上一节分析到Fetcher用于同步网络节点的新区块和新的交易数据，如果新区块和本地最新的区块相隔距离较远，说明本地区块数据太旧，Fetcher就不会同步这些区块。这时候就要借助Downloader来同步完整的区块数据。
一，启动Downloader
ProtocolManager初始化的时候会进行Downloader的初始化：
func New(mode SyncMode, stateDb ethdb.Database, mux *event.TypeMux, chain BlockChain, lightchain LightChain, dropPeer peerDropFn) *Downloader {
if lightchain == nil {
lightchain = chain
}
dl := &Downloader{
mode: mode,
stateDB: stateDb,
mux: mux,
queue: newQueue(),
peers: newPeerSet(),
rttEstimate: uint64(rttMaxEstimate),
rttConfidence: uint64(1000000),
blockchain: chain,
lightchain: lightchain,
dropPeer: dropPeer,
headerCh: make(chan dataPack, 1),
bodyCh: make(chan dataPack, 1),
receiptCh: make(chan dataPack, 1),
bodyWakeCh: make(chan bool, 1),
receiptWakeCh: make(chan bool, 1),
headerProcCh: make(chan []*types.Header, 1),
quitCh: make(chan struct{}),
stateCh: make(chan dataPack),
stateSyncStart: make(chan *stateSync),
trackStateReq: make(chan *stateReq),
}
go dl.qosTuner()
go dl.stateFetcher()
return dl
}
首先初始化Downloader对象的成员，然后启动dl.qosTuner() goroutine计算请求回路时间，启动dl.stateFetcher() goroutine 开启Downloader状态监控。
ProtocolManager收到新的区块消息广播或者有新的P2P网络节点加入的时候会调用ProtocolManager的 synchronise(peer *peer)方法，这时候会调用Downloader的Synchronise(peer.id, pHead, pTd, mode)方法。
Synchronise方法，重置d.queue和d.peers，清空d.bodyWakeCh, d.receiptWakeCh，d.headerCh, d.bodyCh, d.receiptCh，d.headerProcCh。调用d.syncWithPeer(p, hash, td)方法：
func (d *Downloader) syncWithPeer(p *peerConnection, hash common.Hash, td *big.Int) (err error) {
d.mux.Post(StartEvent{})
defer func() {
// reset on error
if err != nil {
d.mux.Post(FailedEvent{err})
} else {
d.mux.Post(DoneEvent{})
}
}()
if p.version < 62 {
return errTooOld
}
log.Debug("Synchronising with the network", "peer", p.id, "eth", p.version, "head", hash, "td", td, "mode", d.mode)
defer func(start time.Time) {
log.Debug("Synchronisation terminated", "elapsed", time.Since(start))
}(time.Now())
// Look up the sync boundaries: the common ancestor and the target block
latest, err := d.fetchHeight(p)
if err != nil {
return err
}
height := latest.Number.Uint64()
origin, err := d.findAncestor(p, height)
if err != nil {
return err
}
d.syncStatsLock.Lock()
if d.syncStatsChainHeight <= origin || d.syncStatsChainOrigin > origin {
d.syncStatsChainOrigin = origin
}
d.syncStatsChainHeight = height
d.syncStatsLock.Unlock()
// Ensure our origin point is below any fast sync pivot point
pivot := uint64(0)
if d.mode == FastSync {
if height <= uint64(fsMinFullBlocks) {
origin = 0
} else {
pivot = height - uint64(fsMinFullBlocks)
if pivot <= origin {
origin = pivot - 1
}
}
}
d.committed = 1
if d.mode == FastSync && pivot != 0 {
d.committed = 0
}
// Initiate the sync using a concurrent header and content retrieval algorithm
d.queue.Prepare(origin+1, d.mode)
if d.syncInitHook != nil {
d.syncInitHook(origin, height)
}
fetchers := []func() error{
func() error { return d.fetchHeaders(p, origin+1, pivot) }, // Headers are always retrieved
func() error { return d.fetchBodies(origin + 1) }, // Bodies are retrieved during normal and fast sync
func() error { return d.fetchReceipts(origin + 1) }, // Receipts are retrieved during fast sync
func() error { return d.processHeaders(origin+1, pivot, td) },
}
if d.mode == FastSync {
fetchers = append(fetchers, func() error { return d.processFastSyncContent(latest) })
} else if d.mode == FullSync {
fetchers = append(fetchers, d.processFullSyncContent)
}
return d.spawnSync(fetchers)
}
首先调用latest, err := d.fetchHeight(p)获取到peer节点最新的区块头,这个方法有点绕，我们来分析一下：
func (d *Downloader) fetchHeight(p *peerConnection) (*types.Header, error) {
p.log.Debug("Retrieving remote chain height")
// Request the advertised remote head block and wait for the response
head, _ := p.peer.Head()
go p.peer.RequestHeadersByHash(head, 1, 0, false)
ttl := d.requestTTL()
timeout := time.After(ttl)
for {
select {
case <-d.cancelCh:
return nil, errCancelBlockFetch
case packet := <-d.headerCh:
// Discard anything not from the origin peer
if packet.PeerId() != p.id {
log.Debug("Received headers from incorrect peer", "peer", packet.PeerId())
break
}
// Make sure the peer actually gave something valid
headers := packet.(*headerPack).headers
if len(headers) != 1 {
p.log.Debug("Multiple headers for single request", "headers", len(headers))
return nil, errBadPeer
}
head := headers[0]
p.log.Debug("Remote head header identified", "number", head.Number, "hash", head.Hash())
return head, nil
case <-timeout:
p.log.Debug("Waiting for head header timed out", "elapsed", ttl)
return nil, errTimeout
case <-d.bodyCh:
case <-d.receiptCh:
// Out of bounds delivery, ignore
}
}
}
1，调用peer.RequestHeadersByHash(head, 1, 0, false)，给网络节点发送一个GetBlockHeadersMsg的消息
2，然后阻塞住线程，直到收到d.headerCh或者timeout
3，本地节点会收到网络节点的BlockHeadersMsg的消息返回
4，调用downloader.DeliverHeaders(p.id, headers)
5，这时候会把p.id和headers打包发送给d.headerCh
6，这时候select收到d.headerCh，阻塞打开，并返回header内容
syncWithPeer() 方法接着调用 d.findAncestor(p, height)来获取本地节点和网络节点共同的祖先：
func (d *Downloader) findAncestor(p *peerConnection, height uint64) (uint64, error) {
// Figure out the valid ancestor range to prevent rewrite attacks
floor, ceil := int64(-1), d.lightchain.CurrentHeader().Number.Uint64()
if d.mode == FullSync {
ceil = d.blockchain.CurrentBlock().NumberU64()
} else if d.mode == FastSync {
ceil = d.blockchain.CurrentFastBlock().NumberU64()
}
if ceil >= MaxForkAncestry {
floor = int64(ceil - MaxForkAncestry)
}
p.log.Debug("Looking for common ancestor", "local", ceil, "remote", height)
// Request the topmost blocks to short circuit binary ancestor lookup
head := ceil
if head > height {
head = height
}
from := int64(head) - int64(MaxHeaderFetch)
if from < 0 {
from = 0
}
// Span out with 15 block gaps into the future to catch bad head reports
limit := 2 * MaxHeaderFetch / 16
count := 1 + int((int64(ceil)-from)/16)
if count > limit {
count = limit
}
go p.peer.RequestHeadersByNumber(uint64(from), count, 15, false)
// Wait for the remote response to the head fetch
number, hash := uint64(0), common.Hash{}
ttl := d.requestTTL()
timeout := time.After(ttl)
for finished := false; !finished; {
select {
case <-d.cancelCh:
return 0, errCancelHeaderFetch
case packet := <-d.headerCh:
// Discard anything not from the origin peer
if packet.PeerId() != p.id {
log.Debug("Received headers from incorrect peer", "peer", packet.PeerId())
break
}
// Make sure the peer actually gave something valid
headers := packet.(*headerPack).headers
if len(headers) == 0 {
p.log.Warn("Empty head header set")
return 0, errEmptyHeaderSet
}
// Make sure the peer's reply conforms to the request
for i := 0; i < len(headers); i++ {
if number := headers[i].Number.Int64(); number != from+int64(i)*16 {
p.log.Warn("Head headers broke chain ordering", "index", i, "requested", from+int64(i)*16, "received", number)
return 0, errInvalidChain
}
}
// Check if a common ancestor was found
finished = true
for i := len(headers) - 1; i >= 0; i-- {
// Skip any headers that underflow/overflow our requested set
if headers[i].Number.Int64() < from || headers[i].Number.Uint64() > ceil {
continue
}
// Otherwise check if we already know the header or not
if (d.mode == FullSync && d.blockchain.HasBlock(headers[i].Hash(), headers[i].Number.Uint64())) || (d.mode != FullSync && d.lightchain.HasHeader(headers[i].Hash(), headers[i].Number.Uint64())) {
number, hash = headers[i].Number.Uint64(), headers[i].Hash()
// If every header is known, even future ones, the peer straight out lied about its head
if number > height && i == limit-1 {
p.log.Warn("Lied about chain head", "reported", height, "found", number)
return 0, errStallingPeer
}
break
}
}
case <-timeout:
p.log.Debug("Waiting for head header timed out", "elapsed", ttl)
return 0, errTimeout
case <-d.bodyCh:
case <-d.receiptCh:
// Out of bounds delivery, ignore
}
}
// If the head fetch already found an ancestor, return
if !common.EmptyHash(hash) {
if int64(number) <= floor {
p.log.Warn("Ancestor below allowance", "number", number, "hash", hash, "allowance", floor)
return 0, errInvalidAncestor
}
p.log.Debug("Found common ancestor", "number", number, "hash", hash)
return number, nil
}
// Ancestor not found, we need to binary search over our chain
start, end := uint64(0), head
if floor > 0 {
start = uint64(floor)
}
for start+1 < end {
// Split our chain interval in two, and request the hash to cross check
check := (start + end) / 2
ttl := d.requestTTL()
timeout := time.After(ttl)
go p.peer.RequestHeadersByNumber(check, 1, 0, false)
// Wait until a reply arrives to this request
for arrived := false; !arrived; {
select {
case <-d.cancelCh:
return 0, errCancelHeaderFetch
case packer := <-d.headerCh:
// Discard anything not from the origin peer
if packer.PeerId() != p.id {
log.Debug("Received headers from incorrect peer", "peer", packer.PeerId())
break
}
// Make sure the peer actually gave something valid
headers := packer.(*headerPack).headers
if len(headers) != 1 {
p.log.Debug("Multiple headers for single request", "headers", len(headers))
return 0, errBadPeer
}
arrived = true
// Modify the search interval based on the response
if (d.mode == FullSync && !d.blockchain.HasBlock(headers[0].Hash(), headers[0].Number.Uint64())) || (d.mode != FullSync && !d.lightchain.HasHeader(headers[0].Hash(), headers[0].Number.Uint64())) {
end = check
break
}
header := d.lightchain.GetHeaderByHash(headers[0].Hash()) // Independent of sync mode, header surely exists
if header.Number.Uint64() != check {
p.log.Debug("Received non requested header", "number", header.Number, "hash", header.Hash(), "request", check)
return 0, errBadPeer
}
start = check
case <-timeout:
p.log.Debug("Waiting for search header timed out", "elapsed", ttl)
return 0, errTimeout
case <-d.bodyCh:
case <-d.receiptCh:
// Out of bounds delivery, ignore
}
}
}
// Ensure valid ancestry and return
if int64(start) <= floor {
p.log.Warn("Ancestor below allowance", "number", start, "hash", hash, "allowance", floor)
return 0, errInvalidAncestor
}
p.log.Debug("Found common ancestor", "number", start, "hash", hash)
return start, nil
}
1，调用peer.RequestHeadersByNumber(uint64(from), count, 15, false)，获取header。这里传入 count和 15，指从本地最高的header往前数192个区块的头，每16个区块取一个区块头。为了后面select收到d.headerCh时加以验证。
2，select收到了headers，遍历header，看是否在本地是否存在这个header，如果有，并且不为空，就说明找到共同的祖先，返回祖先number
3，如果没有找到共同的祖先，再重新从本地的区块链MaxForkAncestry起的一半的位置开始取区块头，一一验证是否跟网络节点返回的header一致，如果有就说明有共同的祖先，并返回，没有的话就返回0.
继续syncWithPeer()方法，找到同步的轴心的pivot，最后把要同步的数据和同步的方法传给d.spawnSync(fetchers)，并执行。d.spawnSync(fetchers)挨个执行传入的同步方法。
二，Downloader同步数据方法
fetchHeaders()，fetchBodies() , fetchReceipts()
func (d *Downloader) fetchHeaders(p *peerConnection, from uint64, pivot uint64) error {
p.log.Debug("Directing header downloads", "origin", from)
defer p.log.Debug("Header download terminated")
// Create a timeout timer, and the associated header fetcher
skeleton := true // Skeleton assembly phase or finishing up
request := time.Now() // time of the last skeleton fetch request
timeout := time.NewTimer(0) // timer to dump a non-responsive active peer
<-timeout.C // timeout channel should be initially empty
defer timeout.Stop()
var ttl time.Duration
getHeaders := func(from uint64) {
request = time.Now()
ttl = d.requestTTL()
timeout.Reset(ttl)
if skeleton {
p.log.Trace("Fetching skeleton headers", "count", MaxHeaderFetch, "from", from)
go p.peer.RequestHeadersByNumber(from+uint64(MaxHeaderFetch)-1, MaxSkeletonSize, MaxHeaderFetch-1, false)
} else {
p.log.Trace("Fetching full headers", "count", MaxHeaderFetch, "from", from)
go p.peer.RequestHeadersByNumber(from, MaxHeaderFetch, 0, false)
}
}
// Start pulling the header chain skeleton until all is done
getHeaders(from)
for {
select {
case <-d.cancelCh:
return errCancelHeaderFetch
case packet := <-d.headerCh:
// Make sure the active peer is giving us the skeleton headers
if packet.PeerId() != p.id {
log.Debug("Received skeleton from incorrect peer", "peer", packet.PeerId())
break
}
headerReqTimer.UpdateSince(request)
timeout.Stop()
// If the skeleton's finished, pull any remaining head headers directly from the origin
if packet.Items() == 0 && skeleton {
skeleton = false
getHeaders(from)
continue
}
// If no more headers are inbound, notify the content fetchers and return
if packet.Items() == 0 {
// Don't abort header fetches while the pivot is downloading
if atomic.LoadInt32(&d.committed) == 0 && pivot <= from {
p.log.Debug("No headers, waiting for pivot commit")
select {
case <-time.After(fsHeaderContCheck):
getHeaders(from)
continue
case <-d.cancelCh:
return errCancelHeaderFetch
}
}
// Pivot done (or not in fast sync) and no more headers, terminate the process
p.log.Debug("No more headers available")
select {
case d.headerProcCh <- nil:
return nil
case <-d.cancelCh:
return errCancelHeaderFetch
}
}
headers := packet.(*headerPack).headers
// If we received a skeleton batch, resolve internals concurrently
if skeleton {
filled, proced, err := d.fillHeaderSkeleton(from, headers)
if err != nil {
p.log.Debug("Skeleton chain invalid", "err", err)
return errInvalidChain
}
headers = filled[proced:]
from += uint64(proced)
}
// Insert all the new headers and fetch the next batch
if len(headers) > 0 {
p.log.Trace("Scheduling new headers", "count", len(headers), "from", from)
select {
case d.headerProcCh <- headers:
case <-d.cancelCh:
return errCancelHeaderFetch
}
from += uint64(len(headers))
}
getHeaders(from)
case <-timeout.C:
if d.dropPeer == nil {
// The dropPeer method is nil when `--copydb` is used for a local copy.
// Timeouts can occur if e.g. compaction hits at the wrong time, and can be ignored
p.log.Warn("Downloader wants to drop peer, but peerdrop-function is not set", "peer", p.id)
break
}
// Header retrieval timed out, consider the peer bad and drop
p.log.Debug("Header request timed out", "elapsed", ttl)
headerTimeoutMeter.Mark(1)
d.dropPeer(p.id)
// Finish the sync gracefully instead of dumping the gathered data though
for _, ch := range []chan bool{d.bodyWakeCh, d.receiptWakeCh} {
select {
case ch <- false:
case <-d.cancelCh:
}
}
select {
case d.headerProcCh <- nil:
case <-d.cancelCh:
}
return errBadPeer
}
}
}
1，getHeaders()调用peer.RequestHeadersByNumber()方法 获取网络节点的headers。
2，有两种获取方式，首先走的是skeleton方式，从查找到的共同祖先区块+192个区块位置开始，每隔192个区块，获取128个区块头。非skeleton方式，从共同祖先区块开始，获取192个区块头。
3，如果第一种方式获取不到区块头，则执行第二种获取方式，如果第二种方式还是没有获取到区块头的话，直接返回
4，如果是skeleton获取到的，调用fillHeaderSkeleton()方法加入到skeleton header chain
5，然后调整from值，再递归调用getHeaders()方法
func (d *Downloader) fillHeaderSkeleton(from uint64, skeleton []*types.Header) ([]*types.Header, int, error) {
log.Debug("Filling up skeleton", "from", from)
d.queue.ScheduleSkeleton(from, skeleton)
var (
deliver = func(packet dataPack) (int, error) {
pack := packet.(*headerPack)
return d.queue.DeliverHeaders(pack.peerId, pack.headers, d.headerProcCh)
}
expire = func() map[string]int { return d.queue.ExpireHeaders(d.requestTTL()) }
throttle = func() bool { return false }
reserve = func(p *peerConnection, count int) (*fetchRequest, bool, error) {
return d.queue.ReserveHeaders(p, count), false, nil
}
fetch = func(p *peerConnection, req *fetchRequest) error { return p.FetchHeaders(req.From, MaxHeaderFetch) }
capacity = func(p *peerConnection) int { return p.HeaderCapacity(d.requestRTT()) }
setIdle = func(p *peerConnection, accepted int) { p.SetHeadersIdle(accepted) }
)
err := d.fetchParts(errCancelHeaderFetch, d.headerCh, deliver, d.queue.headerContCh, expire,
d.queue.PendingHeaders, d.queue.InFlightHeaders, throttle, reserve,
nil, fetch, d.queue.CancelHeaders, capacity, d.peers.HeaderIdlePeers, setIdle, "headers")
log.Debug("Skeleton fill terminated", "err", err)
filled, proced := d.queue.RetrieveHeaders()
return filled, proced, err
}
a) 把skeleton的headers加入queue.ScheduleSkeleton调度队列，
b) 然后执行d.fetchParts()方法。
d.fetchParts()方法主要做了这几件事情
1，对收到的headers执行d.queue.DeliverHeaders()方法。
2，如果d.queue.PendingHeaders有pending的headers，调用d.peers.HeaderIdlePeers获取到idle的peers
3，调用d.queue.ReserveHeaders把pending的headers储备到idle的peers里面
4，用idle的peers调用p.FetchHeaders(req.From, MaxHeaderFetch)去获取headers
c) 最后执行d.queue.RetrieveHeaders()，获取到filled进去的headers
其他同步区块数据的方法d.fetchBodies() , d.fetchReceipts() 和fetchHeaders()流程类似，还更简单一些。
三，Downloader同步数据过程
d.processHeaders(), d.processFastSyncContent(latest) , d.processFullSyncContent
1，d.processHeaders() 方法
func (d *Downloader) processHeaders(origin uint64, pivot uint64, td *big.Int) error {
// Keep a count of uncertain headers to roll back
rollback := []*types.Header{}
defer func() {
if len(rollback) > 0 {
// Flatten the headers and roll them back
hashes := make([]common.Hash, len(rollback))
for i, header := range rollback {
hashes[i] = header.Hash()
}
lastHeader, lastFastBlock, lastBlock := d.lightchain.CurrentHeader().Number, common.Big0, common.Big0
if d.mode != LightSync {
lastFastBlock = d.blockchain.CurrentFastBlock().Number()
lastBlock = d.blockchain.CurrentBlock().Number()
}
d.lightchain.Rollback(hashes)
curFastBlock, curBlock := common.Big0, common.Big0
if d.mode != LightSync {
curFastBlock = d.blockchain.CurrentFastBlock().Number()
curBlock = d.blockchain.CurrentBlock().Number()
}
log.Warn("Rolled back headers", "count", len(hashes),
"header", fmt.Sprintf("%d->%d", lastHeader, d.lightchain.CurrentHeader().Number),
"fast", fmt.Sprintf("%d->%d", lastFastBlock, curFastBlock),
"block", fmt.Sprintf("%d->%d", lastBlock, curBlock))
}
}()
// Wait for batches of headers to process
gotHeaders := false
for {
select {
case <-d.cancelCh:
return errCancelHeaderProcessing
case headers := <-d.headerProcCh:
// Terminate header processing if we synced up
if len(headers) == 0 {
// Notify everyone that headers are fully processed
for _, ch := range []chan bool{d.bodyWakeCh, d.receiptWakeCh} {
select {
case ch <- false:
case <-d.cancelCh:
}
}
if d.mode != LightSync {
head := d.blockchain.CurrentBlock()
if !gotHeaders && td.Cmp(d.blockchain.GetTd(head.Hash(), head.NumberU64())) > 0 {
return errStallingPeer
}
}
if d.mode == FastSync || d.mode == LightSync {
head := d.lightchain.CurrentHeader()
if td.Cmp(d.lightchain.GetTd(head.Hash(), head.Number.Uint64())) > 0 {
return errStallingPeer
}
}
// Disable any rollback and return
rollback = nil
return nil
}
// Otherwise split the chunk of headers into batches and process them
gotHeaders = true
for len(headers) > 0 {
// Terminate if something failed in between processing chunks
select {
case <-d.cancelCh:
return errCancelHeaderProcessing
default:
}
// Select the next chunk of headers to import
limit := maxHeadersProcess
if limit > len(headers) {
limit = len(headers)
}
chunk := headers[:limit]
// In case of header only syncing, validate the chunk immediately
if d.mode == FastSync || d.mode == LightSync {
// Collect the yet unknown headers to mark them as uncertain
unknown := make([]*types.Header, 0, len(headers))
for _, header := range chunk {
if !d.lightchain.HasHeader(header.Hash(), header.Number.Uint64()) {
unknown = append(unknown, header)
}
}
// If we're importing pure headers, verify based on their recentness
frequency := fsHeaderCheckFrequency
if chunk[len(chunk)-1].Number.Uint64()+uint64(fsHeaderForceVerify) > pivot {
frequency = 1
}
if n, err := d.lightchain.InsertHeaderChain(chunk, frequency); err != nil {
// If some headers were inserted, add them too to the rollback list
if n > 0 {
rollback = append(rollback, chunk[:n]...)
}
log.Debug("Invalid header encountered", "number", chunk[n].Number, "hash", chunk[n].Hash(), "err", err)
return errInvalidChain
}
// All verifications passed, store newly found uncertain headers
rollback = append(rollback, unknown...)
if len(rollback) > fsHeaderSafetyNet {
rollback = append(rollback[:0], rollback[len(rollback)-fsHeaderSafetyNet:]...)
}
}
// Unless we're doing light chains, schedule the headers for associated content retrieval
if d.mode == FullSync || d.mode == FastSync {
// If we've reached the allowed number of pending headers, stall a bit
for d.queue.PendingBlocks() >= maxQueuedHeaders || d.queue.PendingReceipts() >= maxQueuedHeaders {
select {
case <-d.cancelCh:
return errCancelHeaderProcessing
case <-time.After(time.Second):
}
}
// Otherwise insert the headers for content retrieval
inserts := d.queue.Schedule(chunk, origin)
if len(inserts) != len(chunk) {
log.Debug("Stale headers")
return errBadPeer
}
}
headers = headers[limit:]
origin += uint64(limit)
}
// Signal the content downloaders of the availablility of new tasks
for _, ch := range []chan bool{d.bodyWakeCh, d.receiptWakeCh} {
select {
case ch <- true:
default:
}
}
}
}
}
1，收到从fetchHeaders()方法 中d.headerProcCh发送过来的headers
2，如果是FastSync或者LightSync模式，直接调用lightchain.InsertHeaderChain(chunk, frequency)插入到headerChain。
3，如果是FullSync或者FastSyn模式，调用d.queue.Schedule(chunk, origin)，放入downloader.queue来调度
2，processFastSyncContent() 方法
func (d *Downloader) processFastSyncContent(latest *types.Header) error {
// Start syncing state of the reported head block. This should get us most of
// the state of the pivot block.
stateSync := d.syncState(latest.Root)
defer stateSync.Cancel()
go func() {
if err := stateSync.Wait(); err != nil && err != errCancelStateFetch {
d.queue.Close() // wake up WaitResults
}
}()
// Figure out the ideal pivot block. Note, that this goalpost may move if the
// sync takes long enough for the chain head to move significantly.
pivot := uint64(0)
if height := latest.Number.Uint64(); height > uint64(fsMinFullBlocks) {
pivot = height - uint64(fsMinFullBlocks)
}
// To cater for moving pivot points, track the pivot block and subsequently
// accumulated download results separatey.
var (
oldPivot *fetchResult // Locked in pivot block, might change eventually
oldTail []*fetchResult // Downloaded content after the pivot
)
for {
// Wait for the next batch of downloaded data to be available, and if the pivot
// block became stale, move the goalpost
results := d.queue.Results(oldPivot == nil) // Block if we're not monitoring pivot staleness
if len(results) == 0 {
// If pivot sync is done, stop
if oldPivot == nil {
return stateSync.Cancel()
}
// If sync failed, stop
select {
case <-d.cancelCh:
return stateSync.Cancel()
default:
}
}
if d.chainInsertHook != nil {
d.chainInsertHook(results)
}
if oldPivot != nil {
results = append(append([]*fetchResult{oldPivot}, oldTail...), results...)
}
// Split around the pivot block and process the two sides via fast/full sync
if atomic.LoadInt32(&d.committed) == 0 {
latest = results[len(results)-1].Header
if height := latest.Number.Uint64(); height > pivot+2*uint64(fsMinFullBlocks) {
log.Warn("Pivot became stale, moving", "old", pivot, "new", height-uint64(fsMinFullBlocks))
pivot = height - uint64(fsMinFullBlocks)
}
}
P, beforeP, afterP := splitAroundPivot(pivot, results)
if err := d.commitFastSyncData(beforeP, stateSync); err != nil {
return err
}
if P != nil {
// If new pivot block found, cancel old state retrieval and restart
if oldPivot != P {
stateSync.Cancel()
stateSync = d.syncState(P.Header.Root)
defer stateSync.Cancel()
go func() {
if err := stateSync.Wait(); err != nil && err != errCancelStateFetch {
d.queue.Close() // wake up WaitResults
}
}()
oldPivot = P
}
// Wait for completion, occasionally checking for pivot staleness
select {
case <-stateSync.done:
if stateSync.err != nil {
return stateSync.err
}
if err := d.commitPivotBlock(P); err != nil {
return err
}
oldPivot = nil
case <-time.After(time.Second):
oldTail = afterP
continue
}
}
// Fast sync done, pivot commit done, full import
if err := d.importBlockResults(afterP); err != nil {
return err
}
}
}
1，同步最新的状态信息，的到最新的pivot值
2，不停的从d.queue 的result缓存中获取要处理的result数据
3，如果results数据为空，同时pivot也为空的时候，说明同步完成了，并返回
4，根据pivot值和results计算：pivot值对应的result，和pivot值之前的results和pivot值之后的results
5，调用commitFastSyncData把pivot值之前的results 插入本地区块链中，带上收据和交易数据
6，更新同步状态信息后，把pivot值对应的result 调用commitPivotBlock插入本地区块链中，并调用FastSyncCommitHead，记录这个pivot的hash值
7，调用d.importBlockResults把pivot值之后的results插入本地区块链中，这时候不插入区块交易收据数据。
3，processFullSyncContent()方法
func (d *Downloader) processFullSyncContent() error {
for {
results := d.queue.Results(true)
if len(results) == 0 {
return nil
}
if d.chainInsertHook != nil {
d.chainInsertHook(results)
}
if err := d.importBlockResults(results); err != nil {
return err
}
}
}
func (d *Downloader) importBlockResults(results []*fetchResult) error {
// Check for any early termination requests
if len(results) == 0 {
return nil
}
select {
case <-d.quitCh:
return errCancelContentProcessing
default:
}
// Retrieve the a batch of results to import
first, last := results[0].Header, results[len(results)-1].Header
log.Debug("Inserting downloaded chain", "items", len(results),
"firstnum", first.Number, "firsthash", first.Hash(),
"lastnum", last.Number, "lasthash", last.Hash(),
)
blocks := make([]*types.Block, len(results))
for i, result := range results {
blocks[i] = types.NewBlockWithHeader(result.Header).WithBody(result.Transactions, result.Uncles)
}
if index, err := d.blockchain.InsertChain(blocks); err != nil {
log.Debug("Downloaded item processing failed", "number", results[index].Header.Number, "hash", results[index].Header.Hash(), "err", err)
return errInvalidChain
}
return nil
}
processFullSyncContent方法比较简单：直接获取缓存的results数据，并插入到本地区块链中。
总结：
Downloader看似非常复杂，其实逻辑还好，如果没有light模式，读起来会好很多。其实light模式不太成熟，基本也没什么用。fast模式比full模式逻辑上面多了一个pivot，处理起来就复杂很多。但是fast模式在本地存储了收据数据，大大减少了区块交易验证的时间。如果要更清楚明白fast模式的原理，可以看看以太坊白皮书关于fast模式同步这一部分：https://github.com/ethereum/go-ethereum/pull/1889
