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背景
Fabric提供了大量的API来开发智能合约#xff0c;支持 Go, Node.js, 和Java。本…hi好久没有更新Fabric相关文章今天给大家带来fabric-contract-api-go快速上手相较于原文省略较多希望深入理解的小伙伴可以点原文学习。
背景
Fabric提供了大量的API来开发智能合约支持 Go, Node.js, 和Java。本文对fabric-contract-api-go进行简单梳理可以使读者快速上手。
原文https://github.com/hyperledger/fabric-contract-api-go/blob/main/tutorials/getting-started.md
一、环境准备
装好Docker、Go的ubuntu版本尽量新一点。详细请参考原文。
二、contractapi 简述
contractapi 通过打包一个或多个合约打包成一个chaincode链码在链码中使用的合约需要实现 contractapi.ContractInterface接口实现接口相当于继承其中的方法与属性最简单的方式就是在我们自己创建的合约中嵌入contractapi.Contract结构体。代码示例
package main
import (errorsfmtgithub.com/hyperledger/fabric-contract-api-go/contractapi
)
// SimpleContract contract for handling writing and reading from the world state
type SimpleContract struct {contractapi.Contract
}三、合约函数编写的一些规则
合约仅可以返回0个、1个或2个值。0个值的情况下所有调用都返回成功1个值的情况下可以返回规定中的任意类型或error2个值的情况下第一个值是数据第二个值是error。
四、Create合约函数解释
Create函数可以在Fabric的world state中存储键值对。因为需要和world state交互我们需要传入交易的上下文在示例代码中使用了默认的contractapi.TransactionContextInterfaceTransactionContextInterface是一个接口类型实现该接口的交易上下文可以传入。然后交易上下文获取
// Create adds a new key with value to the world state
func (sc *SimpleContract) Create(ctx contractapi.TransactionContextInterface, key string, value string) error {existing, err : ctx.GetStub().GetState(key)if err ! nil {return errors.New(Unable to interact with world state)}if existing ! nil {return fmt.Errorf(Cannot create world state pair with key %s. Already exists, key)}err ctx.GetStub().PutState(key, []byte(value))if err ! nil {return errors.New(Unable to interact with world state)}return nil
}附上package shim的官方解释
// Package shim provides APIs for the chaincode to access its state
// variables, transaction context and call other chaincodes.stub的官方解释
// ChaincodeStub is an object passed to chaincode for shim side handling of
// APIs.个人理解我们在编写合约时使用stub来对账本进行操作shim提供了API进行实际的操作即链码与peer节点之间的通信。
五、完整的合约
package mainimport (errorsfmtgithub.com/hyperledger/fabric-contract-api-go/contractapi
)// SimpleContract contract for handling writing and reading from the world state
type SimpleContract struct {contractapi.Contract
}// Create adds a new key with value to the world state
func (sc *SimpleContract) Create(ctx contractapi.TransactionContextInterface, key string, value string) error {existing, err : ctx.GetStub().GetState(key)if err ! nil {return errors.New(Unable to interact with world state)}if existing ! nil {return fmt.Errorf(Cannot create world state pair with key %s. Already exists, key)}err ctx.GetStub().PutState(key, []byte(value))if err ! nil {return errors.New(Unable to interact with world state)}return nil
}// Update changes the value with key in the world state
func (sc *SimpleContract) Update(ctx contractapi.TransactionContextInterface, key string, value string) error {existing, err : ctx.GetStub().GetState(key)if err ! nil {return errors.New(Unable to interact with world state)}if existing nil {return fmt.Errorf(Cannot update world state pair with key %s. Does not exist, key)}err ctx.GetStub().PutState(key, []byte(value))if err ! nil {return errors.New(Unable to interact with world state)}return nil
}// Read returns the value at key in the world state
func (sc *SimpleContract) Read(ctx contractapi.TransactionContextInterface, key string) (string, error) {existing, err : ctx.GetStub().GetState(key)if err ! nil {return , errors.New(Unable to interact with world state)}if existing nil {return , fmt.Errorf(Cannot read world state pair with key %s. Does not exist, key)}return string(existing), nil
}六、使用合约
在同一个文件夹中创建一个main.go添加main函数。通过 contractapi.NewChaincode()方法使用先前的合约创建出来一个chaincode。
package mainimport (github.com/hyperledger/fabric-contract-api-go/contractapi
)func main() {simpleContract : new(SimpleContract)cc, err : contractapi.NewChaincode(simpleContract)if err ! nil {panic(err.Error())}if err : cc.Start(); err ! nil {panic(err.Error())}
}
