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
    minDesiredPeerCount = 5                // Amount of peers desired to start syncing
    peerCountTimeout    = 12 * time.Second // Amount of time it takes for the peer handler to ignore minDesiredPeerCount
    blockTtl            = 15 * time.Second // The amount of time it takes for a block request to time out
    hashTtl             = 20 * time.Second // The amount of time it takes for a hash request to time out
)

var (
    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) error
type hashIterFn func() (common.Hash, error)
type currentTdFn func() *big.Int

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

    // Callbacks
    hasBlock    hashCheckFn
    insertChain chainInsertFn
    currentTd   currentTdFn

    // Status
    fetchingHashes    int32
    downloadingBlocks int32
    processingBlocks  int32

    // Channels
    newPeerCh chan *peer
    syncCh    chan syncPack
    hashCh    chan []common.Hash
    blockCh   chan blockPack
    quit      chan struct{}
}

type blockPack struct {
    peerId string
    blocks []*types.Block
}

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

func New(hasBlock hashCheckFn, insertChain chainInsertFn, currentTd currentTdFn) *Downloader {
    downloader := &Downloader{
        queue:       newqueue(),
        peers:       make(peers),
        hasBlock:    hasBlock,
        insertChain: insertChain,
        currentTd:   currentTd,
        newPeerCh:   make(chan *peer, 1),
        syncCh:      make(chan syncPack, 1),
        hashCh:      make(chan []common.Hash, 1),
        blockCh:     make(chan blockPack, 1),
        quit:        make(chan struct{}),
    }
    go downloader.peerHandler()
    go downloader.update()

    return downloader
}

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

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

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

func (d *Downloader) peerHandler() {
    // itimer is used to determine when to start ignoring `minDesiredPeerCount`
    itimer := time.NewTimer(peerCountTimeout)
out:
    for {
        select {
        case <-d.newPeerCh:
            itimer.Stop()
            // Meet the `minDesiredPeerCount` before we select our best peer
            if len(d.peers) < minDesiredPeerCount {
                break
            }

            d.selectPeer(d.peers.bestPeer())
        case <-itimer.C:
            // The timer will make sure that the downloader keeps an active state
            // in which it attempts to always check the network for highest td peers
            // Either select the peer or restart the timer if no peers could
            // be selected.
            if peer := d.peers.bestPeer(); peer != nil {
                d.selectPeer(d.peers.bestPeer())
            } else {
                itimer.Reset(5 * time.Second)
            }
        case <-d.quit:
            break out
        }
    }
}

func (d *Downloader) selectPeer(p *peer) {
    // 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() {
        // selected peer must be better than our own
        // XXX we also check the peer's recent hash to make sure we
        // don't have it. Some peers report (i think) incorrect TD.
        if p.td.Cmp(d.currentTd()) <= 0 || d.hasBlock(p.recentHash) {
            return
        }

        glog.V(logger.Detail).Infoln("New peer with highest TD =", p.td)
        d.syncCh <- syncPack{p, p.recentHash, false}
    }

}

func (d *Downloader) update() {
out:
    for {
        select {
        case sync := <-d.syncCh:
            var peer *peer = sync.peer
            err := d.getFromPeer(peer, sync.hash, sync.ignoreInitial)
            if err != nil {
                break
            }

            d.process()
        case <-d.quit:
            break out
        }
    }
}

// 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)

    failureResponse := time.NewTimer(hashTtl)

out:
    for {
        select {
        case hashes := <-d.hashCh:
            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 <-failureResponse.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)

    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(availablePeers) > 0 && d.queue.fetchPool.Size() == 0 {
                    d.queue.reset()

                    return errPeersUnavailable
                }

            } 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()
                    }
                }

            }
        }
    }

    glog.V(logger.Detail).Infoln("Downloaded block(s) in", time.Since(start))

    return nil
}

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

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

    // 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()
}

// 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) process() 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)
    blocks := d.queue.blocks
    if len(blocks) == 0 {
        return nil
    }

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

    var err error
    // 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.
        err = d.insertChain(blocks[:max])
        if err != nil && core.IsParentErr(err) {
            glog.V(logger.Debug).Infoln("Aborting process due to missing parent. Fetching hashes")

            // TODO change this. This shite
            for i, block := range blocks[:max] {
                if !d.hasBlock(block.ParentHash()) {
                    d.syncCh <- syncPack{d.peers.bestPeer(), block.Hash(), true}
                    // remove processed blocks
                    blocks = blocks[i:]

                    break
                }
            }
            break
        } else if err != nil {
            // 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()
}