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")
)

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 syncPack struct {
    peer          *peer
    hash          common.Hash
    ignoreInitial bool
}

type hashPack struct {
    peerId string
    hashes []common.Hash
}

type Downloader struct {
    mu         sync.RWMutex
    queue      *queue
    peers      peers
    activePeer string

    // Callbacks
    hasBlock hashCheckFn
    getBlock getBlockFn

    // Status
    fetchingHashes    int32
    downloadingBlocks int32

    // Channels
    newPeerCh chan *peer
    hashCh    chan hashPack
    blockCh   chan blockPack
}

func New(hasBlock hashCheckFn, getBlock getBlockFn) *Downloader {
    downloader := &Downloader{
        queue:     newQueue(),
        peers:     make(peers),
        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()
}

func (d *Downloader) RegisterPeer(id string, hash common.Hash, getHashes hashFetcherFn, getBlocks blockFetcherFn) error {
    d.mu.Lock()
    defer d.mu.Unlock()

    glog.V(logger.Detail).Infoln("Register peer", id)

    // Create a new peer and add it to the list of known peers
    peer := newPeer(id, hash, getHashes, getBlocks)
    // add peer to our peer set
    d.peers[id] = peer
    // broadcast new peer

    return nil
}

// UnregisterPeer unregisters a peer. This will prevent any action from the specified peer.
func (d *Downloader) UnregisterPeer(id string) {
    d.mu.Lock()
    defer d.mu.Unlock()

    glog.V(logger.Detail).Infoln("Unregister peer", id)

    delete(d.peers, id)
}

// SynchroniseWithPeer will select the peer and use it for synchronizing. 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 it's doing neither. Once done we can restart the
    // downloading process if the TD is higher. For now just get on
    // with whatever is going on. This prevents unnecessary switching.
    if d.isBusy() {
        return errBusy
    }

    // When a synchronization attempt is made while the queue still
    // contains items we abort the sync attempt
    if done, pend := d.queue.Size(); done+pend > 0 {
        return errPendingQueue
    }

    // Fetch the peer using the id or throw an error if the peer couldn't be found
    p := d.peers[id]
    if p == nil {
        return errUnknownPeer
    }

    // Get the hash from the peer and initiate the downloading progress.
    err := d.getFromPeer(p, hash, false)
    if err != nil {
        return err
    }

    return nil
}

// Done lets the downloader know that whatever previous hashes were taken
// are processed. If the block count reaches zero and done is called
// we reset the queue for the next batch of incoming hashes and blocks.
func (d *Downloader) Done() {
    d.queue.Done()
}

// 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)
}

func (d *Downloader) getFromPeer(p *peer, hash common.Hash, ignoreInitial bool) (err error) {
    d.activePeer = p.id
    defer func() {
        // reset on error
        if err != nil {
            d.queue.Reset()
        }
    }()

    glog.V(logger.Detail).Infoln("Synchronising with the network using:", p.id)
    // Start the fetcher. This will block the update entirely
    // interupts need to be send to the appropriate channels
    // respectively.
    if err = d.startFetchingHashes(p, hash, ignoreInitial); err != nil {
        return err
    }

    // Start fetching blocks in paralel. The strategy is simple
    // take any available peers, seserve a chunk for each peer available,
    // let the peer deliver the chunkn and periodically check if a peer
    // has timedout.
    if err = d.startFetchingBlocks(p); err != nil {
        return err
    }

    glog.V(logger.Detail).Infoln("Sync completed")

    return nil
}

// XXX Make synchronous
func (d *Downloader) startFetchingHashes(p *peer, h common.Hash, ignoreInitial bool) error {
    atomic.StoreInt32(&d.fetchingHashes, 1)
    defer atomic.StoreInt32(&d.fetchingHashes, 0)

    if d.queue.Has(h) { // TODO: Is this possible? Shouldn't queue be empty for startFetchingHashes to be even called?
        return errAlreadyInPool
    }

    glog.V(logger.Debug).Infof("Downloading hashes (%x) from %s", h[:4], p.id)

    start := time.Now()

    // We ignore the initial hash in some cases (e.g. we received a block without it's parent)
    // In such circumstances we don't need to download the block so don't add it to the queue.
    if !ignoreInitial {
        // 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 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 id, peer := range d.peers {
                if d.queue.Has(peer.recentHash) && !attemptedPeers[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.Detail).Infof("Downloaded hashes (%d) in %v\n", d.queue.Pending(), time.Since(start))

    return nil
}

func (d *Downloader) startFetchingBlocks(p *peer) error {
    glog.V(logger.Detail).Infoln("Downloading", d.queue.Pending(), "block(s)")

    atomic.StoreInt32(&d.downloadingBlocks, 1)
    defer atomic.StoreInt32(&d.downloadingBlocks, 0)
    // Defer the peer reset. This will empty the peer requested set
    // and makes sure there are no lingering peers with an incorrect
    // state
    defer d.peers.reset()

    start := time.Now()

    // default ticker for re-fetching blocks every now and then
    ticker := time.NewTicker(20 * time.Millisecond)
out:
    for {
        select {
        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 d.peers[blockPack.peerId] != nil {
                err := d.queue.Deliver(blockPack.peerId, blockPack.blocks)
                if err != nil {
                    glog.V(logger.Debug).Infof("deliver failed for peer %s: %v\n", blockPack.peerId, err)
                    // FIXME d.UnregisterPeer(blockPack.peerId)
                    break
                }

                if glog.V(logger.Debug) {
                    glog.Infof("adding %d blocks from: %s\n", len(blockPack.blocks), blockPack.peerId)
                }
                d.peers[blockPack.peerId].promote()
                d.peers.setState(blockPack.peerId, idleState)
            }
        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[pid]; peer != nil {
                    peer.demote()
                    peer.reset()
                }
            }
            // After removing bad peers make sure we actually have sufficient peer left to keep downloading
            if len(d.peers) == 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
                }

                availablePeers := d.peers.get(idleState)
                for _, peer := range availablePeers {
                    // 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
                    }
                    // XXX make fetch blocking.
                    // 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 {
                        // log for tracing
                        glog.V(logger.Debug).Infof("peer %s received double work (state = %v)\n", peer.id, peer.state)
                        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 avaialable = %d. total peers = %d. hashes needed = %d", errPeersUnavailable, len(availablePeers), len(d.peers), 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
}

// Deliver a chunk to the downloader. This is usually done through the BlocksMsg by
// the protocol handler.
func (d *Downloader) DeliverChunk(id string, blocks []*types.Block) {
    d.blockCh <- blockPack{id, blocks}
}

func (d *Downloader) AddHashes(id string, hashes []common.Hash) error {
    // make sure that the hashes that are being added are actually from the peer
    // that's the current active peer. hashes that have been received from other
    // peers are dropped and ignored.
    if d.activePeer != id {
        return fmt.Errorf("received hashes from %s while active peer is %s", id, d.activePeer)
    }

    if glog.V(logger.Detail) && len(hashes) != 0 {
        from, to := hashes[0], hashes[len(hashes)-1]
        glog.Infof("adding %d (T=%d) hashes [ %x / %x ] from: %s\n", len(hashes), d.queue.Pending(), from[:4], to[:4], id)
    }

    d.hashCh <- hashPack{id, hashes}

    return nil
}

func (d *Downloader) isFetchingHashes() bool {
    return atomic.LoadInt32(&d.fetchingHashes) == 1
}

func (d *Downloader) isDownloadingBlocks() bool {
    return atomic.LoadInt32(&d.downloadingBlocks) == 1
}

func (d *Downloader) isBusy() bool {
    return d.isFetchingHashes() || d.isDownloadingBlocks()
}

func (d *Downloader) IsBusy() bool {
    return d.isBusy()
}