path: root/eth/downloader/downloader.go

package downloader

import (
    "math"
    "math/big"
    "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"
    "gopkg.in/fatih/set.v0"
)

const maxBlockFetch = 256

type hashFetcherFn func(common.Hash) error
type blockFetcherFn func([]common.Hash) error
type hashCheckFn func(common.Hash) bool
type chainInsertFn func(types.Blocks) error
type hashIterFn func() (common.Hash, error)

// XXX make threadsafe!!!!
type peers map[string]*peer

func (p peers) get(state int) []*peer {
    var peers []*peer
    for _, peer := range p {
        peer.mu.RLock()
        if peer.state == state {
            peers = append(peers, peer)
        }
        peer.mu.RUnlock()
    }

    return peers
}

func (p peers) setState(id string, state int) {
    if peer, exist := p[id]; exist {
        peer.mu.Lock()
        defer peer.mu.Unlock()
        peer.state = state
    }
}

type Downloader struct {
    queue *queue

    hasBlock    hashCheckFn
    insertChain chainInsertFn

    mu    sync.RWMutex
    peers peers

    currentPeer *peer

    fetchingHashes    int32
    downloadingBlocks int32

    newPeerCh    chan *peer
    selectPeerCh chan *peer
    HashCh       chan []common.Hash
    blockCh      chan blockPack
    quit         chan struct{}
}

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

func New(hasBlock hashCheckFn, insertChain chainInsertFn) *Downloader {
    downloader := &Downloader{
        queue:        newqueue(),
        peers:        make(peers),
        hasBlock:     hasBlock,
        insertChain:  insertChain,
        newPeerCh:    make(chan *peer, 1),
        selectPeerCh: make(chan *peer, 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)

    // 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
}

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() {
    // Fields defined here so we can reduce the amount of locking
    // that needs to be done
    var highestTd = new(big.Int)
out:
    for {
        select {
        case newPeer := <-d.newPeerCh:
            // Check if TD of peer is higher than our current
            if newPeer.td.Cmp(highestTd) > 0 {
                glog.V(logger.Detail).Infoln("New peer with highest TD =", newPeer.td)

                highestTd.Set(newPeer.td)
                // select the peer for downloading
                d.selectPeerCh <- newPeer
            }
        case <-d.quit:
            break out
        }
    }
}

func (d *Downloader) update() {
out:
    for {
        select {
        case selectedPeer := <-d.selectPeerCh:
            // 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.isFetchingHashes() || d.isDownloadingBlocks()) {
                glog.V(logger.Detail).Infoln("Selected new peer", selectedPeer.id)
                // Start the fetcher. This will block the update entirely
                // interupts need to be send to the appropriate channels
                // respectively.
                if err := d.startFetchingHashes(selectedPeer); err != nil {
                    // handle error
                    glog.V(logger.Debug).Infoln("Error fetching hashes:", err)
                    // Reset
                    break
                }

                // 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(selectedPeer); err != nil {
                    glog.V(logger.Debug).Infoln("Error downloading blocks:", err)
                    // reset
                    break
                }

                // 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

                glog.V(logger.Debug).Infoln("Inserting chain with", len(blocks), "blocks")
                // Loop untill we're out of queue
                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.
                    d.insertChain(blocks[:max])
                    blocks = blocks[max:]
                }
            }
        case <-d.quit:
            break out
        }
    }
}

func (d *Downloader) startFetchingHashes(p *peer) error {
    glog.V(logger.Debug).Infoln("Downloading hashes")

    start := time.Now()

    // Get the first batch of hashes
    p.getHashes(p.recentHash)
    atomic.StoreInt32(&d.fetchingHashes, 1)

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)

                    done = true
                    break
                }

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

            // Add hashes to the chunk set
            // Check if we're done fetching
            if !done {
                //fmt.Println("re-fetch. current =", d.queue.hashPool.Size())
                // Get the next set of hashes
                p.getHashes(hashes[len(hashes)-1])
                atomic.StoreInt32(&d.fetchingHashes, 1)
            } else {
                atomic.StoreInt32(&d.fetchingHashes, 0)
                break out
            }
        }
    }
    glog.V(logger.Detail).Infoln("Download hashes: done. Took", time.Since(start))

    return nil
}

func (d *Downloader) DeliverBlocks(id string, block []*types.Block) {
    d.blockCh <- blockPack{id, block}
}

func (d *Downloader) startFetchingBlocks(p *peer) error {
    glog.V(logger.Detail).Infoln("Downloading", d.queue.hashPool.Size(), "blocks")
    atomic.StoreInt32(&d.downloadingBlocks, 1)

    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:
            //fmt.Println("get for", blockPack.peerId)

            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 {
                        //fmt.Println("fetching for", peer.id)
                        // 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)
                        }
                    }
                }
                atomic.StoreInt32(&d.downloadingBlocks, 1)
            } else if len(d.queue.fetching) == 0 {
                // Whene 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
                atomic.StoreInt32(&d.downloadingBlocks, 0)
                // Break out so that we can process with processing blocks
                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) > 5*time.Second {
                        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)
                }

            }
            //fmt.Println(d.queue.hashPool.Size(), len(d.queue.fetching))
        }
    }

    glog.V(logger.Detail).Infoln("Download blocks: done. Took", time.Since(start))

    return nil
}

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

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