path: root/eth/downloader/downloader.go

package downloader

import (
    "errors"
    "fmt"
    "math"
    "math/big"
    "sync"
    "sync/atomic"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/core"
    "github.com/ethereum/go-ethereum/core/types"
    "github.com/ethereum/go-ethereum/logger"
    "github.com/ethereum/go-ethereum/logger/glog"
    "gopkg.in/fatih/set.v0"
)

const (
    maxBlockFetch    = 256              // 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")
    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")
)

type hashCheckFn func(common.Hash) bool
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 Downloader struct {
    mu         sync.RWMutex
    queue      *queue
    peers      peers
    activePeer string

    // Callbacks
    hasBlock    hashCheckFn
    insertChain chainInsertFn

    // Status
    fetchingHashes    int32
    downloadingBlocks int32
    processingBlocks  int32

    // Channels
    newPeerCh chan *peer
    hashCh    chan []common.Hash
    blockCh   chan blockPack
}

func New(hasBlock hashCheckFn, insertChain chainInsertFn) *Downloader {
    downloader := &Downloader{
        queue:       newqueue(),
        peers:       make(peers),
        hasBlock:    hasBlock,
        insertChain: insertChain,
        newPeerCh:   make(chan *peer, 1),
        hashCh:      make(chan []common.Hash, 1),
        blockCh:     make(chan blockPack, 1),
    }

    return downloader
}

func (d *Downloader) Stats() (current int, max int) {
    return d.queue.blockHashes.Size(), d.queue.fetchPool.Size() + d.queue.hashPool.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 unregister's 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 synchronising. If an empty string is given
// it will use the best peer possible and synchronise 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 unecessary switching.
    if d.isBusy() {
        return errBusy
    }

    // 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 d.process(p)
}

func (d *Downloader) getFromPeer(p *peer, hash common.Hash, ignoreInitial bool) error {
    d.activePeer = p.id

    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 {
        // handle error
        glog.V(logger.Debug).Infoln("Error fetching hashes:", err)
        // XXX Reset
        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. When done downloading, process blocks.
    if err := d.startFetchingBlocks(p); err != nil {
        glog.V(logger.Debug).Infoln("Error downloading blocks:", err)
        // XXX reset
        return err
    }

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

    return nil
}

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

    glog.V(logger.Debug).Infof("Downloading hashes (%x) from %s", hash.Bytes()[: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.hashPool.Add(hash)
    }
    // Get the first batch of hashes
    p.getHashes(hash)

    failureResponseTimer := time.NewTimer(hashTtl)

out:
    for {
        select {
        case hashes := <-d.hashCh:
            failureResponseTimer.Reset(hashTtl)

            var done bool // determines whether we're done fetching hashes (i.e. common hash found)
            hashSet := set.New()
            for _, hash := range hashes {
                if d.hasBlock(hash) {
                    glog.V(logger.Debug).Infof("Found common hash %x\n", hash[:4])

                    done = true
                    break
                }

                hashSet.Add(hash)
            }
            d.queue.put(hashSet)

            // Add hashes to the chunk set
            if len(hashes) == 0 { // Make sure the peer actually gave you something valid
                glog.V(logger.Debug).Infof("Peer (%s) responded with empty hash set\n", p.id)
                d.queue.reset()

                return errEmptyHashSet
            } else if !done { // Check if we're done fetching
                // Get the next set of hashes
                p.getHashes(hashes[len(hashes)-1])
            } else { // we're done
                break out
            }
        case <-failureResponseTimer.C:
            glog.V(logger.Debug).Infof("Peer (%s) didn't respond in time for hash request\n", p.id)
            // TODO instead of reseting the queue select a new peer from which we can start downloading hashes.
            // 1. check for peer's best hash to be included in the current hash set;
            // 2. resume from last point (hashes[len(hashes)-1]) using the newly selected peer.
            d.queue.reset()

            return errTimeout
        }
    }
    glog.V(logger.Detail).Infof("Downloaded hashes (%d) in %v\n", d.queue.hashPool.Size(), time.Since(start))

    return nil
}

func (d *Downloader) startFetchingBlocks(p *peer) error {
    glog.V(logger.Detail).Infoln("Downloading", d.queue.hashPool.Size(), "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 everynow 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 {
                d.peers[blockPack.peerId].promote()
                d.queue.deliver(blockPack.peerId, blockPack.blocks)
                d.peers.setState(blockPack.peerId, idleState)
            }
        case <-ticker.C:
            // If there are unrequested hashes left start fetching
            // from the available peers.
            if d.queue.hashPool.Size() > 0 {
                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.
                    chunk := d.queue.get(peer, maxBlockFetch)
                    if chunk == 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(chunk); err != nil {
                        // log for tracing
                        glog.V(logger.Debug).Infof("peer %s received double work (state = %v)\n", peer.id, peer.state)
                        d.queue.put(chunk.hashes)
                    }
                }

                // make sure that we have peers available for fetching. If all peers have been tried
                // and all failed throw an error
                if len(d.queue.fetching) == 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.hashPool.Size())
                }

            } else if len(d.queue.fetching) == 0 {
                // When there are no more queue and no more `fetching`. 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
            } else {
                // 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.
                d.queue.mu.Lock()
                var badPeers []string
                for pid, chunk := range d.queue.fetching {
                    if time.Since(chunk.itime) > blockTtl {
                        badPeers = append(badPeers, pid)
                        // remove peer as good peer from peer list
                        //d.UnregisterPeer(pid)
                    }
                }
                d.queue.mu.Unlock()

                for _, pid := range badPeers {
                    // A nil chunk is delivered so that the chunk's hashes are given
                    // back to the queue objects. When hashes are put back in the queue
                    // other (decent) peers can pick them up.
                    // 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.
                    d.queue.deliver(pid, nil)
                    if peer := d.peers[pid]; peer != nil {
                        peer.demote()
                        peer.reset()
                    }
                }

            }
        }
    }

    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)
    }

    d.hashCh <- hashes

    return nil
}

// Add an (unrequested) block to the downloader. This is usually done through the
// NewBlockMsg by the protocol handler.
// Adding blocks is done synchronously. if there are missing blocks, blocks will be
// fetched first. If the downloader is busy or if some other processed failed an error
// will be returned.
func (d *Downloader) AddBlock(id string, block *types.Block, td *big.Int) error {
    hash := block.Hash()

    if d.hasBlock(hash) {
        return fmt.Errorf("known block %x", hash.Bytes()[:4])
    }

    peer := d.peers.getPeer(id)
    // if the peer is in our healthy list of peers; update the td
    // and add the block. Otherwise just ignore it
    if peer == nil {
        glog.V(logger.Detail).Infof("Ignored block from bad peer %s\n", id)
        return errBadPeer
    }

    peer.mu.Lock()
    peer.recentHash = block.Hash()
    peer.mu.Unlock()
    peer.promote()

    glog.V(logger.Detail).Infoln("Inserting new block from:", id)
    d.queue.addBlock(id, block)

    // if neither go ahead to process
    if d.isBusy() {
        return errBusy
    }

    // Check if the parent of the received block is known.
    // If the block is not know, request it otherwise, request.
    phash := block.ParentHash()
    if !d.hasBlock(phash) {
        glog.V(logger.Detail).Infof("Missing parent %x, requires fetching\n", phash.Bytes()[:4])

        // Get the missing hashes from the peer (synchronously)
        err := d.getFromPeer(peer, peer.recentHash, true)
        if err != nil {
            return err
        }
    }

    return d.process(peer)
}

func (d *Downloader) process(peer *peer) error {
    atomic.StoreInt32(&d.processingBlocks, 1)
    defer atomic.StoreInt32(&d.processingBlocks, 0)

    // XXX this will move when optimised
    // Sort the blocks by number. This bit needs much improvement. Right now
    // it assumes full honesty form peers (i.e. it's not checked when the blocks
    // link). We should at least check whihc queue match. This code could move
    // to a seperate goroutine where it periodically checks for linked pieces.
    types.BlockBy(types.Number).Sort(d.queue.blocks)
    if len(d.queue.blocks) == 0 {
        return nil
    }

    var (
        blocks = d.queue.blocks
        err    error
    )
    glog.V(logger.Debug).Infof("Inserting chain with %d blocks (#%v - #%v)\n", len(blocks), blocks[0].Number(), blocks[len(blocks)-1].Number())

    // Loop untill we're out of blocks
    for len(blocks) != 0 {
        max := int(math.Min(float64(len(blocks)), 256))
        // TODO check for parent error. When there's a parent error we should stop
        // processing and start requesting the `block.hash` so that it's parent and
        // grandparents can be requested and queued.
        var i int
        i, err = d.insertChain(blocks[:max])
        if err != nil && core.IsParentErr(err) {
            // Ignore the missing blocks. Handler should take care of anything that's missing.
            glog.V(logger.Debug).Infof("Ignored block with missing parent (%d)\n", i)
            blocks = blocks[i:]

            continue
        } else if err != nil {
            // immediatly unregister the false peer but do not disconnect
            d.UnregisterPeer(d.activePeer)
            // Reset chain completely. This needs much, much improvement.
            // instead: check all blocks leading down to this block false block and remove it
            blocks = nil
            break
        }
        blocks = blocks[max:]
    }

    // This will allow the GC to remove the in memory blocks
    if len(blocks) == 0 {
        d.queue.blocks = nil
    } else {
        d.queue.blocks = blocks
    }
    return err
}

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) isProcessing() bool {
    return atomic.LoadInt32(&d.processingBlocks) == 1
}

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

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