Hyperledger Composer

Hyperledger Composer is an open-source tool that enables business owners, analysts, system integrators, and developers to create blockchain applications and smart contracts aimed at solving business issues. Developed under the Hyperledger project by the Linux Foundation, it is a suite of high-level tools designed for building blockchain business networks in Hyperledger Fabric.

Hyperledger Composer is particularly useful because it speeds up the development process and simplifies the creation of smart contracts, which are digital contracts that are self-executing with the terms of the agreement directly written into code. Hyperledger Composer significantly reduces the barriers to entry for blockchain application development.

Key Features of Hyperledger Composer

Modeling Language:
- Hyperledger Composer uses a modeling language to define the structure of the business network, including assets, participants, and transactions. The language is easy to understand and allows developers to describe the blockchain logic in a manner that closely resembles business language.
Business Network Archive:
- Users can deploy a business network archive (BNA), which is a package containing all the necessary files for a business network. This includes model files (.cto), script files (.js), access control files (.acl), and query files (.qry).
Integration with Hyperledger Fabric:
- Hyperledger Composer provides a seamless integration with Hyperledger Fabric. Once developed, the business network can be deployed on Hyperledger Fabric, allowing for the use of its robust consensus mechanisms and security features.
Testing:
- Hyperledger Composer includes tools for testing blockchain applications. Developers can write unit tests for the business logic and end-to-end tests for the entire business network.
REST API Generation:
- One of the significant advantages of Hyperledger Composer is its auto-generation of REST APIs from the defined business network model. This allows for easy integration with existing systems and enables front-end applications to interact with the blockchain without needing to handle complex blockchain transactions.
Command Line Interface (CLI):
- Hyperledger Composer offers a powerful CLI tool that allows developers to interact with the business network. The CLI can be used to deploy, test, and manage the business network, as well as interact with the blockchain ledger.
Flexible Deployment:
- Hyperledger Composer provides the flexibility to deploy business networks on various infrastructures, including local machines, clouds, or as part of a Kubernetes cluster. This adaptability ensures that it caters to various organizational needs.

Components of Hyperledger Composer

Business Network Definition

A Business Network Definition (BND) in Hyperledger Composer is a package that defines the declarative and programmatic components of a business network. Each BND is typically composed of multiple files, including:

Model Files (.cto): These define the structure of the business network, describing assets, participants, transactions, and relationships using the Composer Modeling Language.
Script Files (.js): These contain transaction logic for the business network and are written in JavaScript.
Access Control Files (.acl): These specify the rules for permissions and access control within the business network, determining who can read or write to the ledger.
Query Files (.qry): These define complex queries that can be executed on the blockchain ledger using Hyperledger Composer’s query language.

Composer Modeling Language

The modeling language in Hyperledger Composer is crucial for defining the elements of the business network. It allows users to describe:

Participants: Represent individuals or organizations that interact with the business network.
Assets: Represent tangible or intangible items that the business network tracks.
Transactions: Define valid activities that can occur within the business network, affecting assets and participants.
Events: Notification mechanisms that can be emitted by transactions and received by participants.

Composer Playground

The Composer Playground (https://composer-playground.mybluemix.net) is a web-based interface that allows users to model, define, and test their business networks without needing extensive setup. It provides a user-friendly environment to create BNDs, manage identities, and simulate transactions.

Fabric Integration

Hyperledger Composer utilizes Hyperledger Fabric (https://www.hyperledger.org/use/fabric) as the underlying blockchain platform, which provides a modular architecture for distributed ledger solutions. The integration includes seamless deployment of BNDs on a Fabric network, leveraging Fabric’s robust features like consensus mechanisms, channels, MSP (Membership Service Provider), and more.

Developing a Hyperledger Composer Application

Step-by-Step Guide

Set Up the Development Environment:

Install pre-requisites including Node.js, npm, and Docker.

Install Hyperledger Composer CLI tools using npm.

npm install -g composer-cli
npm install -g generator-[hyperledger](../h/hyperledger.html)-composer
npm install -g composer-rest-server
npm install -g yo

Create a Business Network:
- Use Yeoman generator to create a Business Network Definition.
```
yo [hyperledger](../h/hyperledger.html)-composer:businessnetwork
```

Define Models:

Create .cto files to define the participants, assets, and transactions.

// Example model file (models/org.example.basic.cto)
namespace org.example.basic
     
[asset](../a/asset.html) SampleAsset identified by assetId {
  o String assetId
  o String [value](../v/value.html)
}

participant SampleParticipant identified by participantId {
  o String participantId
  o String firstName
  o String lastName
}

[transaction](../t/transaction.html) SampleTransaction {
  --> SampleAsset [asset](../a/asset.html)
  o String newValue
}

Implement Logic:
- Write transaction processor functions in .js files. ```javascript // Example script file (lib/logic.js) /**
  - Sample transaction processor function
  - @param {org.example.basic.SampleTransaction} tx - the sample transaction
  - @transaction */ async function sampleTransaction(tx) { tx.asset.value = tx.newValue; let assetRegistry = await getAssetRegistry(‘org.example.basic.SampleAsset’); await assetRegistry.update(tx.asset); } ```

Define Access Controls:

Create .acl files to manage permissions.

// Example access control file (permissions.acl)
rule ParticipantAccess {
  description: "Allow all participants to read all assets"
  participant: "org.example.basic.SampleParticipant"
  operation: READ
  resource: "org.example.basic.*"
  action: ALLOW
}

Deploy the Business Network:

Package the network and deploy it on Hyperledger Fabric.

composer archive create --sourceType dir --sourceName .
composer network install --card PeerAdmin@hlfv1 --archiveFile <network-name>.bna
composer network start --networkName <network-name> --networkVersion 0.0.1 --card PeerAdmin@hlfv1 --networkAdmin admin --networkAdminEnrollSecret adminpw

Run a REST API Server:
- Generate and start a REST API server to interact with the business network.
```
composer-rest-server -c admin@<network-name> -n always -u true -w true
```
Test and Iterate:
- Conduct tests using Composer Playground or Postman to simulate transactions and validate business logic.

Advantages of Using Hyperledger Composer

Rapid Development

Hyperledger Composer allows for quick and efficient development of blockchain applications by providing high-level abstractions and tools that abstract away many low-level details. This rapid development cycle means businesses can prototype, test, and iterate solutions more quickly.

Simplified Modeling

With the Composer Modeling Language, defining the structure and behavior of blockchain applications becomes straightforward and intuitive, enabling business analysts and developers to collaborate more effectively.

Strong Integration with Enterprise Systems

The tool’s ability to auto-generate REST APIs from the defined business network simplifies the integration of blockchain applications with existing enterprise systems and front-end applications, promoting interoperability and extensibility.

Flexible Deployment Options

Hyperledger Composer supports various deployment options, ranging from local development environments to cloud-based infrastructure and Kubernetes clusters, ensuring that solutions can scale according to business needs.

Community and Support

Being part of the Hyperledger project under the Linux Foundation, Hyperledger Composer benefits from a strong community, abundant resources, and regular updates, ensuring that it remains a reliable and cutting-edge tool for blockchain development.

Challenges and Limitations

Despite its robust features, Hyperledger Composer has certain limitations:

Dependency on Hyperledger Fabric: Hyperledger Composer is tightly coupled with Hyperledger Fabric, which may not be ideal for all types of blockchain use cases.
Learning Curve: While the tool abstracts many complexities, there remains a learning curve associated with understanding both Composer and Fabric’s functionalities and best practices.
Transition to Fabric Transaction Language: With the focus shifting towards Fabric’s native capabilities, the Composer toolset may face less emphasis in future developments.

Conclusion

Hyperledger Composer is a pioneering tool that accelerates the development of blockchain solutions by providing high-level abstractions and tools tailored for business applications. Its strong integration with Hyperledger Fabric, comprehensive modeling language, and the ability to generate REST APIs make it an invaluable asset for enterprises looking to leverage blockchain technology efficiently. Despite some limitations, its advantages in rapid development, simplified modeling, and flexible deployment create significant value for businesses.

For more information and resources, you can visit the official Hyperledger Composer page at Hyperledger Composer.