联盟链Fabric实现牛奶溯源源代码

以下是一个简单的联盟链Fabric实现牛奶溯源的智能合约示例代码：

package main

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

type Milk struct {
    Producer string `json:"producer"`
    CollectionDate string `json:"collection_date"`
    CollectionLocation string `json:"collection_location"`
    ProcessingDate string `json:"processing_date"`
    ProcessingLocation string `json:"processing_location"`
    DistributionDate string `json:"distribution_date"`
    DistributionLocation string `json:"distribution_location"`
    Retailer string `json:"retailer"`
}

type MilkTraceabilityChaincode struct {
}

func (t *MilkTraceabilityChaincode) Init(stub shim.ChaincodeStubInterface) pb.Response {
    return shim.Success(nil)
}

func (t *MilkTraceabilityChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response {
    function, args := stub.GetFunctionAndParameters()

    if function == "recordMilk" {
        return t.recordMilk(stub, args)
    } else if function == "getMilk" {
        return t.getMilk(stub, args)
    }

    return shim.Error("Invalid function name.")
}

func (t *MilkTraceabilityChaincode) recordMilk(stub shim.ChaincodeStubInterface, args []string) pb.Response {
    if len(args) != 8 {
        return shim.Error("Incorrect number of arguments. Expecting 8")
    }

    milk := Milk{
        Producer: args[0],
        CollectionDate: args[1],
        CollectionLocation: args[2],
        ProcessingDate: args[3],
        ProcessingLocation: args[4],
        DistributionDate: args[5],
        DistributionLocation: args[6],
        Retailer: args[7],
    }

    milkAsBytes, err := json.Marshal(milk)
    if err != nil {
        return shim.Error(err.Error())
    }

    err = stub.PutState(args[0], milkAsBytes)
    if err != nil {
        return shim.Error(err.Error())
    }

    return shim.Success(nil)
}

func (t *MilkTraceabilityChaincode) getMilk(stub shim.ChaincodeStubInterface, args []string) pb.Response {
    if len(args) != 1 {
        return shim.Error("Incorrect number of arguments. Expecting 1")
    }

    milkAsBytes, err := stub.GetState(args[0])
    if err != nil {
        return shim.Error(err.Error())
    }

    return shim.Success(milkAsBytes)
}

func main() {
    err := shim.Start(new(MilkTraceabilityChaincode))
    if err != nil {
        fmt.Printf("Error starting MilkTraceabilityChaincode chaincode: %s", err)
    }
}

该智能合约使用了一个名为`Milk`的结构体来表示牛奶的信息。`recordMilk`函数用于记录牛奶的信息，并将其保存在区块链上，`getMilk`函数用于查询已记录的牛奶信息。

您可以使用Hyperledger Fabric的命令行工具或SDK来部署和调用此智能合约。