Fabric 1.4 源码分析 区块同步

本文主要从源码层面介绍fabric peer同步区块过程，peer同步区块主要有2个过程：
1）peer组织的leader与orderer同步区块
2）peer组织间peer同步区块。

1. peer leader和orderer同步区块

首先，orderer对外主要是broadcast和deliver两个服务orderer服务介绍。并且我们知道peer和orderer同步区块肯定是deliver服务实现的，但是到底是peer从orderer拉还是ordrer推送给peer呢？由于peer可以知道orderer信息（配置块）并且是grpc服务，则推断是peer从orderer拉区块。如果是拉区块，那么peer如何获取区块，获取区块的方式是什么？

1.1 Orderer Deliver服务

首先，查看orderer deliver服务是怎么运行的，是如何同步区块的。
当deliver服务被调用时，转到Handle()方法处理

func (h *Handler) Handle(ctx context.Context, srv *Server) error {
    ...
    for {
        logger.Debugf("Attempting to read seek info message from %s", addr)
        // 接受发来envelope
        envelope, err := srv.Recv()
        ...
        // 分发区块
        status, err := h.deliverBlocks(ctx, srv, envelope)
        ...
    }
}

其中，srv.Recv()接收envelope，在根据envelope信息分发block。

func (h *Handler) deliverBlocks(ctx context.Context, srv *Server, envelope *cb.Envelope) (status cb.Status, err error) {
    addr := util.ExtractRemoteAddress(ctx)
    payload, err := utils.UnmarshalPayload(envelope.Payload)
    if payload.Header == nil {
        logger.Warningf("Malformed envelope received from %s with bad header", addr)
        return cb.Status_BAD_REQUEST, nil
    }
    chdr, err := utils.UnmarshalChannelHeader(payload.Header.ChannelHeader)
    err = h.validateChannelHeader(ctx, chdr)
    chain := h.ChainManager.GetChain(chdr.ChannelId)
    defer func() {
        labels := append(labels, "success", strconv.FormatBool(status == cb.Status_SUCCESS))
        h.Metrics.RequestsCompleted.With(labels...).Add(1)
    }()

    accessControl, err := NewSessionAC(chain, envelope, srv.PolicyChecker, chdr.ChannelId, crypto.ExpiresAt)
    if err != nil {
        logger.Warningf("[channel: %s] failed to create access control object due to %s", chdr.ChannelId, err)
        return cb.Status_BAD_REQUEST, nil
    }

    if err := accessControl.Evaluate(); err != nil {
        logger.Warningf("[channel: %s] Client authorization revoked for deliver request from %s: %s", chdr.ChannelId, addr, err)
        return cb.Status_FORBIDDEN, nil
    }

    seekInfo := &ab.SeekInfo{}
    // 返回迭代器及起始区块号
    cursor, number := chain.Reader().Iterator(seekInfo.Start)
    defer cursor.Close()
    var stopNum uint64
    switch stop := seekInfo.Stop.Type.(type) {
    case *ab.SeekPosition_Oldest:
        stopNum = number
    case *ab.SeekPosition_Newest:
        stopNum = chain.Reader().Height() - 1
    case *ab.SeekPosition_Specified:
        stopNum = stop.Specified.Number
        if stopNum < number {
            logger.Warningf("[channel: %s] Received invalid seekInfo message from %s: start number %d greater than stop number %d", chdr.ChannelId, addr, number, stopNum)
            return cb.Status_BAD_REQUEST, nil
        }
    }

    for {
        if seekInfo.Behavior == ab.SeekInfo_FAIL_IF_NOT_READY {
            if number > chain.Reader().Height()-1 {
                return cb.Status_NOT_FOUND, nil
            }
        }

        var block *cb.Block
        var status cb.Status

        iterCh := make(chan struct{})
        go func() {
            // 获取区块
            block, status = cursor.Next()
            close(iterCh)
        }()

        select {
        case <-ctx.Done():
            logger.Debugf("Context canceled, aborting wait for next block")
            return cb.Status_INTERNAL_SERVER_ERROR, errors.Wrapf(ctx.Err(), "context finished before block retrieved")
        case <-erroredChan:
            // TODO, today, the only user of the errorChan is the orderer consensus implementations.  If the peer ever reports
            // this error, we will need to update this error message, possibly finding a way to signal what error text to return.
            logger.Warningf("Aborting deliver for request because the backing consensus implementation indicates an error")
            return cb.Status_SERVICE_UNAVAILABLE, nil
        case <-iterCh:
            // Iterator has set the block and status vars
        }

        if status != cb.Status_SUCCESS {
            logger.Errorf("[channel: %s] Error reading from channel, cause was: %v", chdr.ChannelId, status)
            return status, nil
        }

        // increment block number to support FAIL_IF_NOT_READY deliver behavior
        number++

        if err := accessControl.Evaluate(); err != nil {
            logger.Warningf("[channel: %s] Client authorization revoked for deliver request from %s: %s", chdr.ChannelId, addr, err)
            return cb.Status_FORBIDDEN, nil
        }

        logger.Debugf("[channel: %s] Delivering block for (%p) for %s", chdr.ChannelId, seekInfo, addr)
        // 发送区块
        if err := srv.SendBlockResponse(block); err != nil {
            logger.Warningf("[channel: %s] Error sending to %s: %s", chdr.ChannelId, addr, err)
            return cb.Status_INTERNAL_SERVER_ERROR, err
        }

        h.Metrics.BlocksSent.With(labels...).Add(1)
        // 如果到了client请求对最后区块跳出循环
        if stopNum == block.Header.Number {
            break
        }
    }

    logger.Debugf("[channel: %s] Done delivering to %s for (%p)", chdr.ChannelId, addr, seekInfo)

    return cb.Status_SUCCESS, nil
}

1. 反序列化envelope.Payload
2. 对payload.Header和ChannelHeader进行验证
3. 根据通道获取对应对chain
4. 访问控制相关验证，policy，signature
5. 从payload.data解析出SeekInfo
6. 新建一个迭代器cursor
7. 通过stop.type判断stopNum()
8. cursor.Next()获取下个区块及SendBlockResponse()发送区块
9. 判断是否达到请求的最后区块，是就跳过循环

// Chain encapsulates chain operations and data.
type Chain interface {
    // Sequence returns the current config sequence number, can be used to detect config changes
    Sequence() uint64

    // PolicyManager returns the current policy manager as specified by the chain configuration
    PolicyManager() policies.Manager

    // Reader returns the chain Reader for the chain
    Reader() blockledger.Reader

    // Errored returns a channel which closes when the backing consenter has errored
    Errored() <-chan struct{}
}

type SeekInfo struct {
    Start                *SeekPosition         `protobuf:"bytes,1,opt,name=start,proto3" json:"start,omitempty"`
    Stop                 *SeekPosition         `protobuf:"bytes,2,opt,name=stop,proto3" json:"stop,omitempty"`
    Behavior             SeekInfo_SeekBehavior `protobuf:"varint,3,opt,name=behavior,proto3,enum=orderer.SeekInfo_SeekBehavior" json:"behavior,omitempty"`
    XXX_NoUnkeyedLiteral struct{}              `json:"-"`
    XXX_unrecognized     []byte                `json:"-"`
    XXX_sizecache        int32                 `json:"-"`
}

1.2 peer从orderer同步区块

这里主要解决1个问题：peer如何触发orderer deliver服务？即peer和orderer怎么同步区块的？
在介绍之前参阅peer节点启动流程。在peer节点启动过程中会执行peer.Initialize()方法，对peer所在的所有chain实例化。其中调用了createChain()接口创建链对象。在createChain()方法中调用了GossipService.InitializeChannel()方法。然后调用g.deliveryService[chainID].StartDeliverForChannel()方法获取区块。

func (d *deliverServiceImpl) StartDeliverForChannel(chainID string, ledgerInfo blocksprovider.LedgerInfo, finalizer func()) error {
    d.lock.Lock()
    defer d.lock.Unlock()
    if d.stopping {
        errMsg := fmt.Sprintf("Delivery service is stopping cannot join a new channel %s", chainID)
        logger.Errorf(errMsg)
        return errors.New(errMsg)
    }
    if _, exist := d.blockProviders[chainID]; exist {
        errMsg := fmt.Sprintf("Delivery service - block provider already exists for %s found, can't start delivery", chainID)
        logger.Errorf(errMsg)
        return errors.New(errMsg)
    } else {
        client := d.newClient(chainID, ledgerInfo)
        logger.Debug("This peer will pass blocks from orderer service to other peers for channel", chainID)
        // 创建区块deliver实例
        d.blockProviders[chainID] = blocksprovider.NewBlocksProvider(chainID, client, d.conf.Gossip, d.conf.CryptoSvc)
        // 执行
        go d.launchBlockProvider(chainID, finalizer)
    }
    return nil
}

其中newClient()创建一个broadcastClient，传入参数为requester.RequestBlocks(ledgerInfoProvider)方法。很显然，peer是通过该方法获取区块的，那么该方法主要实现是什么？

func (b *blocksRequester) RequestBlocks(ledgerInfoProvider blocksprovider.LedgerInfo) error {
    height, err := ledgerInfoProvider.LedgerHeight()
    if err != nil {
        logger.Errorf("Can't get ledger height for channel %s from committer [%s]", b.chainID, err)
        return err
    }

    if height > 0 {
        logger.Debugf("Starting deliver with block [%d] for channel %s", height, b.chainID)
        if err := b.seekLatestFromCommitter(height); err != nil {
            return err
        }
    } else {
        logger.Debugf("Starting deliver with oldest block for channel %s", b.chainID)
        if err := b.seekOldest(); err != nil {
            return err
        }
    }

    return nil
}

调用了seek_XXX方法，其中

type SeekInfo struct {
    Start                *SeekPosition         `protobuf:"bytes,1,opt,name=start,proto3" json:"start,omitempty"`
    Stop                 *SeekPosition         `protobuf:"bytes,2,opt,name=stop,proto3" json:"stop,omitempty"`
    Behavior             SeekInfo_SeekBehavior `protobuf:"varint,3,opt,name=behavior,proto3,enum=orderer.SeekInfo_SeekBehavior" json:"behavior,omitempty"`
    XXX_NoUnkeyedLiteral struct{}              `json:"-"`
    XXX_unrecognized     []byte                `json:"-"`
    XXX_sizecache        int32                 `json:"-"`
}

func (b *blocksRequester) seekOldest() error {
    seekInfo := &orderer.SeekInfo{
        Start:    &orderer.SeekPosition{Type: &orderer.SeekPosition_Oldest{Oldest: &orderer.SeekOldest{}}},
        Stop:     &orderer.SeekPosition{Type: &orderer.SeekPosition_Specified{Specified: &orderer.SeekSpecified{Number: math.MaxUint64}}},
        Behavior: orderer.SeekInfo_BLOCK_UNTIL_READY,
    }

    //TODO- epoch and msgVersion may need to be obtained for nowfollowing usage in orderer/configupdate/configupdate.go
    msgVersion := int32(0)
    epoch := uint64(0)
    tlsCertHash := b.getTLSCertHash()
    env, err := utils.CreateSignedEnvelopeWithTLSBinding(common.HeaderType_DELIVER_SEEK_INFO, b.chainID, localmsp.NewSigner(), seekInfo, msgVersion, epoch, tlsCertHash)
    if err != nil {
        return err
    }
    // 发送envelope给orderer获取区块
    return b.client.Send(env)
}

从其中RequestBlocks()调用的2个方法可知,seekInfo的stopNum都为math.MaxUint64，则该方法会持续请求区块知道最大值（可以看作现在到未来的所有区块）。

上文可知，broadcastClient已经实例化，并且通过调用broadcastClient.onConnect向orderer发送获取区块的envelope。在实例化后，调用launchBlockProvider。然后会调用 pb.DeliverBlocks()方法（开始获取区块）。

type broadcastClient struct {
    stopFlag     int32
    stopChan     chan struct{}
    createClient clientFactory
    shouldRetry  retryPolicy
    onConnect    broadcastSetup
    prod         comm.ConnectionProducer

    mutex           sync.Mutex
    blocksDeliverer blocksprovider.BlocksDeliverer
    conn            *connection
    endpoint        string
}

// DeliverBlocks used to pull out blocks from the ordering service to
// distributed them across peers
func (b *blocksProviderImpl) DeliverBlocks() {
    errorStatusCounter := 0
    statusCounter := 0
    defer b.client.Close()
    for !b.isDone() {
        // 接收orderer分发的区块
        msg, err := b.client.Recv()
        if err != nil {
            logger.Warningf("[%s] Receive error: %s", b.chainID, err.Error())
            return
        }
        switch t := msg.Type.(type) {
        case *orderer.DeliverResponse_Status:
            if t.Status == common.Status_SUCCESS {
                logger.Warningf("[%s] ERROR! Received success for a seek that should never complete", b.chainID)
                return
            }
            if t.Status == common.Status_BAD_REQUEST || t.Status == common.Status_FORBIDDEN {
                logger.Errorf("[%s] Got error %v", b.chainID, t)
                errorStatusCounter++
                if errorStatusCounter > b.wrongStatusThreshold {
                    logger.Criticalf("[%s] Wrong statuses threshold passed, stopping block provider", b.chainID)
                    return
                }
            } else {
                errorStatusCounter = 0
                logger.Warningf("[%s] Got error %v", b.chainID, t)
            }
            maxDelay := float64(maxRetryDelay)
            currDelay := float64(time.Duration(math.Pow(2, float64(statusCounter))) * 100 * time.Millisecond)
            time.Sleep(time.Duration(math.Min(maxDelay, currDelay)))
            if currDelay < maxDelay {
                statusCounter++
            }
            if t.Status == common.Status_BAD_REQUEST {
                b.client.Disconnect(false)
            } else {
                b.client.Disconnect(true)
            }
            continue
        case *orderer.DeliverResponse_Block:
            errorStatusCounter = 0
            statusCounter = 0
            blockNum := t.Block.Header.Number

            marshaledBlock, err := proto.Marshal(t.Block)
            if err != nil {
                logger.Errorf("[%s] Error serializing block with sequence number %d, due to %s", b.chainID, blockNum, err)
                continue
            }
            if err := b.mcs.VerifyBlock(gossipcommon.ChainID(b.chainID), blockNum, marshaledBlock); err != nil {
                logger.Errorf("[%s] Error verifying block with sequnce number %d, due to %s", b.chainID, blockNum, err)
                continue
            }

            numberOfPeers := len(b.gossip.PeersOfChannel(gossipcommon.ChainID(b.chainID)))
            // Create payload with a block received
            payload := createPayload(blockNum, marshaledBlock)
            // Use payload to create gossip message
            gossipMsg := createGossipMsg(b.chainID, payload)

            logger.Debugf("[%s] Adding payload to local buffer, blockNum = [%d]", b.chainID, blockNum)
            // Add payload to local state payloads buffer
            if err := b.gossip.AddPayload(b.chainID, payload); err != nil {
                logger.Warningf("Block [%d] received from ordering service wasn't added to payload buffer: %v", blockNum, err)
            }

            // Gossip messages with other nodes
            logger.Debugf("[%s] Gossiping block [%d], peers number [%d]", b.chainID, blockNum, numberOfPeers)
        
            if !b.isDone() {
                // peer节点间通过gossip同步区块
                b.gossip.Gossip(gossipMsg)
            }
        default:
            logger.Warningf("[%s] Received unknown: %v", b.chainID, t)
            return
        }
    }
}

DeliverBlocks()方法介绍，首先调用 b.client.Recv()接收orderer传过来的响应，

// Recv receives a message from the ordering service
func (bc *broadcastClient) Recv() (*orderer.DeliverResponse, error) {
    o, err := bc.try(func() (interface{}, error) {
        if bc.shouldStop() {
            return nil, errors.New("closing")
        }
        return bc.tryReceive()
    })
    if err != nil {
        return nil, err
    }
    return o.(*orderer.DeliverResponse), nil
}

这里我们知道大致是peer从orderer这里拉区块的，但是还存在疑问，那就是peer如何触发orderer的deliver服务的？peer是如何调用requestBlock方法的？

• peer 调用deliver服务
  从Recv()接口会调用try(),try()会调用bc.doAction(action, resetAttemptCounter)，然后调用bc.connect()，里面调用bc.createClient(conn).Deliver(ctx)，从而peer调用了orderer的deliver服务。
• peer 调用requestBlock方法
  从上面可知，requestBlock赋值给broadcastSetup，而broadcastSetup在连接orderer后会立即调用。

// broadcastSetup is a function that is called by the broadcastClient immediately after each
// successful connection to the ordering service

1.3 组织间peer同步区块

peer间同步区块是通过gossip服务来同步的，并且通过上述代码可知，leader和orderer同步区块也是伴随着gossip服务启动（不过是属于leader的）。

    // Gossip messages with other nodes
    logger.Debugf("[%s] Gossiping block [%d], peers number [%d]", b.chainID, blockNum, numberOfPeers)

    if !b.isDone() {
        // peer节点间通过gossip同步区块
        b.gossip.Gossip(gossipMsg)
    }

1.4 peer是如何写区块

首先，其他peer是通过gossip服务同步区块，则保存区块应该是在gossip服务里面调用的，回到peer启动时gossip服务的设置

service.GetGossipService().InitializeChannel(bundle.ConfigtxValidator().ChainID(), ordererAddresses, service.Support{
        Validator:            validator,
        Committer:            c,
        Store:                store,
        Cs:                   simpleCollectionStore,
        IdDeserializeFactory: csStoreSupport,
    })
    

里面会调用

    g.chains[chainID] = state.NewGossipStateProvider(chainID, servicesAdapter, coordinator,
        g.metrics.StateMetrics, getStateConfiguration())

里面会调用

    // Listen for incoming communication
    go s.listen()
    // Deliver in order messages into the incoming channel
    go s.deliverPayloads()

deliverPayloads()会将gossip.payload 区块给写入账本。

func (s *GossipStateProviderImpl) deliverPayloads() {
    defer s.done.Done()

    for {
        select {
        // Wait for notification that next seq has arrived
        case <-s.payloads.Ready():
            logger.Debugf("[%s] Ready to transfer payloads (blocks) to the ledger, next block number is = [%d]", s.chainID, s.payloads.Next())
            // Collect all subsequent payloads
            for payload := s.payloads.Pop(); payload != nil; payload = s.payloads.Pop() {
                rawBlock := &common.Block{}
                if err := pb.Unmarshal(payload.Data, rawBlock); err != nil {
                    logger.Errorf("Error getting block with seqNum = %d due to (%+v)...dropping block", payload.SeqNum, errors.WithStack(err))
                    continue
                }
                if rawBlock.Data == nil || rawBlock.Header == nil {
                    logger.Errorf("Block with claimed sequence %d has no header (%v) or data (%v)",
                        payload.SeqNum, rawBlock.Header, rawBlock.Data)
                    continue
                }
                logger.Debugf("[%s] Transferring block [%d] with %d transaction(s) to the ledger", s.chainID, payload.SeqNum, len(rawBlock.Data.Data))

                // Read all private data into slice
                var p util.PvtDataCollections
                if payload.PrivateData != nil {
                    err := p.Unmarshal(payload.PrivateData)
                    if err != nil {
                        logger.Errorf("Wasn't able to unmarshal private data for block seqNum = %d due to (%+v)...dropping block", payload.SeqNum, errors.WithStack(err))
                        continue
                    }
                }
                // 此处会保存区块
                if err := s.commitBlock(rawBlock, p); err != nil {
                    if executionErr, isExecutionErr := err.(*vsccErrors.VSCCExecutionFailureError); isExecutionErr {
                        logger.Errorf("Failed executing VSCC due to %v. Aborting chain processing", executionErr)
                        return
                    }
                    logger.Panicf("Cannot commit block to the ledger due to %+v", errors.WithStack(err))
                }
            }
        case <-s.stopCh:
            s.stopCh <- struct{}{}
            logger.Debug("State provider has been stopped, finishing to push new blocks.")
            return
        }
    }
}

总结

1. peer启动时会启动gossip服务模块
2. leader启动gossip服务时会从orderer源源不断的请求块
3. peer之间通过gossip同步区块，当leader获取区块后会通过区块
4. peer当gossip模块中会将gossip.payload区块信息写入账本