path: root/eth/downloader/downloader.go

package downloader

import (
    "errors"
    "fmt"
    "sync"
    "sync/atomic"
    "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"
)

const (
    maxBlockFetch    = 128              // Amount of max blocks to be fetched per chunk
    peerCountTimeout = 12 * time.Second // Amount of time it takes for the peer handler to ignore minDesiredPeerCount
    hashTtl          = 20 * time.Second // The amount of time it takes for a hash request to time out
)

var (
    minDesiredPeerCount = 5                // Amount of peers desired to start syncing
    blockTtl            = 20 * time.Second // The amount of time it takes for a block request to time out

    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")
    errBlockNumberOverflow = errors.New("received block which overflows")
    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 Downloader struct {
    mu    sync.RWMutex
    queue *queue
    peers *peerSet

    // Callbacks
    hasBlock hashCheckFn
    getBlock getBlockFn

    // Status
    synchronising 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
}

func New(hasBlock hashCheckFn, getBlock getBlockFn) *Downloader {
    downloader := &Downloader{
        queue:     newQueue(),
        peers:     newPeerSet(),
        hasBlock:  hasBlock,
        getBlock:  getBlock,
        newPeerCh: make(chan *peer, 1),
        hashCh:    make(chan hashPack, 1),
        blockCh:   make(chan blockPack, 1),
    }
    // Set the initial downloader state as canceled (sanity check)
    downloader.cancelCh = make(chan struct{})
    close(downloader.cancelCh)

    return downloader
}

func (d *Downloader) Stats() (current int, max int) {
    return d.queue.Size()
}

// 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)

    // 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()

    // 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 blockTaker handler
// it's possible it yields no blocks
func (d *Downloader) TakeBlocks() types.Blocks {
    // Check that there are blocks available and its parents are known
    head := d.queue.GetHeadBlock()
    if head == nil || !d.hasBlock(head.ParentHash()) {
        return nil
    }
    // Retrieve a full batch of blocks
    return d.queue.TakeBlocks(head)
}

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) {
    defer func() {
        // reset on error
        if err != nil {
            d.queue.Reset()
        }
    }()

    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.RLock()
    close(d.cancelCh)
    d.cancelLock.RUnlock()

    // 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
    d.queue.Insert([]common.Hash{h})

    // Get the first batch of hashes
    p.getHashes(h)

    var (
        failureResponseTimer = time.NewTimer(hashTtl)
        attemptedPeers       = make(map[string]bool) // attempted peers will help with retries
        activePeer           = p                     // active peer will help determine the current active peer
        hash                 common.Hash             // common and last hash
    )
    attemptedPeers[p.id] = true

out:
    for {
        select {
        case <-d.cancelCh:
            return errCancelHashFetch
        case hashPack := <-d.hashCh:
            // Make sure the active peer is giving us the hashes
            if hashPack.peerId != activePeer.id {
                glog.V(logger.Debug).Infof("Received hashes from incorrect peer(%s)\n", hashPack.peerId)
                break
            }

            failureResponseTimer.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", activePeer.id)
                d.queue.Reset()

                return errEmptyHashSet
            }
            // Determine if we're done fetching hashes (queue up all pending), and continue if not done
            done, index := false, 0
            for index, hash = range hashPack.hashes {
                if d.hasBlock(hash) || d.queue.GetBlock(hash) != nil {
                    glog.V(logger.Debug).Infof("Found common hash %x\n", hash[:4])
                    hashPack.hashes = hashPack.hashes[:index]
                    done = true
                    break
                }
            }
            d.queue.Insert(hashPack.hashes)

            if !done {
                activePeer.getHashes(hash)
                continue
            }
            // We're done, allocate the download cache and proceed pulling the blocks
            offset := 0
            if block := d.getBlock(hash); block != nil {
                offset = int(block.NumberU64() + 1)
            }
            d.queue.Alloc(offset)
            break out

        case <-failureResponseTimer.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) && !attemptedPeers[p.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 || (hash == common.Hash{}) {
                d.queue.Reset()
                return ErrTimeout
            }
            // set p to the active peer. this will invalidate any hashes that may be returned
            // by our previous (delayed) peer.
            activePeer = p
            p.getHashes(hash)
            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:
            // 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, but drop the peer if invalid
                if err := d.queue.Deliver(blockPack.peerId, blockPack.blocks); err != nil {
                    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()
            }
        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 {
                d.queue.Reset()
                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 {
                    d.queue.Reset()

                    return fmt.Errorf("%v peers available = %d. total peers = %d. hashes needed = %d", errPeersUnavailable, len(idlePeers), d.peers.Len(), d.queue.Pending())
                }

            } 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
    }
}