Official Go implementation of the Ethereum protocol
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go-ethereum/p2p/discover/lookup.go

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5.8 KiB

// Copyright 2019 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 discover
import (
"context"
"time"
"github.com/ethereum/go-ethereum/p2p/enode"
)
// lookup performs a network search for nodes close to the given target. It approaches the
// target by querying nodes that are closer to it on each iteration. The given target does
// not need to be an actual node identifier.
type lookup struct {
tab *Table
queryfunc func(*node) ([]*node, error)
replyCh chan []*node
cancelCh <-chan struct{}
asked, seen map[enode.ID]bool
result nodesByDistance
replyBuffer []*node
queries int
}
type queryFunc func(*node) ([]*node, error)
func newLookup(ctx context.Context, tab *Table, target enode.ID, q queryFunc) *lookup {
it := &lookup{
tab: tab,
queryfunc: q,
asked: make(map[enode.ID]bool),
seen: make(map[enode.ID]bool),
result: nodesByDistance{target: target},
replyCh: make(chan []*node, alpha),
cancelCh: ctx.Done(),
queries: -1,
}
// Don't query further if we hit ourself.
// Unlikely to happen often in practice.
it.asked[tab.self().ID()] = true
return it
}
// run runs the lookup to completion and returns the closest nodes found.
func (it *lookup) run() []*enode.Node {
for it.advance() {
}
return unwrapNodes(it.result.entries)
}
// advance advances the lookup until any new nodes have been found.
// It returns false when the lookup has ended.
func (it *lookup) advance() bool {
for it.startQueries() {
select {
case nodes := <-it.replyCh:
it.replyBuffer = it.replyBuffer[:0]
for _, n := range nodes {
if n != nil && !it.seen[n.ID()] {
it.seen[n.ID()] = true
it.result.push(n, bucketSize)
it.replyBuffer = append(it.replyBuffer, n)
}
}
it.queries--
if len(it.replyBuffer) > 0 {
return true
}
case <-it.cancelCh:
it.shutdown()
}
}
return false
}
func (it *lookup) shutdown() {
for it.queries > 0 {
<-it.replyCh
it.queries--
}
it.queryfunc = nil
it.replyBuffer = nil
}
func (it *lookup) startQueries() bool {
if it.queryfunc == nil {
return false
}
// The first query returns nodes from the local table.
if it.queries == -1 {
it.tab.mutex.Lock()
closest := it.tab.closest(it.result.target, bucketSize, false)
it.tab.mutex.Unlock()
// Avoid finishing the lookup too quickly if table is empty. It'd be better to wait
// for the table to fill in this case, but there is no good mechanism for that
// yet.
if len(closest.entries) == 0 {
it.slowdown()
}
it.queries = 1
it.replyCh <- closest.entries
return true
}
// Ask the closest nodes that we haven't asked yet.
for i := 0; i < len(it.result.entries) && it.queries < alpha; i++ {
n := it.result.entries[i]
if !it.asked[n.ID()] {
it.asked[n.ID()] = true
it.queries++
go it.query(n, it.replyCh)
}
}
// The lookup ends when no more nodes can be asked.
return it.queries > 0
}
func (it *lookup) slowdown() {
sleep := time.NewTimer(1 * time.Second)
defer sleep.Stop()
select {
case <-sleep.C:
case <-it.tab.closeReq:
}
}
func (it *lookup) query(n *node, reply chan<- []*node) {
fails := it.tab.db.FindFails(n.ID(), n.IP())
r, err := it.queryfunc(n)
if err == errClosed {
// Avoid recording failures on shutdown.
reply <- nil
return
} else if len(r) == 0 {
fails++
it.tab.db.UpdateFindFails(n.ID(), n.IP(), fails)
it.tab.log.Trace("Findnode failed", "id", n.ID(), "failcount", fails, "err", err)
if fails >= maxFindnodeFailures {
it.tab.log.Trace("Too many findnode failures, dropping", "id", n.ID(), "failcount", fails)
it.tab.delete(n)
}
} else if fails > 0 {
// Reset failure counter because it counts _consecutive_ failures.
it.tab.db.UpdateFindFails(n.ID(), n.IP(), 0)
}
// Grab as many nodes as possible. Some of them might not be alive anymore, but we'll
// just remove those again during revalidation.
for _, n := range r {
it.tab.addSeenNode(n)
}
reply <- r
}
// lookupIterator performs lookup operations and iterates over all seen nodes.
// When a lookup finishes, a new one is created through nextLookup.
type lookupIterator struct {
buffer []*node
nextLookup lookupFunc
ctx context.Context
cancel func()
lookup *lookup
}
type lookupFunc func(ctx context.Context) *lookup
func newLookupIterator(ctx context.Context, next lookupFunc) *lookupIterator {
ctx, cancel := context.WithCancel(ctx)
return &lookupIterator{ctx: ctx, cancel: cancel, nextLookup: next}
}
// Node returns the current node.
func (it *lookupIterator) Node() *enode.Node {
if len(it.buffer) == 0 {
return nil
}
return unwrapNode(it.buffer[0])
}
// Next moves to the next node.
func (it *lookupIterator) Next() bool {
// Consume next node in buffer.
if len(it.buffer) > 0 {
it.buffer = it.buffer[1:]
}
// Advance the lookup to refill the buffer.
for len(it.buffer) == 0 {
if it.ctx.Err() != nil {
it.lookup = nil
it.buffer = nil
return false
}
if it.lookup == nil {
it.lookup = it.nextLookup(it.ctx)
continue
}
if !it.lookup.advance() {
it.lookup = nil
continue
}
it.buffer = it.lookup.replyBuffer
}
return true
}
// Close ends the iterator.
func (it *lookupIterator) Close() {
it.cancel()
}