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fetcher.go
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fetcher.go
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// Copyright 2015 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 fetcher contains the block announcement based synchonisation.
package fetcher
import (
"errors"
"fmt"
"math/rand"
"time"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/core"
"github.com/ethereum/go-ethereum/core/types"
"github.com/ethereum/go-ethereum/logger"
"github.com/ethereum/go-ethereum/logger/glog"
"gopkg.in/karalabe/cookiejar.v2/collections/prque"
)
const (
arriveTimeout = 500 * time.Millisecond // Time allowance before an announced block is explicitly requested
gatherSlack = 100 * time.Millisecond // Interval used to collate almost-expired announces with fetches
fetchTimeout = 5 * time.Second // Maximum alloted time to return an explicitly requested block
maxUncleDist = 7 // Maximum allowed backward distance from the chain head
maxQueueDist = 32 // Maximum allowed distance from the chain head to queue
hashLimit = 256 // Maximum number of unique blocks a peer may have announced
blockLimit = 64 // Maximum number of unique blocks a per may have delivered
)
var (
errTerminated = errors.New("terminated")
)
// blockRetrievalFn is a callback type for retrieving a block from the local chain.
type blockRetrievalFn func(common.Hash) *types.Block
// blockRequesterFn is a callback type for sending a block retrieval request.
type blockRequesterFn func([]common.Hash) error
// blockValidatorFn is a callback type to verify a block's header for fast propagation.
type blockValidatorFn func(block *types.Block, parent *types.Block) error
// blockBroadcasterFn is a callback type for broadcasting a block to connected peers.
type blockBroadcasterFn func(block *types.Block, propagate bool)
// chainHeightFn is a callback type to retrieve the current chain height.
type chainHeightFn func() uint64
// chainInsertFn is a callback type to insert a batch of blocks into the local chain.
type chainInsertFn func(types.Blocks) (int, error)
// peerDropFn is a callback type for dropping a peer detected as malicious.
type peerDropFn func(id string)
// announce is the hash notification of the availability of a new block in the
// network.
type announce struct {
hash common.Hash // Hash of the block being announced
time time.Time // Timestamp of the announcement
origin string // Identifier of the peer originating the notification
fetch blockRequesterFn // Fetcher function to retrieve
}
// inject represents a schedules import operation.
type inject struct {
origin string
block *types.Block
}
// Fetcher is responsible for accumulating block announcements from various peers
// and scheduling them for retrieval.
type Fetcher struct {
// Various event channels
notify chan *announce
inject chan *inject
filter chan chan []*types.Block
done chan common.Hash
quit chan struct{}
// Announce states
announces map[string]int // Per peer announce counts to prevent memory exhaustion
announced map[common.Hash][]*announce // Announced blocks, scheduled for fetching
fetching map[common.Hash]*announce // Announced blocks, currently fetching
// Block cache
queue *prque.Prque // Queue containing the import operations (block number sorted)
queues map[string]int // Per peer block counts to prevent memory exhaustion
queued map[common.Hash]*inject // Set of already queued blocks (to dedup imports)
// Callbacks
getBlock blockRetrievalFn // Retrieves a block from the local chain
validateBlock blockValidatorFn // Checks if a block's headers have a valid proof of work
broadcastBlock blockBroadcasterFn // Broadcasts a block to connected peers
chainHeight chainHeightFn // Retrieves the current chain's height
insertChain chainInsertFn // Injects a batch of blocks into the chain
dropPeer peerDropFn // Drops a peer for misbehaving
// Testing hooks
fetchingHook func([]common.Hash) // Method to call upon starting a block fetch
importedHook func(*types.Block) // Method to call upon successful block import
}
// New creates a block fetcher to retrieve blocks based on hash announcements.
func New(getBlock blockRetrievalFn, validateBlock blockValidatorFn, broadcastBlock blockBroadcasterFn, chainHeight chainHeightFn, insertChain chainInsertFn, dropPeer peerDropFn) *Fetcher {
return &Fetcher{
notify: make(chan *announce),
inject: make(chan *inject),
filter: make(chan chan []*types.Block),
done: make(chan common.Hash),
quit: make(chan struct{}),
announces: make(map[string]int),
announced: make(map[common.Hash][]*announce),
fetching: make(map[common.Hash]*announce),
queue: prque.New(),
queues: make(map[string]int),
queued: make(map[common.Hash]*inject),
getBlock: getBlock,
validateBlock: validateBlock,
broadcastBlock: broadcastBlock,
chainHeight: chainHeight,
insertChain: insertChain,
dropPeer: dropPeer,
}
}
// Start boots up the announcement based synchoniser, accepting and processing
// hash notifications and block fetches until termination requested.
func (f *Fetcher) Start() {
go f.loop()
}
// Stop terminates the announcement based synchroniser, canceling all pending
// operations.
func (f *Fetcher) Stop() {
close(f.quit)
}
// Notify announces the fetcher of the potential availability of a new block in
// the network.
func (f *Fetcher) Notify(peer string, hash common.Hash, time time.Time, fetcher blockRequesterFn) error {
block := &announce{
hash: hash,
time: time,
origin: peer,
fetch: fetcher,
}
select {
case f.notify <- block:
return nil
case <-f.quit:
return errTerminated
}
}
// Enqueue tries to fill gaps the the fetcher's future import queue.
func (f *Fetcher) Enqueue(peer string, block *types.Block) error {
op := &inject{
origin: peer,
block: block,
}
select {
case f.inject <- op:
return nil
case <-f.quit:
return errTerminated
}
}
// Filter extracts all the blocks that were explicitly requested by the fetcher,
// returning those that should be handled differently.
func (f *Fetcher) Filter(blocks types.Blocks) types.Blocks {
// Send the filter channel to the fetcher
filter := make(chan []*types.Block)
select {
case f.filter <- filter:
case <-f.quit:
return nil
}
// Request the filtering of the block list
select {
case filter <- blocks:
case <-f.quit:
return nil
}
// Retrieve the blocks remaining after filtering
select {
case blocks := <-filter:
return blocks
case <-f.quit:
return nil
}
}
// Loop is the main fetcher loop, checking and processing various notification
// events.
func (f *Fetcher) loop() {
// Iterate the block fetching until a quit is requested
fetch := time.NewTimer(0)
for {
// Clean up any expired block fetches
for hash, announce := range f.fetching {
if time.Since(announce.time) > fetchTimeout {
f.forgetHash(hash)
}
}
// Import any queued blocks that could potentially fit
height := f.chainHeight()
for !f.queue.Empty() {
op := f.queue.PopItem().(*inject)
// If too high up the chain or phase, continue later
number := op.block.NumberU64()
if number > height+1 {
f.queue.Push(op, -float32(op.block.NumberU64()))
break
}
// Otherwise if fresh and still unknown, try and import
hash := op.block.Hash()
if number+maxUncleDist < height || f.getBlock(hash) != nil {
f.forgetBlock(hash)
continue
}
f.insert(op.origin, op.block)
}
// Wait for an outside event to occur
select {
case <-f.quit:
// Fetcher terminating, abort all operations
return
case notification := <-f.notify:
// A block was announced, make sure the peer isn't DOSing us
announceMeter.Mark(1)
count := f.announces[notification.origin] + 1
if count > hashLimit {
glog.V(logger.Debug).Infof("Peer %s: exceeded outstanding announces (%d)", notification.origin, hashLimit)
break
}
// All is well, schedule the announce if block's not yet downloading
if _, ok := f.fetching[notification.hash]; ok {
break
}
f.announces[notification.origin] = count
f.announced[notification.hash] = append(f.announced[notification.hash], notification)
if len(f.announced) == 1 {
f.reschedule(fetch)
}
case op := <-f.inject:
// A direct block insertion was requested, try and fill any pending gaps
broadcastMeter.Mark(1)
f.enqueue(op.origin, op.block)
case hash := <-f.done:
// A pending import finished, remove all traces of the notification
f.forgetHash(hash)
f.forgetBlock(hash)
case <-fetch.C:
// At least one block's timer ran out, check for needing retrieval
request := make(map[string][]common.Hash)
for hash, announces := range f.announced {
if time.Since(announces[0].time) > arriveTimeout-gatherSlack {
// Pick a random peer to retrieve from, reset all others
announce := announces[rand.Intn(len(announces))]
f.forgetHash(hash)
// If the block still didn't arrive, queue for fetching
if f.getBlock(hash) == nil {
request[announce.origin] = append(request[announce.origin], hash)
f.fetching[hash] = announce
}
}
}
// Send out all block requests
for peer, hashes := range request {
if glog.V(logger.Detail) && len(hashes) > 0 {
list := "["
for _, hash := range hashes {
list += fmt.Sprintf("%x, ", hash[:4])
}
list = list[:len(list)-2] + "]"
glog.V(logger.Detail).Infof("Peer %s: fetching %s", peer, list)
}
// Create a closure of the fetch and schedule in on a new thread
fetcher, hashes := f.fetching[hashes[0]].fetch, hashes
go func() {
if f.fetchingHook != nil {
f.fetchingHook(hashes)
}
fetcher(hashes)
}()
}
// Schedule the next fetch if blocks are still pending
f.reschedule(fetch)
case filter := <-f.filter:
// Blocks arrived, extract any explicit fetches, return all else
var blocks types.Blocks
select {
case blocks = <-filter:
case <-f.quit:
return
}
explicit, download := []*types.Block{}, []*types.Block{}
for _, block := range blocks {
hash := block.Hash()
// Filter explicitly requested blocks from hash announcements
if f.fetching[hash] != nil && f.queued[hash] == nil {
// Discard if already imported by other means
if f.getBlock(hash) == nil {
explicit = append(explicit, block)
} else {
f.forgetHash(hash)
}
} else {
download = append(download, block)
}
}
select {
case filter <- download:
case <-f.quit:
return
}
// Schedule the retrieved blocks for ordered import
for _, block := range explicit {
if announce := f.fetching[block.Hash()]; announce != nil {
f.enqueue(announce.origin, block)
}
}
}
}
}
// reschedule resets the specified fetch timer to the next announce timeout.
func (f *Fetcher) reschedule(fetch *time.Timer) {
// Short circuit if no blocks are announced
if len(f.announced) == 0 {
return
}
// Otherwise find the earliest expiring announcement
earliest := time.Now()
for _, announces := range f.announced {
if earliest.After(announces[0].time) {
earliest = announces[0].time
}
}
fetch.Reset(arriveTimeout - time.Since(earliest))
}
// enqueue schedules a new future import operation, if the block to be imported
// has not yet been seen.
func (f *Fetcher) enqueue(peer string, block *types.Block) {
hash := block.Hash()
// Ensure the peer isn't DOSing us
count := f.queues[peer] + 1
if count > blockLimit {
glog.V(logger.Debug).Infof("Peer %s: discarded block #%d [%x], exceeded allowance (%d)", peer, block.NumberU64(), hash.Bytes()[:4], blockLimit)
return
}
// Discard any past or too distant blocks
if dist := int64(block.NumberU64()) - int64(f.chainHeight()); dist < -maxUncleDist || dist > maxQueueDist {
glog.V(logger.Debug).Infof("Peer %s: discarded block #%d [%x], distance %d", peer, block.NumberU64(), hash.Bytes()[:4], dist)
discardMeter.Mark(1)
return
}
// Schedule the block for future importing
if _, ok := f.queued[hash]; !ok {
op := &inject{
origin: peer,
block: block,
}
f.queues[peer] = count
f.queued[hash] = op
f.queue.Push(op, -float32(block.NumberU64()))
if glog.V(logger.Debug) {
glog.Infof("Peer %s: queued block #%d [%x], total %v", peer, block.NumberU64(), hash.Bytes()[:4], f.queue.Size())
}
}
}
// insert spawns a new goroutine to run a block insertion into the chain. If the
// block's number is at the same height as the current import phase, if updates
// the phase states accordingly.
func (f *Fetcher) insert(peer string, block *types.Block) {
hash := block.Hash()
// Run the import on a new thread
glog.V(logger.Debug).Infof("Peer %s: importing block #%d [%x]", peer, block.NumberU64(), hash[:4])
go func() {
defer func() { f.done <- hash }()
// If the parent's unknown, abort insertion
parent := f.getBlock(block.ParentHash())
if parent == nil {
return
}
// Quickly validate the header and propagate the block if it passes
switch err := f.validateBlock(block, parent); err {
case nil:
// All ok, quickly propagate to our peers
broadcastTimer.UpdateSince(block.ReceivedAt)
go f.broadcastBlock(block, true)
case core.BlockFutureErr:
futureMeter.Mark(1)
// Weird future block, don't fail, but neither propagate
default:
// Something went very wrong, drop the peer
glog.V(logger.Debug).Infof("Peer %s: block #%d [%x] verification failed: %v", peer, block.NumberU64(), hash[:4], err)
f.dropPeer(peer)
return
}
// Run the actual import and log any issues
if _, err := f.insertChain(types.Blocks{block}); err != nil {
glog.V(logger.Warn).Infof("Peer %s: block #%d [%x] import failed: %v", peer, block.NumberU64(), hash[:4], err)
return
}
// If import succeeded, broadcast the block
announceTimer.UpdateSince(block.ReceivedAt)
go f.broadcastBlock(block, false)
// Invoke the testing hook if needed
if f.importedHook != nil {
f.importedHook(block)
}
}()
}
// forgetHash removes all traces of a block announcement from the fetcher's
// internal state.
func (f *Fetcher) forgetHash(hash common.Hash) {
// Remove all pending announces and decrement DOS counters
for _, announce := range f.announced[hash] {
f.announces[announce.origin]--
if f.announces[announce.origin] == 0 {
delete(f.announces, announce.origin)
}
}
delete(f.announced, hash)
// Remove any pending fetches and decrement the DOS counters
if announce := f.fetching[hash]; announce != nil {
f.announces[announce.origin]--
if f.announces[announce.origin] == 0 {
delete(f.announces, announce.origin)
}
delete(f.fetching, hash)
}
}
// forgetBlock removes all traces of a queued block frmo the fetcher's internal
// state.
func (f *Fetcher) forgetBlock(hash common.Hash) {
if insert := f.queued[hash]; insert != nil {
f.queues[insert.origin]--
if f.queues[insert.origin] == 0 {
delete(f.queues, insert.origin)
}
delete(f.queued, hash)
}
}