OBP - Writing Blockchain chaincode in Node JS

[OBP]

This post is to show how to write a chain code in NodeJS. Since version 1.2, the opensource Hyperledger fabric blockchain framework supports nodeJS to write chain codes. As Oracle Blockchain Platform (OBP) built on Hyperledger fabric and it upgrades to Hyperledger fabric 1.3 (latest version), we can also write chain codes using NodeJS in OBP.

Let's see a sample chain code. Below is the procedure to write and deploy a chain code into OBP written in Node JS.

• Create a package.json file with the basic details and dependencies of the libraries
• Create node js file/files (.js) and configure them to the above package.json
• Zip the folder with both js and package.json files
• Click on "Deploy chain code" in OBP under "Chaincodes" tab and select the zip file

Note: You just need to create package.json, not required to run npm commands to install the dependent libraries in the folder before packaging(zip) the project as the OBP will run internally once you deploy the code.

Below is the sample package.json file.

{

"name": "reviews",

"version": "1.0.0",

"description": "Chaincode implemented in node.js",

"engines": {

"node": ">=8.4.0",

"npm": ">=5.3.0"

},

"scripts": { "start" : "node reviews.js" },

"engine-strict": true,

"license": "Apache-2.0",

"dependencies": {

"fabric-shim": "~1.1.0"

}

}

Below is the sample Node js file.

const shim = require('fabric-shim');




const Chaincode = class {




    async Init(stub) {

        return shim.success();

    }




    async Invoke(stub) {

        let ret = stub.getFunctionAndParameters();

        let method = this[ret.fcn];

        console.log("Inside invoke. Calling method: " + ret.fcn);

        if (!method) {

            shim.error(Buffer.from('Received unknown function ' + ret.fcn + ' invocation'));

        }




        try {

            let payload = await method(stub, ret.params);

            return shim.success(payload);

        } catch (err) {

            console.log(err);

            return shim.error(err);

        }

    }

    //Method to save or update a user review to a product

    async saveReview(stub, args) {

        console.log("inside saveReview: " + JSON.stringify(args));

        if (args.length < 3) {

            throw 'Incorrect number of arguments. Expecting productid,userid and rating.';

        }

        var assetReview = {};

        assetReview.productid = args[0];//String

        assetReview.userid = args[1];//String

        assetReview.rating = args[2];//Number

        assetReview.comment = args[3];//String

        await stub.putState(assetReview.userid, Buffer.from(JSON.stringify(assetReview)));




    }//End of method




}




shim.start(new Chaincode());


Note: In the above js sample, the first statement requires fabric-shim package which is mandatory to execute the chain code.