Fabric:关于链码的编写及部署的问题记录

本文主要是介绍Fabric:关于链码的编写及部署的问题记录，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

本篇主要记录里在链码的编写及配置过程中遇到的问题及解决方法。

1. Init方法

在Hyperledger Fabric中，链码的Init()方法是一个可选的方法，它主要用于链码实例化时执行一些初始化操作。如果希望账本的初始化方法可以在链码部署完成时执行，则可以将相关方法的执行放到Init()方法中。举例如下：

func (s *SmartContract) Init(ctx contractapi.TransactionContextInterface) error {//账本初始化操作err := s.InitLedger(ctx)if err != nil {return err}return nil
}
func (s *SmartContract) InitLedger(ctx contractapi.TransactionContextInterface) error {assets := []Asset{{ID: "asset1", Color: "blue", Size: 5, Owner: "Tomoko", AppraisedValue: 300},{ID: "asset2", Color: "red", Size: 5, Owner: "Brad", AppraisedValue: 400},{ID: "asset3", Color: "green", Size: 10, Owner: "Jin Soo", AppraisedValue: 500},{ID: "asset4", Color: "yellow", Size: 10, Owner: "Max", AppraisedValue: 600},{ID: "asset5", Color: "black", Size: 15, Owner: "Adriana", AppraisedValue: 700},{ID: "asset6", Color: "white", Size: 15, Owner: "Michel", AppraisedValue: 800},}for _, asset := range assets {assetJSON, err := json.Marshal(asset)if err != nil {return err}err = ctx.GetStub().PutState(asset.ID, assetJSON)if err != nil {return fmt.Errorf("failed to put to world state. %v", err)}}return nil
}

但关于这种写法，有以下几点需要说明：

这种利用Init()方法进行账本初始化的操作不一定能生效，在用Fabric-gateway-go调用链码时能生效，但使用Peer CLI调用链码时不生效，仍然需要使用peer invoke命令执行InitLedger方法。原因暂时不明。
虽然在fabric-contract-api-go的官方文档中的Init方法的返回类型为peer.Response。假如按照这种返回类型编写Init写法，具体如下：

func (s *SmartContract) Init(ctx contractapi.TransactionContextInterface) peer.Response {err := s.InitLedger(ctx)if err != nil {return peer.Response{Status:500,Message: "账本初始化失败",}}return peer.Response{Status:200,Message: "账本初始化成功",}
}

则在链码部署时会提示如下错误： Error creating business chaincode: Cannot use metadata. Metadata did not match schema:components.schemas..required: Array must have at least 1 items(需要进入链码所在的docker容器中才能该错误提示信息)

2. 链码返回类型

如果希望链码返回由多个JSON串组成的数组时，如果用[][]byte，则可能产生Error: endorsement failure during query. response: status:500 message:"Error handling success response. Value did not match schema:\n1. return: Invalid type. Expected: array, given: string" 。这种情况下，最后将返回类型改成[]string。具体案例如下：

func (s *SmartContract) GetTableAllItems(ctx contractapi.TransactionContextInterface, tableName string) ([]string, error) {query := `{"selector":{"docType":"` + tableName + `"}}`resultsIterator, err := ctx.GetStub().GetQueryResult(query)if err != nil {return nil, err}defer resultsIterator.Close()var tableItems []stringfor resultsIterator.HasNext() {queryResponse, err := resultsIterator.Next()if err != nil {return nil, err}tableItems = append(tableItems, string(queryResponse.Value))}return tableItems, nil
}

3. Struct、byte和string等的互相转换

在Hyperledger Fabric的链码编写中，通常都遇到JSON串的编码、解码等问题，这里就涉及到很多byte和string及其数组的相互转换问题。这里就以简单的go语言代码为例做一个简单的说明。

3.1 Struct转化为JSON串和string类型

Go语言中用[]byte表示JSON串。从Struct变量到JSON串和string类型的转换举例如下：

package mainimport ("encoding/json""fmt"
)type User struct {UserID string `json:"customerID"`Name   string `json:"name"`Age    int    `json:"age"`Email  string `json:"email"`
}func main() {usersList := []User{{UserID: "user1", Name: "Alice", Age: 25, Email: "alice@example.com"},{UserID: "user2", Name: "Bob", Age: 30, Email: "bob@example.com"},{UserID: "user3", Name: "Charlie", Age: -5, Email: "charlie@example.com"},{UserID: "user4", Name: "David", Age: 40, Email: "david@@example.com"},{UserID: "user5", Name: "Eve", Age: 35, Email: "eve@example,com"},}//将Struct数组转换成JSON串，返回类型为[]byteuserListJson, err := json.Marshal(usersList)if err != nil {fmt.Println(err)}//将[]byte转换为stringfmt.Println(string(userListJson))//将单独的Struct变量转换成JSON串，返回类型仍然为[]byteuserJson, err := json.Marshal(usersList[0])fmt.Println(string(userJson))
}

代码执行结果如下：

[{"customerID":"user1","name":"Alice","age":25,"email":"alice@example.com"},{"customerID":"user2","name":"Bob","age":30,"email":"bob@example.com"},{"customerID":"user3","name":"Charlie","age":-5,"email":"charlie@example.com"},{"customerID":"user4","name":"David","age":40,"email":"david@@example.com"},{"customerID":"user5","name":"Eve","age":35,"email":"eve@example,com"}]
{"customerID":"user1","name":"Alice","age":25,"email":"alice@example.com"}

从上述代码中可以看到，无论是单独的Struct变量还是Struct变量组成的数组，使用json.Marshal()方法生成的JSON串都是[]byte类型。

3.2 JSON串转化为Struct变量

这里先用string类型保存JSON串，再转化为Struct变量。其具体代码如下：

package mainimport ("encoding/json""fmt"
)type User struct {UserID    string `json:"customerID"`UserName  string `json:"name"`UserAge   int    `json:"age"`UserEmail string `json:"email"`
}func main() {userString := `[{"customerID":"user1","name":"Alice","age":25,"email":"alice@example.com"},{"customerID":"user2","name":"Bob","age":30,"email":"bob@example.com"}]`userJSON := []byte(userString)var user []Usererr := json.Unmarshal(userJSON, &user)if err != nil {fmt.Println(err)}fmt.Println(user)
}

其代码执行结果如下：

[{user1 Alice 25 alice@example.com} {user2 Bob 30 bob@example.com}]

3.3 json.Indent方法

在Go语言中，json.Indent是一个非常有用的函数，用于将原本压缩或者未格式化的JSON数据进行缩进处理，使其更加易读。它将JSON数据格式化为带有缩进和换行的形式，方便进行调试或展示。

package mainimport ("bytes""encoding/json""fmt"
)func main() {userString := `[{"customerID":"user1","name":"Alice","age":25,"email":"alice@example.com"},{"customerID":"user2","name":"Bob","age":30,"email":"bob@example.com"}]`userJSON := []byte(userString)var prettyJSON bytes.Buffererr := json.Indent(&prettyJSON, userJSON, "", "  ")if err != nil {fmt.Println(err)}fmt.Println(prettyJSON.String())
}

其代码执行结果如下：

[{"customerID": "user1","name": "Alice","age": 25,"email": "alice@example.com"},{"customerID": "user2","name": "Bob","age": 30,"email": "bob@example.com"}
]