path: root/eth/fetcher/fetcher.go

// Package fetcher contains the block announcement based synchonisation.
package fetcher

import (
    "errors"
    "fmt"
    "math/rand"
    "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/karalabe/cookiejar.v2/collections/prque"
)

const (
    arriveTimeout = 500 * time.Millisecond // Time allowance before an announced block is explicitly requested
    gatherSlack   = 100 * time.Millisecond // Interval used to collate almost-expired announces with fetches
    fetchTimeout  = 5 * time.Second        // Maximum alloted time to return an explicitly requested block
    maxUncleDist  = 7                      // Maximum allowed backward distance from the chain head
    maxQueueDist  = 32                     // Maximum allowed distance from the chain head to queue
    announceLimit = 256                    // Maximum number of unique blocks a peer may have announced
)

var (
    errTerminated = errors.New("terminated")
)

// blockRetrievalFn is a callback type for retrieving a block from the local chain.
type blockRetrievalFn func(common.Hash) *types.Block

// blockRequesterFn is a callback type for sending a block retrieval request.
type blockRequesterFn func([]common.Hash) error

// blockValidatorFn is a callback type to verify a block's header for fast propagation.
type blockValidatorFn func(block *types.Block, parent *types.Block) error

// blockBroadcasterFn is a callback type for broadcasting a block to connected peers.
type blockBroadcasterFn func(block *types.Block, propagate bool)

// chainHeightFn is a callback type to retrieve the current chain height.
type chainHeightFn func() uint64

// chainInsertFn is a callback type to insert a batch of blocks into the local chain.
type chainInsertFn func(types.Blocks) (int, error)

// peerDropFn is a callback type for dropping a peer detected as malicious.
type peerDropFn func(id string)

// announce is the hash notification of the availability of a new block in the
// network.
type announce struct {
    hash common.Hash // Hash of the block being announced
    time time.Time   // Timestamp of the announcement

    origin string           // Identifier of the peer originating the notification
    fetch  blockRequesterFn // Fetcher function to retrieve
}

// inject represents a schedules import operation.
type inject struct {
    origin string
    block  *types.Block
}

// Fetcher is responsible for accumulating block announcements from various peers
// and scheduling them for retrieval.
type Fetcher struct {
    // Various event channels
    notify chan *announce
    inject chan *inject
    filter chan chan []*types.Block
    done   chan common.Hash
    quit   chan struct{}

    // Announce states
    announces map[string]int              // Per peer announce counts to prevent memory exhaustion
    announced map[common.Hash][]*announce // Announced blocks, scheduled for fetching
    fetching  map[common.Hash]*announce   // Announced blocks, currently fetching

    // Block cache
    queue  *prque.Prque             // Queue containing the import operations (block number sorted)
    queued map[common.Hash]struct{} // Presence set of already queued blocks (to dedup imports)

    // Callbacks
    getBlock       blockRetrievalFn   // Retrieves a block from the local chain
    validateBlock  blockValidatorFn   // Checks if a block's headers have a valid proof of work
    broadcastBlock blockBroadcasterFn // Broadcasts a block to connected peers
    chainHeight    chainHeightFn      // Retrieves the current chain's height
    insertChain    chainInsertFn      // Injects a batch of blocks into the chain
    dropPeer       peerDropFn         // Drops a peer for misbehaving
}

// New creates a block fetcher to retrieve blocks based on hash announcements.
func New(getBlock blockRetrievalFn, validateBlock blockValidatorFn, broadcastBlock blockBroadcasterFn, chainHeight chainHeightFn, insertChain chainInsertFn, dropPeer peerDropFn) *Fetcher {
    return &Fetcher{
        notify:         make(chan *announce),
        inject:         make(chan *inject),
        filter:         make(chan chan []*types.Block),
        done:           make(chan common.Hash),
        quit:           make(chan struct{}),
        announces:      make(map[string]int),
        announced:      make(map[common.Hash][]*announce),
        fetching:       make(map[common.Hash]*announce),
        queue:          prque.New(),
        queued:         make(map[common.Hash]struct{}),
        getBlock:       getBlock,
        validateBlock:  validateBlock,
        broadcastBlock: broadcastBlock,
        chainHeight:    chainHeight,
        insertChain:    insertChain,
        dropPeer:       dropPeer,
    }
}

// Start boots up the announcement based synchoniser, accepting and processing
// hash notifications and block fetches until termination requested.
func (f *Fetcher) Start() {
    go f.loop()
}

// Stop terminates the announcement based synchroniser, canceling all pending
// operations.
func (f *Fetcher) Stop() {
    close(f.quit)
}

// Notify announces the fetcher of the potential availability of a new block in
// the network.
func (f *Fetcher) Notify(peer string, hash common.Hash, time time.Time, fetcher blockRequesterFn) error {
    block := &announce{
        hash:   hash,
        time:   time,
        origin: peer,
        fetch:  fetcher,
    }
    select {
    case f.notify <- block:
        return nil
    case <-f.quit:
        return errTerminated
    }
}

// Enqueue tries to fill gaps the the fetcher's future import queue.
func (f *Fetcher) Enqueue(peer string, block *types.Block) error {
    op := &inject{
        origin: peer,
        block:  block,
    }
    select {
    case f.inject <- op:
        return nil
    case <-f.quit:
        return errTerminated
    }
}

// Filter extracts all the blocks that were explicitly requested by the fetcher,
// returning those that should be handled differently.
func (f *Fetcher) Filter(blocks types.Blocks) types.Blocks {
    // Send the filter channel to the fetcher
    filter := make(chan []*types.Block)

    select {
    case f.filter <- filter:
    case <-f.quit:
        return nil
    }
    // Request the filtering of the block list
    select {
    case filter <- blocks:
    case <-f.quit:
        return nil
    }
    // Retrieve the blocks remaining after filtering
    select {
    case blocks := <-filter:
        return blocks
    case <-f.quit:
        return nil
    }
}

// Loop is the main fetcher loop, checking and processing various notification
// events.
func (f *Fetcher) loop() {
    // Iterate the block fetching until a quit is requested
    fetch := time.NewTimer(0)
    for {
        // Clean up any expired block fetches
        for hash, announce := range f.fetching {
            if time.Since(announce.time) > fetchTimeout {
                f.forgetBlock(hash)
            }
        }
        // Import any queued blocks that could potentially fit
        height := f.chainHeight()
        for !f.queue.Empty() {
            op := f.queue.PopItem().(*inject)
            number := op.block.NumberU64()

            // If too high up the chain or phase, continue later
            if number > height+1 {
                f.queue.Push(op, -float32(op.block.NumberU64()))
                break
            }
            // Otherwise if fresh and still unknown, try and import
            if number+maxUncleDist < height || f.getBlock(op.block.Hash()) != nil {
                continue
            }
            f.insert(op.origin, op.block)
        }
        // Wait for an outside event to occur
        select {
        case <-f.quit:
            // Fetcher terminating, abort all operations
            return

        case notification := <-f.notify:
            // A block was announced, make sure the peer isn't DOSing us
            count := f.announces[notification.origin] + 1
            if count > announceLimit {
                glog.V(logger.Debug).Infof("Peer %s: exceeded outstanding announces (%d)", notification.origin, announceLimit)
                break
            }
            // All is well, schedule the announce if block's not yet downloading
            if _, ok := f.fetching[notification.hash]; ok {
                break
            }
            f.announces[notification.origin] = count
            f.announced[notification.hash] = append(f.announced[notification.hash], notification)
            if len(f.announced) == 1 {
                f.reschedule(fetch)
            }

        case op := <-f.inject:
            // A direct block insertion was requested, try and fill any pending gaps
            f.enqueue(op.origin, op.block)

        case hash := <-f.done:
            // A pending import finished, remove all traces of the notification
            f.forgetBlock(hash)
            delete(f.queued, hash)

        case <-fetch.C:
            // At least one block's timer ran out, check for needing retrieval
            request := make(map[string][]common.Hash)

            for hash, announces := range f.announced {
                if time.Since(announces[0].time) > arriveTimeout-gatherSlack {
                    // Pick a random peer to retrieve from, reset all others
                    announce := announces[rand.Intn(len(announces))]
                    f.forgetBlock(hash)

                    // If the block still didn't arrive, queue for fetching
                    if f.getBlock(hash) == nil {
                        request[announce.origin] = append(request[announce.origin], hash)
                        f.fetching[hash] = announce
                    }
                }
            }
            // Send out all block requests
            for peer, hashes := range request {
                if glog.V(logger.Detail) && len(hashes) > 0 {
                    list := "["
                    for _, hash := range hashes {
                        list += fmt.Sprintf("%x, ", hash[:4])
                    }
                    list = list[:len(list)-2] + "]"

                    glog.V(logger.Detail).Infof("Peer %s: fetching %s", peer, list)
                }
                go f.fetching[hashes[0]].fetch(hashes)
            }
            // Schedule the next fetch if blocks are still pending
            f.reschedule(fetch)

        case filter := <-f.filter:
            // Blocks arrived, extract any explicit fetches, return all else
            var blocks types.Blocks
            select {
            case blocks = <-filter:
            case <-f.quit:
                return
            }

            explicit, download := []*types.Block{}, []*types.Block{}
            for _, block := range blocks {
                hash := block.Hash()

                // Filter explicitly requested blocks from hash announcements
                if _, ok := f.fetching[hash]; ok {
                    // Discard if already imported by other means
                    if f.getBlock(hash) == nil {
                        explicit = append(explicit, block)
                    } else {
                        f.forgetBlock(hash)
                    }
                } else {
                    download = append(download, block)
                }
            }

            select {
            case filter <- download:
            case <-f.quit:
                return
            }
            // Schedule the retrieved blocks for ordered import
            for _, block := range explicit {
                if announce := f.fetching[block.Hash()]; announce != nil {
                    f.enqueue(announce.origin, block)
                }
            }
        }
    }
}

// reschedule resets the specified fetch timer to the next announce timeout.
func (f *Fetcher) reschedule(fetch *time.Timer) {
    // Short circuit if no blocks are announced
    if len(f.announced) == 0 {
        return
    }
    // Otherwise find the earliest expiring announcement
    earliest := time.Now()
    for _, announces := range f.announced {
        if earliest.After(announces[0].time) {
            earliest = announces[0].time
        }
    }
    fetch.Reset(arriveTimeout - time.Since(earliest))
}

// enqueue schedules a new future import operation, if the block to be imported
// has not yet been seen.
func (f *Fetcher) enqueue(peer string, block *types.Block) {
    hash := block.Hash()

    // Discard any past or too distant blocks
    if dist := int64(block.NumberU64()) - int64(f.chainHeight()); dist < -maxUncleDist || dist > maxQueueDist {
        glog.V(logger.Debug).Infof("Peer %s: discarded block #%d [%x], distance %d", peer, block.NumberU64(), hash.Bytes()[:4], dist)
        return
    }
    // Schedule the block for future importing
    if _, ok := f.queued[hash]; !ok {
        f.queued[hash] = struct{}{}
        f.queue.Push(&inject{origin: peer, block: block}, -float32(block.NumberU64()))

        if glog.V(logger.Debug) {
            glog.Infof("Peer %s: queued block #%d [%x], total %v", peer, block.NumberU64(), hash.Bytes()[:4], f.queue.Size())
        }
    }
}

// insert spawns a new goroutine to run a block insertion into the chain. If the
// block's number is at the same height as the current import phase, if updates
// the phase states accordingly.
func (f *Fetcher) insert(peer string, block *types.Block) {
    hash := block.Hash()

    // Run the import on a new thread
    glog.V(logger.Debug).Infof("Peer %s: importing block #%d [%x]", peer, block.NumberU64(), hash[:4])
    go func() {
        defer func() { f.done <- hash }()

        // If the parent's unknown, abort insertion
        parent := f.getBlock(block.ParentHash())
        if parent == nil {
            return
        }
        // Quickly validate the header and propagate the block if it passes
        if err := f.validateBlock(block, parent); err != nil {
            glog.V(logger.Debug).Infof("Peer %s: block #%d [%x] verification failed: %v", peer, block.NumberU64(), hash[:4], err)
            f.dropPeer(peer)
            return
        }
        go f.broadcastBlock(block, true)

        // Run the actual import and log any issues
        if _, err := f.insertChain(types.Blocks{block}); err != nil {
            glog.V(logger.Warn).Infof("Peer %s: block #%d [%x] import failed: %v", peer, block.NumberU64(), hash[:4], err)
            return
        }
        // If import succeeded, broadcast the block
        go f.broadcastBlock(block, false)
    }()
}

// forgetBlock removes all traces of a block from the fetcher's internal state.
func (f *Fetcher) forgetBlock(hash common.Hash) {
    // Remove all pending announces and decrement DOS counters
    for _, announce := range f.announced[hash] {
        f.announces[announce.origin]--
        if f.announces[announce.origin] == 0 {
            delete(f.announces, announce.origin)
        }
    }
    delete(f.announced, hash)

    // Remove any pending fetches and decrement the DOS counters
    if announce := f.fetching[hash]; announce != nil {
        f.announces[announce.origin]--
        if f.announces[announce.origin] == 0 {
            delete(f.announces, announce.origin)
        }
        delete(f.fetching, hash)
    }
}