chaincode是由go語言寫的，實作了定義的接口。其他語言例如JAVA也是支援的。通過application的transaction，chaincode可以初始化并管理Ledger狀态。
本文基于一個用于在Ledger上建立資産（鍵值對）的簡單案例來講述如何在fabric開發智能合約代碼
1.1 首選需要确定Go的環境被安裝以及被合适的配置。
為了簡單起見，我們使用以下指令：
mkdir -p $GOPATH/src/chaincode-example && cd $GOPATH/src/chaincode-example
接下來，我們建立源碼檔案
touch chaincode-example.go
1.2 Housekeeping
每一個chaincode都實作了Chaincode接口特别是Init以及Invoke函數。是以，我們引入
package main
import (
"fmt"
"github.com/hyperledger/fabric/core/chaincode/shim"
"github.com/hyperledger/fabric/protos/peer"
)
1.3 初始化chaincode
接下來，我們事先Init函數
// Init is called during chaincode instantiation to initialize any data.
func (t *SimpleAsset) Init(stub shim.ChaincodeStubInterface) peer.Response {
}
接下來，我們調用ChaincodeStubInterface.GetStringArgs方法擷取Init中需要的參數，并檢查參數的有效性。我們期望擷取的參數是一個鍵值對。
// 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")
}
}
接下來，由于我們的調用是有效的，我們将會在Ledger上存儲初始狀态。為了實作狀态的存儲，我們将會調用ChaincodeStubInterface.PutState方法，并把鍵值作為參數進行輸入。假設一切都工作正常，則會傳回一個peer.Response對象，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 調用chaincode
首先，添加Invoke函數簽名
// 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的函數那樣，我們需要通過ChaincodeStubInterface擷取參數。Invoke函數的參數就是需要調用chaincode應用的名稱。在我們的例子中，我們的應用有兩個簡單的函數set與get，允許asset的值被設定，同時允許擷取現在的狀态。我們首先調用ChaincodeStubInterface.GetFunctionAndParameters用來擷取chaincode應用的函數名稱與參數。
// 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，我們設定set與get函數名稱，并調用這些chaincode應用函數，通過shim傳回一個合适的響應。Error函數将會把一個響應序列化成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 實作chaincode應用
我們的chaincode應用實作了兩個函數，能夠通過Invoke進行調用。接下來實作這些函數。就像我們上面所提到的，我使用chaincode shim API的ChaincodeStubInterface.PutState與ChaincodeStubInterface.GetState來通路access的狀态。
// 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 合并上述代碼
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 測試
我們利用CLI容器去調用這些方法
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
接下來改變a的值為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
最後查詢
peer chaincode query -n mycc -c '{"Args":["query","a"]}' -C mychannel
注意：目前基于搭建的容器環境 隻能添加chaincode_example字首的自定義合約代碼
![Hyperledger Fabric（術語表）[圖]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)