		return []byte{s.byteval}, nil
 	}
-	// the original header has already been read and is no longer
-	// available. read content and put a new header in front of it.
+	// The original header has already been read and is no longer
+	// available. Read content and put a new header in front of it.
 	start := headsize(size)
 	buf := make([]byte, uint64(start)+size)
 	if err := s.readFull(buf[start:]); err != nil {
@@ -730,7 +724,14 @@ func (s *Stream) List() (size uint64, err error) {
 	if kind != List {
 		return 0, ErrExpectedList
 	}
-	s.stack = append(s.stack, listpos{0, size})
+
+	// Remove size of inner list from outer list before pushing the new size
+	// onto the stack. This ensures that the remaining outer list size will
+	// be correct after the matching call to ListEnd.
+	if inList, limit := s.listLimit(); inList {
+		s.stack[len(s.stack)-1] = limit - size
+	}
+	s.stack = append(s.stack, size)
 	s.kind = -1
 	s.size = 0
 	return size, nil
@@ -739,17 +740,13 @@ func (s *Stream) List() (size uint64, err error) {
 // ListEnd returns to the enclosing list.
 // The input reader must be positioned at the end of a list.
 func (s *Stream) ListEnd() error {
-	if len(s.stack) == 0 {
+	// Ensure that no more data is remaining in the current list.
+	if inList, listLimit := s.listLimit(); !inList {
 		return errNotInList
-	}
-	tos := s.stack[len(s.stack)-1]
-	if tos.pos != tos.size {
+	} else if listLimit > 0 {
 		return errNotAtEOL
 	}
 	s.stack = s.stack[:len(s.stack)-1] // pop
-	if len(s.stack) > 0 {
-		s.stack[len(s.stack)-1].pos += tos.size
-	}
 	s.kind = -1
 	s.size = 0
 	return nil
@@ -777,7 +774,7 @@ func (s *Stream) Decode(val interface{}) error {
 
 	err = decoder(s, rval.Elem())
 	if decErr, ok := err.(*decodeError); ok && len(decErr.ctx) > 0 {
-		// add decode target type to error so context has more meaning
+		// Add decode target type to error so context has more meaning.
 		decErr.ctx = append(decErr.ctx, fmt.Sprint("(", rtyp.Elem(), ")"))
 	}
 	return err
@@ -800,6 +797,9 @@ func (s *Stream) Reset(r io.Reader, inputLimit uint64) {
 		case *bytes.Reader:
 			s.remaining = uint64(br.Len())
 			s.limited = true
+		case *bytes.Buffer:
+			s.remaining = uint64(br.Len())
+			s.limited = true
 		case *strings.Reader:
 			s.remaining = uint64(br.Len())
 			s.limited = true
@@ -818,10 +818,8 @@ func (s *Stream) Reset(r io.Reader, inputLimit uint64) {
 	s.size = 0
 	s.kind = -1
 	s.kinderr = nil
-	if s.uintbuf == nil {
-		s.uintbuf = make([]byte, 8)
-	}
 	s.byteval = 0
+	s.uintbuf = [8]byte{}
 }
 
 // Kind returns the kind and size of the next value in the
@@ -836,35 +834,29 @@ func (s *Stream) Reset(r io.Reader, inputLimit uint64) {
 // the value. Subsequent calls to Kind (until the value is decoded)
 // will not advance the input reader and return cached information.
 func (s *Stream) Kind() (kind Kind, size uint64, err error) {
-	var tos *listpos
-	if len(s.stack) > 0 {
-		tos = &s.stack[len(s.stack)-1]
+	if s.kind >= 0 {
+		return s.kind, s.size, s.kinderr
 	}
-	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 {
+
+	// Check for end of list. This needs to be done here because readKind
+	// checks against the list size, and would return the wrong error.
+	inList, listLimit := s.listLimit()
+	if inList && listLimit == 0 {
 		return 0, 0, EOL
 	}
+	// Read the actual size tag.
 	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 {
+		// Check the data size of the value ahead against input limits. This
+		// is done here because many decoders require allocating an input
+		// buffer matching the value size. Checking it here protects those
+		// decoders from inputs declaring very large value size.
+		if inList && s.size > listLimit {
+			s.kinderr = ErrElemTooLarge
+		} else 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
 	}
-			}
-		}
-	}
-	// Note: this might return a sticky error generated
-	// by an earlier call to readKind.
 	return s.kind, s.size, s.kinderr
 }
 
@@ -891,37 +883,35 @@ func (s *Stream) readKind() (kind Kind, size uint64, err error) {
 		s.byteval = b
 		return Byte, 0, nil
 	case b < 0xB8:
-		// Otherwise, if a string is 0-55 bytes long,
-		// the RLP encoding consists of a single byte with value 0x80 plus the
-		// length of the string followed by the string. The range of the first
-		// byte is thus [0x80, 0xB7].
+		// Otherwise, if a string is 0-55 bytes long, the RLP encoding consists
+		// of a single byte with value 0x80 plus the length of the string
+		// followed by the string. The range of the first byte is thus [0x80, 0xB7].
 		return String, uint64(b - 0x80), nil
 	case b < 0xC0:
-		// If a string is more than 55 bytes long, the
-		// RLP encoding consists of a single byte with value 0xB7 plus the length
-		// of the length of the string in binary form, followed by the length of
-		// the string, followed by the string. For example, a length-1024 string
-		// would be encoded as 0xB90400 followed by the string. The range of
-		// the first byte is thus [0xB8, 0xBF].
+		// If a string is more than 55 bytes long, the RLP encoding consists of a
+		// single byte with value 0xB7 plus the length of the length of the
+		// string in binary form, followed by the length of the string, followed
+		// by the string. For example, a length-1024 string 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
-		// (i.e. the combined length of all its items) is 0-55 bytes long, the
-		// RLP encoding consists of a single byte with value 0xC0 plus the length
-		// of the list followed by the concatenation of the RLP encodings of the
-		// items. The range of the first byte is thus [0xC0, 0xF7].
+		// If the total payload of a list (i.e. the combined length of all its
+		// items) is 0-55 bytes long, the RLP encoding consists of a single byte
+		// with value 0xC0 plus the length of the list followed by the
+		// concatenation of the RLP encodings of the items. The range of the
+		// first byte is thus [0xC0, 0xF7].
 		return List, uint64(b - 0xC0), nil
 	default:
-		// If the total payload of a list is more than 55 bytes long,
-		// the RLP encoding consists of a single byte with value 0xF7
-		// plus the length of the length of the payload in binary
-		// form, followed by the length of the payload, followed by
-		// the concatenation of the RLP encodings of the items. The
-		// range of the first byte is thus [0xF8, 0xFF].
+		// If the total payload of a list is more than 55 bytes long, the RLP
+		// encoding consists of a single byte with value 0xF7 plus the length of
+		// the length of the payload in binary form, followed by the length of
+		// the payload, followed by 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
@@ -940,22 +930,20 @@ func (s *Stream) readUint(size byte) (uint64, error) {
 		return uint64(b), err
 	default:
 		start := int(8 - size)
-		for i := 0; i < start; i++ {
-			s.uintbuf[i] = 0
-		}
+		s.uintbuf = [8]byte{}
 		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.
+			// 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
+		return binary.BigEndian.Uint64(s.uintbuf[:]), nil
 	}
 }
 
+// readFull reads into buf from the underlying stream.
 func (s *Stream) readFull(buf []byte) (err error) {
 	if err := s.willRead(uint64(len(buf))); err != nil {
 		return err
@@ -977,6 +965,7 @@ func (s *Stream) readFull(buf []byte) (err error) {
 	return err
 }
 
+// readByte reads a single byte from the underlying stream.
 func (s *Stream) readByte() (byte, error) {
 	if err := s.willRead(1); err != nil {
 		return 0, err
@@ -988,16 +977,16 @@ func (s *Stream) readByte() (byte, error) {
 	return b, err
 }
 
+// willRead is called before any read from the underlying stream. It checks
+// n against size limits, and updates the limits if n doesn't overflow them.
 func (s *Stream) willRead(n uint64) error {
 	s.kind = -1 // rearm Kind
 
-	if len(s.stack) > 0 {
-		// check list overflow
-		tos := s.stack[len(s.stack)-1]
-		if n > tos.size-tos.pos {
+	if inList, limit := s.listLimit(); inList {
+		if n > limit {
 			return ErrElemTooLarge
 		}
-		s.stack[len(s.stack)-1].pos += n
+		s.stack[len(s.stack)-1] = limit - n
 	}
 	if s.limited {
 		if n > s.remaining {
@@ -1007,3 +996,11 @@ func (s *Stream) willRead(n uint64) error {
 	}
 	return nil
 }
+
+// listLimit returns the amount of data remaining in the innermost list.
+func (s *Stream) listLimit() (inList bool, limit uint64) {
+	if len(s.stack) == 0 {
+		return false, 0
+	}
+	return true, s.stack[len(s.stack)-1]
+}