ledger部分的接口

持续更新中，目前更新到PeerLedgerProvider的实现部分

首先在core/ledger/ledger_interface.go文件中确定了ledger用到的各种接口

PeerLedgerProvider :

给ledger实例提供handle ，代码实现如下

type PeerLedgerProvider interface {
    // Create creates a new ledger with the given genesis block.
    // This function guarantees that the creation of ledger and committing the genesis block would an atomic action
    // The chain id retrieved from the genesis block is treated as a ledger id
    Create(genesisBlock *common.Block) (PeerLedger, error)
    // Open opens an already created ledger
    Open(ledgerID string) (PeerLedger, error)
    // Exists tells whether the ledger with given id exists
    Exists(ledgerID string) (bool, error)
    // List lists the ids of the existing ledgers
    List() ([]string, error)
    // Close closes the PeerLedgerProvider
    Close()
}

方法的实现在core/ledger/kvldger/kv_ledger_provider.go里，在这个文件中还有与blockstore相关的部分。provider与blockstore相关。
provider的结构：
一个DB
三个接口，分别是
1.BlockStoreProvider
2.VersionedDBProvider
3.HistoryDBProvider

新建一个provider，函数实现如下

func NewProvider() (ledger.PeerLedgerProvider, error)

create方法：

从Block中获取chain的id，为chain/block获取Block进行存储，然后commit创始区块

func (provider *Provider) Create(genesisBlock *common.Block) (ledger.PeerLedger, error)

create先从block中获取chaincode的id

ledgerID, err := utils.GetChainIDFromBlock(genesisBlock)

接着创建上面提到的三个provider，并打开相关DB的连接，为chain/block获取存储空间，返回的是一个PeerLdger

ledger, err := provider.openInternal(ledgerID)

过程中创建了kvLedger(Ledger的数据结构实现)，代码实现如下：

type kvLedger struct {
    ledgerID   string
    blockStore blkstorage.BlockStore
    txtmgmt    txmgr.TxMgr
    historyDB  historydb.HistoryDB
}

最后：

err := ledger.Commit(genesisBlock)

这句是提交create中传入的genesisBlock。具体实现在kv_ledger.go文件中，commit的过程：
1.是验证块，涉及到的新的接口在core/ledger/txmgmt/txmgr/txmgr.go中的TxMgr(具体细节放到以后看)；
2.是向storage提交block(获取存储空间)；
3.把block中的交易存入state database(注意这里又用到了另一个commit()方法)
4.根据配置文件的配置，决定是否将交易信息写入history database。(这一步可能没有)
到这commit的流程结束。

open方法：

首先根据ledgerID判断kvledger是否存在，代码如下：

exists, err := provider.idStore.ledgerIDExists(ledgerID)

存在就直接根据ledgerID获取存储空间，代码如下：

return provider.openInternal(ledgerID)

不存在就返回nil，并报错。

openinternal方法

为chain/block获取存储空间

func (provider *Provider) openInternal(ledgerID string) (ledger.PeerLedger, error)

具体流程如下：
1.与其他provider连接，代码如下：

blockStore, err := provider.blockStoreProvider.OpenBlockStore(ledgerID)
vDB, err := provider.vdbProvider.GetDBHandle(ledgerID)
historyDB, err := provider.historydbProvider.GetDBHandle(ledgerID)

2.新建一个kvledger，代码如下：

l, err := newKVLedger(ledgerID, blockStore, vDB, historyDB)

newKVLedger代码如下：

func newKVLedger(ledgerID string, blockStore blkstorage.BlockStore,versionedDB statedb.VersionedDB, historyDB historydb.HistoryDB) (*kvLedger, error)

流程如下：
2.1.初始化一个transaction manager，代码如下：

var txmgmt txmgr.TxMgr
    txmgmt = lockbasedtxmgr.NewLockBasedTxMgr(versionedDB)

2.2.赋值，代码如下：

l := &kvLedger{ledgerID, blockStore, txmgmt, historyDB}

2.3如果它们与块存储不同步，则可以恢复状态数据库和历史数据库，代码如下：

err := l.recoverDBs()

PeerLedger ：

与OrderLedger不同的是维护一个位掩码，用来区分有效交易和无效交易，代码实现如下：

type PeerLedger interface {
    commonledger.Ledger
    // GetTransactionByID retrieves a transaction by id
    GetTransactionByID(txID string) (*peer.ProcessedTransaction, error)
    // GetBlockByHash returns a block given it's hash
    GetBlockByHash(blockHash []byte) (*common.Block, error)
    // GetBlockByTxID returns a block which contains a transaction
    GetBlockByTxID(txID string) (*common.Block, error)
    // GetTxValidationCodeByTxID returns reason code of transaction validation
    GetTxValidationCodeByTxID(txID string) (peer.TxValidationCode, error)
    // NewTxSimulator gives handle to a transaction simulator.
    // A client can obtain more than one 'TxSimulator's for parallel execution.
    // Any snapshoting/synchronization should be performed at the implementation level if required
    NewTxSimulator() (TxSimulator, error)
    // NewQueryExecutor gives handle to a query executor.
    // A client can obtain more than one 'QueryExecutor's for parallel execution.
    // Any synchronization should be performed at the implementation level if required
    NewQueryExecutor() (QueryExecutor, error)
    // NewHistoryQueryExecutor gives handle to a history query executor.
    // A client can obtain more than one 'HistoryQueryExecutor's for parallel execution.
    // Any synchronization should be performed at the implementation level if required
    NewHistoryQueryExecutor() (HistoryQueryExecutor, error)
    //Prune prunes the blocks/transactions that satisfy the given policy
    Prune(policy commonledger.PrunePolicy) error
}

ValidatedLedger :

代表的是去掉所有无效交易的PeerLedger，代码实现如下：

type ValidatedLedger interface {
    commonledger.Ledger
}

QueryExecutor ：

字面意思用来执行查询，代码实现如下：

type QueryExecutor interface {
    // GetState gets the value for given namespace and key. For a chaincode, the namespace corresponds to the chaincodeId
    GetState(namespace string, key string) ([]byte, error)
    // GetStateMultipleKeys gets the values for multiple keys in a single call
    GetStateMultipleKeys(namespace string, keys []string) ([][]byte, error)
    // GetStateRangeScanIterator returns an iterator that contains all the key-values between given key ranges.
    // startKey is included in the results and endKey is excluded. An empty startKey refers to the first available key
    // and an empty endKey refers to the last available key. For scanning all the keys, both the startKey and the endKey
    // can be supplied as empty strings. However, a full scan shuold be used judiciously for performance reasons.
    // The returned ResultsIterator contains results of type *KV which is defined in protos/ledger/queryresult.
    GetStateRangeScanIterator(namespace string, startKey string, endKey string) (commonledger.ResultsIterator, error)
    // ExecuteQuery executes the given query and returns an iterator that contains results of type specific to the underlying data store.
    // Only used for state databases that support query
    // For a chaincode, the namespace corresponds to the chaincodeId
    // The returned ResultsIterator contains results of type *KV which is defined in protos/ledger/queryresult.
    ExecuteQuery(namespace, query string) (commonledger.ResultsIterator, error)
    // Done releases resources occupied by the QueryExecutor
    Done()
}

HistoryQueryExecutor：

执行历史查询，代码实现如下：

type HistoryQueryExecutor interface {
    // GetHistoryForKey retrieves the history of values for a key.
    // The returned ResultsIterator contains results of type *KeyModification which is defined in protos/ledger/queryresult.
    GetHistoryForKey(namespace string, key string) (commonledger.ResultsIterator, error)
}

TxSimulator :

模拟了一条交易，该交易的快照是“尽可能是最近状态”，代码如下：

type TxSimulator interface {
    QueryExecutor
    // SetState sets the given value for the given namespace and key. For a chaincode, the namespace corresponds to the chaincodeId
    SetState(namespace string, key string, value []byte) error
    // DeleteState deletes the given namespace and key
    DeleteState(namespace string, key string) error
    // SetMultipleKeys sets the values for multiple keys in a single call
    SetStateMultipleKeys(namespace string, kvs map[string][]byte) error
    // ExecuteUpdate for supporting rich data model (see comments on QueryExecutor above)
    ExecuteUpdate(query string) error
    // GetTxSimulationResults encapsulates the results of the transaction simulation.
    // This should contain enough detail for
    // - The update in the state that would be caused if the transaction is to be committed
    // - The environment in which the transaction is executed so as to be able to decide the validity of the environment
    //   (at a later time on a different peer) during committing the transactions
    // Different ledger implementation (or configurations of a single implementation) may want to represent the above two pieces
    // of information in different way in order to support different data-models or optimize the information representations.
    GetTxSimulationResults() ([]byte, error)
}

以上接口涉及到的其他文件中的接口：

在common/ledger/ledger_interface.go中：

Ledger接口：

Ledger捕捉“PeerLedger”，“OrdererLedger”和“ValidatedLedger”中常见的方法。代码实现如下：

type Ledger interface {
    // GetBlockchainInfo returns basic info about blockchain
    GetBlockchainInfo() (*common.BlockchainInfo, error)
    // GetBlockByNumber returns block at a given height
    // blockNumber of  math.MaxUint64 will return last block
    GetBlockByNumber(blockNumber uint64) (*common.Block, error)
    // GetBlocksIterator returns an iterator that starts from `startBlockNumber`(inclusive).
    // The iterator is a blocking iterator i.e., it blocks till the next block gets available in the ledger
    // ResultsIterator contains type BlockHolder
    GetBlocksIterator(startBlockNumber uint64) (ResultsIterator, error)
    // Close closes the ledger
    Close()
    // Commit adds a new block
    Commit(block *common.Block) error
}