Step 1: A chain of blocks?

nambrot · Nov 12, 2017 · 761c267 · 761c267
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diff --git a/.gitignore b/.gitignore
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+# See https://help.github.com/ignore-files/ for more about ignoring files.
+
+# dependencies
+/node_modules
+
+# testing
+/coverage
+
+# production
+/build
+/screencaps
+
+# misc
+.DS_Store
+.env.local
+.env.development.local
+.env.test.local
+.env.production.local
+
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
diff --git a/README.md b/README.md
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+# Build your own Blockchain in Javascript
+
+With all the hype about blockchains and cryptocurrencies, I decided to learn a bit more about it. And what better way to learn than to try to build it? Here you will find my attempts to build blockchains from their basic principles, and hopefully in the process it helps someone else to learn something from this as well. Let's get started
+
+## Step 1: A chain of blocks?
+
+To understand how blockchains work, let's start with the name. Blockchain? A chain of blocks?
+
+A common misconception is that a blockchain is a single chain of blocks, when in reality, it's more like a tree of blocks. So at any given time, there are multiple chains for blocks by pointing to their respective parent. The pointing happens via hashes which are calculated based upon the data inside the block (i.e. hash of the parent, transaction data and other important stuff)
+
+By pointing via hashes of blocks, we can enforce a specific order of blocks. I.e given a chain of blocks, you can't just take a block in the middle of the chain and change its data, since that would change its hash and subsequently also all blocks that are descendents of the block in question.
+
+```javascript
+class Block {
+  constructor(blockchain, parentHash, nonce = sha256(new Date().getTime().toString()).toString()) {
+    this.blockchain = blockchain;
+    this.nonce = nonce;
+    this.parentHash = parentHash;
+    this.hash = sha256(this.nonce + this.parentHash).toString()
+  }
+```
+
+If you look at the code, you can see how the P2P aspect of blockchains comes into play. Once a node decided it "mined" a block, it can broadcast that block to all other nodes, you can verify it and then add it to their tree, as well.
+
+![blockbroadcast](https://user-images.githubusercontent.com/571810/32704273-37b7b07a-c7d0-11e7-900c-851031c81ad4.gif)
diff --git a/package.json b/package.json
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+{
+  "name": "blockchain-js",
+  "version": "0.1.0",
+  "private": true,
+  "dependencies": {
+    "@blueprintjs/core": "^1.32.0",
+    "@blueprintjs/labs": "^0.12.0",
+    "crypto-js": "^3.1.9-1",
+    "express": "^4.16.2",
+    "ramda": "^0.25.0",
+    "react": "^16.1.0",
+    "react-addons-css-transition-group": "^15.6.2",
+    "react-dom": "^16.1.0",
+    "react-scripts": "1.0.17",
+    "react-sortable-tree": "^1.5.0",
+    "socket.io": "^2.0.4",
+    "socket.io-client": "^2.0.4"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
diff --git a/public/favicon.ico b/public/favicon.ico
diff --git a/public/index.html b/public/index.html
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+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
+    <meta name="theme-color" content="#000000">
+    <!--
+      manifest.json provides metadata used when your web app is added to the
+      homescreen on Android. See https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/
+    -->
+    <link rel="manifest" href="%PUBLIC_URL%/manifest.json">
+    <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
+    <!--
+      Notice the use of %PUBLIC_URL% in the tags above.
+      It will be replaced with the URL of the `public` folder during the build.
+      Only files inside the `public` folder can be referenced from the HTML.
+
+      Unlike "/favicon.ico" or "favicon.ico", "%PUBLIC_URL%/favicon.ico" will
+      work correctly both with client-side routing and a non-root public URL.
+      Learn how to configure a non-root public URL by running `npm run build`.
+    -->
+    <title>React App</title>
+  </head>
+  <body>
+    <noscript>
+      You need to enable JavaScript to run this app.
+    </noscript>
+    <div id="root"></div>
+    <!--
+      This HTML file is a template.
+      If you open it directly in the browser, you will see an empty page.
+
+      You can add webfonts, meta tags, or analytics to this file.
+      The build step will place the bundled scripts into the <body> tag.
+
+      To begin the development, run `npm start` or `yarn start`.
+      To create a production bundle, use `npm run build` or `yarn build`.
+    -->
+  </body>
+</html>
diff --git a/public/manifest.json b/public/manifest.json
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+{
+  "short_name": "React App",
+  "name": "Create React App Sample",
+  "icons": [
+    {
+      "src": "favicon.ico",
+      "sizes": "64x64 32x32 24x24 16x16",
+      "type": "image/x-icon"
+    }
+  ],
+  "start_url": "./index.html",
+  "display": "standalone",
+  "theme_color": "#000000",
+  "background_color": "#ffffff"
+}
diff --git a/src/App.css b/src/App.css
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+@import "../node_modules/@blueprintjs/core/dist/blueprint.css";
+
+.App {
+  text-align: center;
+}
+
+.App-logo {
+  animation: App-logo-spin infinite 20s linear;
+  height: 80px;
+}
+
+.App-header {
+  background-color: #222;
+  height: 150px;
+  padding: 20px;
+  color: white;
+}
+
+.App-title {
+  font-size: 1.5em;
+}
+
+.App-intro {
+  font-size: large;
+}
+
+@keyframes App-logo-spin {
+  from { transform: rotate(0deg); }
+  to { transform: rotate(360deg); }
+}
diff --git a/src/App.js b/src/App.js
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+import React, { Component } from 'react';
+import './App.css';
+import BlockchainWelcome from './components/BlockchainWelcome'
+import { Button } from "@blueprintjs/core";
+import { action } from './store';
+
+class App extends Component {
+  state = {
+    ownBlockchainName: ''
+  }
+  pickBlockchain = (name) => {
+    action({ type: 'PICK_BLOCKCHAIN', name })
+  }
+  render() {
+    return (
+      <div className="">
+        <nav className='pt-navbar'>
+          <div className="pt-navbar-group pt-align-left">
+            <div className="pt-navbar-heading">Build your own Blockchain</div>
+          </div>
+
+          <div className="pt-navbar-group pt-align-right">
+            <select
+              onChange={(evt) => {
+                this.pickBlockchain(evt.target.value)
+              }}
+              value={this.props.appState.selectedBlockchain ? this.props.appState.selectedBlockchain.name : ''}
+            >
+              {
+                [<option key='default' value=''>Pick a blockchain or</option>].concat(this.props.appState.blockchains.map((b) => <option key={b.name} value={b.name}>{b.name}</option>))
+              }
+            </select>
+
+            <div className='pt-control-group'>
+              <div className='pt-input-group'>
+                <input
+                  className='pt-input'
+                  placeholder="create your own"
+                  value={this.state.ownBlockchainName}
+                  style={{paddingRight: '150px'}}
+                  onChange={(evt) => this.setState({ownBlockchainName: evt.target.value})}
+                />
+              <div className="pt-input-action">
+                <Button
+                  text='Create'
+                  onClick={() => this.pickBlockchain(this.state.ownBlockchainName)}
+                />
+              </div>
+              </div>
+            </div>
+          </div>
+        </nav>
+        <div className="container" style={{padding: 24}}>
+          { this.props.appState.selectedBlockchain === undefined &&
+            <p>
+              Learn more about blockchains. Start by picking or create a new blockchain in the top-right corner.
+            </p>
+          }
+          {
+            this.props.appState.selectedBlockchain !== undefined &&
+            <BlockchainWelcome blockchain={this.props.appState.selectedBlockchain} />
+          }
+        </div>
+      </div>
+    );
+  }
+}
+
+export default App;
diff --git a/src/App.test.js b/src/App.test.js
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+import React from 'react';
+import ReactDOM from 'react-dom';
+import App from './App';
+
+it('renders without crashing', () => {
+  const div = document.createElement('div');
+  ReactDOM.render(<App />, div);
+});
diff --git a/src/components/BlockchainWelcome.js b/src/components/BlockchainWelcome.js
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+import React, { Component } from 'react';
+import SortableTree from 'react-sortable-tree';
+import {getTreeFromFlatData} from 'react-sortable-tree';
+import {Button} from '@blueprintjs/core';
+
+class BlockchainWelcome extends Component {
+  state = {
+    treeData: [{ title: 'Chicken', children: [ { title: 'Egg' } ] }],
+  }
+  render() {
+    const treeData = getTreeFromFlatData({
+      flatData: Object.values(this.props.blockchain.blocks),
+      getKey: (block) => block.hash,
+      getParentKey: (block) => block.parentHash,
+      rootKey: this.props.blockchain.genesis.parentHash
+    });
+    return (
+      <div>
+        <div style={{height: 800}}>
+          <SortableTree
+            treeData={treeData}
+            canDrag={false}
+            onChange={treeData => this.setState({ treeData })}
+            generateNodeProps={({ node, path }) => ({
+              buttons: [
+                <Button
+                  text='Add block from here'
+                  onClick={() => {
+                    const block = this.props.blockchain.blocks[node.hash]
+                    block.addChild();
+                  }}
+                />
+              ]
+            })}
+          />
+        </div>
+      </div>
+    )
+
+  }
+}
+
+export default BlockchainWelcome;
diff --git a/src/index.css b/src/index.css
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+body {
+  margin: 0;
+  padding: 0;
+  font-family: sans-serif;
+}
diff --git a/src/index.js b/src/index.js
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+
+import {action, state} from './store';
+import {subscribeTo, publish} from './network'
+action({})
+
+subscribeTo('BLOCKCHAIN_BROADCAST', (names) => {
+  action({ type: 'BLOCKCHAIN_BROADCAST', names })
+})
+
+subscribeTo('BLOCKCHAIN_BROADCAST_REQUEST', () => {
+  publish('BLOCKCHAIN_BROADCAST', state.blockchains.map((b) => b.name))
+})
+
+publish('BLOCKCHAIN_BROADCAST_REQUEST', {})
diff --git a/src/logo.svg b/src/logo.svg
diff --git a/src/models/Block.js b/src/models/Block.js
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+import sha256 from 'crypto-js/sha256';
+
+class Block {
+  constructor(blockchain, parentHash, nonce = sha256(new Date().getTime().toString()).toString()) {
+    this.blockchain = blockchain;
+    this.nonce = nonce;
+    this.parentHash = parentHash;
+    this.hash = sha256(this.nonce + this.parentHash).toString()
+
+    // for visualization purposes
+    this.title = `Block ${this.hash.substr(0, 10)}`;
+    this.expanded = true;
+  }
+
+  addChild() {
+    this.blockchain.addBlock(this);
+  }
+
+  toJSON() {
+    return {
+      hash: this.hash,
+      nonce: this.nonce,
+      parentHash: this.parentHash
+    }
+  }
+}
+
+export default Block;
+
+export function fromJSON(blockchain, data) {
+  return new Block(blockchain, data.parentHash, data.nonce)
+}
diff --git a/src/models/Blockchain.js b/src/models/Blockchain.js
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+import Block from './Block';
+import {fromJSON} from './Block';
+import {rerender} from "../store";
+import {publish, subscribeTo} from "../network";
+
+class Blockchain {
+  constructor(name) {
+    this.name = name;
+    this.genesis = null;
+    this.blocks = {};
+
+    this.createGenesisBlock();
+
+    subscribeTo('BLOCKS_BROADCAST', ({ blocks, blockchainName }) => {
+      if (blockchainName === this.name) {
+        blocks.forEach(block => this._addBlock(fromJSON(this, block)))
+      }
+    })
+
+    publish('REQUEST_BLOCKS', { blockchainName: this.name })
+    subscribeTo('REQUEST_BLOCKS', ({ blockchainName }) => {
+      if (blockchainName === this.name)
+        publish('BLOCKS_BROADCAST', { blockchainName, blocks: Object.values(this.blocks).map(b => b.toJSON())})
+    })
+  }
+
+  createGenesisBlock() {
+    const block = new Block(this, 'root', this.name);
+    this.blocks[block.hash] = block;
+    this.genesis = block;
+  }
+
+  containsBlock(block) {
+    return this.blocks[block.hash] !== undefined
+  }
+
+  addBlock(parent) {
+    const newBlock = new Block(this, parent.hash);
+    this._addBlock(newBlock)
+    publish('BLOCKS_BROADCAST', { blocks: [newBlock.toJSON()], blockchainName: this.name })
+  }
+
+  _addBlock(block) {
+    if (!this.containsBlock(block)) {
+      this.blocks[block.hash] = block;
+      rerender()
+    }
+  }
+}
+export default Blockchain;