rlp: add Split functions

These functions allow destructuring of raw rlp-encoded bytes
without the overhead of reflection or copying.

rlp/raw.go

@@ -0,0 +1,140 @@
+// Copyright 2015 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package rlp
+
+import "io"
+
+// Split returns the content of first RLP value and any
+// bytes after the value as subslices of b.
+func Split(b []byte) (k Kind, content, rest []byte, err error) {
+	k, ts, cs, err := readKind(b)
+	if err != nil {
+		return 0, nil, b, err
+	}
+	return k, b[ts : ts+cs], b[ts+cs:], nil
+}
+
+// SplitString splits b into the content of an RLP string
+// and any remaining bytes after the string.
+func SplitString(b []byte) (content, rest []byte, err error) {
+	k, content, rest, err := Split(b)
+	if err != nil {
+		return nil, b, err
+	}
+	if k == List {
+		return nil, b, ErrExpectedString
+	}
+	return content, rest, nil
+}
+
+// SplitList splits b into the content of a list and any remaining
+// bytes after the list.
+func SplitList(b []byte) (content, rest []byte, err error) {
+	k, content, rest, err := Split(b)
+	if err != nil {
+		return nil, b, err
+	}
+	if k != List {
+		return nil, b, ErrExpectedList
+	}
+	return content, rest, nil
+}
+
+// CountValues counts the number of encoded values in b.
+func CountValues(b []byte) (int, error) {
+	i := 0
+	for ; len(b) > 0; i++ {
+		_, tagsize, size, err := readKind(b)
+		if err != nil {
+			return 0, err
+		}
+		b = b[tagsize+size:]
+	}
+	return i, nil
+}
+
+func readKind(buf []byte) (k Kind, tagsize, contentsize uint64, err error) {
+	if len(buf) == 0 {
+		return 0, 0, 0, io.ErrUnexpectedEOF
+	}
+	b := buf[0]
+	switch {
+	case b < 0x80:
+		k = Byte
+		tagsize = 0
+		contentsize = 1
+	case b < 0xB8:
+		k = String
+		tagsize = 1
+		contentsize = uint64(b - 0x80)
+		// Reject strings that should've been single bytes.
+		if contentsize == 1 && buf[1] < 128 {
+			return 0, 0, 0, ErrCanonSize
+		}
+	case b < 0xC0:
+		k = String
+		tagsize = uint64(b-0xB7) + 1
+		contentsize, err = readSize(buf[1:], b-0xB7)
+	case b < 0xF8:
+		k = List
+		tagsize = 1
+		contentsize = uint64(b - 0xC0)
+	default:
+		k = List
+		tagsize = uint64(b-0xF7) + 1
+		contentsize, err = readSize(buf[1:], b-0xF7)
+	}
+	if err != nil {
+		return 0, 0, 0, err
+	}
+	// Reject values larger than the input slice.
+	if contentsize > uint64(len(buf))-tagsize {
+		return 0, 0, 0, ErrValueTooLarge
+	}
+	return k, tagsize, contentsize, err
+}
+
+func readSize(b []byte, slen byte) (uint64, error) {
+	if int(slen) > len(b) {
+		return 0, io.ErrUnexpectedEOF
+	}
+	var s uint64
+	switch slen {
+	case 1:
+		s = uint64(b[0])
+	case 2:
+		s = uint64(b[0])<<8 | uint64(b[1])
+	case 3:
+		s = uint64(b[0])<<16 | uint64(b[1])<<8 | uint64(b[2])
+	case 4:
+		s = uint64(b[0])<<24 | uint64(b[1])<<16 | uint64(b[2])<<8 | uint64(b[3])
+	case 5:
+		s = uint64(b[0])<<32 | uint64(b[1])<<24 | uint64(b[2])<<16 | uint64(b[3])<<8 | uint64(b[4])
+	case 6:
+		s = uint64(b[0])<<40 | uint64(b[1])<<32 | uint64(b[2])<<24 | uint64(b[3])<<16 | uint64(b[4])<<8 | uint64(b[5])
+	case 7:
+		s = uint64(b[0])<<48 | uint64(b[1])<<40 | uint64(b[2])<<32 | uint64(b[3])<<24 | uint64(b[4])<<16 | uint64(b[5])<<8 | uint64(b[6])
+	case 8:
+		s = uint64(b[0])<<56 | uint64(b[1])<<48 | uint64(b[2])<<40 | uint64(b[3])<<32 | uint64(b[4])<<24 | uint64(b[5])<<16 | uint64(b[6])<<8 | uint64(b[7])
+	}
+	// Reject sizes < 56 (shouldn't have separate size) and sizes with
+	// leading zero bytes.
+	if s < 56 || b[0] == 0 {
+		return 0, ErrCanonSize
+	}
+	return s, nil
+}