兄弟连区块链教程Fabric1.0源代码分析Tx RWSet（读

　　兄弟连区块链教程Fabric1.0源代码分析Tx RWSet（读写集），2018年下半年，区块链行业正逐渐褪去发展之初的浮躁、回归理性，表面上看相关人才需求与身价似乎正在回落。但事实上，正是初期泡沫的渐退，让人们更多的关注点放在了区块链真正的技术之上。

# Fabric 1.0源代码笔记 之 Tx #RWSet（读写集）

## 1、RWSet概述

在背书节点模拟Transaction期间，为交易准备了一个读写集合。

Read Set包含模拟Transaction读取的Key和版本的列表，Write Set包含Key、写入的新值、以及删除标记（是否删除Key）。

RWSet相关代码分布在protos/ledger/rwset、core/ledger/kvledger/txmgmt/rwsetutil目录下。目录结构如下：

* protos/ledger/rwset目录：

    * rwset.pb.go，TxReadWriteSet和NsReadWriteSet结构体定义。

    * kv_rwset.pb.go，KVRWSet、KVRead、KVWrite、Version、RangeQueryInfo结构体定义，以及isRangeQueryInfo_ReadsInfo接口定义。

* core/ledger/kvledger/txmgmt/rwsetutil目录：

    * rwset_proto_util.go，TxRwSet和NsRwSet结构体及方法。

    * rwset_builder.go，RWSetBuilder结构体及方法。

    * query_results_helper.go，RangeQueryResultsHelper结构体及方法。

## 2、TxReadWriteSet结构体（protos）

TxReadWriteSet结构体：

```go

type TxReadWriteSet_DataModel int32

const (

    TxReadWriteSet_KV TxReadWriteSet_DataModel = 0

)

type TxReadWriteSet struct {

    DataModel TxReadWriteSet_DataModel

    NsRwset   []*NsReadWriteSet

}

type NsReadWriteSet struct {

    Namespace string

    Rwset     []byte //KVRWSet 序列化

}

//代码在protos/ledger/rwset/rwset.pb.go

```

KVRWSet结构体：

```go

type KVRWSet struct {

    Reads            []*KVRead

    RangeQueriesInfo []*RangeQueryInfo

    Writes           []*KVWrite

}

type KVRead struct {

    Key     string

    Version *Version

}

type KVWrite struct {

    Key      string

    IsDelete bool

    Value    []byte

}

type Version struct {

    BlockNum uint64

    TxNum    uint64

}

type RangeQueryInfo struct {

    StartKey     string

    EndKey       string

    ItrExhausted bool

    ReadsInfo isRangeQueryInfo_ReadsInfo

}

代码在protos/ledger/rwset/kvrwset/kv_rwset.pb.go

```

## 3、TxRwSet结构体及方法（core）

```go

type TxRwSet struct {

    NsRwSets []*NsRwSet

}

type NsRwSet struct {

    NameSpace string

    KvRwSet   *kvrwset.KVRWSet

}

//按TxRwSet构造TxReadWriteSet并序列化

func (txRwSet *TxRwSet) ToProtoBytes() ([]byte, error)

//[]byte反序列化为TxReadWriteSet，按TxReadWriteSet构造TxRwSet

func (txRwSet *TxRwSet) FromProtoBytes(protoBytes []byte) error

//构造KVRead

func NewKVRead(key string, version *version.Height) *kvrwset.KVRead

//构造version.Height

func NewVersion(protoVersion *kvrwset.Version) *version.Height

//构造Version

func newProtoVersion(height *version.Height) *kvrwset.Version

//构造KVWrite

func newKVWrite(key string, value []byte) *kvrwset.KVWrite

//代码在core/ledger/kvledger/txmgmt/rwsetutil/rwset_proto_util.go

```

## 4、RWSetBuilder结构体及方法

RWSetBuilder结构体定义：

```go

type RWSetBuilder struct {

    rwMap map[string]*nsRWs //Namespace

}

type nsRWs struct {

    readMap          map[string]*kvrwset.KVRead //KVRead map

    writeMap         map[string]*kvrwset.KVWrite //KVWrite map

    rangeQueriesMap  map[rangeQueryKey]*kvrwset.RangeQueryInfo //RangeQueryInfo map

    rangeQueriesKeys []rangeQueryKey //rangeQueryKey数组

}

type rangeQueryKey struct {

    startKey     string

    endKey       string

    itrExhausted bool //迭代器是否用尽

}

//代码在core/ledger/kvledger/txmgmt/rwsetutil/rwset_builder.go

```

涉及方法如下：

```go

//构造nsRWs

func newNsRWs() *nsRWs

//构造RWSetBuilder

func NewRWSetBuilder() *RWSetBuilder

//构造KVRead，并加入nsRWs.readMap

func (rws *RWSetBuilder) AddToReadSet(ns string, key string, version *version.Height)

//构造KVWrite，并加入nsRWs.writeMap

func (rws *RWSetBuilder) AddToWriteSet(ns string, key string, value []byte)

//用RangeQueryInfo构造rangeQueryKey，并将rangeQueryKey和RangeQueryInfo加入nsRWs.rangeQueriesKeys和nsRWs.rangeQueriesMap

func (rws *RWSetBuilder) AddToRangeQuerySet(ns string, rqi *kvrwset.RangeQueryInfo)

从RWSetBuilder构造TxRwSet

func (rws *RWSetBuilder) GetTxReadWriteSet() *TxRwSet

//获取或创建nsRWs

func (rws *RWSetBuilder) getOrCreateNsRW(ns string) *nsRWs

//代码在core/ledger/kvledger/txmgmt/rwsetutil/rwset_builder.go

```

## 5、RangeQueryResultsHelper结构体及方法（**什么用途呢？？？**）

### 5.1、merkleTree（默克尔树）

Merkle Tree，也称Hash Tree，即存储hash值的一棵树。

Merkle树的叶子是数据块的hash值，非叶节点是其对应子节点串联字符串的hash。

```go

type MerkleTreeLevel uint32

type Hash []byte

const leafLevel = MerkleTreeLevel(1)

type merkleTree struct {

    tree      map[MerkleTreeLevel][]Hash

    maxLevel  MerkleTreeLevel //1

    maxDegree uint32 //单层最大个数

}

//代码在core/ledger/kvledger/txmgmt/rwsetutil/query_results_helper.go

```

涉及方法如下：

```go

//构造merkleTree

func newMerkleTree(maxDegree uint32) (*merkleTree, error)

//加入哈希，从第一层开始加，直至当前层哈希数量没有超过限额为止

func (m *merkleTree) update(nextLeafLevelHash Hash) error

func (m *merkleTree) done() error

func (m *merkleTree) getSummery() *kvrwset.QueryReadsMerkleSummary //构造QueryReadsMerkleSummary

func (m *merkleTree) getMaxLevel() MerkleTreeLevel //获取maxLevel

func (m *merkleTree) getMaxLevelHashes() []Hash //maxLevel层哈希数组

func (m *merkleTree) isEmpty() bool  //maxLevel为1且第1层哈希数组为空

func (m *merkleTree) String() string //String

//计算哈希数组合并后哈希

func computeCombinedHash(hashes []Hash) (Hash, error)

//[]Hash转换为[][]byte

func hashesToBytes(hashes []Hash) [][]byte

//代码在core/ledger/kvledger/txmgmt/rwsetutil/query_results_helper.go

```

func (m *merkleTree) update(nextLeafLevelHash Hash) error代码如下:

```go

//const leafLevel = MerkleTreeLevel(1)

m.tree[leafLevel] = append(m.tree[leafLevel], nextLeafLevelHash) //先加入第一层

currentLevel := leafLevel

for {

    currentLevelHashes := m.tree[currentLevel]

    //如果当前层数量没有超过限额，则返回，即Hash加到没有数量超出限额的层为止

    if uint32(len(currentLevelHashes)) <= m.maxDegree {

        return nil

    }

    //如果当前层数量超过限额

    nextLevelHash, err := computeCombinedHash(currentLevelHashes) //计算当前层合并哈希

    delete(m.tree, currentLevel) //删除当前层

    nextLevel := currentLevel + 1 //进入更高一层

    m.tree[nextLevel] = append(m.tree[nextLevel], nextLevelHash) //合并哈希加入更高一层

    if nextLevel > m.maxLevel { //如果更高一层层高超过原定最大高度，则重置最大高度为更高一层层高

        m.maxLevel = nextLevel

    }

    currentLevel = nextLevel //更新当前层为更高一层

}

//代码在core/ledger/kvledger/txmgmt/rwsetutil/query_results_helper.go

```

func (m *merkleTree) done() error代码如下：

```go

currentLevel := leafLevel //从第一层开始

var h Hash

var err error

for currentLevel < m.maxLevel { //循环至最高层

    currentLevelHashes := m.tree[currentLevel]

    switch len(currentLevelHashes) {

    case 0: //当前层数量为0，进入更高一层

        currentLevel++

        continue

    case 1: //当前层数量为1，获取当前值

        h = currentLevelHashes[0]

    default: //当前层数量1个，计算合并哈希

        h, err = computeCombinedHash(currentLevelHashes)

    }

    delete(m.tree, currentLevel) //删除当前层

    currentLevel++ //进入更高一层

    m.tree[currentLevel] = append(m.tree[currentLevel], h) //前一层合并哈希加入本层

}

finalHashes := m.tree[m.maxLevel] //最高一层

if uint32(len(finalHashes)) > m.maxDegree { //如果最高一层超出限额

    delete(m.tree, m.maxLevel) //删除本层

    m.maxLevel++ //进入更高一层

    combinedHash, err := computeCombinedHash(finalHashes) //计算合并哈希

    m.tree[m.maxLevel] = []Hash{combinedHash} //哈并哈希加入新的最高层

}

return nil

//代码在core/ledger/kvledger/txmgmt/rwsetutil/query_results_helper.go

```

### 5.2 RangeQueryResultsHelper

RangeQueryResultsHelper定义：

```go

type RangeQueryResultsHelper struct {

    pendingResults []*kvrwset.KVRead

    mt             *merkleTree //merkleTree

    maxDegree      uint32

    hashingEnabled bool

}

//代码在core/ledger/kvledger/txmgmt/rwsetutil/query_results_helper.go

```

涉及方法如下：

```go

//构造RangeQueryResultsHelper，如果启用哈希将构造merkleTree

func NewRangeQueryResultsHelper(enableHashing bool, maxDegree uint32) (*RangeQueryResultsHelper, error)

//添加KVRead加入pendingResults，如果pendingResults数量超过限额，执行processPendingResults

func (helper *RangeQueryResultsHelper) AddResult(kvRead *kvrwset.KVRead) error

//执行processPendingResults，并执行merkleTree.done()

func (helper *RangeQueryResultsHelper) Done() ([]*kvrwset.KVRead, *kvrwset.QueryReadsMerkleSummary, error)

//获取QueryReadsMerkleSummary

func (helper *RangeQueryResultsHelper) GetMerkleSummary() *kvrwset.QueryReadsMerkleSummary

//pendingResults序列化并哈希后，加入merkleTree，并清空pendingResults

func (helper *RangeQueryResultsHelper) processPendingResults() error

//KVRead序列化

func serializeKVReads(kvReads []*kvrwset.KVRead) ([]byte, error)

```

补充 QueryReadsMerkleSummary：

```go

type QueryReadsMerkleSummary struct {

    MaxDegree      uint32

    MaxLevel       uint32

    MaxLevelHashes [][]byte

}

//代码在protos/ledger/rwset/kvrwset/kv_rwset.pb.go

```

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