package downloader import ( "errors" "math/rand" "sync" "sync/atomic" "time" "github.com/ethereum/go-ethereum/common" "github.com/ethereum/go-ethereum/core/types" "github.com/ethereum/go-ethereum/event" "github.com/ethereum/go-ethereum/logger" "github.com/ethereum/go-ethereum/logger/glog" ) const ( MinHashFetch = 512 // Minimum amount of hashes to not consider a peer stalling MaxHashFetch = 2048 // Amount of hashes to be fetched per retrieval request MaxBlockFetch = 128 // Amount of blocks to be fetched per retrieval request 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 ) 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("peers TD is too low") ErrBusy = errors.New("busy") errUnknownPeer = errors.New("peer is unknown or unhealthy") ErrBadPeer = errors.New("action from bad peer ignored") ErrStallingPeer = errors.New("peer is stalling") 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") ) type hashCheckFn func(common.Hash) bool type getBlockFn func(common.Hash) *types.Block type chainInsertFn func(types.Blocks) (int, error) type hashIterFn func() (common.Hash, error) type blockPack struct { peerId string blocks []*types.Block } type hashPack struct { peerId string hashes []common.Hash } type crossCheck struct { expire time.Time parent common.Hash } 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]*crossCheck // Pending cross checks to verify a hash chain // Callbacks hasBlock hashCheckFn getBlock getBlockFn // 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 } // Block is an origin-tagged blockchain block. type Block struct { RawBlock *types.Block OriginPeer string } func New(mux *event.TypeMux, hasBlock hashCheckFn, getBlock getBlockFn) *Downloader { 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), } return downloader } func (d *Downloader) Stats() (current int, max int) { return d.queue.Size() } // 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 } 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 } // 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]*crossCheck) // 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() []*Block { 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 } glog.V(logger.Debug).Infoln("Synchronization completed") return nil } // 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) start := time.Now() // Add the hash to the queue first, and start hash retrieval d.queue.Insert([]common.Hash{h}) p.getHashes(h) 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; { 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) // 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] 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 { // Check that the peer is not stalling the sync if len(inserts) < MinHashFetch { return ErrStallingPeer } // 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 cross := rand.Intn(len(inserts) - 1) origin, parent := inserts[cross], inserts[cross+1] glog.V(logger.Detail).Infof("Cross checking (%s) with %x/%x", active.id, origin, parent) d.checks[origin] = &crossCheck{ expire: time.Now().Add(blockTTL), parent: parent, } active.getBlocks([]common.Hash{origin}) // Also fetch a fresh active.getHashes(head) continue } // 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 check, ok := d.checks[block.Hash()]; ok { if block.ParentHash() != check.parent { 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, check := range d.checks { if time.Now().After(check.expire) { 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) } } glog.V(logger.Debug).Infof("Downloaded hashes (%d) in %v\n", d.queue.Pending(), time.Since(start)) 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)") start := time.Now() // default ticker for re-fetching blocks every now and then ticker := time.NewTicker(20 * time.Millisecond) out: for { select { case <-d.cancelCh: return errCancelBlockFetch 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) && len(blockPack.blocks) > 0 { 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() } 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 } // 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 } // 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) } } // 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 // 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 } } // 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() select { case d.hashCh <- hashPack{id, hashes}: return nil case <-cancel: return errNoSyncActive } }