cosmos源码分析之七Tendermint架构分析
一、介绍
Tendermint在网络有人把它当成一个共识，有人把它当成一个通信组件。这都是可以理解的。Tendermint融合了共识和网络通信部分。它类似于一个软件包，通过使用Tendermint可以很容易的开发一个和Cosmos相兼容的区块链（当然，如果使用Cosmos-sdk会更简单，但是会屏蔽更多的细节）。可以把它理解成Cosmos的一个底层架构，提供类似于基础服务的一个平台。Tendermint可以提供一个Cosmos标准的跨链的基础应用。
在前面分析完成Cosmos-sdk后，现在深入到网络通信和共识来看一看cosmos到底有什么特别之处？
二、整体架构
1、BFT
Tendermint使用的共识算法是拜占庭容错共识协议，它是来源于DLS共识算法。使用这种算法的目的是可以简单方便的解决区块链的分叉机制。这种BFT的机制要求有固定的一组验证人，然后他们会尝试在某个区块上达成共识。每个区块的共识轮流进行，每一轮都有一个提议者来发起区块，之后由验证人来决定是否接受穿上区块或者进入下一轮投票。
Tendermint采用由绝对多数的选票（三分之二）待定的最优拜占庭算法。因此它可以确定的做到：
如果想做恶，必须要有三分之一以上的选票出现问题，并且提交了两个值。
如果任何验证组引起安全问题，就会被发现并对冲突进行投票，同时广播有问题的那些选票。
因为使用了BFT，所以其共识的速度在所有的共识中最相当快速的，很容易达到并维持每秒千笔交易的速度。
2、P2P
Tendermint中的网络底层通信，使用的是一种普通的反应器，它通过参数来查找需要连接的P2P节点，在Tendermint的节点连接中，维护着两组映射来管理连接自己和自己连接的对象，分别称做inbound,outbound.
outbound中，有两种连接，一种是连接时指定的seed,一种是在初始化时检测出来的节点。一般情况下，outbound的数量少于10个。而inbound控制在50个左右的连接。
既然是基于反应器的，那么编程的复杂性就大大降低了。只需要服务监听就可以了。这里不再细节赘述网络通信部分。
网络在启动时，会启动一个协和，定时轮询outbound的数量，来控制连接的稳定性。
3、架构
Tendermint的设计目的是为了创建一个统一的区块链开发的基础组件。通过将区块链中主要的P2P和共识抽象出来，实现区块链开发过程中的组件式管理。这样做的优势有以下几点：
一个是代码重用。对通用的网络通信和共识就不必再重复的造轮子。
二是解放了区块链编程的语言。比如以太坊用go,c++，但是通过Tendermint的抽象后，可以使用任何语言（觉得和当初JAVA才提出时一次编译的想法有些相似啊）。特别是对于智能合约，这个优点就更显得明显了。
4、Tendermint的共识过程
Tendermint共识机制中通过作验证人（Validators）来对区块达成共识，这个在前面已经介绍过，一组验证人负责对每一轮的新区块进行提议和投票。整个共识达成的过程如下图所示。
每一轮的开始（New Round），节点对新一轮的区块进行提议。之后，合格的提议区块首先经过一轮预投票（Prevote）。在提议区块获得2/3以上的投票后，进入下一轮的预认可（Precommit），同样是待获得2/3以上的验证人预认可后，被提议区块就正式获得了认可（Commit）。而得到认可的这个区块就被添加的到区块链中。
下面为详细的过程：
在Tendermint算法中，如果遇到对同一特定区块的同意及否决信息同时超过2/3的情况，需要启用外部的维护机制去核查是否存在超过1/3的验证节点伪造签名或者投出双重选票。
三、源码分析
1、共识部分
共识中有一个重要的数据结构，那就是共识的状态，它决定的共识进行的步骤：
type ConsensusState struct {
cmn.BaseService
// config details
config *cfg.ConsensusConfig
privValidator types.PrivValidator // for signing votes
// services for creating and executing blocks
// TODO: encapsulate all of this in one "BlockManager"
blockExec *sm.BlockExecutor
blockStore types.BlockStore
mempool types.Mempool
evpool types.EvidencePool
// internal state
mtx sync.Mutex
cstypes.RoundState
state sm.State // State until height-1.
// state changes may be triggered by: msgs from peers,
// msgs from ourself, or by timeouts
peerMsgQueue chan msgInfo
internalMsgQueue chan msgInfo
timeoutTicker TimeoutTicker
// we use eventBus to trigger msg broadcasts in the reactor,
// and to notify external subscribers, eg. through a websocket
eventBus *types.EventBus
// a Write-Ahead Log ensures we can recover from any kind of crash
// and helps us avoid signing conflicting votes
wal WAL
replayMode bool // so we don't log signing errors during replay
doWALCatchup bool // determines if we even try to do the catchup
// for tests where we want to limit the number of transitions the state makes
nSteps int
// some functions can be overwritten for testing
decideProposal func(height int64, round int)
doPrevote func(height int64, round int)
setProposal func(proposal *types.Proposal) error
// closed when we finish shutting down
done chan struct{
}
// synchronous pubsub between consensus state and reactor.
// state only emits EventNewRoundStep, EventVote and EventProposalHeartbeat
evsw tmevents.EventSwitch
}
所以在共识要首先创建一个Proposal：
func (cs *ConsensusState) createProposalBlock() (block *types.Block, blockParts *types.PartSet) {
var commit *types.Commit
if cs.Height == 1 {
// We're creating a proposal for the first block.
// The commit is empty, but not nil.
commit = &types.Commit{
}
} else if cs.LastCommit.HasTwoThirdsMajority() {
// Make the commit from LastCommit
commit = cs.LastCommit.MakeCommit()
} else {
// This shouldn't happen.
cs.Logger.Error("enterPropose: Cannot propose anything: No commit for the previous block.")
return
}
// Mempool validated transactions
txs := cs.mempool.Reap(cs.config.MaxBlockSizeTxs)
block, parts := cs.state.MakeBlock(cs.Height, txs, commit)
evidence := cs.evpool.PendingEvidence()
block.AddEvidence(evidence)
return block, parts
}
func NewProposal(height int64, round int, blockPartsHeader PartSetHeader, polRound int, polBlockID BlockID) *Proposal {
return &Proposal{
Height: height,
Round: round,
Timestamp: time.Now().UTC(),
BlockPartsHeader: blockPartsHeader,
POLRound: polRound,
POLBlockID: polBlockID,
}
}
然后进行验证：
// Implements PrivValidator.
func (pv *MockPV) SignProposal(chainID string, proposal *Proposal) error {
signBytes := proposal.SignBytes(chainID)
sig := pv.privKey.Sign(signBytes)
proposal.Signature = sig
return nil
}
广播：
type peer struct {
cmn.BaseService
// raw peerConn and the multiplex connection
peerConn
mconn *tmconn.MConnection
// peer's node info and the channel it knows about
// channels = nodeInfo.Channels
// cached to avoid copying nodeInfo in hasChannel
nodeInfo NodeInfo
channels []byte
// User data
Data *cmn.CMap
}
func (p *peer) Send(chID byte, msgBytes []byte) bool {
if !p.IsRunning() {
// see Switch#Broadcast, where we fetch the list of peers and loop over
// them - while we're looping, one peer may be removed and stopped.
return false
} else if !p.hasChannel(chID) {
return false
}
return p.mconn.Send(chID, msgBytes)
}
真正的共识算法过程在state中：
type RoundState struct {
Height int64 `json:"height"` // Height we are working on
Round int `json:"round"`
Step RoundStepType `json:"step"`
StartTime time.Time `json:"start_time"`
CommitTime time.Time `json:"commit_time"` // Subjective time when +2/3 precommits for Block at Round were found
Validators *types.ValidatorSet `json:"validators"`
Proposal *types.Proposal `json:"proposal"`
ProposalBlock *types.Block `json:"proposal_block"`
ProposalBlockParts *types.PartSet `json:"proposal_block_parts"`
LockedRound int `json:"locked_round"`
LockedBlock *types.Block `json:"locked_block"`
LockedBlockParts *types.PartSet `json:"locked_block_parts"`
ValidRound int `json:"valid_round"` // Last known round with POL for non-nil valid block.
ValidBlock *types.Block `json:"valid_block"` // Last known block of POL mentioned above.
ValidBlockParts *types.PartSet `json:"valid_block_parts"` // Last known block parts of POL metnioned above.
Votes *HeightVoteSet `json:"votes"`
CommitRound int `json:"commit_round"` //
LastCommit *types.VoteSet `json:"last_commit"` // Last precommits at Height-1
LastValidators *types.ValidatorSet `json:"last_validators"`
}
func (hvs *HeightVoteSet) POLInfo() (polRound int, polBlockID types.BlockID) {
hvs.mtx.Lock()
defer hvs.mtx.Unlock()
for r := hvs.round; r >= 0; r-- {
rvs := hvs.getVoteSet(r, types.VoteTypePrevote)
polBlockID, ok := rvs.TwoThirdsMajority()
if ok {
return r, polBlockID
}
}
return -1, types.BlockID{
}
}
//启动一轮新的共识
func (cs *ConsensusState) startRoutines(maxSteps int) {
err := cs.timeoutTicker.Start()
if err != nil {
cs.Logger.Error("Error starting timeout ticker", "err", err)
return
}
go cs.receiveRoutine(maxSteps)
}
// Updates ConsensusState and increments height to match that of state.
// The round becomes 0 and cs.Step becomes cstypes.RoundStepNewHeight.
func (cs *ConsensusState) updateToState(state sm.State) {
if cs.CommitRound > -1 && 0 < cs.Height && cs.Height != state.LastBlockHeight {
cmn.PanicSanity(cmn.Fmt("updateToState() expected state height of %v but found %v",
cs.Height, state.LastBlockHeight))
}
if !cs.state.IsEmpty() && cs.state.LastBlockHeight+1 != cs.Height {
// This might happen when someone else is mutating cs.state.
// Someone forgot to pass in state.Copy() somewhere?!
cmn.PanicSanity(cmn.Fmt("Inconsistent cs.state.LastBlockHeight+1 %v vs cs.Height %v",
cs.state.LastBlockHeight+1, cs.Height))
}
// If state isn't further out than cs.state, just ignore.
// This happens when SwitchToConsensus() is called in the reactor.
// We don't want to reset e.g. the Votes.
if !cs.state.IsEmpty() && (state.LastBlockHeight <= cs.state.LastBlockHeight) {
cs.Logger.Info("Ignoring updateToState()", "newHeight", state.LastBlockHeight+1, "oldHeight", cs.state.LastBlockHeight+1)
return
}
// Reset fields based on state.
validators := state.Validators
lastPrecommits := (*types.VoteSet)(nil)
if cs.CommitRound > -1 && cs.Votes != nil {
if !cs.Votes.Precommits(cs.CommitRound).HasTwoThirdsMajority() {
cmn.PanicSanity("updateToState(state) called but last Precommit round didn't have +2/3")
}
lastPrecommits = cs.Votes.Precommits(cs.CommitRound)
}
// Next desired block height
height := state.LastBlockHeight + 1
// RoundState fields
cs.updateHeight(height)
cs.updateRoundStep(0, cstypes.RoundStepNewHeight)
if cs.CommitTime.IsZero() {
// "Now" makes it easier to sync up dev nodes.
// We add timeoutCommit to allow transactions
// to be gathered for the first block.
// And alternative solution that relies on clocks:
// cs.StartTime = state.LastBlockTime.Add(timeoutCommit)
cs.StartTime = cs.config.Commit(time.Now())
} else {
cs.StartTime = cs.config.Commit(cs.CommitTime)
}
cs.Validators = validators
cs.Proposal = nil
cs.ProposalBlock = nil
cs.ProposalBlockParts = nil
cs.LockedRound = 0
cs.LockedBlock = nil
cs.LockedBlockParts = nil
cs.ValidRound = 0
cs.ValidBlock = nil
cs.ValidBlockParts = nil
cs.Votes = cstypes.NewHeightVoteSet(state.ChainID, height, validators)
cs.CommitRound = -1
cs.LastCommit = lastPrecommits
cs.LastValidators = state.LastValidators
cs.state = state
// Finally, broadcast RoundState
cs.newStep()
}
细节之处其实就是BFT的三阶段提交，对着代码就可以看得很清楚。
2、P2P部分
首先看一下连接的数据结构体：
type MConnection struct {
cmn.BaseService
conn net.Conn
bufConnReader *bufio.Reader
bufConnWriter *bufio.Writer
sendMonitor *flow.Monitor
recvMonitor *flow.Monitor
send chan struct{
}
pong chan struct{
}
channels []*Channel
channelsIdx map[byte]*Channel
onReceive receiveCbFunc
onError errorCbFunc
errored uint32
config *MConnConfig
quit chan struct{
}
flushTimer *cmn.ThrottleTimer // flush writes as necessary but throttled.
pingTimer *cmn.RepeatTimer // send pings periodically
// close conn if pong is not received in pongTimeout
pongTimer *time.Timer
pongTimeoutCh chan bool // true - timeout, false - peer sent pong
chStatsTimer *cmn.RepeatTimer // update channel stats periodically
created time.Time // time of creation
}
其中的代码还是比较容易看清楚的，每一个Peer需要有一个这个结构体的变量的实例。它可以发送数据：
// Queues a message to be sent to channel.
func (c *MConnection) Send(chID byte, msgBytes []byte) bool {
if !c.IsRunning() {
return false
}
c.Logger.Debug("Send", "channel", chID, "conn", c, "msgBytes", fmt.Sprintf("%X", msgBytes))
// Send message to channel.
channel, ok := c.channelsIdx[chID]
if !ok {
c.Logger.Error(cmn.Fmt("Cannot send bytes, unknown channel %X", chID))
return false
}
success := channel.sendBytes(msgBytes)
if success {
// Wake up sendRoutine if necessary
select {
case c.send <- struct{
}{
}:
default:
}
} else {
c.Logger.Error("Send failed", "channel", chID, "conn", c, "msgBytes", fmt.Sprintf("%X", msgBytes))
}
return success
}
当然，它还有很多功能，这里就不再都列举出来。下面看一下Peer的代码：
type Peer interface {
cmn.Service
ID() ID // peer's cryptographic ID
RemoteIP() net.IP // remote IP of the connection
IsOutbound() bool // did we dial the peer
IsPersistent() bool // do we redial this peer when we disconnect
NodeInfo() NodeInfo // peer's info
Status() tmconn.ConnectionStatus
Send(byte, []byte) bool
TrySend(byte, []byte) bool
Set(string, interface{
})
Get(string) interface{
}
}
//----------------------------------------------------------
// peerConn contains the raw connection and its config.
type peerConn struct {
outbound bool
persistent bool
config *PeerConfig
conn net.Conn // source connection
ip net.IP
}
它的两类连接：
func newOutboundPeerConn(addr *NetAddress, config *PeerConfig, persistent bool, ourNodePrivKey crypto.PrivKey) (peerConn, error) {
var pc peerConn
conn, err := dial(addr, config)
if err != nil {
return pc, cmn.ErrorWrap(err, "Error creating peer")
}
pc, err = newPeerConn(conn, config, true, persistent, ourNodePrivKey)
if err != nil {
if err2 := conn.Close(); err2 != nil {
return pc, cmn.ErrorWrap(err, err2.Error())
}
return pc, err
}
// ensure dialed ID matches connection ID
if addr.ID != pc.ID() {
if err2 := conn.Close(); err2 != nil {
return pc, cmn.ErrorWrap(err, err2.Error())
}
return pc, ErrSwitchAuthenticationFailure{
addr, pc.ID()}
}
return pc, nil
}
func newInboundPeerConn(conn net.Conn, config *PeerConfig, ourNodePrivKey crypto.PrivKey) (peerConn, error) {
// TODO: issue PoW challenge
return newPeerConn(conn, config, false, false, ourNodePrivKey)
}
func newPeerConn(rawConn net.Conn,
config *PeerConfig, outbound, persistent bool,
ourNodePrivKey crypto.PrivKey) (pc peerConn, err error) {
conn := rawConn
// Fuzz connection
if config.Fuzz {
// so we have time to do peer handshakes and get set up
conn = FuzzConnAfterFromConfig(conn, 10*time.Second, config.FuzzConfig)
}
// Set deadline for secret handshake
if err := conn.SetDeadline(time.Now().Add(config.HandshakeTimeout * time.Second)); err != nil {
return pc, cmn.ErrorWrap(err, "Error setting deadline while encrypting connection")
}
// Encrypt connection
conn, err = tmconn.MakeSecretConnection(conn, ourNodePrivKey)
if err != nil {
return pc, cmn.ErrorWrap(err, "Error creating peer")
}
// Only the information we already have
return peerConn{
config: config,
outbound: outbound,
persistent: persistent,
conn: conn,
}, nil
}
它们由一个公共的接口来控制：
type Reactor interface {
cmn.Service // Start, Stop
// SetSwitch allows setting a switch.
SetSwitch(*Switch)
// GetChannels returns the list of channel descriptors.
GetChannels() []*conn.ChannelDescriptor
// AddPeer is called by the switch when a new peer is added.
AddPeer(peer Peer)
// RemovePeer is called by the switch when the peer is stopped (due to error
// or other reason).
RemovePeer(peer Peer, reason interface{
})
// Receive is called when msgBytes is received from peer.
//
// NOTE reactor can not keep msgBytes around after Receive completes without
// copying.
//
// CONTRACT: msgBytes are not nil.
Receive(chID byte, peer Peer, msgBytes []byte)
}
//--------------------------------------
type BaseReactor struct {
cmn.BaseService // Provides Start, Stop, .Quit
Switch *Switch
}
节点的管理和控制都要通过这个接口继承的相关的结构体来处理。
服务器的监听由listener.go来实现：
type Listener interface {
Connections() <-chan net.Conn
InternalAddress() *NetAddress
ExternalAddress() *NetAddress
String() string
Stop() error
}
// Implements Listener
type DefaultListener struct {
cmn.BaseService
listener net.Listener
intAddr *NetAddress
extAddr *NetAddress
connections chan net.Conn
}
启动监听：
// Accept connections and pass on the channel
func (l *DefaultListener) listenRoutine() {
for {
conn, err := l.listener.Accept()
if !l.IsRunning() {
break // Go to cleanup
}
// listener wasn't stopped,
// yet we encountered an error.
if err != nil {
panic(err)
}
l.connections <- conn
}
// Cleanup
close(l.connections)
for range l.connections {
// Drain
}
}
总体上来讲，这波代码写得中规中矩，没有什么出彩的地方。估计Tendermint是搂草打兔子，重点还是在共识和通信协议的处理以及对整个模块的封装上。
四、总结
通过上面的分析可以看到，其实Tendermint的重点在于共识和P2P，相关的通信的协议和接口在前面介绍过。将二者抽象出来的有利之处在于，可以让开发者忽略对网络通信和共识的复杂性。直接进行业务层面的开发，而在前面也提到了SDK的封装，这进一步减少了业务上对非相关的逻辑的考虑，大大减少了开发者生产一条区块链的复杂度，而这也恰恰是Tendermint和cosmos-sdk所想达到的目的。