Hyperledger Fabriс Research.

Part 2

We continue our series of publications about the solution developed on the Hyperledger blockchain. Data about beneficiaries will be written and read inside the Hyperledger blockchain with the help of this solution.

In the previous part, you learned:

• Why we chose Hyperledger blockchain;
• Details about dependencies;
• Steps of installing dependencies;
• How samples and containers are loaded;
• Про запуск и тест блокчейн сети.

Launching and testing the blockchain network.

Research piece on Hyperledger Fabric.

By the way, after reading it, you can try your hand at launching your own Hyperledger-based blockchain network

For today, we will take an in-depth look at the chaincode description.

Link to the documentation:

Class: ChaincodeStub

Let’s start off by describing the functions in the smartchain located in path: /chaincode/fabcar/node/fabcar.js

The smartchain contains functions/methods for writing and reading data inside the blockchain. The use case implies that we will be receiving and sending requests to peers for further recording in the state (key-value store) via an application that will utilize the SDK.

Chaincode description

1. Initialization method

• Let’s create an empty array of keys

const arr = []

• Now, let’s convert the array to a string

const arrString = JSON.stringify(arr);

• Saving the array on the blockchain in the byte string format

await stub.putState('ARR', Buffer.from(arrString));

• Finally, we send a response to the client about the successful creation of the array of keys

return getResult("CREATE_EMPTY_ARRAY_OF_KEYS_OK");                                  }

2. Method to get and invoke the class method

• Getting an object containing the class method name to invoke, and the array of arguments to pass to the target method

let ret = stub.getFunctionAndParameters();

• Checking if the method exists

let method = this[ret.fcn];if (!method) {…}

• Invoking the chaincode method to pass the arguments into it

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

3. Method to add a beneficiary

• Let’s get a key and convert it to a regular string

const key = (args[0] + "").toString();

• Getting the name of a beneficiary and converting it to a regular string

const nameString = (args[1] + "").toString();

• Let’s take retrieve an array of keys in the form of a byte string, from the blockchain

const arrBuffer = await stub.getState("ARR");

• Converting the byte string to a regular string

let arrString = arrBuffer.toString();

• Converting the string to an array

const arr = JSON.parse(arrString);

• Checking if the key exists inside the array

for(let i = 0; i < arr.length; i++) {

• If a match is found, we return an error indicating that a beneficiary with such id already exists

if(arr[i] === key) {
throw new Error("BENEFICIARY_ALREADY_EXISTS"); 
 
 }
}

• Let’s add the key to the end of the array

arr.push(key);

• Converting the modified array of keys to a JSON string

arrString = JSON.stringify(arr);

• Adding the modified array in the byte string format, to the blockchain

await stub.putState('ARR', Buffer.from(arrString));

• Let’s add the beneficiary and his key in the byte string format, to the blockchain

await stub.putState(key, Buffer.from(nameString));

• Returning a response about the beneficiary being successfully added

return getResult("CREATE_NEW_BENEFICIARY_OK");}

4. Method to add data to the blockchain and check if a beneficiary exists

• Let’s get a key and convert it to a regular string

const key = (args[0] + "").toString();

• Getting the result of the check and convert it to a regular string

const checkString = (args[1] + "").toString();

• Getting the data and converting it to a JSON object

const cheks = JSON.parse(checkString);

• Let’s take an array of keys in the form of a byte string, from the blockchain

const arrBuffer = await stub.getState("ARR");

• Converting the byte string to a regular string

let arrString = arrBuffer.toString();

• Converting the string to an array

const arr = JSON.parse(arrString);

• Checking if the key exists inside the array of keys

for(let i = 0; i < arr.length; i++) {

• If a match is found, we take from the blockchain an array of the data we received when searching by key, in the form of a byte string,

if(arr[i] === key) {
const valueBuffer = await stub.getState(key);
let valueString = valueBuffer.toString();

• Let’s add values from the received data

const addCheck = valueString + ", " + checkString;
await stub.putState(key, Buffer.from(addCheck));

• Returning a response about the successful adding.

return getResult("valueBuffer: " + valueBuffer + " checkString: " + checkString); }}

• If NO matches were found, we show an error.

throw new Error("BENEFICIARY_NOT_EXISTS"); }

5. Method to get an array of keys

• Let’s take an array of keys in the form of a byte string, from the blockchain

const arrBuffer = await stub.getState("ARR")

• Converting the byte string to a regular string

const arrString = arrBuffer.toString()

• Sending the array in the JSON format to the client

return getResult(arrString);}

6. Method to receive data by key

• Let’s get a key and convert it to a regular string

const key = (args[0] + "").toString();

• Taking an array of keys in the form of a byte string, from the blockchain

const arrBuffer = await stub.getState("ARR");

• Converting the byte string to a regular string

let arrString = arrBuffer.toString();

• Converting the string to an array

const arr = JSON.parse(arrString);

• Checking if the key exists inside the array of keys

for (let i = 0; i < arr.length; i++) {

• If a match is found, the data is sent

if (arr[i] === key) {const value = await stub.getState(key);return getResult(value); };};

• If not, we generate an error

throw new Error("KEY_IS_NOT_FOUND"); };

You can find the published repository on GitHub via the link:

roobee-platform/HyperLedger_research

Subscribe to Roobee’s social media channels, so you don’t miss the next part.

Telegram | Chat | Twitter |Facebook | Reddit | Medium | Instagram | YouTube | Bitcointalk