plugeth/eth/downloader/downloader.go

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package downloader
import (
"errors"
"math/rand"
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"sync"
"sync/atomic"
"time"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/core/types"
"github.com/ethereum/go-ethereum/event"
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"github.com/ethereum/go-ethereum/logger"
"github.com/ethereum/go-ethereum/logger/glog"
)
const (
maxHashFetch = 512 // Amount of hashes to be fetched per chunk
maxBlockFetch = 128 // Amount of blocks to be fetched per chunk
peerCountTimeout = 12 * time.Second // Amount of time it takes for the peer handler to ignore minDesiredPeerCount
hashTTL = 5 * time.Second // Time it takes for a hash request to time out
)
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var (
blockTTL = 5 * time.Second // Time it takes for a block request to time out
crossCheckCycle = time.Second // Period after which to check for expired cross checks
minDesiredPeerCount = 5 // Amount of peers desired to start syncing
)
var (
errLowTd = errors.New("peer's TD is too low")
ErrBusy = errors.New("busy")
errUnknownPeer = errors.New("peer's unknown or unhealthy")
ErrBadPeer = errors.New("action from bad peer ignored")
errNoPeers = errors.New("no peers to keep download active")
ErrPendingQueue = errors.New("pending items in queue")
ErrTimeout = errors.New("timeout")
errEmptyHashSet = errors.New("empty hash set by peer")
errPeersUnavailable = errors.New("no peers available or all peers tried for block download process")
errAlreadyInPool = errors.New("hash already in pool")
ErrInvalidChain = errors.New("retrieved hash chain is invalid")
ErrCrossCheckFailed = errors.New("block cross-check failed")
errCancelHashFetch = errors.New("hash fetching cancelled (requested)")
errCancelBlockFetch = errors.New("block downloading cancelled (requested)")
errNoSyncActive = errors.New("no sync active")
)
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type hashCheckFn func(common.Hash) bool
type getBlockFn func(common.Hash) *types.Block
type chainInsertFn func(types.Blocks) (int, error)
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type hashIterFn func() (common.Hash, error)
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type blockPack struct {
peerId string
blocks []*types.Block
}
type hashPack struct {
peerId string
hashes []common.Hash
}
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type Downloader struct {
mux *event.TypeMux
mu sync.RWMutex
queue *queue // Scheduler for selecting the hashes to download
peers *peerSet // Set of active peers from which download can proceed
checks map[common.Hash]time.Time // Pending cross checks to verify a hash chain
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// Callbacks
hasBlock hashCheckFn
getBlock getBlockFn
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// Status
synchronising int32
notified int32
// Channels
newPeerCh chan *peer
hashCh chan hashPack
blockCh chan blockPack
cancelCh chan struct{} // Channel to cancel mid-flight syncs
cancelLock sync.RWMutex // Lock to protect the cancel channel in delivers
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}
func New(mux *event.TypeMux, hasBlock hashCheckFn, getBlock getBlockFn) *Downloader {
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downloader := &Downloader{
mux: mux,
queue: newQueue(),
peers: newPeerSet(),
hasBlock: hasBlock,
getBlock: getBlock,
newPeerCh: make(chan *peer, 1),
hashCh: make(chan hashPack, 1),
blockCh: make(chan blockPack, 1),
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}
return downloader
}
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func (d *Downloader) Stats() (current int, max int) {
return d.queue.Size()
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}
// Synchronising returns the state of the downloader
func (d *Downloader) Synchronising() bool {
return atomic.LoadInt32(&d.synchronising) > 0
}
// RegisterPeer injects a new download peer into the set of block source to be
// used for fetching hashes and blocks from.
func (d *Downloader) RegisterPeer(id string, head common.Hash, getHashes hashFetcherFn, getBlocks blockFetcherFn) error {
glog.V(logger.Detail).Infoln("Registering peer", id)
if err := d.peers.Register(newPeer(id, head, getHashes, getBlocks)); err != nil {
glog.V(logger.Error).Infoln("Register failed:", err)
return err
}
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return nil
}
// UnregisterPeer remove a peer from the known list, preventing any action from
// the specified peer.
func (d *Downloader) UnregisterPeer(id string) error {
glog.V(logger.Detail).Infoln("Unregistering peer", id)
if err := d.peers.Unregister(id); err != nil {
glog.V(logger.Error).Infoln("Unregister failed:", err)
return err
}
return nil
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}
// Synchronise will select the peer and use it for synchronising. If an empty string is given
// it will use the best peer possible and synchronize if it's TD is higher than our own. If any of the
// checks fail an error will be returned. This method is synchronous
func (d *Downloader) Synchronise(id string, hash common.Hash) error {
// Make sure only one goroutine is ever allowed past this point at once
if !atomic.CompareAndSwapInt32(&d.synchronising, 0, 1) {
return ErrBusy
}
defer atomic.StoreInt32(&d.synchronising, 0)
// Post a user notification of the sync (only once per session)
if atomic.CompareAndSwapInt32(&d.notified, 0, 1) {
glog.V(logger.Info).Infoln("Block synchronisation started")
}
// Create cancel channel for aborting mid-flight
d.cancelLock.Lock()
d.cancelCh = make(chan struct{})
d.cancelLock.Unlock()
// Abort if the queue still contains some leftover data
if _, cached := d.queue.Size(); cached > 0 && d.queue.GetHeadBlock() != nil {
return ErrPendingQueue
}
// Reset the queue and peer set to clean any internal leftover state
d.queue.Reset()
d.peers.Reset()
d.checks = make(map[common.Hash]time.Time)
// Retrieve the origin peer and initiate the downloading process
p := d.peers.Peer(id)
if p == nil {
return errUnknownPeer
}
return d.syncWithPeer(p, hash)
}
// TakeBlocks takes blocks from the queue and yields them to the caller.
func (d *Downloader) TakeBlocks() types.Blocks {
return d.queue.TakeBlocks()
}
func (d *Downloader) Has(hash common.Hash) bool {
return d.queue.Has(hash)
}
// syncWithPeer starts a block synchronization based on the hash chain from the
// specified peer and head hash.
func (d *Downloader) syncWithPeer(p *peer, hash common.Hash) (err error) {
d.mux.Post(StartEvent{})
defer func() {
// reset on error
if err != nil {
d.Cancel()
d.mux.Post(FailedEvent{err})
} else {
d.mux.Post(DoneEvent{})
}
}()
glog.V(logger.Debug).Infoln("Synchronizing with the network using:", p.id)
if err = d.fetchHashes(p, hash); err != nil {
return err
}
if err = d.fetchBlocks(); err != nil {
return err
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}
glog.V(logger.Debug).Infoln("Synchronization completed")
return nil
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}
// Cancel cancels all of the operations and resets the queue. It returns true
// if the cancel operation was completed.
func (d *Downloader) Cancel() bool {
// If we're not syncing just return.
hs, bs := d.queue.Size()
if atomic.LoadInt32(&d.synchronising) == 0 && hs == 0 && bs == 0 {
return false
}
// Close the current cancel channel
d.cancelLock.Lock()
select {
case <-d.cancelCh:
// Channel was already closed
default:
close(d.cancelCh)
}
d.cancelLock.Unlock()
// reset the queue
d.queue.Reset()
return true
}
// XXX Make synchronous
func (d *Downloader) fetchHashes(p *peer, h common.Hash) error {
glog.V(logger.Debug).Infof("Downloading hashes (%x) from %s", h[:4], p.id)
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start := time.Now()
// Add the hash to the queue first, and start hash retrieval
d.queue.Insert([]common.Hash{h})
p.getHashes(h)
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var (
active = p // active peer will help determine the current active peer
head = common.Hash{} // common and last hash
timeout = time.NewTimer(hashTTL) // timer to dump a non-responsive active peer
attempted = make(map[string]bool) // attempted peers will help with retries
crossTicker = time.NewTicker(crossCheckCycle) // ticker to periodically check expired cross checks
)
defer crossTicker.Stop()
attempted[p.id] = true
for finished := false; !finished; {
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select {
case <-d.cancelCh:
return errCancelHashFetch
case hashPack := <-d.hashCh:
// Make sure the active peer is giving us the hashes
if hashPack.peerId != active.id {
glog.V(logger.Debug).Infof("Received hashes from incorrect peer(%s)\n", hashPack.peerId)
break
}
timeout.Reset(hashTTL)
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// Make sure the peer actually gave something valid
if len(hashPack.hashes) == 0 {
glog.V(logger.Debug).Infof("Peer (%s) responded with empty hash set\n", active.id)
return errEmptyHashSet
}
// Determine if we're done fetching hashes (queue up all pending), and continue if not done
done, index := false, 0
for index, head = range hashPack.hashes {
if d.hasBlock(head) || d.queue.GetBlock(head) != nil {
glog.V(logger.Debug).Infof("Found common hash %x\n", head[:4])
hashPack.hashes = hashPack.hashes[:index]
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done = true
break
}
}
// Insert all the new hashes, but only continue if got something useful
inserts := d.queue.Insert(hashPack.hashes)
if len(inserts) == 0 && !done {
glog.V(logger.Debug).Infof("Peer (%s) responded with stale hashes\n", active.id)
return ErrBadPeer
}
if !done {
// Try and fetch a random block to verify the hash batch
// Skip the last hash as the cross check races with the next hash fetch
if len(inserts) > 1 {
cross := inserts[rand.Intn(len(inserts)-1)]
glog.V(logger.Detail).Infof("Cross checking (%s) with %x", active.id, cross)
d.checks[cross] = time.Now().Add(blockTTL)
active.getBlocks([]common.Hash{cross})
}
// Also fetch a fresh
active.getHashes(head)
continue
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}
// We're done, allocate the download cache and proceed pulling the blocks
offset := 0
if block := d.getBlock(head); block != nil {
offset = int(block.NumberU64() + 1)
}
d.queue.Alloc(offset)
finished = true
case blockPack := <-d.blockCh:
// Cross check the block with the random verifications
if blockPack.peerId != active.id || len(blockPack.blocks) != 1 {
continue
}
block := blockPack.blocks[0]
if _, ok := d.checks[block.Hash()]; ok {
if !d.queue.Has(block.ParentHash()) {
return ErrCrossCheckFailed
}
delete(d.checks, block.Hash())
}
case <-crossTicker.C:
// Iterate over all the cross checks and fail the hash chain if they're not verified
for hash, deadline := range d.checks {
if time.Now().After(deadline) {
glog.V(logger.Debug).Infof("Cross check timeout for %x", hash)
return ErrCrossCheckFailed
}
}
case <-timeout.C:
glog.V(logger.Debug).Infof("Peer (%s) didn't respond in time for hash request\n", p.id)
var p *peer // p will be set if a peer can be found
// Attempt to find a new peer by checking inclusion of peers best hash in our
// already fetched hash list. This can't guarantee 100% correctness but does
// a fair job. This is always either correct or false incorrect.
for _, peer := range d.peers.AllPeers() {
if d.queue.Has(peer.head) && !attempted[peer.id] {
p = peer
break
}
}
// if all peers have been tried, abort the process entirely or if the hash is
// the zero hash.
if p == nil || (head == common.Hash{}) {
return ErrTimeout
}
// set p to the active peer. this will invalidate any hashes that may be returned
// by our previous (delayed) peer.
active = p
p.getHashes(head)
glog.V(logger.Debug).Infof("Hash fetching switched to new peer(%s)\n", p.id)
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}
}
glog.V(logger.Debug).Infof("Downloaded hashes (%d) in %v\n", d.queue.Pending(), time.Since(start))
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return nil
}
// fetchBlocks iteratively downloads the entire schedules block-chain, taking
// any available peers, reserving a chunk of blocks for each, wait for delivery
// and periodically checking for timeouts.
func (d *Downloader) fetchBlocks() error {
glog.V(logger.Debug).Infoln("Downloading", d.queue.Pending(), "block(s)")
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start := time.Now()
// default ticker for re-fetching blocks every now and then
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ticker := time.NewTicker(20 * time.Millisecond)
out:
for {
select {
case <-d.cancelCh:
return errCancelBlockFetch
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case blockPack := <-d.blockCh:
// Short circuit if it's a stale cross check
if len(blockPack.blocks) == 1 {
block := blockPack.blocks[0]
if _, ok := d.checks[block.Hash()]; ok {
delete(d.checks, block.Hash())
continue
}
}
// If the peer was previously banned and failed to deliver it's pack
// in a reasonable time frame, ignore it's message.
if peer := d.peers.Peer(blockPack.peerId); peer != nil {
// Deliver the received chunk of blocks
if err := d.queue.Deliver(blockPack.peerId, blockPack.blocks); err != nil {
if err == ErrInvalidChain {
// The hash chain is invalid (blocks are not ordered properly), abort
return err
}
// Peer did deliver, but some blocks were off, penalize
glog.V(logger.Debug).Infof("Failed delivery for peer %s: %v\n", blockPack.peerId, err)
peer.Demote()
break
}
if glog.V(logger.Debug) {
glog.Infof("Added %d blocks from: %s\n", len(blockPack.blocks), blockPack.peerId)
}
// Promote the peer and update it's idle state
peer.Promote()
peer.SetIdle()
}
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case <-ticker.C:
// Check for bad peers. Bad peers may indicate a peer not responding
// to a `getBlocks` message. A timeout of 5 seconds is set. Peers
// that badly or poorly behave are removed from the peer set (not banned).
// Bad peers are excluded from the available peer set and therefor won't be
// reused. XXX We could re-introduce peers after X time.
badPeers := d.queue.Expire(blockTTL)
for _, pid := range badPeers {
// XXX We could make use of a reputation system here ranking peers
// in their performance
// 1) Time for them to respond;
// 2) Measure their speed;
// 3) Amount and availability.
if peer := d.peers.Peer(pid); peer != nil {
peer.Demote()
}
}
// After removing bad peers make sure we actually have sufficient peer left to keep downloading
if d.peers.Len() == 0 {
return errNoPeers
}
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// If there are unrequested hashes left start fetching
// from the available peers.
if d.queue.Pending() > 0 {
// Throttle the download if block cache is full and waiting processing
if d.queue.Throttle() {
continue
}
// Send a download request to all idle peers, until throttled
idlePeers := d.peers.IdlePeers()
for _, peer := range idlePeers {
// Short circuit if throttling activated since above
if d.queue.Throttle() {
break
}
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// Get a possible chunk. If nil is returned no chunk
// could be returned due to no hashes available.
request := d.queue.Reserve(peer, maxBlockFetch)
if request == nil {
continue
}
// Fetch the chunk and check for error. If the peer was somehow
// already fetching a chunk due to a bug, it will be returned to
// the queue
if err := peer.Fetch(request); err != nil {
glog.V(logger.Error).Infof("Peer %s received double work\n", peer.id)
d.queue.Cancel(request)
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}
}
// Make sure that we have peers available for fetching. If all peers have been tried
// and all failed throw an error
if d.queue.InFlight() == 0 {
return errPeersUnavailable
}
} else if d.queue.InFlight() == 0 {
// When there are no more queue and no more in flight, We can
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// safely assume we're done. Another part of the process will check
// for parent errors and will re-request anything that's missing
break out
}
}
}
glog.V(logger.Detail).Infoln("Downloaded block(s) in", time.Since(start))
return nil
}
// DeliverBlocks injects a new batch of blocks received from a remote node.
// This is usually invoked through the BlocksMsg by the protocol handler.
func (d *Downloader) DeliverBlocks(id string, blocks []*types.Block) error {
// Make sure the downloader is active
if atomic.LoadInt32(&d.synchronising) == 0 {
return errNoSyncActive
}
// Deliver or abort if the sync is canceled while queuing
d.cancelLock.RLock()
cancel := d.cancelCh
d.cancelLock.RUnlock()
select {
case d.blockCh <- blockPack{id, blocks}:
return nil
case <-cancel:
return errNoSyncActive
}
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}
// DeliverHashes injects a new batch of hashes received from a remote node into
// the download schedule. This is usually invoked through the BlockHashesMsg by
// the protocol handler.
func (d *Downloader) DeliverHashes(id string, hashes []common.Hash) error {
// Make sure the downloader is active
if atomic.LoadInt32(&d.synchronising) == 0 {
return errNoSyncActive
}
// Deliver or abort if the sync is canceled while queuing
d.cancelLock.RLock()
cancel := d.cancelCh
d.cancelLock.RUnlock()
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select {
case d.hashCh <- hashPack{id, hashes}:
return nil
case <-cancel:
return errNoSyncActive
}
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}