1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140

// This file is part of Substrate.

// Copyright (C) 2015-2021 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! `TrieStream` implementation for Substrate's trie format.

use hash_db::Hasher;
use trie_root;
use codec::Encode;
use sp_std::vec::Vec;
use crate::trie_constants;
use crate::node_header::{NodeKind, size_and_prefix_iterator};
use crate::node_codec::Bitmap;

const BRANCH_NODE_NO_VALUE: u8 = 254;
const BRANCH_NODE_WITH_VALUE: u8 = 255;

#[derive(Default, Clone)]
/// Codec-flavored TrieStream.
pub struct TrieStream {
	buffer: Vec<u8>,
}

impl TrieStream {
	// useful for debugging but not used otherwise
	pub fn as_raw(&self) -> &[u8] { &self.buffer }
}

fn branch_node_bit_mask(has_children: impl Iterator<Item = bool>) -> (u8, u8) {
	let mut bitmap: u16 = 0;
	let mut cursor: u16 = 1;
	for v in has_children {
		if v { bitmap |= cursor }
		cursor <<= 1;
	}
	((bitmap % 256 ) as u8, (bitmap / 256 ) as u8)
}


/// Create a leaf/branch node, encoding a number of nibbles.
fn fuse_nibbles_node<'a>(nibbles: &'a [u8], kind: NodeKind) -> impl Iterator<Item = u8> + 'a {
	let size = sp_std::cmp::min(trie_constants::NIBBLE_SIZE_BOUND, nibbles.len());

	let iter_start = match kind {
		NodeKind::Leaf => size_and_prefix_iterator(size, trie_constants::LEAF_PREFIX_MASK),
		NodeKind::BranchNoValue => size_and_prefix_iterator(size, trie_constants::BRANCH_WITHOUT_MASK),
		NodeKind::BranchWithValue => size_and_prefix_iterator(size, trie_constants::BRANCH_WITH_MASK),
	};
	iter_start
		.chain(if nibbles.len() % 2 == 1 { Some(nibbles[0]) } else { None })
		.chain(nibbles[nibbles.len() % 2..].chunks(2).map(|ch| ch[0] << 4 | ch[1]))
}


impl trie_root::TrieStream for TrieStream {

	fn new() -> Self {
		TrieStream {
			buffer: Vec::new()
		}
	}

	fn append_empty_data(&mut self) {
		self.buffer.push(trie_constants::EMPTY_TRIE);
	}

	fn append_leaf(&mut self, key: &[u8], value: &[u8]) {
		self.buffer.extend(fuse_nibbles_node(key, NodeKind::Leaf));
		value.encode_to(&mut self.buffer);
	}

	fn begin_branch(
		&mut self,
		maybe_partial: Option<&[u8]>,
		maybe_value: Option<&[u8]>,
		has_children: impl Iterator<Item = bool>,
	) {
		if let Some(partial) = maybe_partial {
			if maybe_value.is_some() {
				self.buffer.extend(fuse_nibbles_node(partial, NodeKind::BranchWithValue));
			} else {
				self.buffer.extend(fuse_nibbles_node(partial, NodeKind::BranchNoValue));
			}
			let bm = branch_node_bit_mask(has_children);
			self.buffer.extend([bm.0,bm.1].iter());
		} else {
			debug_assert!(false, "trie stream codec only for no extension trie");
			self.buffer.extend(&branch_node(maybe_value.is_some(), has_children));
		}
		if let Some(value) = maybe_value {
			value.encode_to(&mut self.buffer);
		}
	}

	fn append_extension(&mut self, _key: &[u8]) {
		debug_assert!(false, "trie stream codec only for no extension trie");
	}

	fn append_substream<H: Hasher>(&mut self, other: Self) {
		let data = other.out();
		match data.len() {
			0..=31 => data.encode_to(&mut self.buffer),
			_ => H::hash(&data).as_ref().encode_to(&mut self.buffer),
		}
	}

	fn out(self) -> Vec<u8> { self.buffer }
}

fn branch_node(has_value: bool, has_children: impl Iterator<Item = bool>) -> [u8; 3] {
	let mut result = [0, 0, 0];
	branch_node_buffered(has_value, has_children, &mut result[..]);
	result
}

fn branch_node_buffered<I>(has_value: bool, has_children: I, output: &mut[u8])
	where
		I: Iterator<Item = bool>,
{
	let first = if has_value {
		BRANCH_NODE_WITH_VALUE
	} else {
		BRANCH_NODE_NO_VALUE
	};
	output[0] = first;
	Bitmap::encode(has_children, &mut output[1..]);
}