In this tutorial, we’re gonna build an API that allows us to interact with our Blockchain.
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Overview
We will create a server using Express.js, then build three endpoints that will allow us to interact with our Blockchain (in previous article):
const express = require('express');
app.get('/blockchain', function (req, res) {
...
});
app.post('/transaction', function (req, res) {
...
});
app.get('/mine', function (req, res) {
...
});
– GET /blockchain allows us to fetch our entire Blockchain so that we can look at the data inside.
– POST /transaction to create a new transaction.
– GET /mine for mining new Block using the Proof of Work method.
Practice
Setup Environment
This was our project folder before:
Now, under src folder, create new javascript file named api.js.
Install Express.js
Run command: npm install express.
Inside app.js, import and initialize Express.js:
const express = require('express');
const app = express();
Install Body Parser
This is Node.js body parsing middleware that can parse incoming request bodies before handlers, available under the req.body property.
To install it, run command: npm install body-parser.
Inside app.js, add the code below:
const bodyParser = require('body-parser');
app.use(bodyParser.json());
bodyParser.json() returns middleware that only parses json.
Install nodemon
During development of a NodeJs based application, nodemon will watch the files in the directory, and if any files change, it will automatically restart our node application.
To install it, run command: npm install nodemon.
Then add start script to package.json file:
{
"name": "blockchain",
"version": "1.0.0",
"description": "JSA blockchain demo",
"main": "index.js",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1",
"start": "nodemon --watch src -e js src/api.js"
},
"author": "JavaSampleApproach",
"license": "ISC",
"dependencies": {
"body-parser": "^1.18.3",
"express": "^4.16.3",
"nodemon": "^1.17.5",
"sha256": "^0.2.0"
},
"keywords": [
"jsa-blockchain"
]
}
After setup environment, our project folder structure will be like:
Build Blockchain API
Add code for endpoints in app.js:
const express = require('express');
const app = express();
const bodyParser = require('body-parser');
app.use(bodyParser.json());
const nodeAddr = 'JavaSampleApproach';
const Blockchain = require('../src/blockchain');
const bitcoin = new Blockchain();
app.get('/blockchain', function (req, res) {
res.send(bitcoin);
});
app.post('/transaction', function (req, res) {
const blockIndex = bitcoin.makeNewTransaction(
req.body.amount,
req.body.sender,
req.body.recipient
);
res.json(
{
message: `Transaction is added to block with index: ${blockIndex}`
}
);
});
app.get('/mine', function (req, res) {
const latestBlock = bitcoin.getLatestBlock();
const prevBlockHash = latestBlock.hash;
const currentBlockData = {
transactions: bitcoin.pendingTransactions,
index: latestBlock.index + 1
}
const nonce = bitcoin.proofOfWork(prevBlockHash, currentBlockData);
const blockHash = bitcoin.hashBlock(prevBlockHash, currentBlockData, nonce);
// reward for mining
bitcoin.makeNewTransaction(1, '00000', nodeAddr);
const newBlock = bitcoin.creatNewBlock(nonce, prevBlockHash, blockHash)
res.json(
{
message: 'Mining new Block successfully!',
newBlock
}
);
});
app.listen(3000, function () {
console.log('> listening on port 3000...');
});
Run and Check results
– Run the API with command: npm start.
– Open browser with url: http://localhost:3000/blockchain.
– http://localhost:3000/mine:
– http://localhost:3000/blockchain again:
– POST a transaction with Advanced REST client:
– http://localhost:3000/blockchain:
– http://localhost:3000/mine:
– POST other 2 transactions, then http://localhost:3000/blockchain:
– http://localhost:3000/mine again:
– http://localhost:3000/blockchain:
This is all Blocks inside our Blockchain:
{
"chain":[
{
"index":1,
"timestamp":1527739433288,
"transactions":[
],
"nonce":100,
"hash":"Genesis block",
"prevBlockHash":"0"
},
{
"index":2,
"timestamp":1527739588736,
"transactions":[
{
"amount":1,
"sender":"00000",
"recipient":"JavaSampleApproach"
}
],
"nonce":44,
"hash":"00669af06fa8d395bea4f6325d39f43a3c87788152fc3050608aa23e55dfe964",
"prevBlockHash":"Genesis block"
},
{
"index":3,
"timestamp":1527739995327,
"transactions":[
{
"amount":190,
"sender":"JACKIE",
"recipient":"HELEN"
},
{
"amount":1,
"sender":"00000",
"recipient":"JavaSampleApproach"
}
],
"nonce":71,
"hash":"00766767c03993c1c5269bd531599c7e67f414c27f0d8bd56b5de2c7f5964e5f",
"prevBlockHash":"00669af06fa8d395bea4f6325d39f43a3c87788152fc3050608aa23e55dfe964"
},
{
"index":4,
"timestamp":1527740237053,
"transactions":[
{
"amount":60,
"sender":"JASON",
"recipient":"KATHERIN"
},
{
"amount":210,
"sender":"JASON",
"recipient":"ADAM"
},
{
"amount":1,
"sender":"00000",
"recipient":"JavaSampleApproach"
}
],
"nonce":376,
"hash":"00ca5d9c8ea5686547394d4d0ceaf612cee64fcc2f4f57b63d006eb48da60c55",
"prevBlockHash":"00766767c03993c1c5269bd531599c7e67f414c27f0d8bd56b5de2c7f5964e5f"
}
],
"pendingTransactions":[
]
}
