259 lines
7.4 KiB
Go
259 lines
7.4 KiB
Go
// Package fetcher contains the block announcement based synchonisation.
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package fetcher
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import (
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"errors"
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"math/rand"
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"time"
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"github.com/ethereum/go-ethereum/common"
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"github.com/ethereum/go-ethereum/core/types"
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"github.com/ethereum/go-ethereum/logger"
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"github.com/ethereum/go-ethereum/logger/glog"
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)
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const (
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arriveTimeout = 500 * time.Millisecond // Time allowance before an announced block is explicitly requested
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fetchTimeout = 5 * time.Second // Maximum alloted time to return an explicitly requested block
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)
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var (
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errTerminated = errors.New("terminated")
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)
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// hashCheckFn is a callback type for verifying a hash's presence in the local chain.
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type hashCheckFn func(common.Hash) bool
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// blockRequesterFn is a callback type for sending a block retrieval request.
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type blockRequesterFn func([]common.Hash) error
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// blockImporterFn is a callback type for trying to inject a block into the local chain.
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type blockImporterFn func(peer string, block *types.Block) error
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// announce is the hash notification of the availability of a new block in the
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// network.
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type announce struct {
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hash common.Hash // Hash of the block being announced
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time time.Time // Timestamp of the announcement
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origin string // Identifier of the peer originating the notification
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fetch blockRequesterFn // Fetcher function to retrieve
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}
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// Fetcher is responsible for accumulating block announcements from various peers
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// and scheduling them for retrieval.
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type Fetcher struct {
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// Various event channels
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notify chan *announce
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filter chan chan []*types.Block
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quit chan struct{}
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// Callbacks
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hasBlock hashCheckFn // Checks if a block is present in the chain
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importBlock blockImporterFn // Injects a block from an origin peer into the chain
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}
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// New creates a block fetcher to retrieve blocks based on hash announcements.
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func New(hasBlock hashCheckFn, importBlock blockImporterFn) *Fetcher {
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return &Fetcher{
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notify: make(chan *announce),
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filter: make(chan chan []*types.Block),
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quit: make(chan struct{}),
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hasBlock: hasBlock,
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importBlock: importBlock,
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}
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}
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// Start boots up the announcement based synchoniser, accepting and processing
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// hash notifications and block fetches until termination requested.
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func (f *Fetcher) Start() {
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go f.loop()
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}
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// Stop terminates the announcement based synchroniser, canceling all pending
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// operations.
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func (f *Fetcher) Stop() {
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close(f.quit)
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}
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// Notify announces the fetcher of the potential availability of a new block in
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// the network.
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func (f *Fetcher) Notify(peer string, hash common.Hash, time time.Time, fetcher blockRequesterFn) error {
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block := &announce{
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hash: hash,
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time: time,
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origin: peer,
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fetch: fetcher,
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}
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select {
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case f.notify <- block:
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return nil
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case <-f.quit:
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return errTerminated
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}
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}
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// Filter extracts all the blocks that were explicitly requested by the fetcher,
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// returning those that should be handled differently.
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func (f *Fetcher) Filter(blocks types.Blocks) types.Blocks {
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// Send the filter channel to the fetcher
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filter := make(chan []*types.Block)
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select {
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case f.filter <- filter:
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case <-f.quit:
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return nil
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}
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// Request the filtering of the block list
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select {
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case filter <- blocks:
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case <-f.quit:
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return nil
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}
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// Retrieve the blocks remaining after filtering
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select {
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case blocks := <-filter:
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return blocks
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case <-f.quit:
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return nil
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}
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}
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// Loop is the main fetcher loop, checking and processing various notification
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// events.
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func (f *Fetcher) loop() {
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announced := make(map[common.Hash][]*announce)
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fetching := make(map[common.Hash]*announce)
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fetch := time.NewTimer(0)
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done := make(chan common.Hash)
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// Iterate the block fetching until a quit is requested
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for {
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// Clean up any expired block fetches
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for hash, announce := range fetching {
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if time.Since(announce.time) > fetchTimeout {
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delete(announced, hash)
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delete(fetching, hash)
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}
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}
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// Wait for an outside event to occur
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select {
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case <-f.quit:
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// Fetcher terminating, abort all operations
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return
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case notification := <-f.notify:
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// A block was announced, schedule if it's not yet downloading
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glog.V(logger.Debug).Infof("Peer %s: scheduling %x", notification.origin, notification.hash[:4])
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if _, ok := fetching[notification.hash]; ok {
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break
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}
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if len(announced) == 0 {
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fetch.Reset(arriveTimeout)
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}
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announced[notification.hash] = append(announced[notification.hash], notification)
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case hash := <-done:
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// A pending import finished, remove all traces of the notification
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delete(announced, hash)
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delete(fetching, hash)
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case <-fetch.C:
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// At least one block's timer ran out, check for needing retrieval
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request := make(map[string][]common.Hash)
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for hash, announces := range announced {
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if time.Since(announces[0].time) > arriveTimeout {
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announce := announces[rand.Intn(len(announces))]
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if !f.hasBlock(hash) {
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request[announce.origin] = append(request[announce.origin], hash)
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fetching[hash] = announce
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}
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delete(announced, hash)
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}
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}
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// Send out all block requests
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for peer, hashes := range request {
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glog.V(logger.Debug).Infof("Peer %s: explicitly fetching %d blocks", peer, len(hashes))
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go fetching[hashes[0]].fetch(hashes)
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}
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// Schedule the next fetch if blocks are still pending
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if len(announced) > 0 {
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nearest := time.Now()
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for _, announces := range announced {
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if nearest.Before(announces[0].time) {
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nearest = announces[0].time
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}
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}
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fetch.Reset(arriveTimeout + time.Since(nearest))
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}
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case filter := <-f.filter:
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// Blocks arrived, extract any explicit fetches, return all else
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var blocks types.Blocks
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select {
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case blocks = <-filter:
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case <-f.quit:
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return
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}
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explicit, download := []*types.Block{}, []*types.Block{}
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for _, block := range blocks {
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hash := block.Hash()
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// Filter explicitly requested blocks from hash announcements
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if _, ok := fetching[hash]; ok {
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// Discard if already imported by other means
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if !f.hasBlock(hash) {
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explicit = append(explicit, block)
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} else {
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delete(fetching, hash)
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}
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} else {
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download = append(download, block)
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}
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}
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select {
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case filter <- download:
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case <-f.quit:
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return
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}
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// Create a closure with the retrieved blocks and origin peers
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peers := make([]string, 0, len(explicit))
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blocks = make([]*types.Block, 0, len(explicit))
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for _, block := range explicit {
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hash := block.Hash()
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if announce := fetching[hash]; announce != nil {
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// Drop the block if it surely cannot fit
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if f.hasBlock(hash) || !f.hasBlock(block.ParentHash()) {
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// delete(fetching, hash) // if we drop, it will re-fetch it, wait for timeout?
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continue
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}
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// Otherwise accumulate for import
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peers = append(peers, announce.origin)
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blocks = append(blocks, block)
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}
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}
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// If any explicit fetches were replied to, import them
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if count := len(blocks); count > 0 {
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glog.V(logger.Debug).Infof("Importing %d explicitly fetched blocks", len(blocks))
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go func() {
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// Make sure all hashes are cleaned up
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for _, block := range blocks {
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hash := block.Hash()
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defer func() { done <- hash }()
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}
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// Try and actually import the blocks
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for i := 0; i < len(blocks); i++ {
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if err := f.importBlock(peers[i], blocks[i]); err != nil {
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glog.V(logger.Detail).Infof("Failed to import explicitly fetched block: %v", err)
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return
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}
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}
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}()
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}
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}
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}
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}
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