Hyperledger fabric 链码篇GO(四)

Hyperledger fabric 链码篇GO(四)

fabric中的链码也就是我们区块链所认知的智能合约,fabric中可由nodejs,java,go编写,本篇只针对GO语言编写链码。将详细介绍链码编写所必须的函数以及相关功能函数。

1、常识

  • 链码的包名指定

    // xxx.go
    package main
    
  • 必须要引入的包

    import(
        "github.com/hyperledger/fabric/core/chaincode/shim"
        pb "github.com/hyperledger/fabric/protos/peer"
        //pb为别名的意思
    )
    
  • 链码的书写要求

    //自定义结构体,类,基于这个类实现接口函数
    type Test struct{
    	//空着即可
    }
    
    
  • 链码API查询

    //go语言的链码包shim
    https://godoc.org/github.com/hyperledger/fabric-chaincode-go/shim
    

注意事项

要注意put写入的数据状态不会立刻得到获取,因为put只是执行链码的模拟交易,并不会真正将状态保存在账本中,必须经过orderer达成共识之后,将数据状态保存在区块中,然后保存在各peer节点的账本中

2、函数及链码基本结构

  • success

    // Success ... status:200
    //链码执行后返回成功信息
    func Success(payload []byte) pb.Response {
    	return pb.Response{
    		Status:  OK,
    		Payload: payload,
    	}
    }
    
  • error

    // Error ...status:500
    //链码执行后返回错误信息
    func Error(msg string) pb.Response {
    	return pb.Response{
    		Status:  ERROR,
    		Message: msg,
    	}
    }
    

2.1、基本结构

下面是编写一个链码的基本框架,由空结构体,Init函数和Invoke函数,主函数组成

package main
//引入必要的包
import (
	"fmt"
	"strconv"
	"github.com/hyperledger/fabric/core/chaincode/shim"
    //别名pb
	pb "github.com/hyperledger/fabric/protos/peer"
)
// 声明一个结构体,必备,为空
type SimpleChaincode struct {
}
//添加Init函数
func (t *SimpleChaincode) Init(stub shim.ChaincodeStubInterface) pb.Response {
		//实现链码初始化或升级时的处理逻辑
       //编写时可灵活使用stub中的API
}
//添加Invoke函数
func (t *SimpleChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response {
	//实现链码运行中被调用或查询时的处理逻辑
    //编写时可灵活使用stub中的API
}
//主函数,需要调用shim.Start()方法启动链码
func main() {
	err := shim.Start(new(SimpleChaincode))
	if err != nil {
		fmt.Printf("Error starting Simple chaincode: %s", err)
	}
}

2.2、Init函数

Init方法是系统初始化方法,当执行命令peer chaincode instantiate实例化chaincode时会调用该方法,同时命令中-c选项后面内容为会作为参数传入Init方法中。

#shell 命令
$ peer chaincode instantiate -o orderer.example.com:7050  -C $CHANNEL_NAME -n mycc -v 1.0 -c '{"Args":["init","a","100", "b", "100"]}' 

Args中共有5个参数,第一个为固定值,后面4个为参数,如果传入数据太多,可以采用json等数据格式

func (t *SimpleChaincode) Init(stub shim.ChaincodeStubInterface) pb.Response {
		 _ ,args := stub.GetFunctionAndParameters()
    return shim.Success ([]byte("success init!!!"))
}

2.3、Invoke函数

Invoke方法的主要作用为写入数据,比如发起交易等,在执行命令 peer chaincode invoke 时系统会调用该方法,并把-c后的参数传入invoke方法中。

参数原理和init类似

3、账本操作API

ChaincodeStubInterface

3.1、参数解析API

含义:调用链码时需要给被调用的目标函数/方法传递参数,与参数解析相关的API 提供了获取这些参数(包括被调用的目标函数/方法名称)的方法

GetFunctionAndParameters

  • 获取客户端传入的参数GetFunctionAndParameters()
//源码
func (s *ChaincodeStub) GetFunctionAndParameters() (function string, params []string) {
	allargs := s.GetStringArgs()
	function = ""
	params = []string{}
	if len(allargs) >= 1 {
        //返回时第一个为函数名,后面为其他参数
		function = allargs[0]
		params = allargs[1:]
	}
	return
}
//执行命令
peer chaincode invoke -o orderer.example.com:7050  -C $CHANNEL_NAME -n mycc -v 1.0 -c '{"Args":["invoke","a", "b", "10"]}' 
//示例代码
func (t *SimpleChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response {
    _ ,args := stub.GetFunctionAndParameters()
    //获取执行命令中的参数a,b,10
    var a_parm = args[0]
    var b_parm = args[1]
    var c_parm = args[2]
    return shim.Success ([]byte("success invoke!!!"))
}

3.2、账本数据状态操作API

含义:该类型API提供了对账本数据状态进行操作的方法,包括对状态数据的查询以及事务处理

GetState

  • GetState(key string) ([]byte, error) :根据指定的key查询相应的数据状态

    func (s *ChaincodeStub) GetState(key string) ([]byte, error) {
    	// Access public data by setting the collection to empty string
    	collection := ""
    	return s.handler.handleGetState(collection, key, s.ChannelID, s.TxID)
    }
    //示例代码
    func (t *SimpleChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response {
        keyvalue, err := stub.GetState("user1")
        return shim.Success(keyvalue)
    }
    

PutState

  • PutState(key string, value []byte) error:根据指定的key,将相应的value保存在分类账本中

    func (s *ChaincodeStub) PutState(key string, value []byte) error {
    	if key == "" {
    		return errors.New("key must not be an empty string")
    	}
    	// Access public data by setting the collection to empty string
    	collection := ""
    	return s.handler.handlePutState(collection, key, value, s.ChannelID, s.TxID)
    }
    //示例代码
    func (t *SimpleChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response {
        stub.PutState("user1",[]byte("putvalue"))
        return shim.Success([]byte("sucess invoke putstate"))
    }
    

DelState

  • DelState(key string) error:根据指定的key将对应的数据状态删除

    func (s *ChaincodeStub) DelState(key string) error {
    	// Access public data by setting the collection to empty string
    	collection := ""
    	return s.handler.handleDelState(collection, key, s.ChannelID, s.TxID)
    }
    func (t *SimpleChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response {
        err :=stub.DelState("user1")
        return shim.Success("delete success")
    }
    

GetStateByRange

  • GetStateByRange(startKey, endKey string) (StateQueryIteratorInterface, error):根据指定的开始key和结束key,查询范围内的所有数据状态,注意,结束key对应的数据状态不包含在返回的结果集中

    func (s *ChaincodeStub) GetStateByRange(startKey, endKey string) (StateQueryIteratorInterface, error) {
    	if startKey == "" {
    		startKey = emptyKeySubstitute
    	}
    	if err := validateSimpleKeys(startKey, endKey); err != nil {
    		return nil, err
    	}
    	collection := ""
    
    	// ignore QueryResponseMetadata as it is not applicable for a range query without pagination
    	iterator, _, err := s.handleGetStateByRange(collection, startKey, endKey, nil)
    	return iterator, err
    }
    //示例代码
    func (t *SimpleChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response {
        startKey = "startKey"
        endKey = "endKey"
        //根据范围查询,得到StateQueryIteratorInterface迭代器接口
        keyIter , err := stub.getStateByRange(startKey,endKey)
        //关闭迭代器接口
        defer keyIter.close()
        var keys []string
        for keyIter.HasNext(){            //如果有下一个节点
            //得到下一个键值对
            response, iterErr := keysIter.Next()
            if iterErr != nil{
            	return shim.Error(fmt.Sprintf("find an error  %s",iterErr))
            }
            keys = append(keys,response.Key)            //存储键值到数组中
        }
        //遍历key数组
        for key, value := range keys{
            fmt.Printf("key %d contains %s",key ,value)
        }
        //编码keys数组为json格式
        jsonKeys ,err = json.Marshal(keys)
        if err != nil{
            return shim.Error(fmt.Sprintf("data marshal json error:  %s",err))
        }
        //将编码之后的json字符串传递给客户端
        return shim.Success(jsonKeys)
    }
    

GetHistoryForKey

  • GetHistoryForKey(key string) (HistoryQueryIteratorInterface, error):根据指定的key查询所有的历史记录信息

    func (s *ChaincodeStub) GetHistoryForKey(key string) (HistoryQueryIteratorInterface, error) {
    	response, err := s.handler.handleGetHistoryForKey(key, s.ChannelID, s.TxID)
    	if err != nil {
    		return nil, err
    	}
    	return &HistoryQueryIterator{CommonIterator: &CommonIterator{s.handler, s.ChannelID, s.TxID, response, 0}}, nil
    }
    
    //示例代码
    func (t *SimpleChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response {
        
        keyIter , err := stub.GetHistoryForKey("user1")
        if err != nil{
                return shim.Error(fmt.Sprintf("GetHistoryForKey error:  %s",err))
            }
        //关闭迭代器接口
        defer keyIter.close()
        var keys []string
        for keyIter.HasNext(){            //如果有下一个节点
            //得到下一个键值对
            response, iterErr := keysIter.Next()
            if iterErr != nil{
            	return shim.Error(fmt.Sprintf("find an error  %s",iterErr))
            }
            //交易编号
            txid := response.TxId 
            //交易的值
            txvalue = response.Value
            //当前交易的状态
            txstatus = response.IsDelete	
            //交易发生的时间戳
            txtimestamp = response.Timestamp
            keys = append(keys,txid)            //存储键值到数组中
        }
        //编码keys数组为json格式
        jsonKeys ,err = json.Marshal(keys)
        if err != nil{
            return shim.Error(fmt.Sprintf("data marshal json error:  %s",err))
        }
        //将编码之后的json字符串传递给客户端
        return shim.Success(jsonKeys)
    }
    

CreateCompositeKey

  • CreateCompositeKey(objectType string, attributes []string) (string, error):创建一个复合键

    func (s *ChaincodeStub) CreateCompositeKey(objectType string, attributes []string) (string, error) {
    	return CreateCompositeKey(objectType, attributes)
    }
    
    func CreateCompositeKey(objectType string, attributes []string) (string, error) {
    	if err := validateCompositeKeyAttribute(objectType); err != nil {
    		return "", err
    	}
    	ck := compositeKeyNamespace + objectType + string(minUnicodeRuneValue)
    	for _, att := range attributes {
    		if err := validateCompositeKeyAttribute(att); err != nil {
    			return "", err
    		}
    		ck += att + string(minUnicodeRuneValue)
    	}
    	return ck, nil
    }
    

SplitCompositeKey

  • SplitCompositeKey(compositeKey string) (string, []string, error):对指定的复合键进行分割

    func (s *ChaincodeStub) SplitCompositeKey(compositeKey string) (string, []string, error) {
    	return splitCompositeKey(compositeKey)
    }
    
    func splitCompositeKey(compositeKey string) (string, []string, error) {
    	componentIndex := 1
    	components := []string{}
    	for i := 1; i < len(compositeKey); i++ {
    		if compositeKey[i] == minUnicodeRuneValue {
    			components = append(components, compositeKey[componentIndex:i])
    			componentIndex = i + 1
    		}
    	}
    	return components[0], components[1:], nil
    }
    

GetQueryResult

  • GetQueryResult(query string) (StateQueryIteratorInterface, error) :对状态数据库进行富查询,目前支持富查询的只有CouchDB

    func (s *ChaincodeStub) GetQueryResult(query string) (StateQueryIteratorInterface, error) {
    	// Access public data by setting the collection to empty string
    	collection := ""
    	// ignore QueryResponseMetadata as it is not applicable for a rich query without pagination
    	iterator, _, err := s.handleGetQueryResult(collection, query, nil)
    
    	return iterator, err
    }
    

InvokeChaincode

  • InvokeChaincode(chaincodeName string, args [][]byte, channel string):调用其他链码

    //链码名,传递参数,通道名
    func (s *ChaincodeStub) InvokeChaincode(chaincodeName string, args [][]byte, channel string) pb.Response {
    	// Internally we handle chaincode name as a composite name
    	if channel != "" {
    		chaincodeName = chaincodeName + "/" + channel
    	}
    	return s.handler.handleInvokeChaincode(chaincodeName, args, s.ChannelID, s.TxID)
    }
    //示例代码
    func (t *SimpleChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response {
        //设置参数,a向b转账11
        trans := [][]byte{[]byte("invoke"),[]byte("a"),[]byte("b"),[]byte("11")}
        //调用chaincode
        response := stub.InvokeChaincode("mycc",trans,"mychannel")
        //判断是否操作成功
        if  response.Status != shim.OK {
            errStr := fmt.Sprintf("Invoke failed ,error : %s ", response.Payload)
            return shim.Error(errStr)
        }
        return shim.Success([]byte"转账成功")
    }
    

3.3、交易信息API

含义:获取提交的交易信息的相关API

GetTxID

  • GetTxID() string :返回交易提案中指定的交易ID

    func (s *ChaincodeStub) GetTxID() string {
    	return s.TxID
    }
    

GetChannelID

  • GetChannelID() string:返回交易提案中指定通道的ID

    func (s *ChaincodeStub) GetChannelID() string {
    	return s.ChannelID
    }
    

GetTxTimestamp

  • GetTxTimestamp() (*timestamp.Timestamp, error):返回交易创建的时间戳,这个时间戳时peer接收到交易的具体时间

    func (s *ChaincodeStub) GetTxTimestamp() (*timestamp.Timestamp, error) {
    	hdr := &common.Header{}
    	if err := proto.Unmarshal(s.proposal.Header, hdr); err != nil {
    		return nil, fmt.Errorf("error unmarshaling Header: %s", err)
    	}
    
    	chdr := &common.ChannelHeader{}
    	if err := proto.Unmarshal(hdr.ChannelHeader, chdr); err != nil {
    		return nil, fmt.Errorf("error unmarshaling ChannelHeader: %s", err)
    	}
    
    	return chdr.GetTimestamp(), nil
    }
    

GetBinding

  • GetBinding() ([]byte, error):返回交易的绑定信息,如一些临时性信息,以避免重复性攻击

    func (s *ChaincodeStub) GetBinding() ([]byte, error) {
    	return s.binding, nil
    }
    

GetSignedProposal

  • GetSignedProposal() (*pb.SignedProposal, error):返回与交易提案相关的签名身份信息

    func (s *ChaincodeStub) GetSignedProposal() (*pb.SignedProposal, error) {
    	return s.signedProposal, nil
    }
    

    GetCreator

  • GetCreator() ([]byte, error) :返回该交易提交者的身份信息

    func (s *ChaincodeStub) GetCreator() ([]byte, error) {
    	return s.creator, nil
    }
    

GetTransient

  • GetTransient() (map[string][]byte, error):返回交易中不会被写至账本中的一些临时性信息

    func (s *ChaincodeStub) GetTransient() (map[string][]byte, error) {
    	return s.transient, nil
    }
    

3.4、事件处理API

含义:与事件处理相关的API

SetEvent

  • SetEvent(name string, payload []byte) error:设置事件,包括事件名称和内容

    // SetEvent documentation can be found in interfaces.go
    func (s *ChaincodeStub) SetEvent(name string, payload []byte) error {
    	if name == "" {
    		return errors.New("event name can not be empty string")
    	}
    	s.chaincodeEvent = &pb.ChaincodeEvent{EventName: name, Payload: payload}
    	return nil
    }
    

3.5、对PrivateData操作的API

含义:hyperledger fabric在1.2.0版本中新增的对私有数据操作的相关API

//根据指定key,从指定的私有数据集中查询对应的私有数据
func (s *ChaincodeStub) GetPrivateData(collection string, key string) ([]byte, error)
//根据给定的部分组合键的集合,查询给定的私有状态
func (s *ChaincodeStub) GetPrivateDataByPartialCompositeKey(collection, objectType string, attributes []string) (StateQueryIteratorInterface, error)
//根据指定的开始key和结束key查询范围内的私有数据(不包括结束key)
func (s *ChaincodeStub) GetPrivateDataByRange(collection, startKey, endKey string) (StateQueryIteratorInterface, error)
//根据指定的查询字符串执行富查询
func (s *ChaincodeStub) GetPrivateDataQueryResult(collection, query string) (StateQueryIteratorInterface, error)
//将指定的key与value保存到私有数据集中
func (s *ChaincodeStub) PutPrivateData(collection string, key string, value []byte) error
//根据key删除相应数据
func (s *ChaincodeStub) DelPrivateData(collection string, key string) error

4、背书策略

背书的过程就是一笔交易被确认的过程,而背书策略就是用来指示相关的参与方如何对交易进行确认。背书策略的设置是通过部署链码实例化时instantiate命令中的-P参数来设置的

peer chaincode instantiate -o orderer.example.com:7050 --tls --cafile /opt/gopath/src/github.com/hyperledger/fabric/peer/crypto/ordererOrganizations/example.com/orderers/orderer.example.com/msp/tlscacerts/tlsca.example.com-cert.pem -C $CHANNEL_NAME -n mycc -v 1.0 -c '{"Args":["init","a", "100", "b","200"]}' -P "AND ('Org1MSP.member','Org2MSP.member')"

此命令表示需要组织1和组织2中任意一个用户共同来参与交易的确认并且同意,这样的交易才能生效并被记录到去区块链中

#也可以指定背书节点,使用peerAddresses来指定背书节点
peer chaincode invoke -o orderer.example.com:7050 --tls true --cafile /opt/gopath/src/github.com/hyperledger/fabric/peer/crypto/ordererOrganizations/example.com/orderers/orderer.example.com/msp/tlscacerts/tlsca.example.com-cert.pem -C $CHANNEL_NAME -n mycc --peerAddresses peer0.org1.example.com:7051 --tlsRootCertFiles /opt/gopath/src/github.com/hyperledger/fabric/peer/crypto/peerOrganizations/org1.example.com/peers/peer0.org1.example.com/tls/ca.crt --peerAddresses peer0.org2.example.com:9051 --tlsRootCertFiles /opt/gopath/src/github.com/hyperledger/fabric/peer/crypto/peerOrganizations/org2.example.com/peers/peer0.org2.example.com/tls/ca.crt -c '{"Args":["invoke","a","b","10"]}'
  • 背书规则示例1

    #需要组织中任意用户共同参与背书
    "AND ('Org1MSP.member',  'Org2MSP.member')"
    
  • 背书规则示例2

    #只要组织中任意一个用户验证即可
    "OR ('Org1MSP.member',  'Org2MSP.member')"
    
  • 背书规则示例3

    #两种方法让交易生效
    #    1、组织1中有成员验证成功
    #    2、组织2和组织3中有成员共同参与验证成功
    "OR ('Org1MSP.member', AND ('Org2MSP.member',  'Org3MSP.member'))"
    

注意:背书规则只针对写入数据的操作进行校验,对于查询类的背书不操作

5、应用示例

设计了一个链码,实现了资产管理,转账交易的功能,主要实现了以下几个函数

  • init函数

    初始化链码,设定账户名称及资产额度

  • invoke函数

    实现函数的识别,并转到不同的函数功能

  • del函数

    删除账户

  • find函数

    查看账户额度

  • set函数

    根据账户名称设定要存入的金额

  • get函数

    根据账户名称设定要取出的金额

package main

import (
	"fmt"
	"github.com/hyperledger/fabric/core/chaincode/shim"
	"github.com/hyperledger/fabric/protos/peer"
	"strconv"
)

type AssetChaincode struct {
	//empty
}

//Init function
func (t *AssetChaincode) Init(stub shim.ChaincodeStubInterface) peer.Response {
	_, args := stub.GetFunctionAndParameters()
	if len(args) != 4 {
		return shim.Error("Must four initialization parameters, representing name and money ,respectively")
	}
	var a = args[0]
	var acount = args[1]
	var b = args[2]
	var bcount = args[3]
	if len(a) < 2 {
		return shim.Error("the length of name must not less than 2")
	}
	if len(b) < 2 {
		return shim.Error("the length of name must not less than 2")
	}
	_, err := strconv.Atoi(acount)
	if err != nil {
		return shim.Error(a + " account is false")
	}
	_, err = strconv.Atoi(bcount)
	if err != nil {
		return shim.Error(b + " account is false")
	}

	err = stub.PutState(a, []byte(acount))
	if err != nil {
		return shim.Error(a + " Occuring error when saving the data")
	}
	err = stub.PutState(b, []byte(bcount))
	if err != nil {
		return shim.Error(b + " Occuring error when saving the data")
	}
	return shim.Success([]byte("Init success"))
}

//Invoke function
func (t *AssetChaincode) Invoke(stub shim.ChaincodeStubInterface) peer.Response {
	fun, args := stub.GetFunctionAndParameters()
	if fun == "set" {
		return set(stub, args)
	} else if fun == "get" {
		return get(stub, args)
	} else if fun == "payment" {
		return payment(stub, args)
	} else if fun == "del" {
		return del(stub, args)
	} else if fun == "find" {
		return find(stub, args)
	}
	return shim.Error("not have this ability")
}

//find function
func find(stub shim.ChaincodeStubInterface, args []string) peer.Response {
	if len(args) != 1 {
		return shim.Error("the number of parameters must one")
	}
	result, err := stub.GetState(args[0])
	if err != nil {
		return shim.Error("occor error when reading the data")
	}
	if result == nil {
		return shim.Error("no data by the key")
	}
	return shim.Success(result)
}

//payment function
func payment(stub shim.ChaincodeStubInterface, args []string) peer.Response {
	if len(args) != 3 {
		return shim.Error("payment format error")
	}

	var source, target string
	source = args[0]
	target = args[1]
	asset, err := strconv.Atoi(args[2])
	if err != nil {
		return shim.Error("transfer amount atoi failed")
	}
	sourceS, err := stub.GetState(source)
	if err != nil {
		return shim.Error("query source asset failed")
	}
	targetS, err := stub.GetState(target)
	if err != nil {
		return shim.Error("query target asset failed")
	}
	sourceasset, err := strconv.Atoi(string(sourceS))
	if err != nil {
		return shim.Error("source asset transform int failed")
	}
	targetasset, err := strconv.Atoi(string(targetS))
	if err != nil {
		return shim.Error("target asset transform int failed")
	}
	if sourceasset < asset {
		return shim.Error("source asset don't have enough balance")
	}
	sourceasset -= asset
	targetasset += asset
	err = stub.PutState(source, []byte(strconv.Itoa(sourceasset)))
	if err != nil {
		return shim.Error("after save payment soure asset failed")
	}
	err = stub.PutState(target, []byte(strconv.Itoa(targetasset)))
	if err != nil {
		return shim.Error("after save payment target asset failed")
	}
	return shim.Success([]byte("payment success"))
}

//delete function
func del(stub shim.ChaincodeStubInterface, args []string) peer.Response {
	if len(args)!=1{
		return shim.Error("elete account format error")
	}
	err := stub.DelState(args[0])
	if err!= nil{
		return shim.Error("delete account error")
	}
	return shim.Success([]byte("delete account success"+args[0]))
}

//set function
func set(stub shim.ChaincodeStubInterface, args []string) peer.Response {
	if len(args) != 2 {
		return shim.Error("set account asset format error")
	}
	result, err := stub.GetState(args[0])
	if err != nil {
		return shim.Error("occor error when reading the data")
	}
	if result == nil {
		return shim.Error("no data by the key")
	}
	asset,err := strconv.Atoi(string(result))
	if err!= nil{
		return shim.Error("transfrom account balance error")
	}
	val,err := strconv.Atoi(string(args[1]))
	if err!= nil{
		return shim.Error("transfrom set balance error")
	}
	val += asset
	err = stub.PutState(args[0],[]byte(strconv.Itoa(val)))
	if err != nil {
		return shim.Error("save balance error")
	}
	return shim.Success([]byte("set asset success!"))
}

//get function
func get(stub shim.ChaincodeStubInterface, args []string) peer.Response {
	if len(args) != 2 {
		return shim.Error("t account asset format error")
	}
	result, err := stub.GetState(args[0])
	if err != nil {
		return shim.Error("occor error when reading the data")
	}
	if result == nil {
		return shim.Error("no data by the key")
	}
	asset,err := strconv.Atoi(string(result))
	if err!= nil{
		return shim.Error("transfrom account balance error")
	}
	val,err := strconv.Atoi(string(args[1]))
	if err!= nil{
		return shim.Error("transfrom set balance error")
	}
	if asset<val{
		return shim.Error("not have enough asset")
	}
	asset -= val
	err = stub.PutState(args[0],[]byte(strconv.Itoa(asset)))
	if err != nil {
		return shim.Error("save balance error")
	}
	return shim.Success([]byte("get asset success!"))
}

//main function
func main() {
	err := shim.Start(new(AssetChaincode))
	if err != nil {
		fmt.Printf("start assetchaincode error!,the message is :%s", err)
	}
}

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