上一篇我们分享了Composer的概念，提到了Composer将一个区块链应用抽象成若干概念，本篇我们将看看Composer如何将这些概念体现到开发流程的。

Composer开发体系架构

照例先放出一张官网的示意图:

ComposerArchitecture.png

可以发现相比直接使用Fabric，已经减少了大量的工作。可以通过generator-hyperledger-composer生成Angular的应用，然后通过Hyperledger Composer的SDK部署并运行在Fabric网络环境中。

整个Composer由以下组件构成:

• 执行环境
• JavaScript SDK
• 命令行接口
• REST Server
• LoopBack连接器
• Playground Web UI
• Yeoman代码生成器
• VSCode和Atom编辑器插件

执行环境

Hyperledger Composer设计支持多种可插拔的运行环境，目前已经实现了三种运行环境:

• Hyperledger Fabric v1.1. State存储在分布式账本
• Web. 直接在Web内部执行，用于Playground演示。State存储在浏览器的local storage中
• 内嵌环境。直接在Node.js进程内部执行，主要用于商业逻辑的单元测试。State以KV形式存储在内存中

Connection Profiles

Connection Profiles用于指明Composer如何连接到一个执行环境的。每一种执行环境都有不同的配置选项。

JavaScript SDK

这是一组Node.js API，给开发者提供创建应用操控和部署Business Network。这些API分成两个npm模块:

• compser-client: 提交交易请求到business network，以及对资产和参与者执行的CURD操作
• composer-admin: 用于管理business network，安装、启动、升级等

命令行接口

composer命令行工具提供部署和管理business network的功能

REST Server

Hyperledger Composer REST Server会自动为business network创建一个Open API(利用Swagger) REST接口。REST Server(基于LoopBack技术)将Composer模型转换为Open API的定义，并且实现CURD支持。

LoopBack连接器

Hyperledger Composer LoopBack连接器可以被REST Server使用，也可以通过支持LoopBack的集成工具单独使用。当然也可以通过LoopBack工具创建一个更复杂的自定义REST API。

Playground Web User Interface

这玩意用于定义和测试business network的。可以让商业分析人在Web上快速导入样本和商业逻辑模型。

Yeoman代码生成器

创建以下工程的脚手架:

• Angular web application
• Node.js application
• business network的脚手架

VSCode和Atom编辑器插件

尽管没有直接的IDE支持，但是这个插件可以替代一些IDE功能。

第一个Composer应用

基本概念介绍完毕之后，让我们动手创建和部署一个应用试试看。

第一步: 创建一个business network结构

Hyperledger Composer的一个关键构成就是business network definition (BND)，BND为区块链定义了数据模型，交易逻辑和访问控制规则。

最简单的方式是直接通过Yeoman创建一个脚手架business network工程:

$ yo hyperledger-composer:businessnetwork
Welcome to the business network generator
? Business network name: tutorial-network
? Description: Here is a hello world example
? Author name:  Feng Yu
? Author email: abcfy2@163.com
? License: Apache-2.0
? Namespace: org.example.mynetwork
? Do you want to generate an empty template network? No: generate a populated sample network
   create package.json
   create README.md
   create models/org.example.mynetwork.cto
   create permissions.acl
   create .eslintrc.yml
   create features/sample.feature
   create features/support/index.js
   create test/logic.js
   create lib/logic.js

在一系列交互式询问之后，我们就创建了一个business network应用程序。

第二步: 定义一个business network

一个business network是由资产、参与者、交易、访问控制规则，以及可选的时间和查询组成的。在之前创建的脚手架工程中，已经有一个model(.cto)文件了，包含了定义了在business network中存在的所有资产、参与者、交易。这个工程同样也包含了一个访问控制规则(permissions.acl)，一个包含了交易过程的函数脚本(logic.js)，package.json包含了business network的元数据。

模型化资产、参与者以及交易

模型文件(.cto)是由Hyperledger Composer Modelling Language编写的，我们直接编辑org.example.mynetwork.cto文件:

/**
 * My commodity trading network
 */
namespace org.example.mynetwork
asset Commodity identified by tradingSymbol {
    o String tradingSymbol
    o String description
    o String mainExchange
    o Double quantity
    --> Trader owner
}
participant Trader identified by tradeId {
    o String tradeId
    o String firstName
    o String lastName
}
transaction Trade {
    --> Commodity commodity
    --> Trader newOwner
}

添加JavaScript交易逻辑代码。model中用transaction声明的Trade，指明了一个交易和参与者之间的关系。后面需要定义具体的逻辑实现。编辑logic.js文件:

/**
 * Track the trade of a commodity from one trader to another
 * @param {org.example.mynetwork.Trade} trade - the trade to be processed
 * @transaction
 */
async function tradeCommodity(trade) {
    trade.commodity.owner = trade.newOwner;
    let assetRegistry = await getAssetRegistry('org.example.mynetwork.Commodity');
    await assetRegistry.update(trade.commodity);
}

添加访问控制permission.acl:

/**
 * Access control rules for tutorial-network
 */
rule Default {
    description: "Allow all participants access to all resources"
    participant: "ANY"
    operation: ALL
    resource: "org.example.mynetwork.*"
    action: ALLOW
}

rule SystemACL {
  description:  "System ACL to permit all access"
  participant: "ANY"
  operation: ALL
  resource: "org.hyperledger.composer.system.**"
  action: ALLOW
}

第三步: 打包business network

在tutorial-network/目录下执行以下命令:

$ composer archive create -t dir -n .
Creating Business Network Archive


Looking for package.json of Business Network Definition
        Input directory: /home/vagrant/tutorial-network

Found:
        Description: Here is a hello world example
        Name: tutorial-network
        Identifier: tutorial-network@0.0.1

Written Business Network Definition Archive file to
        Output file: tutorial-network@0.0.1.bna

Command succeeded

整个工程被打包成了.bna文件。

第四步: 部署business network

需要按照安装Composer的文档，将docker环境启动(./startFabric.sh)，然后部署：

$ composer network install --card PeerAdmin@hlfv1 --archiveFile tutorial-network@0.0.1.bna
✔ Installing business network. This may take a minute...
Successfully installed business network tutorial-network, version 0.0.1

Command succeeded

之后就可以运行了:

composer network start --networkName tutorial-network --networkVersion 0.0.1 --networkAdmin admin --networkAdminEnrollSecret adminpw --card PeerAdmin@hlfv1 --file networkadmin.card
Starting business network tutorial-network at version 0.0.1

Processing these Network Admins:
        userName: admin

✔ Starting business network definition. This may take a minute...
Successfully created business network card:
        Filename: networkadmin.card

Command succeeded

然后导入网络管理员身份作为可用的business network card:

$ composer card import --file networkadmin.card

Successfully imported business network card
        Card file: networkadmin.card
        Card name: admin@tutorial-network

Command succeeded

检查已部署的网络可以用以下命令:

$ composer network ping --card admin@tutorial-network
The connection to the network was successfully tested: tutorial-network
        Business network version: 0.0.1
        Composer runtime version: 0.19.7
        participant: org.hyperledger.composer.system.NetworkAdmin#admin
        identity: org.hyperledger.composer.system.Identity#67624c0918f6ae837d7d3b90e7df8dc305b0cb4e412cc8d4265fbf4f72823600

Command succeeded

第五步: 生成一个REST server

$ composer-rest-server
? Enter the name of the business network card to use: admin@tutorial-network
? Specify if you want namespaces in the generated REST API: never use namespaces
? Specify if you want to use an API key to secure the REST API: No
? Specify if you want to enable authentication for the REST API using Passport: Yes
? Specify if you want to enable multiple user and identity management using wallets: No
? Specify if you want to enable event publication over WebSockets: Yes
? Specify if you want to enable TLS security for the REST API: No

To restart the REST server using the same options, issue the following command:
   composer-rest-server -c admin@tutorial-network -n never -a true -w true

Discovering types from business network definition ...
Discovered types from business network definition
Generating schemas for all types in business network definition ...
Generated schemas for all types in business network definition
Adding schemas for all types to Loopback ...
Added schemas for all types to Loopback
Web server listening at: http://localhost:3000
Browse your REST API at http://localhost:3000/explorer

第六步: 生成应用程序

$ yo hyperledger-composer:angular
Welcome to the Hyperledger Composer Angular project generator
? Do you want to connect to a running Business Network? Yes
? Project name: angular-app
? Description: Hyperledger Composer Angular project
? Author name: Feng Yu
? Author email: abcfy2@163.com
? License: Apache-2.0
? Name of the Business Network card: admin@tutorial-network
? Do you want to generate a new REST API or connect to an existing REST API?  Connect to an existing REST API
? REST server address: http://localhost
? REST server port: 3000
? Should namespaces be used in the generated REST API? Namespaces are not used
Created application!
Completed generation process
   create app.js
   create Dockerfile
   create e2e/app.e2e-spec.ts
   create e2e/app.po.ts
   create e2e/tsconfig.e2e.json
   create e2e/tsconfig.json
   create karma.conf.js
   create manifest.yml
   create package.json
   create protractor.conf.js
   create proxy.conf.js
   create README.md
   create src/app/app-routing.module.ts
   create src/app/app.component.css
   create src/app/app.component.html
   create src/app/app.component.spec.ts
   create src/app/app.component.ts
   create src/app/app.module.ts
   create src/app/asset/images/delete_noun_cc.svg
   create src/app/asset/images/edit_noun_cc.svg
   create src/app/asset/images/failed_noun_cc.svg
   create src/app/asset/images/success_noun_cc.svg
   create src/app/data.service.ts
   create src/app/home/home.component.css
   create src/app/home/home.component.html
   create src/app/home/home.component.ts
   create src/environments/environment.prod.ts
   create src/environments/environment.ts
   create src/favicon.ico
   create src/index.html
   create src/main.ts
   create src/polyfills.ts
   create src/styles.css
   create src/test.ts
   create src/tsconfig.app.json
   create src/tsconfig.json
   create src/tsconfig.spec.json
   create tsconfig.json
   create tslint.json
   create .angular-cli.json
   create .editorconfig
   create .gitignore
   create .dockerignore
   create .cfignore
   create .npmignore
   create src/app/Commodity/Commodity.component.ts
   create src/app/Commodity/Commodity.service.ts
   create src/app/Commodity/Commodity.component.spec.ts
   create src/app/Commodity/Commodity.component.html
   create src/app/Commodity/Commodity.component.css
   create src/app/Trader/Trader.component.ts
   create src/app/Trader/Trader.service.ts
   create src/app/Trader/Trader.component.spec.ts
   create src/app/Trader/Trader.component.html
   create src/app/Trader/Trader.component.css
   create src/app/Trade/Trade.component.ts
   create src/app/Trade/Trade.service.ts
   create src/app/Trade/Trade.component.spec.ts
   create src/app/Trade/Trade.component.html
   create src/app/Trade/Trade.component.css


I'm all done. Running npm install for you to install the required dependencies. If this fails, try running the command yourself.

最后在angular工程下运行

npm start

最后用http://localhost:4200即可访问应用。

小结

本篇文档大致展示了一下使用composer通过快速脚手架生成工程代码，快速部署Fabric应用。总体来说Composer开发体验比直接使用Fabric API的体验太好了。在大致了解Fabric的文档之后，开发者完全可以通过Composer上手开发应用，而不需要对接非常底层的Fabric。