Official Go implementation of the Ethereum protocol
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go-ethereum/les/fetcher.go

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// Copyright 2016 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 les
import (
"math/big"
"math/rand"
"sync"
"time"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/consensus"
"github.com/ethereum/go-ethereum/core"
"github.com/ethereum/go-ethereum/core/rawdb"
"github.com/ethereum/go-ethereum/core/types"
"github.com/ethereum/go-ethereum/eth/fetcher"
"github.com/ethereum/go-ethereum/ethdb"
"github.com/ethereum/go-ethereum/light"
"github.com/ethereum/go-ethereum/log"
"github.com/ethereum/go-ethereum/p2p/enode"
)
const (
blockDelayTimeout = 10 * time.Second // Timeout for retrieving the headers from the peer
gatherSlack = 100 * time.Millisecond // Interval used to collate almost-expired requests
cachedAnnosThreshold = 64 // The maximum queued announcements
)
// announce represents an new block announcement from the les server.
type announce struct {
data *announceData
trust bool
peerid enode.ID
}
// request represents a record when the header request is sent.
type request struct {
reqid uint64
peerid enode.ID
sendAt time.Time
hash common.Hash
}
// response represents a response packet from network as well as a channel
// to return all un-requested data.
type response struct {
reqid uint64
headers []*types.Header
peerid enode.ID
remain chan []*types.Header
}
// fetcherPeer holds the fetcher-specific information for each active peer
type fetcherPeer struct {
latest *announceData // The latest announcement sent from the peer
// These following two fields can track the latest announces
// from the peer with limited size for caching. We hold the
// assumption that all enqueued announces are td-monotonic.
announces map[common.Hash]*announce // Announcement map
announcesList []common.Hash // FIFO announces list
}
// addAnno enqueues an new trusted announcement. If the queued announces overflow,
// evict from the oldest.
func (fp *fetcherPeer) addAnno(anno *announce) {
// Short circuit if the anno already exists. In normal case it should
// never happen since only monotonic anno is accepted. But the adversary
// may feed us fake announces with higher td but same hash. In this case,
// ignore the anno anyway.
hash := anno.data.Hash
if _, exist := fp.announces[hash]; exist {
return
}
fp.announces[hash] = anno
fp.announcesList = append(fp.announcesList, hash)
// Evict oldest if the announces are oversized.
if len(fp.announcesList)-cachedAnnosThreshold > 0 {
for i := 0; i < len(fp.announcesList)-cachedAnnosThreshold; i++ {
delete(fp.announces, fp.announcesList[i])
}
copy(fp.announcesList, fp.announcesList[len(fp.announcesList)-cachedAnnosThreshold:])
fp.announcesList = fp.announcesList[:cachedAnnosThreshold]
}
}
// forwardAnno removes all announces from the map with a number lower than
// the provided threshold.
func (fp *fetcherPeer) forwardAnno(td *big.Int) []*announce {
var (
cutset int
evicted []*announce
)
for ; cutset < len(fp.announcesList); cutset++ {
anno := fp.announces[fp.announcesList[cutset]]
if anno == nil {
continue // In theory it should never ever happen
}
if anno.data.Td.Cmp(td) > 0 {
break
}
evicted = append(evicted, anno)
delete(fp.announces, anno.data.Hash)
}
if cutset > 0 {
copy(fp.announcesList, fp.announcesList[cutset:])
fp.announcesList = fp.announcesList[:len(fp.announcesList)-cutset]
}
return evicted
}
// lightFetcher implements retrieval of newly announced headers. It reuses
// the eth.BlockFetcher as the underlying fetcher but adding more additional
// rules: e.g. evict "timeout" peers.
type lightFetcher struct {
// Various handlers
ulc *ulc
chaindb ethdb.Database
reqDist *requestDistributor
peerset *serverPeerSet // The global peerset of light client which shared by all components
chain *light.LightChain // The local light chain which maintains the canonical header chain.
fetcher *fetcher.BlockFetcher // The underlying fetcher which takes care block header retrieval.
// Peerset maintained by fetcher
plock sync.RWMutex
peers map[enode.ID]*fetcherPeer
// Various channels
announceCh chan *announce
requestCh chan *request
deliverCh chan *response
syncDone chan *types.Header
closeCh chan struct{}
wg sync.WaitGroup
// Callback
synchronise func(peer *serverPeer)
// Test fields or hooks
noAnnounce bool
newHeadHook func(*types.Header)
newAnnounce func(*serverPeer, *announceData)
}
// newLightFetcher creates a light fetcher instance.
func newLightFetcher(chain *light.LightChain, engine consensus.Engine, peers *serverPeerSet, ulc *ulc, chaindb ethdb.Database, reqDist *requestDistributor, syncFn func(p *serverPeer)) *lightFetcher {
// Construct the fetcher by offering all necessary APIs
validator := func(header *types.Header) error {
// Disable seal verification explicitly if we are running in ulc mode.
return engine.VerifyHeader(chain, header, ulc == nil)
}
heighter := func() uint64 { return chain.CurrentHeader().Number.Uint64() }
dropper := func(id string) { peers.unregister(id) }
inserter := func(headers []*types.Header) (int, error) {
// Disable PoW checking explicitly if we are running in ulc mode.
checkFreq := 1
if ulc != nil {
checkFreq = 0
}
return chain.InsertHeaderChain(headers, checkFreq)
}
f := &lightFetcher{
ulc: ulc,
peerset: peers,
chaindb: chaindb,
chain: chain,
reqDist: reqDist,
fetcher: fetcher.NewBlockFetcher(true, chain.GetHeaderByHash, nil, validator, nil, heighter, inserter, nil, dropper),
peers: make(map[enode.ID]*fetcherPeer),
synchronise: syncFn,
announceCh: make(chan *announce),
requestCh: make(chan *request),
deliverCh: make(chan *response),
syncDone: make(chan *types.Header),
closeCh: make(chan struct{}),
}
peers.subscribe(f)
return f
}
func (f *lightFetcher) start() {
f.wg.Add(1)
f.fetcher.Start()
go f.mainloop()
}
func (f *lightFetcher) stop() {
close(f.closeCh)
f.fetcher.Stop()
f.wg.Wait()
}
// registerPeer adds an new peer to the fetcher's peer set
func (f *lightFetcher) registerPeer(p *serverPeer) {
f.plock.Lock()
defer f.plock.Unlock()
f.peers[p.ID()] = &fetcherPeer{announces: make(map[common.Hash]*announce)}
}
// unregisterPeer removes the specified peer from the fetcher's peer set
func (f *lightFetcher) unregisterPeer(p *serverPeer) {
f.plock.Lock()
defer f.plock.Unlock()
delete(f.peers, p.ID())
}
// peer returns the peer from the fetcher peerset.
func (f *lightFetcher) peer(id enode.ID) *fetcherPeer {
f.plock.RLock()
defer f.plock.RUnlock()
return f.peers[id]
}
// forEachPeer iterates the fetcher peerset, abort the iteration if the
// callback returns false.
func (f *lightFetcher) forEachPeer(check func(id enode.ID, p *fetcherPeer) bool) {
f.plock.RLock()
defer f.plock.RUnlock()
for id, peer := range f.peers {
if !check(id, peer) {
return
}
}
}
// mainloop is the main event loop of the light fetcher, which is responsible for
// - announcement maintenance(ulc)
// If we are running in ultra light client mode, then all announcements from
// the trusted servers are maintained. If the same announcements from trusted
// servers reach the threshold, then the relevant header is requested for retrieval.
//
// - block header retrieval
// Whenever we receive announce with higher td compared with local chain, the
// request will be made for header retrieval.
//
// - re-sync trigger
// If the local chain lags too much, then the fetcher will enter "synnchronise"
// mode to retrieve missing headers in batch.
func (f *lightFetcher) mainloop() {
defer f.wg.Done()
var (
syncInterval = uint64(1) // Interval used to trigger a light resync.
syncing bool // Indicator whether the client is syncing
ulc = f.ulc != nil
headCh = make(chan core.ChainHeadEvent, 100)
fetching = make(map[uint64]*request)
requestTimer = time.NewTimer(0)
// Local status
localHead = f.chain.CurrentHeader()
localTd = f.chain.GetTd(localHead.Hash(), localHead.Number.Uint64())
)
sub := f.chain.SubscribeChainHeadEvent(headCh)
defer sub.Unsubscribe()
// reset updates the local status with given header.
reset := func(header *types.Header) {
localHead = header
localTd = f.chain.GetTd(header.Hash(), header.Number.Uint64())
}
// trustedHeader returns an indicator whether the header is regarded as
// trusted. If we are running in the ulc mode, only when we receive enough
// same announcement from trusted server, the header will be trusted.
trustedHeader := func(hash common.Hash, number uint64) (bool, []enode.ID) {
var (
agreed []enode.ID
trusted bool
)
f.forEachPeer(func(id enode.ID, p *fetcherPeer) bool {
if anno := p.announces[hash]; anno != nil && anno.trust && anno.data.Number == number {
agreed = append(agreed, id)
if 100*len(agreed)/len(f.ulc.keys) >= f.ulc.fraction {
trusted = true
return false // abort iteration
}
}
return true
})
return trusted, agreed
}
for {
select {
case anno := <-f.announceCh:
peerid, data := anno.peerid, anno.data
log.Debug("Received new announce", "peer", peerid, "number", data.Number, "hash", data.Hash, "reorg", data.ReorgDepth)
peer := f.peer(peerid)
if peer == nil {
log.Debug("Receive announce from unknown peer", "peer", peerid)
continue
}
// Announced tds should be strictly monotonic, drop the peer if
// the announce is out-of-order.
if peer.latest != nil && data.Td.Cmp(peer.latest.Td) <= 0 {
f.peerset.unregister(peerid.String())
log.Debug("Non-monotonic td", "peer", peerid, "current", data.Td, "previous", peer.latest.Td)
continue
}
peer.latest = data
// Filter out any stale announce, the local chain is ahead of announce
if localTd != nil && data.Td.Cmp(localTd) <= 0 {
continue
}
peer.addAnno(anno)
// If we are not syncing, try to trigger a single retrieval or re-sync
if !ulc && !syncing {
// Two scenarios lead to re-sync:
// - reorg happens
// - local chain lags
// We can't retrieve the parent of the announce by single retrieval
// in both cases, so resync is necessary.
if data.Number > localHead.Number.Uint64()+syncInterval || data.ReorgDepth > 0 {
syncing = true
go f.startSync(peerid)
log.Debug("Trigger light sync", "peer", peerid, "local", localHead.Number, "localhash", localHead.Hash(), "remote", data.Number, "remotehash", data.Hash)
continue
}
f.fetcher.Notify(peerid.String(), data.Hash, data.Number, time.Now(), f.requestHeaderByHash(peerid), nil)
log.Debug("Trigger header retrieval", "peer", peerid, "number", data.Number, "hash", data.Hash)
}
// Keep collecting announces from trusted server even we are syncing.
if ulc && anno.trust {
// Notify underlying fetcher to retrieve header or trigger a resync if
// we have receive enough announcements from trusted server.
trusted, agreed := trustedHeader(data.Hash, data.Number)
if trusted && !syncing {
if data.Number > localHead.Number.Uint64()+syncInterval || data.ReorgDepth > 0 {
syncing = true
go f.startSync(peerid)
log.Debug("Trigger trusted light sync", "local", localHead.Number, "localhash", localHead.Hash(), "remote", data.Number, "remotehash", data.Hash)
continue
}
p := agreed[rand.Intn(len(agreed))]
f.fetcher.Notify(p.String(), data.Hash, data.Number, time.Now(), f.requestHeaderByHash(p), nil)
log.Debug("Trigger trusted header retrieval", "number", data.Number, "hash", data.Hash)
}
}
case req := <-f.requestCh:
fetching[req.reqid] = req // Tracking all in-flight requests for response latency statistic.
if len(fetching) == 1 {
f.rescheduleTimer(fetching, requestTimer)
}
case <-requestTimer.C:
for reqid, request := range fetching {
if time.Since(request.sendAt) > blockDelayTimeout-gatherSlack {
delete(fetching, reqid)
f.peerset.unregister(request.peerid.String())
log.Debug("Request timeout", "peer", request.peerid, "reqid", reqid)
}
}
f.rescheduleTimer(fetching, requestTimer)
case resp := <-f.deliverCh:
if req := fetching[resp.reqid]; req != nil {
delete(fetching, resp.reqid)
f.rescheduleTimer(fetching, requestTimer)
// The underlying fetcher does not check the consistency of request and response.
// The adversary can send the fake announces with invalid hash and number but always
// delivery some mismatched header. So it can't be punished by the underlying fetcher.
// We have to add two more rules here to detect.
if len(resp.headers) != 1 {
f.peerset.unregister(req.peerid.String())
log.Debug("Deliver more than requested", "peer", req.peerid, "reqid", req.reqid)
continue
}
if resp.headers[0].Hash() != req.hash {
f.peerset.unregister(req.peerid.String())
log.Debug("Deliver invalid header", "peer", req.peerid, "reqid", req.reqid)
continue
}
resp.remain <- f.fetcher.FilterHeaders(resp.peerid.String(), resp.headers, time.Now())
} else {
// Discard the entire packet no matter it's a timeout response or unexpected one.
resp.remain <- resp.headers
}
case ev := <-headCh:
// Short circuit if we are still syncing.
if syncing {
continue
}
reset(ev.Block.Header())
// Clean stale announcements from les-servers.
var droplist []enode.ID
f.forEachPeer(func(id enode.ID, p *fetcherPeer) bool {
removed := p.forwardAnno(localTd)
for _, anno := range removed {
if header := f.chain.GetHeaderByHash(anno.data.Hash); header != nil {
if header.Number.Uint64() != anno.data.Number {
droplist = append(droplist, id)
break
}
// In theory td should exists.
td := f.chain.GetTd(anno.data.Hash, anno.data.Number)
if td != nil && td.Cmp(anno.data.Td) != 0 {
droplist = append(droplist, id)
break
}
}
}
return true
})
for _, id := range droplist {
f.peerset.unregister(id.String())
log.Debug("Kicked out peer for invalid announcement")
}
if f.newHeadHook != nil {
f.newHeadHook(localHead)
}
case origin := <-f.syncDone:
syncing = false // Reset the status
// Rewind all untrusted headers for ulc mode.
if ulc {
head := f.chain.CurrentHeader()
ancestor := rawdb.FindCommonAncestor(f.chaindb, origin, head)
var untrusted []common.Hash
for head.Number.Cmp(ancestor.Number) > 0 {
hash, number := head.Hash(), head.Number.Uint64()
if trusted, _ := trustedHeader(hash, number); trusted {
break
}
untrusted = append(untrusted, hash)
head = f.chain.GetHeader(head.ParentHash, number-1)
}
if len(untrusted) > 0 {
for i, j := 0, len(untrusted)-1; i < j; i, j = i+1, j-1 {
untrusted[i], untrusted[j] = untrusted[j], untrusted[i]
}
f.chain.Rollback(untrusted)
}
}
// Reset local status.
reset(f.chain.CurrentHeader())
if f.newHeadHook != nil {
f.newHeadHook(localHead)
}
log.Debug("light sync finished", "number", localHead.Number, "hash", localHead.Hash())
case <-f.closeCh:
return
}
}
}
// announce processes a new announcement message received from a peer.
func (f *lightFetcher) announce(p *serverPeer, head *announceData) {
if f.newAnnounce != nil {
f.newAnnounce(p, head)
}
if f.noAnnounce {
return
}
select {
case f.announceCh <- &announce{peerid: p.ID(), trust: p.trusted, data: head}:
case <-f.closeCh:
return
}
}
// trackRequest sends a reqID to main loop for in-flight request tracking.
func (f *lightFetcher) trackRequest(peerid enode.ID, reqid uint64, hash common.Hash) {
select {
case f.requestCh <- &request{reqid: reqid, peerid: peerid, sendAt: time.Now(), hash: hash}:
case <-f.closeCh:
}
}
// requestHeaderByHash constructs a header retrieval request and sends it to
// local request distributor.
//
// Note, we rely on the underlying eth/fetcher to retrieve and validate the
// response, so that we have to obey the rule of eth/fetcher which only accepts
// the response from given peer.
func (f *lightFetcher) requestHeaderByHash(peerid enode.ID) func(common.Hash) error {
return func(hash common.Hash) error {
req := &distReq{
getCost: func(dp distPeer) uint64 { return dp.(*serverPeer).getRequestCost(GetBlockHeadersMsg, 1) },
canSend: func(dp distPeer) bool { return dp.(*serverPeer).ID() == peerid },
request: func(dp distPeer) func() {
peer, id := dp.(*serverPeer), rand.Uint64()
cost := peer.getRequestCost(GetBlockHeadersMsg, 1)
peer.fcServer.QueuedRequest(id, cost)
return func() {
f.trackRequest(peer.ID(), id, hash)
peer.requestHeadersByHash(id, hash, 1, 0, false)
}
},
}
f.reqDist.queue(req)
return nil
}
}
// requestResync invokes synchronisation callback to start syncing.
func (f *lightFetcher) startSync(id enode.ID) {
defer func(header *types.Header) {
f.syncDone <- header
}(f.chain.CurrentHeader())
peer := f.peerset.peer(id.String())
if peer == nil || peer.onlyAnnounce {
return
}
f.synchronise(peer)
}
// deliverHeaders delivers header download request responses for processing
func (f *lightFetcher) deliverHeaders(peer *serverPeer, reqid uint64, headers []*types.Header) []*types.Header {
remain := make(chan []*types.Header, 1)
select {
case f.deliverCh <- &response{reqid: reqid, headers: headers, peerid: peer.ID(), remain: remain}:
case <-f.closeCh:
return nil
}
return <-remain
}
// rescheduleTimer resets the specified timeout timer to the next request timeout.
func (f *lightFetcher) rescheduleTimer(requests map[uint64]*request, timer *time.Timer) {
// Short circuit if no inflight requests
if len(requests) == 0 {
timer.Stop()
return
}
// Otherwise find the earliest expiring request
earliest := time.Now()
for _, req := range requests {
if earliest.After(req.sendAt) {
earliest = req.sendAt
}
}
timer.Reset(blockDelayTimeout - time.Since(earliest))
}