兄弟連區塊鏈教程Fabric1.0源代碼分析Tx RWSet（讀寫集）

　　兄弟連區塊鏈教程Fabric1.0源代碼分析Tx RWSet（讀寫集），2018年下半年，區塊鏈行業正逐漸褪去發展之初的浮躁、迴歸理性，表面上看相關人才需求與身價似乎正在回落。但事實上，正是初期泡沫的漸退，讓人們更多的關注點放在了區塊鏈真正的技術之上。

Fabric 1.0源代碼筆記 之 Tx #RWSet（讀寫集）

1、RWSet概述

在背書節點模擬Transaction期間，爲交易準備了一個讀寫集合。
Read Set包含模擬Transaction讀取的Key和版本的列表，Write Set包含Key、寫入的新值、以及刪除標記（是否刪除Key）。

RWSet相關代碼分佈在protos/ledger/rwset、core/ledger/kvledger/txmgmt/rwsetutil目錄下。目錄結構如下：

• protos/ledger/rwset目錄：
      * rwset.pb.go，TxReadWriteSet和NsReadWriteSet結構體定義。

    * kv_rwset.pb.go，KVRWSet、KVRead、KVWrite、Version、RangeQueryInfo結構體定義，以及isRangeQueryInfo_ReadsInfo接口定義。

• core/ledger/kvledger/txmgmt/rwsetutil目錄：
      * rwset_proto_util.go，TxRwSet和NsRwSet結構體及方法。

    * rwset_builder.go，RWSetBuilder結構體及方法。
    * query_results_helper.go，RangeQueryResultsHelper結構體及方法。

2、TxReadWriteSet結構體（protos）

有個圖5

TxReadWriteSet結構體：

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
}
//代碼在protos/ledger/rwset/rwset.pb.go

KVRWSet結構體：

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
}
代碼在protos/ledger/rwset/kvrwset/kv_rwset.pb.go

3、TxRwSet結構體及方法（core）

有個圖6

type TxRwSet struct {
    NsRwSets []*NsRwSet
}

type NsRwSet struct {
    NameSpace string
    KvRwSet   *kvrwset.KVRWSet
}

//按TxRwSet構造TxReadWriteSet並序列化
func (txRwSet *TxRwSet) ToProtoBytes() ([]byte, error)
//[]byte反序列化爲TxReadWriteSet，按TxReadWriteSet構造TxRwSet
func (txRwSet *TxRwSet) FromProtoBytes(protoBytes []byte) error
//構造KVRead
func NewKVRead(key string, version *version.Height) *kvrwset.KVRead
//構造version.Height
func NewVersion(protoVersion *kvrwset.Version) *version.Height
//構造Version
func newProtoVersion(height *version.Height) *kvrwset.Version
//構造KVWrite
func newKVWrite(key string, value []byte) *kvrwset.KVWrite
//代碼在core/ledger/kvledger/txmgmt/rwsetutil/rwset_proto_util.go

4、RWSetBuilder結構體及方法

RWSetBuilder結構體定義：

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數組
}

type rangeQueryKey struct {
    startKey     string
    endKey       string
    itrExhausted bool //迭代器是否用盡
}
//代碼在core/ledger/kvledger/txmgmt/rwsetutil/rwset_builder.go

涉及方法如下：

//構造nsRWs
func newNsRWs() *nsRWs
//構造RWSetBuilder
func NewRWSetBuilder() *RWSetBuilder
//構造KVRead，並加入nsRWs.readMap
func (rws *RWSetBuilder) AddToReadSet(ns string, key string, version *version.Height)
//構造KVWrite，並加入nsRWs.writeMap
func (rws *RWSetBuilder) AddToWriteSet(ns string, key string, value []byte)
//用RangeQueryInfo構造rangeQueryKey，並將rangeQueryKey和RangeQueryInfo加入nsRWs.rangeQueriesKeys和nsRWs.rangeQueriesMap
func (rws *RWSetBuilder) AddToRangeQuerySet(ns string, rqi *kvrwset.RangeQueryInfo)
從RWSetBuilder構造TxRwSet
func (rws *RWSetBuilder) GetTxReadWriteSet() *TxRwSet
//獲取或創建nsRWs
func (rws *RWSetBuilder) getOrCreateNsRW(ns string) *nsRWs
//代碼在core/ledger/kvledger/txmgmt/rwsetutil/rwset_builder.go

5、RangeQueryResultsHelper結構體及方法（什麼用途呢？？？）

5.1、merkleTree（默克爾樹）

Merkle Tree，也稱Hash Tree，即存儲hash值的一棵樹。
Merkle樹的葉子是數據塊的hash值，非葉節點是其對應子節點串聯字符串的hash。

type MerkleTreeLevel uint32
type Hash []byte
const leafLevel = MerkleTreeLevel(1)

type merkleTree struct {
    tree      map[MerkleTreeLevel][]Hash
    maxLevel  MerkleTreeLevel //1
    maxDegree uint32 //單層最大個數
}
//代碼在core/ledger/kvledger/txmgmt/rwsetutil/query_results_helper.go

涉及方法如下：

//構造merkleTree
func newMerkleTree(maxDegree uint32) (*merkleTree, error) 
//加入哈希，從第一層開始加，直至當前層哈希數量沒有超過限額爲止
func (m *merkleTree) update(nextLeafLevelHash Hash) error 
func (m *merkleTree) done() error 
func (m *merkleTree) getSummery() *kvrwset.QueryReadsMerkleSummary //構造QueryReadsMerkleSummary
func (m *merkleTree) getMaxLevel() MerkleTreeLevel //獲取maxLevel
func (m *merkleTree) getMaxLevelHashes() []Hash //maxLevel層哈希數組
func (m *merkleTree) isEmpty() bool  //maxLevel爲1且第1層哈希數組爲空
func (m *merkleTree) String() string //String
//計算哈希數組合並後哈希
func computeCombinedHash(hashes []Hash) (Hash, error) 
//[]Hash轉換爲[][]byte
func hashesToBytes(hashes []Hash) [][]byte 
//代碼在core/ledger/kvledger/txmgmt/rwsetutil/query_results_helper.go

func (m *merkleTree) update(nextLeafLevelHash Hash) error代碼如下:

//const leafLevel = MerkleTreeLevel(1)
m.tree[leafLevel] = append(m.tree[leafLevel], nextLeafLevelHash) //先加入第一層
currentLevel := leafLevel
for {
    currentLevelHashes := m.tree[currentLevel]
    //如果當前層數量沒有超過限額，則返回，即Hash加到沒有數量超出限額的層爲止
    if uint32(len(currentLevelHashes)) <= m.maxDegree {
        return nil
    }
    //如果當前層數量超過限額
    nextLevelHash, err := computeCombinedHash(currentLevelHashes) //計算當前層合併哈希
    delete(m.tree, currentLevel) //刪除當前層
    nextLevel := currentLevel + 1 //進入更高一層
    m.tree[nextLevel] = append(m.tree[nextLevel], nextLevelHash) //合併哈希加入更高一層
    if nextLevel > m.maxLevel { //如果更高一層層高超過原定最大高度，則重置最大高度爲更高一層層高
        m.maxLevel = nextLevel
    }
    currentLevel = nextLevel //更新當前層爲更高一層
}
//代碼在core/ledger/kvledger/txmgmt/rwsetutil/query_results_helper.go

func (m *merkleTree) done() error代碼如下：

currentLevel := leafLevel //從第一層開始
var h Hash
var err error
for currentLevel < m.maxLevel { //循環至最高層
    currentLevelHashes := m.tree[currentLevel]
    switch len(currentLevelHashes) {
    case 0: //當前層數量爲0，進入更高一層
        currentLevel++
        continue
    case 1: //當前層數量爲1，獲取當前值
        h = currentLevelHashes[0]
    default: //當前層數量1個，計算合併哈希
        h, err = computeCombinedHash(currentLevelHashes)
    }
    delete(m.tree, currentLevel) //刪除當前層
    currentLevel++ //進入更高一層
    m.tree[currentLevel] = append(m.tree[currentLevel], h) //前一層合併哈希加入本層
}

finalHashes := m.tree[m.maxLevel] //最高一層
if uint32(len(finalHashes)) > m.maxDegree { //如果最高一層超出限額
    delete(m.tree, m.maxLevel) //刪除本層
    m.maxLevel++ //進入更高一層
    combinedHash, err := computeCombinedHash(finalHashes) //計算合併哈希
    m.tree[m.maxLevel] = []Hash{combinedHash} //哈並哈希加入新的最高層
}
return nil
//代碼在core/ledger/kvledger/txmgmt/rwsetutil/query_results_helper.go

5.2 RangeQueryResultsHelper

RangeQueryResultsHelper定義：

type RangeQueryResultsHelper struct {
    pendingResults []*kvrwset.KVRead
    mt             *merkleTree //merkleTree
    maxDegree      uint32
    hashingEnabled bool
}
//代碼在core/ledger/kvledger/txmgmt/rwsetutil/query_results_helper.go

涉及方法如下：

//構造RangeQueryResultsHelper，如果啓用哈希將構造merkleTree
func NewRangeQueryResultsHelper(enableHashing bool, maxDegree uint32) (*RangeQueryResultsHelper, error)
//添加KVRead加入pendingResults，如果pendingResults數量超過限額，執行processPendingResults
func (helper *RangeQueryResultsHelper) AddResult(kvRead *kvrwset.KVRead) error
//執行processPendingResults，並執行merkleTree.done()
func (helper *RangeQueryResultsHelper) Done() ([]*kvrwset.KVRead, *kvrwset.QueryReadsMerkleSummary, error)
//獲取QueryReadsMerkleSummary
func (helper *RangeQueryResultsHelper) GetMerkleSummary() *kvrwset.QueryReadsMerkleSummary
//pendingResults序列化並哈希後，加入merkleTree，並清空pendingResults
func (helper *RangeQueryResultsHelper) processPendingResults() error
//KVRead序列化
func serializeKVReads(kvReads []*kvrwset.KVRead) ([]byte, error)

補充 QueryReadsMerkleSummary：

type QueryReadsMerkleSummary struct {
    MaxDegree      uint32
    MaxLevel       uint32
    MaxLevelHashes [][]byte
}
//代碼在protos/ledger/rwset/kvrwset/kv_rwset.pb.go