Go语言+区块链教程Fabric1.0源代码分析Ledger historydb历史数据库，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。
## 1、historydb概述
historydb，用于存储所有块读写集中写集的内容。
代码分布在core/ledger/kvledger/history/historydb目录下，目录结构如下：
* historydb.go，定义核心接口HistoryDBProvider和HistoryDB。
* histmgr_helper.go，historydb工具函数。
* historyleveldb目录，historydb基于leveldb的实现。
* historyleveldb.go，HistoryDBProvider和HistoryDB接口实现，即historyleveldb.HistoryDBProvider和historyleveldb.historyDB结构体及方法。
* historyleveldb_query_executer.go，定义LevelHistoryDBQueryExecutor和historyScanner结构体及方法。
## 2、核心接口定义
HistoryDBProvider接口定义：
```go
type HistoryDBProvider interface {
GetDBHandle(id string) (HistoryDB, error) //获取HistoryDB
Close() //关闭所有HistoryDB
//代码在core/ledger/kvledger/history/historydb/historydb.go
HistoryDB接口定义：
```go
type HistoryDB interface {
//构造 LevelHistoryDBQueryExecutor
NewHistoryQueryExecutor(blockStore blkstorage.BlockStore) (ledger.HistoryQueryExecutor, error)
//提交Block入historyDB
Commit(block *common.Block) error
//获取savePointKey，即version.Height
GetLastSavepoint() (*version.Height, error)
//是否应该恢复，比较lastAvailableBlock和Savepoint
ShouldRecover(lastAvailableBlock uint64) (bool, uint64, error)
//提交丢失的块
CommitLostBlock(block *common.Block) error
//代码在core/ledger/kvledger/history/historydb/historydb.go
补充ledger.HistoryQueryExecutor接口定义：执行历史记录查询。
```go
type HistoryQueryExecutor interface {
GetHistoryForKey(namespace string, key string) (commonledger.ResultsIterator, error) //按key查历史记录
//代码在core/ledger/ledger_interface.go
## 3、historydb工具函数
```go
//构造复合HistoryKey，ns 0x00 key 0x00 blocknum trannum
func ConstructCompositeHistoryKey(ns string, key string, blocknum uint64, trannum uint64) []byte
//构造部分复合HistoryKey，ns 0x00 key 0x00 0xff
func ConstructPartialCompositeHistoryKey(ns string, key string, endkey bool) []byte
//按分隔符separator，分割bytesToSplit
func SplitCompositeHistoryKey(bytesToSplit []byte, separator []byte) ([]byte, []byte)
//代码在core/ledger/kvledger/history/historydb/histmgr_helper.go
## 4、HistoryDB接口实现
HistoryDB接口实现，即historyleveldb.historyDB结构体及方法。historyDB结构体定义如下：
```go
type historyDB struct {
db *leveldbhelper.DBHandle //leveldb
dbName string //dbName
//代码在core/ledger/kvledger/history/historydb/historyleveldb/historyleveldb.go
涉及方法如下：
```go
//构造historyDB
func newHistoryDB(db *leveldbhelper.DBHandle, dbName string) *historyDB
//do nothing
func (historyDB *historyDB) Open() error
//do nothing
func (historyDB *historyDB) Close()
//提交Block入historyDB，将读写集中写集入库，并更新savePointKey
func (historyDB *historyDB) Commit(block *common.Block) error
//构造 LevelHistoryDBQueryExecutor
func (historyDB *historyDB) NewHistoryQueryExecutor(blockStore blkstorage.BlockStore) (ledger.HistoryQueryExecutor, error)
获取savePointKey，即version.Height
func (historyDB *historyDB) GetLastSavepoint() (*version.Height, error)
//是否应该恢复，比较lastAvailableBlock和Savepoint
func (historyDB *historyDB) ShouldRecover(lastAvailableBlock uint64) (bool, uint64, error)
//提交丢失的块，即调用historyDB.Commit(block)
func (historyDB *historyDB) CommitLostBlock(block *common.Block) error
//代码在core/ledger/kvledger/history/historydb/historyleveldb/historyleveldb.go
func (historyDB *historyDB) Commit(block *common.Block) error代码如下：
```go
blockNo := block.Header.Number //区块编号
var tranNo uint64 //交易编号，初始化值为0
dbBatch := leveldbhelper.NewUpdateBatch() //leveldb批量更新
//交易验证代码，type TxValidationFlags []uint8
//交易筛选器
txsFilter := util.TxValidationFlags(block.Metadata.Metadata[common.BlockMetadataIndex_TRANSACTIONS_FILTER])
if len(txsFilter) == 0 {
txsFilter = util.NewTxValidationFlags(len(block.Data.Data))
block.Metadata.Metadata[common.BlockMetadataIndex_TRANSACTIONS_FILTER] = txsFilter
for _, envBytes := range block.Data.Data {
if txsFilter.IsInvalid(int(tranNo)) { //检查指定的交易是否有效
tranNo++
continue
//[]byte反序列化为Envelope
env, err := putils.GetEnvelopeFromBlock(envBytes)
payload, err := putils.GetPayload(env) //e.Payload反序列化为Payload
//[]byte反序列化为ChannelHeader
chdr, err := putils.UnmarshalChannelHeader(payload.Header.ChannelHeader)
if common.HeaderType(chdr.Type) == common.HeaderType_ENDORSER_TRANSACTION { //背书交易，type HeaderType int32
respPayload, err := putils.GetActionFromEnvelope(envBytes) //获取ChaincodeAction
txRWSet := &rwsetutil.TxRwSet{}
err = txRWSet.FromProtoBytes(respPayload.Results) //[]byte反序列化后构造NsRwSet，加入txRWSet.NsRwSets
for _, nsRWSet := range txRWSet.NsRwSets {
ns := nsRWSet.NameSpace
for _, kvWrite := range nsRWSet.KvRwSet.Writes {
writeKey := kvWrite.Key
//txRWSet中写集入库
compositeHistoryKey := historydb.ConstructCompositeHistoryKey(ns, writeKey, blockNo, tranNo)
dbBatch.Put(compositeHistoryKey, emptyValue)
} else {
logger.Debugf("Skipping transaction [%d] since it is not an endorsement transaction\n", tranNo)
tranNo++
height := version.NewHeight(blockNo, tranNo)
dbBatch.Put(savePointKey, height.ToBytes())
err := historyDB.db.WriteBatch(dbBatch, true)
//代码在core/ledger/kvledger/history/historydb/historyleveldb/historyleveldb.go
Tx（Transaction 交易）相关更详细内容，参考：[Fabric 1.0源代码笔记 之 Tx（Transaction 交易）](../tx/README.md)
## 5、HistoryDBProvider接口实现
HistoryDBProvider接口实现，即historyleveldb.HistoryDBProvider结构体和方法。
```go
type HistoryDBProvider struct {
dbProvider *leveldbhelper.Provider
//构造HistoryDBProvider
func NewHistoryDBProvider() *HistoryDBProvider
//获取HistoryDB
func (provider *HistoryDBProvider) GetDBHandle(dbName string) (historydb.HistoryDB, error)
//关闭所有HistoryDB句柄，调取provider.dbProvider.Close()
func (provider *HistoryDBProvider) Close()
//代码在core/ledger/kvledger/history/historydb/historyleveldb/historyleveldb.go
## 6、LevelHistoryDBQueryExecutor和historyScanner结构体及方法
LevelHistoryDBQueryExecutor结构体及方法：实现ledger.HistoryQueryExecutor接口。
```go
type LevelHistoryDBQueryExecutor struct {
historyDB *historyDB
blockStore blkstorage.BlockStore //用于传递给historyScanner
//按key查historyDB，调用q.historyDB.db.GetIterator(compositeStartKey, compositeEndKey)
func (q *LevelHistoryDBQueryExecutor) GetHistoryForKey(namespace string, key string) (commonledger.ResultsIterator, error)
//代码在core/ledger/kvledger/history/historydb/historyleveldb/historyleveldb_query_executer.go
historyScanner结构体及方法：实现ledger.ResultsIterator接口。
```go
type historyScanner struct {
compositePartialKey []byte //ns 0x00 key 0x00
namespace string
key string
dbItr iterator.Iterator //leveldb迭代器
blockStore blkstorage.BlockStore
//构造historyScanner
func newHistoryScanner(compositePartialKey []byte, namespace string, key string, dbItr iterator.Iterator, blockStore blkstorage.BlockStore) *historyScanner
//按迭代器中key取blockNum和tranNum，再按blockNum和tranNum从blockStore中取Envelope，然后从Envelope的txRWSet.NsRwSets中按key查找并构造queryresult.KeyModification
func (scanner *historyScanner) Next() (commonledger.QueryResult, error)
func (scanner *historyScanner) Close() //scanner.dbItr.Release()
从Envelope的txRWSet.NsRwSets中按key查找并构造queryresult.KeyModification
func getKeyModificationFromTran(tranEnvelope *common.Envelope, namespace string, key string) (commonledger.QueryResult, error)
//代码在core/ledger/kvledger/history/historydb/historyleveldb/historyleveldb_query_executer.go
补充queryresult.KeyModification：
```go
type KeyModification struct {
TxId string //交易ID，ChannelHeader.TxId
Value []byte //读写集中Value，KVWrite.Value
Timestamp *google_protobuf.Timestamp //ChannelHeader.Timestamp
IsDelete bool //KVWrite.IsDelete
//代码在protos/ledger/queryresult/kv_query_result.pb.go
