摘要:当前代码是以太坊,如果版本不同,代码上可能存在差异。非产生区块节点的策略图,如图,黄色节点将区块传播给青色节点至此,可以看出以太坊采用以石击水的方式,像水纹一样,层层扩散新产生的区块。
前言
这篇文章从区块传播策略入手,介绍新区块是如何传播到远端节点,以及新区块加入到远端节点本地链的过程,同时会介绍fetcher模块,fetcher的功能是处理Peer通知的区块信息。在介绍过程中,还会涉及到p2p,eth等模块,不会专门介绍,而是专注区块的传播和加入区块链的过程。
当前代码是以太坊Release 1.8,如果版本不同,代码上可能存在差异。
总体过程和传播策略本节从宏观角度介绍,节点产生区块后,为了传播给远端节点做了啥,远端节点收到区块后又做了什么,每个节点都连接了很多Peer,它传播的策略是什么样的?
总体流程和策略可以总结为,传播给远端Peer节点,Peer验证区块无误后,加入到本地区块链,继续传播新区块信息。具体过程如下。
先看总体过程。产生区块后,miner模块会发布一个事件NewMinedBlockEvent,订阅事件的协程收到事件后,就会把新区块的消息,广播给它所有的peer,peer收到消息后,会交给自己的fetcher模块处理,fetcher进行基本的验证后,区块没问题,发现这个区块就是本地链需要的下一个区块,则交给blockChain进一步进行完整的验证,这个过程会执行区块所有的交易,无误后把区块加入到本地链,写入数据库,这个过程就是下面的流程图,图1。
总体流程图,能看到有个分叉,是因为节点传播新区块是有策略的。它的传播策略为:
假如节点连接了N个Peer,它只向Peer列表的sqrt(N)个Peer广播完整的区块消息。
向所有的Peer广播只包含区块Hash的消息。
策略图的效果如图2,红色节点将区块传播给黄色节点:
收到区块Hash的节点,需要从发送给它消息的Peer那里获取对应的完整区块,获取区块后就会按照图1的流程,加入到fetcher队列,最终插入本地区块链后,将区块的Hash值广播给和它相连,但还不知道这个区块的Peer。非产生区块节点的策略图,如图3,黄色节点将区块Hash传播给青色节点:
至此,可以看出以太坊采用以石击水的方式,像水纹一样,层层扩散新产生的区块。
Fetcher模块是干啥的fetcher模块的功能,就是收集其他Peer通知它的区块信息:1)完整的区块2)区块Hash消息。根据通知的消息,获取完整的区块,然后传递给eth模块把区块插入区块链。
如果是完整区块,就可以传递给eth插入区块,如果只有区块Hash,则需要从其他的Peer获取此完整的区块,然后再传递给eth插入区块。
源码解读本节介绍区块传播和处理的细节东西,方式仍然是先用图解释流程,再是代码流程。
产块节点的传播新区块节点产生区块后,广播的流程可以表示为图4:
发布事件
事件处理函数选择要广播完整的Peer,然后将区块加入到它们的队列
事件处理函数把区块Hash添加到所有Peer的另外一个通知队列
每个Peer的广播处理函数,会遍历它的待广播区块队列和通知队列,把数据封装成消息,调用P2P接口发送出去
再看下代码上的细节。
worker.wait()函数发布事件NewMinedBlockEvent。
ProtocolManager.minedBroadcastLoop()是事件处理函数。它调用了2次pm.BroadcastBlock()。
// Mined broadcast loop func (pm *ProtocolManager) minedBroadcastLoop() { // automatically stops if unsubscribe for obj := range pm.minedBlockSub.Chan() { switch ev := obj.Data.(type) { case core.NewMinedBlockEvent: pm.BroadcastBlock(ev.Block, true) // First propagate block to peers pm.BroadcastBlock(ev.Block, false) // Only then announce to the rest } } }
pm.BroadcastBlock()的入参propagate为真时,向部分Peer广播完整的区块,调用peer.AsyncSendNewBlock(),否则向所有Peer广播区块头,调用peer.AsyncSendNewBlockHash(),这2个函数就是把数据放入队列,此处不再放代码。
// BroadcastBlock will either propagate a block to a subset of it"s peers, or // will only announce it"s availability (depending what"s requested). func (pm *ProtocolManager) BroadcastBlock(block *types.Block, propagate bool) { hash := block.Hash() peers := pm.peers.PeersWithoutBlock(hash) // If propagation is requested, send to a subset of the peer // 这种情况,要把区块广播给部分peer if propagate { // Calculate the TD of the block (it"s not imported yet, so block.Td is not valid) // 计算新的总难度 var td *big.Int if parent := pm.blockchain.GetBlock(block.ParentHash(), block.NumberU64()-1); parent != nil { td = new(big.Int).Add(block.Difficulty(), pm.blockchain.GetTd(block.ParentHash(), block.NumberU64()-1)) } else { log.Error("Propagating dangling block", "number", block.Number(), "hash", hash) return } // Send the block to a subset of our peers // 广播区块给部分peer transfer := peers[:int(math.Sqrt(float64(len(peers))))] for _, peer := range transfer { peer.AsyncSendNewBlock(block, td) } log.Trace("Propagated block", "hash", hash, "recipients", len(transfer), "duration", common.PrettyDuration(time.Since(block.ReceivedAt))) return } // Otherwise if the block is indeed in out own chain, announce it // 把区块hash值广播给所有peer if pm.blockchain.HasBlock(hash, block.NumberU64()) { for _, peer := range peers { peer.AsyncSendNewBlockHash(block) } log.Trace("Announced block", "hash", hash, "recipients", len(peers), "duration", common.PrettyDuration(time.Since(block.ReceivedAt))) } }
peer.broadcase()是每个Peer连接的广播函数,它只广播3种消息:交易、完整的区块、区块的Hash,这样表明了节点只会主动广播这3中类型的数据,剩余的数据同步,都是通过请求-响应的方式。
// broadcast is a write loop that multiplexes block propagations, announcements // and transaction broadcasts into the remote peer. The goal is to have an async // writer that does not lock up node internals. func (p *peer) broadcast() { for { select { // 广播交易 case txs := <-p.queuedTxs: if err := p.SendTransactions(txs); err != nil { return } p.Log().Trace("Broadcast transactions", "count", len(txs)) // 广播完整的新区块 case prop := <-p.queuedProps: if err := p.SendNewBlock(prop.block, prop.td); err != nil { return } p.Log().Trace("Propagated block", "number", prop.block.Number(), "hash", prop.block.Hash(), "td", prop.td) // 广播区块Hash case block := <-p.queuedAnns: if err := p.SendNewBlockHashes([]common.Hash{block.Hash()}, []uint64{block.NumberU64()}); err != nil { return } p.Log().Trace("Announced block", "number", block.Number(), "hash", block.Hash()) case <-p.term: return } } }Peer节点处理新区块
本节介绍远端节点收到2种区块同步消息的处理,其中NewBlockMsg的处理流程比较清晰,也简洁。NewBlockHashesMsg消息的处理就绕了2绕,从总体流程图1上能看出来,它需要先从给他发送消息Peer那里获取到完整的区块,剩下的流程和NewBlockMsg又一致了。
这部分涉及的模块多,画出来有种眼花缭乱的感觉,但只要抓住上面的主线,代码看起来还是很清晰的。通过图5先看下整体流程。
消息处理的起点是ProtocolManager.handleMsg,NewBlockMsg的处理流程是蓝色标记的区域,红色区域是多带带的协程,是fetcher处理队列中区块的流程,如果从队列中取出的区块是当前链需要的,校验后,调用blockchian.InsertChain()把区块插入到区块链,最后写入数据库,这是黄色部分。最后,绿色部分是NewBlockHashesMsg的处理流程,代码流程上是比较复杂的,为了能通过图描述整体流程,我把它简化掉了。
仔细看看这幅图,掌握整体的流程后,接下来看每个步骤的细节。
NewBlockMsg的处理本节介绍节点收到完整区块的处理,流程如下:
首先进行RLP编解码,然后标记发送消息的Peer已经知道这个区块,这样本节点最后广播这个区块的Hash时,不会再发送给该Peer。
将区块存入到fetcher的队列,调用fetcher.Enqueue。
更新Peer的Head位置,然后判断本地链是否落后于Peer的链,如果是,则通过Peer更新本地链。
只看handle.Msg()的NewBlockMsg相关的部分。
case msg.Code == NewBlockMsg: // Retrieve and decode the propagated block // 收到新区块,解码,赋值接收数据 var request newBlockData if err := msg.Decode(&request); err != nil { return errResp(ErrDecode, "%v: %v", msg, err) } request.Block.ReceivedAt = msg.ReceivedAt request.Block.ReceivedFrom = p // Mark the peer as owning the block and schedule it for import // 标记peer知道这个区块 p.MarkBlock(request.Block.Hash()) // 为啥要如队列?已经得到完整的区块了 // 答:存入fetcher的优先级队列,fetcher会从队列中选取当前高度需要的块 pm.fetcher.Enqueue(p.id, request.Block) // Assuming the block is importable by the peer, but possibly not yet done so, // calculate the head hash and TD that the peer truly must have. // 截止到parent区块的头和难度 var ( trueHead = request.Block.ParentHash() trueTD = new(big.Int).Sub(request.TD, request.Block.Difficulty()) ) // Update the peers total difficulty if better than the previous // 如果收到的块的难度大于peer之前的,以及自己本地的,就去和这个peer同步 // 问题:就只用了一下块里的hash指,为啥不直接使用这个块呢,如果这个块不能用,干嘛不少发送些数据,减少网络负载呢。 // 答案:实际上,这个块加入到了优先级队列中,当fetcher的loop检查到当前下一个区块的高度,正是队列中有的,则不再向peer请求 // 该区块,而是直接使用该区块,检查无误后交给block chain执行insertChain if _, td := p.Head(); trueTD.Cmp(td) > 0 { p.SetHead(trueHead, trueTD) // Schedule a sync if above ours. Note, this will not fire a sync for a gap of // a singe block (as the true TD is below the propagated block), however this // scenario should easily be covered by the fetcher. currentBlock := pm.blockchain.CurrentBlock() if trueTD.Cmp(pm.blockchain.GetTd(currentBlock.Hash(), currentBlock.NumberU64())) > 0 { go pm.synchronise(p) } } //------------------------ 以上 handleMsg // Enqueue tries to fill gaps the the fetcher"s future import queue. // 发给inject通道,当前协程在handleMsg,通过通道发送给fetcher的协程处理 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 } } //------------------------ 以下 fetcher.loop处理inject部分 case op := <-f.inject: // A direct block insertion was requested, try and fill any pending gaps // 区块加入队列,首先也填入未决的间距 propBroadcastInMeter.Mark(1) f.enqueue(op.origin, op.block) //------------------------ 如队列函数 // enqueue schedules a new future import operation, if the block to be imported // has not yet been seen. // 把导入的新区块放进来 func (f *Fetcher) enqueue(peer string, block *types.Block) { hash := block.Hash() // Ensure the peer isn"t DOSing us // 防止peer的DOS攻击 count := f.queues[peer] + 1 if count > blockLimit { log.Debug("Discarded propagated block, exceeded allowance", "peer", peer, "number", block.Number(), "hash", hash, "limit", blockLimit) propBroadcastDOSMeter.Mark(1) f.forgetHash(hash) return } // Discard any past or too distant blocks // 高度检查:未来太远的块丢弃 if dist := int64(block.NumberU64()) - int64(f.chainHeight()); dist < -maxUncleDist || dist > maxQueueDist { log.Debug("Discarded propagated block, too far away", "peer", peer, "number", block.Number(), "hash", hash, "distance", dist) propBroadcastDropMeter.Mark(1) f.forgetHash(hash) return } // Schedule the block for future importing // 块先加入优先级队列,加入链之前,还有很多要做 if _, ok := f.queued[hash]; !ok { op := &inject{ origin: peer, block: block, } f.queues[peer] = count f.queued[hash] = op f.queue.Push(op, -float32(block.NumberU64())) if f.queueChangeHook != nil { f.queueChangeHook(op.block.Hash(), true) } log.Debug("Queued propagated block", "peer", peer, "number", block.Number(), "hash", hash, "queued", f.queue.Size()) } }fetcher队列处理
本节我们看看,区块加入队列后,fetcher如何处理区块,为何不直接校验区块,插入到本地链?
由于以太坊又Uncle的机制,节点可能收到老一点的一些区块。另外,节点可能由于网络原因,落后了几个区块,所以可能收到“未来”的一些区块,这些区块都不能直接插入到本地链。
区块入的队列是一个优先级队列,高度低的区块会被优先取出来。fetcher.loop是多带带协程,不断运转,清理fecther中的事务和事件。首先会清理正在fetching的区块,但已经超时。然后处理优先级队列中的区块,判断高度是否是下一个区块,如果是则调用f.insert()函数,校验后调用BlockChain.InsertChain(),成功插入后,广播新区块的Hash。
// 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 fetchTimer := time.NewTimer(0) completeTimer := time.NewTimer(0) for { // Clean up any expired block fetches // 清理过期的区块 for hash, announce := range f.fetching { if time.Since(announce.time) > fetchTimeout { f.forgetHash(hash) } } // Import any queued blocks that could potentially fit // 导入队列中合适的块 height := f.chainHeight() for !f.queue.Empty() { op := f.queue.PopItem().(*inject) hash := op.block.Hash() if f.queueChangeHook != nil { f.queueChangeHook(hash, false) } // If too high up the chain or phase, continue later // 块不是链需要的下一个块,再入优先级队列,停止循环 number := op.block.NumberU64() if number > height+1 { f.queue.Push(op, -float32(number)) if f.queueChangeHook != nil { f.queueChangeHook(hash, true) } break } // Otherwise if fresh and still unknown, try and import // 高度正好是我们想要的,并且链上也没有这个块 if number+maxUncleDist < height || f.getBlock(hash) != nil { f.forgetBlock(hash) continue } // 那么,块插入链 f.insert(op.origin, op.block) } //省略 } }
func (f *Fetcher) insert(peer string, block *types.Block) { hash := block.Hash() // Run the import on a new thread log.Debug("Importing propagated block", "peer", peer, "number", block.Number(), "hash", hash) go func() { defer func() { f.done <- hash }() // If the parent"s unknown, abort insertion parent := f.getBlock(block.ParentHash()) if parent == nil { log.Debug("Unknown parent of propagated block", "peer", peer, "number", block.Number(), "hash", hash, "parent", block.ParentHash()) return } // Quickly validate the header and propagate the block if it passes // 验证区块头,成功后广播区块 switch err := f.verifyHeader(block.Header()); err { case nil: // All ok, quickly propagate to our peers propBroadcastOutTimer.UpdateSince(block.ReceivedAt) go f.broadcastBlock(block, true) case consensus.ErrFutureBlock: // Weird future block, don"t fail, but neither propagate default: // Something went very wrong, drop the peer log.Debug("Propagated block verification failed", "peer", peer, "number", block.Number(), "hash", hash, "err", err) f.dropPeer(peer) return } // Run the actual import and log any issues // 调用回调函数,实际是blockChain.insertChain if _, err := f.insertChain(types.Blocks{block}); err != nil { log.Debug("Propagated block import failed", "peer", peer, "number", block.Number(), "hash", hash, "err", err) return } // If import succeeded, broadcast the block propAnnounceOutTimer.UpdateSince(block.ReceivedAt) go f.broadcastBlock(block, false) // Invoke the testing hook if needed if f.importedHook != nil { f.importedHook(block) } }() }NewBlockHashesMsg的处理
本节介绍NewBlockHashesMsg的处理,其实,消息处理是简单的,而复杂一点的是从Peer哪获取完整的区块,下节再看。
流程如下:
对消息进行RLP解码,然后标记Peer已经知道此区块。
寻找出本地区块链不存在的区块Hash值,把这些未知的Hash通知给fetcher。
fetcher.Notify记录好通知信息,塞入notify通道,以便交给fetcher的协程。
fetcher.loop()会对notify中的消息进行处理,确认区块并非DOS攻击,然后检查区块的高度,判断该区块是否已经在fetching或者comleting(代表已经下载区块头,在下载body),如果都没有,则加入到announced中,触发0s定时器,进行处理。
关于announced下节再介绍。
// handleMsg()部分 case msg.Code == NewBlockHashesMsg: var announces newBlockHashesData if err := msg.Decode(&announces); err != nil { return errResp(ErrDecode, "%v: %v", msg, err) } // Mark the hashes as present at the remote node for _, block := range announces { p.MarkBlock(block.Hash) } // Schedule all the unknown hashes for retrieval // 把本地链没有的块hash找出来,交给fetcher去下载 unknown := make(newBlockHashesData, 0, len(announces)) for _, block := range announces { if !pm.blockchain.HasBlock(block.Hash, block.Number) { unknown = append(unknown, block) } } for _, block := range unknown { pm.fetcher.Notify(p.id, block.Hash, block.Number, time.Now(), p.RequestOneHeader, p.RequestBodies) }
// Notify announces the fetcher of the potential availability of a new block in // the network. // 通知fetcher(自己)有新块产生,没有块实体,有hash、高度等信息 func (f *Fetcher) Notify(peer string, hash common.Hash, number uint64, time time.Time, headerFetcher headerRequesterFn, bodyFetcher bodyRequesterFn) error { block := &announce{ hash: hash, number: number, time: time, origin: peer, fetchHeader: headerFetcher, fetchBodies: bodyFetcher, } select { case f.notify <- block: return nil case <-f.quit: return errTerminated } }
// fetcher.loop()的notify通道消息处理 case notification := <-f.notify: // A block was announced, make sure the peer isn"t DOSing us propAnnounceInMeter.Mark(1) count := f.announces[notification.origin] + 1 if count > hashLimit { log.Debug("Peer exceeded outstanding announces", "peer", notification.origin, "limit", hashLimit) propAnnounceDOSMeter.Mark(1) break } // If we have a valid block number, check that it"s potentially useful // 高度检查 if notification.number > 0 { if dist := int64(notification.number) - int64(f.chainHeight()); dist < -maxUncleDist || dist > maxQueueDist { log.Debug("Peer discarded announcement", "peer", notification.origin, "number", notification.number, "hash", notification.hash, "distance", dist) propAnnounceDropMeter.Mark(1) break } } // All is well, schedule the announce if block"s not yet downloading // 检查是否已经在下载,已下载则忽略 if _, ok := f.fetching[notification.hash]; ok { break } if _, ok := f.completing[notification.hash]; ok { break } // 更新peer已经通知给我们的区块数量 f.announces[notification.origin] = count // 把通知信息加入到announced,供调度 f.announced[notification.hash] = append(f.announced[notification.hash], notification) if f.announceChangeHook != nil && len(f.announced[notification.hash]) == 1 { f.announceChangeHook(notification.hash, true) } if len(f.announced) == 1 { // 有通知放入到announced,则重设0s定时器,loop的另外一个分支会处理这些通知 f.rescheduleFetch(fetchTimer) }fetcher获取完整区块
本节介绍fetcher获取完整区块的过程,这也是fetcher最重要的功能,会涉及到fetcher至少80%的代码。多带带拉放一大节吧。
Fetcher的大头Fetcher最主要的功能就是获取完整的区块,然后在合适的实际交给InsertChain去验证和插入到本地区块链。我们还是从宏观入手,看Fetcher是如何工作的,一定要先掌握好宏观,因为代码层面上没有这么清晰。
宏观首先,看两个节点是如何交互,获取完整区块,使用时序图的方式看一下,见图6,流程很清晰不再文字介绍。
再看下获取区块过程中,fetcher内部的状态转移,它使用状态来记录,要获取的区块在什么阶段,见图7。我稍微解释一下:
收到NewBlockHashesMsg后,相关信息会记录到announced,进入announced状态,代表了本节点接收了消息。
announced由fetcher协程处理,经过校验后,会向给他发送消息的Peer发送请求,请求该区块的区块头,然后进入fetching状态。
获取区块头后,如果区块头表示没有交易和uncle,则转移到completing状态,并且使用区块头合成完整的区块,加入到queued优先级队列。
获取区块头后,如果区块头表示该区块有交易和uncle,则转移到fetched状态,然后发送请求,请求交易和uncle,然后转移到completing状态。
收到交易和uncle后,使用头、交易、uncle这3个信息,生成完整的区块,加入到队列queued。
微观接下来就是从代码角度看如何获取完整区块的流程了,有点多,看不懂的时候,再回顾下上面宏观的介绍图。
首先看Fetcher的定义,它存放了通信数据和状态管理,捡加注释的看,上文提到的状态,里面都有。
// Fetcher is responsible for accumulating block announcements from various peers // and scheduling them for retrieval. // 积累块通知,然后调度获取这些块 type Fetcher struct { // Various event channels // 收到区块hash值的通道 notify chan *announce // 收到完整区块的通道 inject chan *inject blockFilter chan chan []*types.Block // 过滤header的通道的通道 headerFilter chan chan *headerFilterTask // 过滤body的通道的通道 bodyFilter chan chan *bodyFilterTask done chan common.Hash quit chan struct{} // Announce states // Peer已经给了本节点多少区块头通知 announces map[string]int // Per peer announce counts to prevent memory exhaustion // 已经announced的区块列表 announced map[common.Hash][]*announce // Announced blocks, scheduled for fetching // 正在fetching区块头的请求 fetching map[common.Hash]*announce // Announced blocks, currently fetching // 已经fetch到区块头,还差body的请求,用来获取body fetched map[common.Hash][]*announce // Blocks with headers fetched, scheduled for body retrieval // 已经得到区块头的 completing map[common.Hash]*announce // Blocks with headers, currently body-completing // Block cache // queue,优先级队列,高度做优先级 // queues,统计peer通告了多少块 // queued,代表这个块如队列了, queue *prque.Prque // Queue containing the import operations (block number sorted) queues map[string]int // Per peer block counts to prevent memory exhaustion queued map[common.Hash]*inject // Set of already queued blocks (to dedupe imports) // Callbacks getBlock blockRetrievalFn // Retrieves a block from the local chain verifyHeader headerVerifierFn // Checks if a block"s headers have a valid proof of work,验证区块头,包含了PoW验证 broadcastBlock blockBroadcasterFn // Broadcasts a block to connected peers,广播给peer chainHeight chainHeightFn // Retrieves the current chain"s height insertChain chainInsertFn // Injects a batch of blocks into the chain,插入区块到链的函数 dropPeer peerDropFn // Drops a peer for misbehaving // Testing hooks announceChangeHook func(common.Hash, bool) // Method to call upon adding or deleting a hash from the announce list queueChangeHook func(common.Hash, bool) // Method to call upon adding or deleting a block from the import queue fetchingHook func([]common.Hash) // Method to call upon starting a block (eth/61) or header (eth/62) fetch completingHook func([]common.Hash) // Method to call upon starting a block body fetch (eth/62) importedHook func(*types.Block) // Method to call upon successful block import (both eth/61 and eth/62) }
NewBlockHashesMsg消息的处理前面的小节已经讲过了,不记得可向前翻看。这里从announced的状态处理说起。loop()中,fetchTimer超时后,代表了收到了消息通知,需要处理,会从announced中选择出需要处理的通知,然后创建请求,请求区块头,由于可能有很多节点都通知了它某个区块的Hash,所以随机的从这些发送消息的Peer中选择一个Peer,发送请求的时候,为每个Peer都创建了多带带的协程。
case <-fetchTimer.C: // At least one block"s timer ran out, check for needing retrieval // 有区块通知,去处理 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 // 可能有很多peer都发送了这个区块的hash值,随机选择一个peer announce := announces[rand.Intn(len(announces))] f.forgetHash(hash) // If the block still didn"t arrive, queue for fetching // 本地还没有这个区块,创建获取区块的请求 if f.getBlock(hash) == nil { request[announce.origin] = append(request[announce.origin], hash) f.fetching[hash] = announce } } } // Send out all block header requests // 把所有的request发送出去 // 为每一个peer都创建一个协程,然后请求所有需要从该peer获取的请求 for peer, hashes := range request { log.Trace("Fetching scheduled headers", "peer", peer, "list", hashes) // Create a closure of the fetch and schedule in on a new thread fetchHeader, hashes := f.fetching[hashes[0]].fetchHeader, hashes go func() { if f.fetchingHook != nil { f.fetchingHook(hashes) } for _, hash := range hashes { headerFetchMeter.Mark(1) fetchHeader(hash) // Suboptimal, but protocol doesn"t allow batch header retrievals } }() } // Schedule the next fetch if blocks are still pending f.rescheduleFetch(fetchTimer)
从Notify的调用中,可以看出,fetcherHeader()的实际函数是RequestOneHeader(),该函数使用的消息是GetBlockHeadersMsg,可以用来请求多个区块头,不过fetcher只请求一个。
pm.fetcher.Notify(p.id, block.Hash, block.Number, time.Now(), p.RequestOneHeader, p.RequestBodies) // RequestOneHeader is a wrapper around the header query functions to fetch a // single header. It is used solely by the fetcher. func (p *peer) RequestOneHeader(hash common.Hash) error { p.Log().Debug("Fetching single header", "hash", hash) return p2p.Send(p.rw, GetBlockHeadersMsg, &getBlockHeadersData{Origin: hashOrNumber{Hash: hash}, Amount: uint64(1), Skip: uint64(0), Reverse: false}) }
GetBlockHeadersMsg的处理如下:因为它是获取多个区块头的,所以处理起来比较“麻烦”,还好,fetcher只获取一个区块头,其处理在20行~33行,获取下一个区块头的处理逻辑,这里就不看了,最后调用SendBlockHeaders()将区块头发送给请求的节点,消息是BlockHeadersMsg。
// handleMsg() // Block header query, collect the requested headers and reply case msg.Code == GetBlockHeadersMsg: // Decode the complex header query var query getBlockHeadersData if err := msg.Decode(&query); err != nil { return errResp(ErrDecode, "%v: %v", msg, err) } hashMode := query.Origin.Hash != (common.Hash{}) // Gather headers until the fetch or network limits is reached // 收集区块头,直到达到限制 var ( bytes common.StorageSize headers []*types.Header unknown bool ) // 自己已知区块 && 少于查询的数量 && 大小小于2MB && 小于能下载的最大数量 for !unknown && len(headers) < int(query.Amount) && bytes < softResponseLimit && len(headers) < downloader.MaxHeaderFetch { // Retrieve the next header satisfying the query // 获取区块头 var origin *types.Header if hashMode { // fetcher 使用的模式 origin = pm.blockchain.GetHeaderByHash(query.Origin.Hash) } else { origin = pm.blockchain.GetHeaderByNumber(query.Origin.Number) } if origin == nil { break } number := origin.Number.Uint64() headers = append(headers, origin) bytes += estHeaderRlpSize // Advance to the next header of the query // 下一个区块头的获取,不同策略,方式不同 switch { case query.Origin.Hash != (common.Hash{}) && query.Reverse: // ... } } return p.SendBlockHeaders(headers)
BlockHeadersMsg的处理很有意思,因为GetBlockHeadersMsg并不是fetcher独占的消息,downloader也可以调用,所以,响应消息的处理需要分辨出是fetcher请求的,还是downloader请求的。它的处理逻辑是:fetcher先过滤收到的区块头,如果fetcher不要的,那就是downloader的,在调用fetcher.FilterHeaders的时候,fetcher就将自己要的区块头拿走了。
// handleMsg() case msg.Code == BlockHeadersMsg: // A batch of headers arrived to one of our previous requests var headers []*types.Header if err := msg.Decode(&headers); err != nil { return errResp(ErrDecode, "msg %v: %v", msg, err) } // If no headers were received, but we"re expending a DAO fork check, maybe it"s that // 检查是不是当前DAO的硬分叉 if len(headers) == 0 && p.forkDrop != nil { // Possibly an empty reply to the fork header checks, sanity check TDs verifyDAO := true // If we already have a DAO header, we can check the peer"s TD against it. If // the peer"s ahead of this, it too must have a reply to the DAO check if daoHeader := pm.blockchain.GetHeaderByNumber(pm.chainconfig.DAOForkBlock.Uint64()); daoHeader != nil { if _, td := p.Head(); td.Cmp(pm.blockchain.GetTd(daoHeader.Hash(), daoHeader.Number.Uint64())) >= 0 { verifyDAO = false } } // If we"re seemingly on the same chain, disable the drop timer if verifyDAO { p.Log().Debug("Seems to be on the same side of the DAO fork") p.forkDrop.Stop() p.forkDrop = nil return nil } } // Filter out any explicitly requested headers, deliver the rest to the downloader // 过滤是不是fetcher请求的区块头,去掉fetcher请求的区块头再交给downloader filter := len(headers) == 1 if filter { // If it"s a potential DAO fork check, validate against the rules // 检查是否硬分叉 if p.forkDrop != nil && pm.chainconfig.DAOForkBlock.Cmp(headers[0].Number) == 0 { // Disable the fork drop timer p.forkDrop.Stop() p.forkDrop = nil // Validate the header and either drop the peer or continue if err := misc.VerifyDAOHeaderExtraData(pm.chainconfig, headers[0]); err != nil { p.Log().Debug("Verified to be on the other side of the DAO fork, dropping") return err } p.Log().Debug("Verified to be on the same side of the DAO fork") return nil } // Irrelevant of the fork checks, send the header to the fetcher just in case // 使用fetcher过滤区块头 headers = pm.fetcher.FilterHeaders(p.id, headers, time.Now()) } // 剩下的区块头交给downloader if len(headers) > 0 || !filter { err := pm.downloader.DeliverHeaders(p.id, headers) if err != nil { log.Debug("Failed to deliver headers", "err", err) } }
FilterHeaders()是一个很有大智慧的函数,看起来耐人寻味,但实在妙。它要把所有的区块头,都传递给fetcher协程,还要获取fetcher协程处理后的结果。fetcher.headerFilter是存放通道的通道,而filter是存放包含区块头过滤任务的通道。它先把filter传递给了headerFilter,这样fetcher协程就在另外一段等待了,而后将headerFilterTask传入filter,fetcher就能读到数据了,处理后,再将数据写回filter而刚好被FilterHeaders函数处理了,该函数实际运行在handleMsg()的协程中。
每个Peer都会分配一个ProtocolManager然后处理该Peer的消息,但fetcher只有一个事件处理协程,如果不创建一个filter,fetcher哪知道是谁发给它的区块头呢?过滤之后,该如何发回去呢?
// FilterHeaders extracts all the headers that were explicitly requested by the fetcher, // returning those that should be handled differently. // 寻找出fetcher请求的区块头 func (f *Fetcher) FilterHeaders(peer string, headers []*types.Header, time time.Time) []*types.Header { log.Trace("Filtering headers", "peer", peer, "headers", len(headers)) // Send the filter channel to the fetcher // 任务通道 filter := make(chan *headerFilterTask) select { // 任务通道发送到这个通道 case f.headerFilter <- filter: case <-f.quit: return nil } // Request the filtering of the header list // 创建过滤任务,发送到任务通道 select { case filter <- &headerFilterTask{peer: peer, headers: headers, time: time}: case <-f.quit: return nil } // Retrieve the headers remaining after filtering // 从任务通道,获取过滤的结果并返回 select { case task := <-filter: return task.headers case <-f.quit: return nil } }
接下来要看f.headerFilter的处理,这段代码有90行,它做了一下几件事:
从f.headerFilter取出filter,然后取出过滤任务task。
它把区块头分成3类:unknown这不是分是要返回给调用者的,即handleMsg(), incomplete存放还需要获取body的区块头,complete存放只包含区块头的区块。遍历所有的区块头,填到到对应的分类中,具体的判断可看18行的注释,记住宏观中将的状态转移图。
把unknonw中的区块返回给handleMsg()。
把 incomplete的区块头获取状态移动到fetched状态,然后触发定时器,以便去处理complete的区块。
把compelete的区块加入到queued。
// fetcher.loop() case filter := <-f.headerFilter: // Headers arrived from a remote peer. Extract those that were explicitly // requested by the fetcher, and return everything else so it"s delivered // to other parts of the system. // 收到从远端节点发送的区块头,过滤出fetcher请求的 // 从任务通道获取过滤任务 var task *headerFilterTask select { case task = <-filter: case <-f.quit: return } headerFilterInMeter.Mark(int64(len(task.headers))) // Split the batch of headers into unknown ones (to return to the caller), // known incomplete ones (requiring body retrievals) and completed blocks. // unknown的不是fetcher请求的,complete放没有交易和uncle的区块,有头就够了,incomplete放 // 还需要获取uncle和交易的区块 unknown, incomplete, complete := []*types.Header{}, []*announce{}, []*types.Block{} // 遍历所有收到的header for _, header := range task.headers { hash := header.Hash() // Filter fetcher-requested headers from other synchronisation algorithms // 是正在获取的hash,并且对应请求的peer,并且未fetched,未completing,未queued if announce := f.fetching[hash]; announce != nil && announce.origin == task.peer && f.fetched[hash] == nil && f.completing[hash] == nil && f.queued[hash] == nil { // If the delivered header does not match the promised number, drop the announcer // 高度校验,竟然不匹配,扰乱秩序,peer肯定是坏蛋。 if header.Number.Uint64() != announce.number { log.Trace("Invalid block number fetched", "peer", announce.origin, "hash", header.Hash(), "announced", announce.number, "provided", header.Number) f.dropPeer(announce.origin) f.forgetHash(hash) continue } // Only keep if not imported by other means // 本地链没有当前区块 if f.getBlock(hash) == nil { announce.header = header announce.time = task.time // If the block is empty (header only), short circuit into the final import queue // 如果区块没有交易和uncle,加入到complete if header.TxHash == types.DeriveSha(types.Transactions{}) && header.UncleHash == types.CalcUncleHash([]*types.Header{}) { log.Trace("Block empty, skipping body retrieval", "peer", announce.origin, "number", header.Number, "hash", header.Hash()) block := types.NewBlockWithHeader(header) block.ReceivedAt = task.time complete = append(complete, block) f.completing[hash] = announce continue } // Otherwise add to the list of blocks needing completion // 否则就是不完整的区块 incomplete = append(incomplete, announce) } else { log.Trace("Block already imported, discarding header", "peer", announce.origin, "number", header.Number, "hash", header.Hash()) f.forgetHash(hash) } } else { // Fetcher doesn"t know about it, add to the return list // 没请求过的header unknown = append(unknown, header) } } // 把未知的区块头,再传递会filter headerFilterOutMeter.Mark(int64(len(unknown))) select { case filter <- &headerFilterTask{headers: unknown, time: task.time}: case <-f.quit: return } // Schedule the retrieved headers for body completion // 把未完整的区块加入到fetched,跳过已经在completeing中的,然后触发completeTimer定时器 for _, announce := range incomplete { hash := announce.header.Hash() if _, ok := f.completing[hash]; ok { continue } f.fetched[hash] = append(f.fetched[hash], announce) if len(f.fetched) == 1 { f.rescheduleComplete(completeTimer) } } // Schedule the header-only blocks for import // 把只有头的区块入队列 for _, block := range complete { if announce := f.completing[block.Hash()]; announce != nil { f.enqueue(announce.origin, block) } }
跟随状态图的转义,剩下的工作是fetched转移到completing,上面的流程已经触发了completeTimer定时器,超时后就会处理,流程与请求Header类似,不再赘述,此时发送的请求消息是GetBlockBodiesMsg,实际调的函数是RequestBodies。
// fetcher.loop() case <-completeTimer.C: // At least one header"s timer ran out, retrieve everything // 至少有1个header已经获取完了 request := make(map[string][]common.Hash) // 遍历所有待获取body的announce for hash, announces := range f.fetched { // Pick a random peer to retrieve from, reset all others // 随机选一个Peer发送请求,因为可能已经有很多Peer通知它这个区块了 announce := announces[rand.Intn(len(announces))] f.forgetHash(hash) // If the block still didn"t arrive, queue for completion // 如果本地没有这个区块,则放入到completing,创建请求 if f.getBlock(hash) == nil { request[announce.origin] = append(request[announce.origin], hash) f.completing[hash] = announce } } // Send out all block body requests // 发送所有的请求,获取body,依然是每个peer一个多带带协程 for peer, hashes := range request { log.Trace("Fetching scheduled bodies", "peer", peer, "list", hashes) // Create a closure of the fetch and schedule in on a new thread if f.completingHook != nil { f.completingHook(hashes) } bodyFetchMeter.Mark(int64(len(hashes))) go f.completing[hashes[0]].fetchBodies(hashes) } // Schedule the next fetch if blocks are still pending f.rescheduleComplete(completeTimer)
handleMsg()处理该消息也是干净利落,直接获取RLP格式的body,然后发送响应消息。
// handleMsg() case msg.Code == GetBlockBodiesMsg: // Decode the retrieval message msgStream := rlp.NewStream(msg.Payload, uint64(msg.Size)) if _, err := msgStream.List(); err != nil { return err } // Gather blocks until the fetch or network limits is reached var ( hash common.Hash bytes int bodies []rlp.RawValue ) // 遍历所有请求 for bytes < softResponseLimit && len(bodies) < downloader.MaxBlockFetch { // Retrieve the hash of the next block if err := msgStream.Decode(&hash); err == rlp.EOL { break } else if err != nil { return errResp(ErrDecode, "msg %v: %v", msg, err) } // Retrieve the requested block body, stopping if enough was found // 获取body,RLP格式 if data := pm.blockchain.GetBodyRLP(hash); len(data) != 0 { bodies = append(bodies, data) bytes += len(data) } } return p.SendBlockBodiesRLP(bodies)
响应消息BlockBodiesMsg的处理与处理获取header的处理原理相同,先交给fetcher过滤,然后剩下的才是downloader的。需要注意一点,响应消息里只包含交易列表和叔块列表。
// handleMsg() case msg.Code == BlockBodiesMsg: // A batch of block bodies arrived to one of our previous requests var request blockBodiesData if err := msg.Decode(&request); err != nil { return errResp(ErrDecode, "msg %v: %v", msg, err) } // Deliver them all to the downloader for queuing // 传递给downloader去处理 transactions := make([][]*types.Transaction, len(request)) uncles := make([][]*types.Header, len(request)) for i, body := range request { transactions[i] = body.Transactions uncles[i] = body.Uncles } // Filter out any explicitly requested bodies, deliver the rest to the downloader // 先让fetcher过滤去fetcher请求的body,剩下的给downloader filter := len(transactions) > 0 || len(uncles) > 0 if filter { transactions, uncles = pm.fetcher.FilterBodies(p.id, transactions, uncles, time.Now()) } // 剩下的body交给downloader if len(transactions) > 0 || len(uncles) > 0 || !filter { err := pm.downloader.DeliverBodies(p.id, transactions, uncles) if err != nil { log.Debug("Failed to deliver bodies", "err", err) } }
过滤函数的原理也与Header相同。
// FilterBodies extracts all the block bodies that were explicitly requested by // the fetcher, returning those that should be handled differently. // 过去出fetcher请求的body,返回它没有处理的,过程类型header的处理 func (f *Fetcher) FilterBodies(peer string, transactions [][]*types.Transaction, uncles [][]*types.Header, time time.Time) ([][]*types.Transaction, [][]*types.Header) { log.Trace("Filtering bodies", "peer", peer, "txs", len(transactions), "uncles", len(uncles)) // Send the filter channel to the fetcher filter := make(chan *bodyFilterTask) select { case f.bodyFilter <- filter: case <-f.quit: return nil, nil } // Request the filtering of the body list select { case filter <- &bodyFilterTask{peer: peer, transactions: transactions, uncles: uncles, time: time}: case <-f.quit: return nil, nil } // Retrieve the bodies remaining after filtering select { case task := <-filter: return task.transactions, task.uncles case <-f.quit: return nil, nil } }
实际过滤body的处理瞧一下,这和Header的处理是不同的。直接看不点:
它要的区块,多带带取出来存到blocks中,它不要的继续留在task中。
判断是不是fetcher请求的方法:如果交易列表和叔块列表计算出的hash值与区块头中的一样,并且消息来自请求的Peer,则就是fetcher请求的。
将blocks中的区块加入到queued,终结。
case filter := <-f.bodyFilter: // Block bodies arrived, extract any explicitly requested blocks, return the rest var task *bodyFilterTask select { case task = <-filter: case <-f.quit: return } bodyFilterInMeter.Mark(int64(len(task.transactions))) blocks := []*types.Block{} // 获取的每个body的txs列表和uncle列表 // 遍历每个区块的txs列表和uncle列表,计算hash后判断是否是当前fetcher请求的body for i := 0; i < len(task.transactions) && i < len(task.uncles); i++ { // Match up a body to any possible completion request matched := false // 遍历所有保存的请求,因为tx和uncle,不知道它是属于哪个区块的,只能去遍历所有的请求,通常量不大,所以遍历没有性能影响 for hash, announce := range f.completing { if f.queued[hash] == nil { // 把传入的每个块的hash和unclehash和它请求出去的记录进行对比,匹配则说明是fetcher请求的区块body txnHash := types.DeriveSha(types.Transactions(task.transactions[i])) uncleHash := types.CalcUncleHash(task.uncles[i]) if txnHash == announce.header.TxHash && uncleHash == announce.header.UncleHash && announce.origin == task.peer { // Mark the body matched, reassemble if still unknown matched = true // 如果当前链还没有这个区块,则收集这个区块,合并成新区块 if f.getBlock(hash) == nil { block := types.NewBlockWithHeader(announce.header).WithBody(task.transactions[i], task.uncles[i]) block.ReceivedAt = task.time blocks = append(blocks, block) } else { f.forgetHash(hash) } } } } // 从task中移除fetcher请求的数据 if matched { task.transactions = append(task.transactions[:i], task.transactions[i+1:]...) task.uncles = append(task.uncles[:i], task.uncles[i+1:]...) i-- continue } } // 将剩余的数据返回 bodyFilterOutMeter.Mark(int64(len(task.transactions))) select { case filter <- task: case <-f.quit: return } // Schedule the retrieved blocks for ordered import // 把收集的区块加入到队列 for _, block := range blocks { if announce := f.completing[block.Hash()]; announce != nil { f.enqueue(announce.origin, block) } } }
至此,fetcher获取完整区块的流程讲完了,fetcher模块中80%的代码也都贴出来了,还有2个值得看看的函数:
forgetHash(hash common.Hash) :用于清空指定hash指的记/状态录信息。
forgetBlock(hash common.Hash):用于从队列中移除一个区块。
最后了,再回到开始看看fetcher模块和新区块的传播流程,有没有豁然开朗。
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摘要:接下来我们将从以下角度介绍矿工角色。我们分别使用矿长副矿长矿工进行类比。副矿长,负责具体挖矿工作的安排,把挖矿任务安排给。矿工的主要函数介绍和的主要函数,他们是矿工的具体运作机制。负责处理外部事件。 前言 矿工在PoW中负责了产生区块的工作,把一大堆交易交给它,它生成一个证明自己做了很多工作的区块,然后将这个区块加入到本地区块链并且广播给其他节点。 接下来我们将从以下角度介绍矿工: ...
摘要:下面来看看具体是怎么实现接口的可以看到,启动了多个线程调用函数,当有线程挖到时,会通过传入的通道传出结果。可以看到在主要循环中,不断递增的值,调用函数计算上面公式中的左边,而则是公式的右边。 前言 挖矿(mine)是指矿工节点互相竞争生成新区块以写入整个区块链获得奖励的过程.共识(consensus)是指区块链各个节点对下一个区块的内容形成一致的过程在以太坊中, miner包向外提供挖...
摘要:是以太坊中存储区块数据的核心数据结构,它和融合一个树形结构,理解结构对之后学习以太坊区块以及智能合约状态存储结构的模块源码很有帮助。 MPT(Merkle Patricia Tries)是以太坊中存储区块数据的核心数据结构,它Merkle Tree和Patricia Tree融合一个树形结构,理解MPT结构对之后学习以太坊区块header以及智能合约状态存储结构的模块源码很有帮助。 首...
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