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// 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
}