forked from cerc-io/ipld-eth-server
114 lines
3.5 KiB
Go
114 lines
3.5 KiB
Go
// Copyright 2014 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package trie
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// Trie keys are dealt with in three distinct encodings:
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//
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// KEYBYTES encoding contains the actual key and nothing else. This encoding is the
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// input to most API functions.
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//
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// HEX encoding contains one byte for each nibble of the key and an optional trailing
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// 'terminator' byte of value 0x10 which indicates whether or not the node at the key
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// contains a value. Hex key encoding is used for nodes loaded in memory because it's
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// convenient to access.
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//
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// COMPACT encoding is defined by the Ethereum Yellow Paper (it's called "hex prefix
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// encoding" there) and contains the bytes of the key and a flag. The high nibble of the
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// first byte contains the flag; the lowest bit encoding the oddness of the length and
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// the second-lowest encoding whether the node at the key is a value node. The low nibble
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// of the first byte is zero in the case of an even number of nibbles and the first nibble
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// in the case of an odd number. All remaining nibbles (now an even number) fit properly
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// into the remaining bytes. Compact encoding is used for nodes stored on disk.
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func hexToCompact(hex []byte) []byte {
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terminator := byte(0)
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if hasTerm(hex) {
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terminator = 1
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hex = hex[:len(hex)-1]
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}
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buf := make([]byte, len(hex)/2+1)
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buf[0] = terminator << 5 // the flag byte
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if len(hex)&1 == 1 {
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buf[0] |= 1 << 4 // odd flag
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buf[0] |= hex[0] // first nibble is contained in the first byte
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hex = hex[1:]
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}
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decodeNibbles(hex, buf[1:])
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return buf
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}
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func compactToHex(compact []byte) []byte {
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base := keybytesToHex(compact)
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// delete terminator flag
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if base[0] < 2 {
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base = base[:len(base)-1]
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}
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// apply odd flag
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chop := 2 - base[0]&1
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return base[chop:]
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}
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func keybytesToHex(str []byte) []byte {
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l := len(str)*2 + 1
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var nibbles = make([]byte, l)
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for i, b := range str {
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nibbles[i*2] = b / 16
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nibbles[i*2+1] = b % 16
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}
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nibbles[l-1] = 16
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return nibbles
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}
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// hexToKeybytes turns hex nibbles into key bytes.
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// This can only be used for keys of even length.
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func hexToKeybytes(hex []byte) []byte {
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if hasTerm(hex) {
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hex = hex[:len(hex)-1]
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}
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if len(hex)&1 != 0 {
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panic("can't convert hex key of odd length")
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}
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key := make([]byte, len(hex)/2)
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decodeNibbles(hex, key)
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return key
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}
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func decodeNibbles(nibbles []byte, bytes []byte) {
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for bi, ni := 0, 0; ni < len(nibbles); bi, ni = bi+1, ni+2 {
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bytes[bi] = nibbles[ni]<<4 | nibbles[ni+1]
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}
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}
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// prefixLen returns the length of the common prefix of a and b.
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func prefixLen(a, b []byte) int {
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var i, length = 0, len(a)
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if len(b) < length {
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length = len(b)
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}
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for ; i < length; i++ {
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if a[i] != b[i] {
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break
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}
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}
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return i
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}
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// hasTerm returns whether a hex key has the terminator flag.
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func hasTerm(s []byte) bool {
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return len(s) > 0 && s[len(s)-1] == 16
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}
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