path: root/eth/sync.go

package eth

import (
    "math/rand"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/core/types"
    "github.com/ethereum/go-ethereum/logger"
    "github.com/ethereum/go-ethereum/logger/glog"
    "github.com/ethereum/go-ethereum/p2p/discover"
)

const (
    forceSyncCycle      = 10 * time.Second       // Time interval to force syncs, even if few peers are available
    notifyCheckCycle    = 100 * time.Millisecond // Time interval to allow hash notifies to fulfill before hard fetching
    notifyArriveTimeout = 500 * time.Millisecond // Time allowance before an announced block is explicitly requested
    notifyFetchTimeout  = 5 * time.Second        // Maximum alloted time to return an explicitly requested block
    minDesiredPeerCount = 5                      // Amount of peers desired to start syncing

    // This is the target size for the packs of transactions sent by txsyncLoop.
    // A pack can get larger than this if a single transactions exceeds this size.
    txsyncPackSize = 100 * 1024
)

// blockAnnounce is the hash notification of the availability of a new block in
// the network.
type blockAnnounce struct {
    hash common.Hash
    peer *peer
    time time.Time
}

type txsync struct {
    p   *peer
    txs []*types.Transaction
}

// syncTransactions starts sending all currently pending transactions to the given peer.
func (pm *ProtocolManager) syncTransactions(p *peer) {
    txs := pm.txpool.GetTransactions()
    if len(txs) == 0 {
        return
    }
    select {
    case pm.txsyncCh <- &txsync{p, txs}:
    case <-pm.quitSync:
    }
}

// txsyncLoop takes care of the initial transaction sync for each new
// connection. When a new peer appears, we relay all currently pending
// transactions. In order to minimise egress bandwidth usage, we send
// the transactions in small packs to one peer at a time.
func (pm *ProtocolManager) txsyncLoop() {
    var (
        pending = make(map[discover.NodeID]*txsync)
        sending = false               // whether a send is active
        pack    = new(txsync)         // the pack that is being sent
        done    = make(chan error, 1) // result of the send
    )

    // send starts a sending a pack of transactions from the sync.
    send := func(s *txsync) {
        // Fill pack with transactions up to the target size.
        size := common.StorageSize(0)
        pack.p = s.p
        pack.txs = pack.txs[:0]
        for i := 0; i < len(s.txs) && size < txsyncPackSize; i++ {
            pack.txs = append(pack.txs, s.txs[i])
            size += s.txs[i].Size()
        }
        // Remove the transactions that will be sent.
        s.txs = s.txs[:copy(s.txs, s.txs[len(pack.txs):])]
        if len(s.txs) == 0 {
            delete(pending, s.p.ID())
        }
        // Send the pack in the background.
        glog.V(logger.Detail).Infof("%v: sending %d transactions (%v)", s.p.Peer, len(pack.txs), size)
        sending = true
        go func() { done <- pack.p.sendTransactions(pack.txs) }()
    }

    // pick chooses the next pending sync.
    pick := func() *txsync {
        if len(pending) == 0 {
            return nil
        }
        n := rand.Intn(len(pending)) + 1
        for _, s := range pending {
            if n--; n == 0 {
                return s
            }
        }
        return nil
    }

    for {
        select {
        case s := <-pm.txsyncCh:
            pending[s.p.ID()] = s
            if !sending {
                send(s)
            }
        case err := <-done:
            sending = false
            // Stop tracking peers that cause send failures.
            if err != nil {
                glog.V(logger.Debug).Infof("%v: tx send failed: %v", pack.p.Peer, err)
                delete(pending, pack.p.ID())
            }
            // Schedule the next send.
            if s := pick(); s != nil {
                send(s)
            }
        case <-pm.quitSync:
            return
        }
    }
}

// fetcher is responsible for collecting hash notifications, and periodically
// checking all unknown ones and individually fetching them.
func (pm *ProtocolManager) fetcher() {
    announces := make(map[common.Hash][]*blockAnnounce)
    request := make(map[*peer][]common.Hash)
    pending := make(map[common.Hash]*blockAnnounce)
    cycle := time.Tick(notifyCheckCycle)
    done := make(chan common.Hash)

    // Iterate the block fetching until a quit is requested
    for {
        select {
        case notifications := <-pm.newHashCh:
            // A batch of hashes the notified, schedule them for retrieval
            glog.V(logger.Debug).Infof("Scheduling %d hash announcements from %s", len(notifications), notifications[0].peer.id)
            for _, announce := range notifications {
                // Skip if it's already pending fetch
                if _, ok := pending[announce.hash]; ok {
                    continue
                }
                // Otherwise queue up the peer as a potential source
                announces[announce.hash] = append(announces[announce.hash], announce)
            }

        case hash := <-done:
            // A pending import finished, remove all traces
            delete(pending, hash)

        case <-cycle:
            // Clean up any expired block fetches
            for hash, announce := range pending {
                if time.Since(announce.time) > notifyFetchTimeout {
                    delete(pending, hash)
                }
            }
            // Check if any notified blocks failed to arrive
            for hash, all := range announces {
                if time.Since(all[0].time) > notifyArriveTimeout {
                    announce := all[rand.Intn(len(all))]
                    if !pm.chainman.HasBlock(hash) {
                        request[announce.peer] = append(request[announce.peer], hash)
                        pending[hash] = announce
                    }
                    delete(announces, hash)
                }
            }
            if len(request) == 0 {
                break
            }
            // Send out all block requests
            for peer, hashes := range request {
                glog.V(logger.Debug).Infof("Explicitly fetching %d blocks from %s", len(hashes), peer.id)
                go peer.requestBlocks(hashes)
            }
            request = make(map[*peer][]common.Hash)

        case filter := <-pm.newBlockCh:
            // Blocks arrived, extract any explicit fetches, return all else
            var blocks types.Blocks
            select {
            case blocks = <-filter:
            case <-pm.quitSync:
                return
            }

            explicit, download := []*types.Block{}, []*types.Block{}
            for _, block := range blocks {
                hash := block.Hash()

                // Filter explicitly requested blocks from hash announcements
                if _, ok := pending[hash]; ok {
                    // Discard if already imported by other means
                    if !pm.chainman.HasBlock(hash) {
                        explicit = append(explicit, block)
                    } else {
                        delete(pending, hash)
                    }
                } else {
                    download = append(download, block)
                }
            }

            select {
            case filter <- download:
            case <-pm.quitSync:
                return
            }
            // Create a closure with the retrieved blocks and origin peers
            peers := make([]*peer, 0, len(explicit))
            blocks = make([]*types.Block, 0, len(explicit))
            for _, block := range explicit {
                hash := block.Hash()
                if announce := pending[hash]; announce != nil {
                    // Drop the block if it surely cannot fit
                    if pm.chainman.HasBlock(hash) || !pm.chainman.HasBlock(block.ParentHash()) {
                        // delete(pending, hash) // if we drop, it will re-fetch it, wait for timeout?
                        continue
                    }
                    // Otherwise accumulate for import
                    peers = append(peers, announce.peer)
                    blocks = append(blocks, block)
                }
            }
            // If any explicit fetches were replied to, import them
            if count := len(blocks); count > 0 {
                glog.V(logger.Debug).Infof("Importing %d explicitly fetched blocks", len(blocks))
                go func() {
                    // Make sure all hashes are cleaned up
                    for _, block := range blocks {
                        hash := block.Hash()
                        defer func() { done <- hash }()
                    }
                    // Try and actually import the blocks
                    for i := 0; i < len(blocks); i++ {
                        if err := pm.importBlock(peers[i], blocks[i], nil); err != nil {
                            glog.V(logger.Detail).Infof("Failed to import explicitly fetched block: %v", err)
                            return
                        }
                    }
                }()
            }

        case <-pm.quitSync:
            return
        }
    }
}

// syncer is responsible for periodically synchronising with the network, both
// downloading hashes and blocks as well as retrieving cached ones.
func (pm *ProtocolManager) syncer() {
    // Abort any pending syncs if we terminate
    defer pm.downloader.Cancel()

    forceSync := time.Tick(forceSyncCycle)
    for {
        select {
        case <-pm.newPeerCh:
            // Make sure we have peers to select from, then sync
            if pm.peers.Len() < minDesiredPeerCount {
                break
            }
            go pm.synchronise(pm.peers.BestPeer())

        case <-forceSync:
            // Force a sync even if not enough peers are present
            go pm.synchronise(pm.peers.BestPeer())

        case <-pm.quitSync:
            return
        }
    }
}

// synchronise tries to sync up our local block chain with a remote peer, both
// adding various sanity checks as well as wrapping it with various log entries.
func (pm *ProtocolManager) synchronise(peer *peer) {
    // Short circuit if no peers are available
    if peer == nil {
        return
    }
    // Make sure the peer's TD is higher than our own. If not drop.
    if peer.Td().Cmp(pm.chainman.Td()) <= 0 {
        return
    }
    // Otherwise try to sync with the downloader
    pm.downloader.Synchronise(peer.id, peer.Head())
}