chaincode是由go语言写的，实现了定义的接口。其他语言例如JAVA也是支持的。通过application的transaction，chaincode可以初始化并管理Ledger状态。
本文基于一个用于在Ledger上创建资产（键值对）的简单案例来讲述如何在fabric开发智能合约代码
1.1 首选需要确定Go的环境被安装以及被合适的配置。
为了简单起见，我们使用以下命令：
mkdir -p $GOPATH/src/chaincode-example && cd $GOPATH/src/chaincode-example
接下来，我们创建源码文件
touch chaincode-example.go
1.2 Housekeeping
每一个chaincode都实现了Chaincode接口特别是Init以及Invoke函数。因此，我们引入
package main
import (
"fmt"
"github.com/hyperledger/fabric/core/chaincode/shim"
"github.com/hyperledger/fabric/protos/peer"
)
1.3 初始化chaincode
接下来，我们事先Init函数
// Init is called during chaincode instantiation to initialize any data.
func (t *SimpleAsset) Init(stub shim.ChaincodeStubInterface) peer.Response {
}
接下来，我们调用ChaincodeStubInterface.GetStringArgs方法获取Init中需要的参数，并检查参数的有效性。我们期望获取的参数是一个键值对。
// Init is called during chaincode instantiation to initialize any
// data. Note that chaincode upgrade also calls this function to reset
// or to migrate data, so be careful to avoid a scenario where you
// inadvertently clobber your ledger's data!
func (t *SimpleAsset) Init(stub shim.ChaincodeStubInterface) peer.Response {
// Get the args from the transaction proposal
args := stub.GetStringArgs()
if len(args) != 2 {
return shim.Error("Incorrect arguments. Expecting a key and a value")
}
}
接下来，由于我们的调用是有效的，我们将会在Ledger上存储初始状态。为了实现状态的存储，我们将会调用ChaincodeStubInterface.PutState方法，并把键值作为参数进行输入。假设一切都工作正常，则会返回一个peer.Response对象，表面初始化成功。
// Init is called during chaincode instantiation to initialize any
// data. Note that chaincode upgrade also calls this function to reset
// or to migrate data, so be careful to avoid a scenario where you
// inadvertently clobber your ledger's data!
func (t *SimpleAsset) Init(stub shim.ChaincodeStubInterface) peer.Response {
// Get the args from the transaction proposal
args := stub.GetStringArgs()
if len(args) != 2 {
return shim.Error("Incorrect arguments. Expecting a key and a value")
}
// Set up any variables or assets here by calling stub.PutState()
// We store the key and the value on the ledger
err := stub.PutState(args[0], []byte(args[1]))
if err != nil {
return shim.Error(fmt.Sprintf("Failed to create asset: %s", args[0]))
}
return shim.Success(nil)
}
1.4 调用chaincode
首先，添加Invoke函数签名
// Invoke is called per transaction on the chaincode. Each transaction is
// either a 'get' or a 'set' on the asset created by Init function. The 'set'
// method may create a new asset by specifying a new key-value pair.
func (t *SimpleAsset) Invoke(stub shim.ChaincodeStubInterface) peer.Response {
}
就像上述Init的函数那样，我们需要通过ChaincodeStubInterface获取参数。Invoke函数的参数就是需要调用chaincode应用的名称。在我们的例子中，我们的应用有两个简单的函数set与get，允许asset的值被设定，同时允许获取现在的状态。我们首先调用ChaincodeStubInterface.GetFunctionAndParameters用来获取chaincode应用的函数名称与参数。
// Invoke is called per transaction on the chaincode. Each transaction is
// either a 'get' or a 'set' on the asset created by Init function. The Set
// method may create a new asset by specifying a new key-value pair.
func (t *SimpleAsset) Invoke(stub shim.ChaincodeStubInterface) peer.Response {
// Extract the function and args from the transaction proposal
fn, args := stub.GetFunctionAndParameters()
}
接着，我们设置set与get函数名称，并调用这些chaincode应用函数，通过shim返回一个合适的响应。Error函数将会把一个响应序列化成gRPC protobuf消息。
// Invoke is called per transaction on the chaincode. Each transaction is
// either a 'get' or a 'set' on the asset created by Init function. The Set
// method may create a new asset by specifying a new key-value pair.
func (t *SimpleAsset) Invoke(stub shim.ChaincodeStubInterface) peer.Response {
// Extract the function and args from the transaction proposal
fn, args := stub.GetFunctionAndParameters()
var result string
var err error
if fn == "set" {
result, err = set(stub, args)
} else {
result, err = get(stub, args)
}
if err != nil {
return shim.Error(err.Error())
}
// Return the result as success payload
return shim.Success([]byte(result))
}
1.5 实现chaincode应用
我们的chaincode应用实现了两个函数，能够通过Invoke进行调用。接下来实现这些函数。就像我们上面所提到的，我使用chaincode shim API的ChaincodeStubInterface.PutState与ChaincodeStubInterface.GetState来访问access的状态。
// Set stores the asset (both key and value) on the ledger. If the key exists,
// it will override the value with the new one
func set(stub shim.ChaincodeStubInterface, args []string) (string, error) {
if len(args) != 2 {
return "", fmt.Errorf("Incorrect arguments. Expecting a key and a value")
}
err := stub.PutState(args[0], []byte(args[1]))
if err != nil {
return "", fmt.Errorf("Failed to set asset: %s", args[0])
}
return args[1], nil
}
// Get returns the value of the specified asset key
func get(stub shim.ChaincodeStubInterface, args []string) (string, error) {
if len(args) != 1 {
return "", fmt.Errorf("Incorrect arguments. Expecting a key")
}
value, err := stub.GetState(args[0])
if err != nil {
return "", fmt.Errorf("Failed to get asset: %s with error: %s", args[0], err)
}
if value == nil {
return "", fmt.Errorf("Asset not found: %s", args[0])
}
return string(value), nil
}
1. 6 合并上述代码
package main
import (
"fmt"
"github.com/hyperledger/fabric/core/chaincode/shim"
"github.com/hyperledger/fabric/protos/peer"
)
// SimpleAsset implements a simple chaincode to manage an asset
type SimpleAsset struct {
}
// Init is called during chaincode instantiation to initialize any
// data. Note that chaincode upgrade also calls this function to reset
// or to migrate data.
func (t *SimpleAsset) Init(stub shim.ChaincodeStubInterface) peer.Response {
// Get the args from the transaction proposal
args := stub.GetStringArgs()
if len(args) != 2 {
return shim.Error("Incorrect arguments. Expecting a key and a value")
}
// Set up any variables or assets here by calling stub.PutState()
// We store the key and the value on the ledger
err := stub.PutState(args[0], []byte(args[1]))
if err != nil {
return shim.Error(fmt.Sprintf("Failed to create asset: %s", args[0]))
}
return shim.Success(nil)
}
// Invoke is called per transaction on the chaincode. Each transaction is
// either a 'get' or a 'set' on the asset created by Init function. The Set
// method may create a new asset by specifying a new key-value pair.
func (t *SimpleAsset) Invoke(stub shim.ChaincodeStubInterface) peer.Response {
// Extract the function and args from the transaction proposal
fn, args := stub.GetFunctionAndParameters()
var result string
var err error
if fn == "set" {
result, err = set(stub, args)
} else { // assume 'get' even if fn is nil
result, err = get(stub, args)
}
if err != nil {
return shim.Error(err.Error())
}
// Return the result as success payload
return shim.Success([]byte(result))
}
// Set stores the asset (both key and value) on the ledger. If the key exists,
// it will override the value with the new one
func set(stub shim.ChaincodeStubInterface, args []string) (string, error) {
if len(args) != 2 {
return "", fmt.Errorf("Incorrect arguments. Expecting a key and a value")
}
err := stub.PutState(args[0], []byte(args[1]))
if err != nil {
return "", fmt.Errorf("Failed to set asset: %s", args[0])
}
return args[1], nil
}
// Get returns the value of the specified asset key
func get(stub shim.ChaincodeStubInterface, args []string) (string, error) {
if len(args) != 1 {
return "", fmt.Errorf("Incorrect arguments. Expecting a key")
}
value, err := stub.GetState(args[0])
if err != nil {
return "", fmt.Errorf("Failed to get asset: %s with error: %s", args[0], err)
}
if value == nil {
return "", fmt.Errorf("Asset not found: %s", args[0])
}
return string(value), nil
}
// main function starts up the chaincode in the container during instantiate
func main() {
if err := shim.Start(new(SimpleAsset)); err != nil {
fmt.Printf("Error starting SimpleAsset chaincode: %s", err)
}
}
1.7 测试
我们利用CLI容器去调用这些方法
docker exec -it cli bash
peer chaincode install -p chaincodedev/chaincode/chaincode-example -n mycc -v 1.0
peer chaincode instantiate --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 -n mycc -v 1.0 -c '{"Args":["a","10"]}' -C mychannel
接下来改变a的值为20.
peer chaincode invoke
--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
-n mycc -c '{"Args":["set", "a", "20"]}' -C mychannel
最后查询
peer chaincode query -n mycc -c '{"Args":["query","a"]}' -C mychannel
注意：目前基于搭建的容器环境 只能添加chaincode_example前缀的自定义合约代码
![Hyperledger Fabric（术语表）[图]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)