eth-iterator-utils/iterator.go

151 lines
4.7 KiB
Go

//
// Copyright © 2020 Vulcanize, Inc
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program 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 Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
package iterator
import (
"bytes"
"math/bits"
"github.com/ethereum/go-ethereum/trie"
)
// IteratorConstructor is a constructor returning a NodeIterator, which is used to decouple this
// code from the trie implementation.
type IteratorConstructor = func(startKey []byte) trie.NodeIterator
// PrefixBoundIterator is a NodeIterator constrained by a lower & upper bound (as hex path prefixes)
type PrefixBoundIterator struct {
trie.NodeIterator
StartPath, EndPath []byte
}
// NewPrefixBoundIterator returns an iterator with an upper bound value (hex path prefix)
func NewPrefixBoundIterator(it trie.NodeIterator, to []byte) *PrefixBoundIterator {
return &PrefixBoundIterator{NodeIterator: it, StartPath: it.Path(), EndPath: to}
}
func (it *PrefixBoundIterator) Next(descend bool) bool {
if it.EndPath == nil {
return it.NodeIterator.Next(descend)
}
if !it.NodeIterator.Next(descend) {
return false
}
// Stop if underlying iterator went past upper bound.
// Note: this results in a single node of overlap between binned iterators. The more correct
// behavior would be to make this a strict less-than, so that iterators cover mutually disjoint
// subtries. Unfortunately, the NodeIterator constructor takes a compact path, meaning
// odd-length paths must be padded with a 0, so e.g. [8] becomes [8, 0], which means we would
// skip [8]. So, we use <= here to cover that node for the "next" bin.
return bytes.Compare(it.Path(), it.EndPath) <= 0
}
func (it *PrefixBoundIterator) Bounds() ([]byte, []byte) {
return it.StartPath, it.EndPath
}
// generates nibble slice prefixes at uniform intervals
type prefixGenerator struct {
current []byte
step byte
stepIndex uint
}
func newPrefixGenerator(nbins uint) prefixGenerator {
if bits.OnesCount(nbins) != 1 {
panic("nbins must be a power of 2")
}
// determine step dist. and path index at which to step
var step byte
var stepIndex uint
for ; nbins != 0; stepIndex++ {
divisor := byte(nbins & 0xF)
if divisor != 0 {
step = 0x10 / divisor
}
nbins = nbins >> 4
}
return prefixGenerator{
current: make([]byte, stepIndex),
step: step,
stepIndex: stepIndex - 1,
}
}
func (gen *prefixGenerator) Value() []byte {
return gen.current
}
func (gen *prefixGenerator) HasNext() bool {
return gen.current[0] < 0x10
}
func (gen *prefixGenerator) Next() {
// increment the cursor, and handle overflow
gen.current[gen.stepIndex] += gen.step
overflow := false
for ix := 0; ix < len(gen.current); ix++ {
rix := len(gen.current) - 1 - ix // index in prefix is reverse
if overflow { // apply overflow
gen.current[rix]++
overflow = false
}
// detect overflow at this index
if rix != 0 && gen.current[rix] > 0xf {
gen.current[rix] = 0
overflow = true
}
}
}
// MakePaths generates paths that cut trie domain into `nbins` uniform conterminous bins (w/ opt. prefix)
// eg. MakePaths([], 2) => [[0] [8]]
// MakePaths([4], 32) => [[4 0 0] [4 0 8] [4 1 0]... [4 f 8]]
func MakePaths(prefix []byte, nbins uint) [][]byte {
var res [][]byte
for it := newPrefixGenerator(nbins); it.HasNext(); it.Next() {
next := make([]byte, len(prefix))
copy(next, prefix)
next = append(next, it.Value()...)
res = append(res, next)
}
return res
}
func eachPrefixRange(prefix []byte, nbins uint, callback func([]byte, []byte)) {
prefixes := MakePaths(prefix, nbins)
prefixes = append(prefixes, nil) // include tail
prefixes[0] = nil // set bin 0 left bound to nil to include root
for i := 0; i < len(prefixes)-1; i++ {
key := prefixes[i]
if len(key)%2 != 0 { // zero-pad for odd-length keys
key = append(key, 0)
}
callback(key, prefixes[i+1])
}
}
// SubtrieIterators cuts a trie by path prefix, returning `nbins` iterators covering its subtries
func SubtrieIterators(makeIterator IteratorConstructor, nbins uint) []trie.NodeIterator {
var iters []trie.NodeIterator
eachPrefixRange(nil, nbins, func(from []byte, to []byte) {
it := makeIterator(HexToKeyBytes(from))
iters = append(iters, NewPrefixBoundIterator(it, to))
})
return iters
}