这篇文章给大家分享的是有关Hyperledger fabric Chaincode开发的示例分析的内容。小编觉得挺实用的，因此分享给大家做个参考，一起跟随小编过来看看吧。
shim.ChaincodeStubInterface 接口有三个方法，分别是：Init、Query 和 Invoke
package main
import ( "fmt" "strconv" "github.com/hyperledger/fabric/core/chaincode/shim" pb "github.com/hyperledger/fabric/protos/peer" )
type SimpleChaincode struct {
}负责初始化工作，链码首次部署到区块链网络时调用，将由部署自己的链代码实例的每个对等节点执行。此方法可用于任何与初始化、引导或设置相关的任务。
func (t *SimpleChaincode) Init(stub shim.ChaincodeStubInterface) pb.Response {
}只要在区块链状态上执行任何读取/获取/查询操作，就需要调用 Query 方法。如果尝试在 Query 方法内修改区块链的状态，将会抛出异常。
此方法主要是做修改操作，但是很多例子中一些用户也在 Invoke 做查询。
put, get, del 等操作都在可以在 Invoke 中运行
func (t *SimpleChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response {
}参考例子
func (s *SmartContract) Invoke(stub shim.ChaincodeStubInterface) sc.Response {
// Retrieve the requested Smart Contract function and arguments
function, args := stub.GetFunctionAndParameters()
// Route to the appropriate handler function to interact with the ledger appropriately
if function == "balanceToken" {
return s.balanceToken(stub, args)
} else if function == "initLedger" {
return s.initLedger(stub)
} else if function == "transferToken" {
return s.transferToken(stub, args)
}
return shim.Error("Invalid Smart Contract function name.")
}在 Invoke 函数中，首先使用 stub.GetFunctionAndParameters() 获取合约函数 function, args := stub.GetFunctionAndParameters() 然后判断函数名称，实现对应的逻辑关系。 if function == "balanceToken" { return s.balanceToken(stub, args) } else if function == "initLedger" { return s.initLedger(stub) } else if function == "transferToken" { return s.transferToken(stub, args) }
任何 Go 程序的都需要 main 函数，他是程序的入口，因此该函数被用于引导/启动链代码。当对peer节点部署chaincode并实例化时，就会执行 main 函数。
func main() {
err := shim.Start(new(SimpleChaincode))
if err != nil {
fmt.Printf("Error starting Simple chaincode: %s", err)
}
}shim.Start(new(SampleChaincode)) 启动链代码并注册到peer 节点。
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。
写入数据如果是 struct 结构体，需要序列化，通常使用 json,其他形式的序列化也可以，只要能反序列化即可。
写入区块联系
func (s *SmartContract) initLedger(stub shim.ChaincodeStubInterface) sc.Response {
token := &Token{
Owner: "netkiller",
TotalSupply: 10000,
TokenName: "代币通正",
TokenSymbol: "COIN",
BalanceOf: map[string]uint{}}
token.initialSupply()
tokenAsBytes, _ := json.Marshal(token)
stub.PutState("Token", tokenAsBytes)
fmt.Println("Added", tokenAsBytes)
return shim.Success(nil)
}通过key获取区块信息
func (s *SmartContract) balanceToken(stub shim.ChaincodeStubInterface, args []string) sc.Response {
if len(args) != 1 {
return shim.Error("Incorrect number of arguments. Expecting 1")
}
tokenAsBytes, _ := stub.GetState(args[0])
token := Token{}
json.Unmarshal(tokenAsBytes, &token)
amount := token.balance(args[1])
return shim.Success(amount)
}删除区块信息
func (s *SmartContract) deleteData(stub shim.ChaincodeStubInterface, args []string) sc.Response {
if len(args) != 1 {
return shim.Error("Incorrect number of arguments. Expecting 1")
}
err= stub.DelState(args[0])
if err != nil {
return shim.Error("Failed to delete Student from DB, key is: "+key)
}
return shim.Success(nil)
}State 数据库并没有提供修改功能，修改数据可以先读取，再修改，最后写入
func (s *SmartContract) transferToken(stub shim.ChaincodeStubInterface, args []string) sc.Response {
if len(args) != 3 {
return shim.Error("Incorrect number of arguments. Expecting 2")
}
tokenAsBytes, _ := stub.GetState(args[0])
token := Token{}
json.Unmarshal(tokenAsBytes, &token)
token.transfer(args[1],args[2],args[3])
tokenAsBytes, _ = json.Marshal(token)
stub.PutState(args[0], tokenAsBytes)
return shim.Success(nil)
}区块链是一个线性的数据结构，只要知道开始位置，结束位置，就能够取出中间部分的数据。
func (s *SmartContract) queryAllCars(APIstub shim.ChaincodeStubInterface) sc.Response {
startKey := "CAR0"
endKey := "CAR999"
resultsIterator, err := APIstub.GetStateByRange(startKey, endKey)
if err != nil {
return shim.Error(err.Error())
}
defer resultsIterator.Close()
// buffer is a JSON array containing QueryResults
var buffer bytes.Buffer
buffer.WriteString("[")
bArrayMemberAlreadyWritten := false
for resultsIterator.HasNext() {
queryResponse, err := resultsIterator.Next()
if err != nil {
return shim.Error(err.Error())
}
// Add a comma before array members, suppress it for the first array member
if bArrayMemberAlreadyWritten == true {
buffer.WriteString(",")
}
buffer.WriteString("{\"Key\":")
buffer.WriteString("\"")
buffer.WriteString(queryResponse.Key)
buffer.WriteString("\"")
buffer.WriteString(", \"Record\":")
// Record is a JSON object, so we write as-is
buffer.WriteString(string(queryResponse.Value))
buffer.WriteString("}")
bArrayMemberAlreadyWritten = true
}
buffer.WriteString("]")
fmt.Printf("- queryAllCars:\n%s\n", buffer.String())
return shim.Success(buffer.Bytes())
}GetQueryResult 能查询 json 里面的数据
下面例子是 Name = Neo Chen 的所有数据。
func (t *SimpleChaincode) getQueryResult(stub shim.ChaincodeStubInterface, args []string) pb.Response{
name:="Neo Chen" //需要查询的名字
queryString := fmt.Sprintf("{\"selector\":{\"Name\":\"%s\"}}", name)
resultsIterator,err:= stub.GetQueryResult(queryString)//必须是CouchDB才行
if err!=nil{
return shim.Error("query failed")
}
person,err:=getListResult(resultsIterator)
if err!=nil{
return shim.Error("query failed")
}
return shim.Success(person)
}通过key获取历史数据
func (t *SimpleChaincode) historyQuery(stub shim.ChaincodeStubInterface, args []string) pb.Response{
if len(args) != 1 {
return shim.Error("Incorrect number of arguments. Expecting 1")
}
it,err:= stub.GetHistoryForKey(args[0])
if err!=nil{
return shim.Error(err.Error())
}
var result,_= getHistoryListResult(it)
return shim.Success(result)
}func getHistoryListResult(resultsIterator shim.HistoryQueryIteratorInterface) ([]byte,error){
defer resultsIterator.Close()
// buffer is a JSON array containing QueryRecords
var buffer bytes.Buffer
buffer.WriteString("[")
bArrayMemberAlreadyWritten := false
for resultsIterator.HasNext() {
queryResponse, err := resultsIterator.Next()
if err != nil {
return nil, err
}
// Add a comma before array members, suppress it for the first array member
if bArrayMemberAlreadyWritten == true {
buffer.WriteString(",")
}
item,_:= json.Marshal( queryResponse)
buffer.Write(item)
bArrayMemberAlreadyWritten = true
}
buffer.WriteString("]")
fmt.Printf("queryResult:\n%s\n", buffer.String())
return buffer.Bytes(), nil
}// maintain the index
indexName := "color~name"
colorNameIndexKey, err := stub.CreateCompositeKey(indexName, []string{marbleJSON.Color, marbleJSON.Name})
if err != nil {
return shim.Error(err.Error())
}
// Delete index entry to state.
err = stub.DelState(colorNameIndexKey)
if err != nil {
return shim.Error("Failed to delete state:" + err.Error())
}// get the color and name from color~name composite key
objectType, compositeKeyParts, err := stub.SplitCompositeKey(responseRange.Key)
if err != nil {
return shim.Error(err.Error())
}
returnedColor := compositeKeyParts[0]
returnedMarbleName := compositeKeyParts[1]Hyperledger Fabic 事件实现了发布/订阅消息队列。您可以自由地在链码中创建和发出自定义事件。例如，区块链的状态发生改变，就会生成一个事件。通过向区块链上的事件中心注册一个事件适配器，客户端应用程序可以订阅和使用这些事件。
func (t *SimpleChaincode) testEvent(stub shim.ChaincodeStubInterface, args []string) pb.Response{
message := "Event send data is here!"
err := stub.SetEvent("evtsender", []byte(message))
if err != nil {
return shim.Error(err.Error())
}
return shim.Success(nil)
}
func (t *SimpleChaincode) testEvent(stub shim.ChaincodeStubInterface, args []string) pb.Response{
event := &Token{
Owner: "netkiller",
TotalSupply: 10000,
TokenName: "代币通正",
TokenSymbol: "COIN",
BalanceOf: map[string]uint{}}
eventBytes, err ;= json.Marshal(&event)
if err != nil {
return nil, err
}
err := stub.SetEvent("evtSender", eventBytes)
if err != nil {
fmt.Println("Could not set event for loan application creation", err)
}
}在当前连码中调用另一个连码，调用连码需要提供连码名和通道名 stub.InvokeChaincode("连码名",调用函数,"通道")
func (t *SimpleChaincode) testInvokeChainCode(stub shim.ChaincodeStubInterface, args []string) pb.Response{
trans:=[][]byte{[]byte("invoke"),[]byte("transfer"),[]byte("netkiller"),[]byte("neo"),[]byte("100")}
response:= stub.InvokeChaincode("token",trans,"mychannel")
fmt.Println(response.Message)
return shim.Success([]byte( response.Message))
}
16.9. 案例
16.9.1. 模仿以太坊 ERC20 规范的 Hyperledger Fabric 实现
package main
import (
"bytes"
"encoding/json"
"fmt"
"strconv"
"github.com/hyperledger/fabric/core/chaincode/shim"
sc "github.com/hyperledger/fabric/protos/peer"
)
// Define the Smart Contract structure
type SmartContract struct {
}
type Token struct {
Owner string `json:"Owner"`
TotalSupply uint `json:"TotalSupply"`
TokenName string `json:"TokenName"`
TokenSymbol string `json:"TokenSymbol"`
BalanceOf map[string]uint `json:"BalanceOf"`
}
func (token *Token) initialSupply(){
token.BalanceOf[token.Owner] = token.TotalSupply;
}
func (token *Token) transfer (_from string, _to string, _value uint){
if(token.BalanceOf[_from] >= _value){
token.BalanceOf[_from] -= _value;
token.BalanceOf[_to] += _value;
}
}
func (token *Token) balance (_from string) uint{
return token.BalanceOf[_from]
}
func (token *Token) burn(_value uint) {
if(token.BalanceOf[token.Owner] >= _value){
token.BalanceOf[token.Owner] -= _value;
token.TotalSupply -= _value;
}
}
func (token *Token) burnFrom(_from string, _value uint) {
if(token.BalanceOf[_from] >= _value){
token.BalanceOf[_from] -= _value;
token.TotalSupply -= _value;
}
}
func (token *Token) mint(_value uint) {
token.BalanceOf[token.Owner] += _value;
token.TotalSupply += _value;
}
func (s *SmartContract) Init(stub shim.ChaincodeStubInterface) sc.Response {
return shim.Success(nil)
}
func (s *SmartContract) initLedger(stub shim.ChaincodeStubInterface) sc.Response {
token := &Token{
Owner: "netkiller",
TotalSupply: 10000,
TokenName: "代币通正",
TokenSymbol: "COIN",
BalanceOf: map[string]uint{}}
token.initialSupply()
tokenAsBytes, _ := json.Marshal(token)
stub.PutState("Token", tokenAsBytes)
fmt.Println("Added", tokenAsBytes)
return shim.Success(nil)
}
func (s *SmartContract) transferToken(stub shim.ChaincodeStubInterface, args []string) sc.Response {
if len(args) != 3 {
return shim.Error("Incorrect number of arguments. Expecting 2")
}
tokenAsBytes, _ := stub.GetState(args[0])
token := Token{}
json.Unmarshal(tokenAsBytes, &token)
token.transfer(args[1],args[2],args[3])
tokenAsBytes, _ = json.Marshal(token)
stub.PutState(args[0], tokenAsBytes)
return shim.Success(nil)
}
func (s *SmartContract) balanceToken(stub shim.ChaincodeStubInterface, args []string) sc.Response {
if len(args) != 1 {
return shim.Error("Incorrect number of arguments. Expecting 1")
}
tokenAsBytes, _ := stub.GetState(args[0])
token := Token{}
json.Unmarshal(tokenAsBytes, &token)
amount := token.balance(args[1])
return shim.Success(amount)
}
func (s *SmartContract) Invoke(stub shim.ChaincodeStubInterface) sc.Response {
// Retrieve the requested Smart Contract function and arguments
function, args := stub.GetFunctionAndParameters()
// Route to the appropriate handler function to interact with the ledger appropriately
if function == "balanceToken" {
return s.balanceToken(stub, args)
} else if function == "initLedger" {
return s.initLedger(stub)
} else if function == "transferToken" {
return s.transferToken(stub, args)
}
return shim.Error("Invalid Smart Contract function name.")
}
// The main function is only relevant in unit test mode. Only included here for completeness.
func main() {
// Create a new Smart Contract
err := shim.Start(new(SmartContract))
if err != nil {
fmt.Printf("Error creating new Smart Contract: %s", err)
}
}感谢各位的阅读！关于“Hyperledger fabric Chaincode开发的示例分析”这篇文章就分享到这里了，希望以上内容可以对大家有一定的帮助，让大家可以学到更多知识，如果觉得文章不错，可以把它分享出去让更多的人看到吧！
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