Hyperledger中数据存取的实现

简介

本文介绍了在Hyperledger中数据存取的实现.

API接口

Hyperledger提供基于key/value的数据存储，其中key是字符串，value则是二进制字节数组，Hyperledger的Go API提供了三个方法用于数据存取：PutState（key, value）用于向Hyperledger中存储数据， GetState(key)用于从Hyperledger中提取数据，而DelState(key)则从Hyperledger中删除数据。

数据存取 Chaincode 示例

以下是一个简单的数据存取Chaincode，以及其相应的REST请求。

package mainimport ("errors""fmt""github.com/hyperledger/fabric/core/chaincode/shim"
)type SaveState1Chaincode struct {
}func (t *SaveState1Chaincode) Init(stub shim.ChaincodeStubInterface, function string, args []string) ([]byte, error) {fmt.Printf("Init called with function %s!\n", function)return nil, nil
}func (t *SaveState1Chaincode) Invoke(stub shim.ChaincodeStubInterface, function string, args []string) ([]byte, error) {fmt.Printf("Invoke called with function %s!\n", function)var key, value stringkey = args[0]value = args[1]var err errorerr = stub.PutState(key, []byte(value))if err != nil {return nil, err} return nil, nil    
}func (t *SaveState1Chaincode) Query(stub shim.ChaincodeStubInterface, function string, args []string) ([]byte, error) {fmt.Printf("Query called with function %s!\n", function)var key stringkey = args[0]valInBytes, err := stub.GetState(key)if err != nil {return nil, errors.New("Failed to get state for " + key)}message := "State for "  + key + " = " + string(valInBytes)return []byte(message), nil;
}func main() {err := shim.Start(new(SaveState1Chaincode))if err != nil {fmt.Printf("Error starting Save State chaincode: %s", err)}
}

存储数据的REST请求

{"jsonrpc": "2.0","method": "invoke","params": {"type": 1,"chaincodeID":{"name":"mycc"},"ctorMsg": {"function":"invoke","args":["testKey", "testValue"]},"secureContext": "jim"},"id": 3}

获取数据的REST请求

 {"jsonrpc": "2.0","method": "query","params": {"type": 1,"chaincodeID":{"name":"mycc"},"ctorMsg": {"function":"query","args":["testKey"]},"secureContext": "jim"},"id": 5}

关于Immutability

以上代码也可以看出Hyperledger和BitCoin和Ethereum等区块链对Immutability的不同理解，在Hyperledger中，数据提交到区块链后不仅可以改变，还甚至可以被删除，而在BitCoin和Ethereum中数据一旦提交到区块链后就不能再被改变。

这也体现在R3的Corda区块链中，R3 CTO Richard Gendal Brown在这里写道：

Immutability

The fourth feature in the “Blockchain Bundle” is often, if misleadingly, termed “immutability”: data, once committed, cannot be changed.

This isn’t quite true: if I have a piece of data then of course I can change it. What we actually mean is that: once committed, nobody else will accept a transaction from me if it tries to build on a modified version of some data that has already been accepted by other stakeholders.

Blockchains achieve this by having transactions commit to the outputs of previous transactions and have blocks commit to the content of previous blocks. Each new step can only be valid if it really does build upon an unchangeable body of previous activity.