fabric-contract-api



The fabric-contract-api provides the contract interface a high level API for application developers to implement Smart Contracts. Working with this API provides a high level entry point to writing business logic.

Within Hyperledger Fabric, Smart Contracts can also be referred to as Chaincode. To be more specific, the term chaincode is preferred to be used to refer to the overall container that is hosting the contracts.

The fabric-shim provides the chaincode interface, a lower level API for implementing "Smart Contracts". It also _currently_ provides the implementation to support communication with Hyperledger Fabric peers for Smart Contracts written using the fabric-contract-api. To confirm that this is the same as the fabric-shim in previous versions of Hyperledger Fabric.

Detailed explanation on the concept and programming model can be found here: https://hyperledger-fabric.readthedocs.io/en/latest/smartcontract/smartcontract.html.

Contract Interface

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``sh
npm install --save fabric-contract-api
`

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Implement a class that ends the contract class, a constructor is needed.
The other functions will be invokable functions of your Smart Contract

`javascript
// updatevalues.js
'use strict';

// SDK Library to asset with writing the logic
const { Contract } = require('fabric-contract-api');

// Business logic (well just util but still it's general purpose logic)
const util = require('util');

/**
* Support the Updating of values within the SmartContract
*/
class UpdateValuesContract extends Contract

constructor(){
super('UpdateValuesContract');
}

async transactionA(ctx, newValue) {
// retrieve existing chaincode states
let oldValue = await ctx.stub.getState(key);

await ctx.stub.putState(key, Buffer.from(newValue));

return Buffer.from(newValue.toString());
}

async transactionB(ctx) {
// .....
}

};

module.exports = UpdateValuesContract
`

As with standard node modules make sure that this class is exported as follows.
`javascript
// index.js
'use strict';

const UpdateValues = require('./updatevalues')
module.exports.contracts = [UpdateValues];
`

Note: In order to make this contract 'runnable' you must also install the fabric-shim module as below, and ensure that the 'start' script in package.json refers to fabric-chaincode-node start

`json
"scripts": {
"start": "fabric-chaincode-node start"
}
`

The fabric-shim provides the fabric-chaincode-node commands; this can also be used to create a skelton metadata file.

Chaincode Interface

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`sh
npm install --save fabric-shim
`

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The chaincode interface contains two methods to be implemented:
`javascript
const shim = require('fabric-shim');

const Chaincode = class {
async Init(stub) {
// use the instantiate input arguments to decide initial chaincode state values

// save the initial states
await stub.putState(key, Buffer.from(aStringValue));

return shim.success(Buffer.from('Initialized Successfully!'));
}

async Invoke(stub) {
// use the invoke input arguments to decide intended changes

// retrieve existing chaincode states
let oldValue = await stub.getState(key);

// calculate new state values and saves them
let newValue = oldValue + delta;
await stub.putState(key, Buffer.from(newValue));

return shim.success(Buffer.from(newValue.toString()));
}
};
`

Start the chaincode process and listen for incoming endorsement requests:
`javascript
shim.start(new Chaincode());
``

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Visit API Reference and click on "Classes" link in the navigation bar on the top to view the list of class APIs.

Support

Tested with Node v12 LTS release.

License

This package is distributed under the
Apache License, Version 2.0,
see LICENSE.txt for more information.