blockchain 区块链200行代码：在JavaScript实现的一个简单的例子

了解blockchain的概念很简单（区块链，交易链块）：它是分布式的（即不是放置在同一台机器上，不同的网络设备上的）数据库支持主办记录日益增长的名单。但是，这也是容易混淆blockchain与我们试图帮他解决了目标 - 在人们心中的那一刻，这个词是相当强烈的交易，合同或智能cryptocurrency的概念有关。
只有在这里blockchain - 是不是一回事比特币，并理解链块的基本知识比它似乎更容易，尤其是在，它是基于源代码的情况下。在本文中，我们提出了建立与在JavaScript中200行代码的简单模型。这个项目，我们称之为NaiveChain的源代码，可以在GitHub上找到。 第1部分和第2部分：如果您需要刷上它的功能，使用我们的备忘单，我们将使用标准的ECMAScript 6。

块结构

第一步 - 确定应包含块的元素。为简单起见，我们只包括最必要的：先前块的指数（指数），时间标记（时间戳），数据（数据），散列和散列，要录制，以保持电路的结构完整性。

class Block {constructor(index, previousHash, timestamp, data, hash) {this.index = index;this.previousHash = previousHash.toString();this.timestamp = timestamp;this.data = data;this.hash = hash.toString();}
}

散列单元

哈希块需要保持数据的完整性。在我们的例子，这适用于算法SHA-256。这种类型的散列是不相关的开采，因为在这种情况下，我们并没有用表现证明实施保护。

var calculateHash = (index, previousHash, timestamp, data) => {return CryptoJS.SHA256(index + previousHash + timestamp + data).toString();
};

产生单元

要生成块，我们需要知道前一个块的哈希，使我们在结构已经确定了元素的其余部分。数据由最终用户提供。

var generateNextBlock = (blockData) => {var previousBlock = getLatestBlock();var nextIndex = previousBlock.index + 1;var nextTimestamp = new Date().getTime() / 1000;var nextHash = calculateHash(nextIndex, previousBlock.hash, nextTimestamp, blockData);return new Block(nextIndex, previousBlock.hash, nextTimestamp, blockData, nextHash);
};

存储单元

使用blockchain 存储阵列。第一个块总是硬编码“创世纪块”。

var getGenesisBlock = () => {return new Block(0, "0", 1465154705, "my genesis block!!", "816534932c2b7154836da6afc367695e6337db8a921823784c14378abed4f7d7");
};var blockchain = [getGenesisBlock()];

确认块的完整性

我们必须始终能够确认单元或电路的完整性。尤其是当你从其他单位新的单位，必须决定是否接受它们。

var isValidNewBlock = (newBlock, previousBlock) => {if (previousBlock.index + 1 !== newBlock.index) {console.log('invalid index');return false;} else if (previousBlock.hash !== newBlock.previousHash) {console.log('invalid previoushash');return false;} else if (calculateHashForBlock(newBlock) !== newBlock.hash) {console.log(typeof (newBlock.hash) + ' ' + typeof calculateHashForBlock(newBlock));console.log('invalid hash: ' + calculateHashForBlock(newBlock) + ' ' + newBlock.hash);return false;}return true;
};

选择链最长的

在电路块的顺序必须被明确指定，但是在发生冲突的情况下（例如，两个节点同时在同一生成的块和相同数量），我们选择电路，其中包含的块的数量较多。

var replaceChain = (newBlocks) => {if (isValidChain(newBlocks) && newBlocks.length > blockchain.length) {console.log('Received blockchain is valid. Replacing current blockchain with received blockchain');blockchain = newBlocks;broadcast(responseLatestMsg());} else {console.log('Received blockchain invalid');}
};

消息到其它网络节点

该网站的一个组成部分 - 与其他节点的数据交换。下列规则用于维护网络同步：
当一个节点产生新的单元，它会报告给网络;
当本机连接到新的盛宴，他要求有关最后生成的块信息;
当一个节点正面临着一个块，其中有一个指标比他还大，他增加了一个块到电路或请求的完整链条的信息。
自动搜索同龄人不执行，所有环节都手动添加。

单元的控制

用户应该能够以某种方式控制节点，通过将HTTP服务器解决。当与节点相互作用有以下功能：
打印所有单元的列表;
创建用户生成内容的新单元;
打印列表，或添加的节日。
互动的最直接的方式 - 通过卷曲：

一个节点上的所有块＃名单
curl http://localhost:3001/blocks

架构

值得注意的是，该网站是指两个Web服务器：HTTP进行用户控制的装置和向所述的WebSocket HTTP来安装节点之间的P2P连接。

如下为js 200行代码

'use strict';
var CryptoJS = require("crypto-js");
var express = require("express");
var bodyParser = require('body-parser');
var WebSocket = require("ws");var http_port = process.env.HTTP_PORT || 3001;
var p2p_port = process.env.P2P_PORT || 6001;
var initialPeers = process.env.PEERS ? process.env.PEERS.split(',') : [];class Block {constructor(index, previousHash, timestamp, data, hash) {this.index = index;this.previousHash = previousHash.toString();this.timestamp = timestamp;this.data = data;this.hash = hash.toString();}
}var sockets = [];
var MessageType = {QUERY_LATEST: 0,QUERY_ALL: 1,RESPONSE_BLOCKCHAIN: 2
};var getGenesisBlock = () => {return new Block(0, "0", 1465154705, "my genesis block!!", "816534932c2b7154836da6afc367695e6337db8a921823784c14378abed4f7d7");
};var blockchain = [getGenesisBlock()];var initHttpServer = () => {var app = express();app.use(bodyParser.json());app.get('/blocks', (req, res) => res.send(JSON.stringify(blockchain)));app.post('/mineBlock', (req, res) => {var newBlock = generateNextBlock(req.body.data);addBlock(newBlock);broadcast(responseLatestMsg());console.log('block added: ' + JSON.stringify(newBlock));res.send();});app.get('/peers', (req, res) => {res.send(sockets.map(s => s._socket.remoteAddress + ':' + s._socket.remotePort));});app.post('/addPeer', (req, res) => {connectToPeers([req.body.peer]);res.send();});app.listen(http_port, () => console.log('Listening http on port: ' + http_port));
};var initP2PServer = () => {var server = new WebSocket.Server({port: p2p_port});server.on('connection', ws => initConnection(ws));console.log('listening websocket p2p port on: ' + p2p_port);};var initConnection = (ws) => {sockets.push(ws);initMessageHandler(ws);initErrorHandler(ws);write(ws, queryChainLengthMsg());
};var initMessageHandler = (ws) => {ws.on('message', (data) => {var message = JSON.parse(data);console.log('Received message' + JSON.stringify(message));switch (message.type) {case MessageType.QUERY_LATEST:write(ws, responseLatestMsg());break;case MessageType.QUERY_ALL:write(ws, responseChainMsg());break;case MessageType.RESPONSE_BLOCKCHAIN:handleBlockchainResponse(message);break;}});
};var initErrorHandler = (ws) => {var closeConnection = (ws) => {console.log('connection failed to peer: ' + ws.url);sockets.splice(sockets.indexOf(ws), 1);};ws.on('close', () => closeConnection(ws));ws.on('error', () => closeConnection(ws));
};var generateNextBlock = (blockData) => {var previousBlock = getLatestBlock();var nextIndex = previousBlock.index + 1;var nextTimestamp = new Date().getTime() / 1000;var nextHash = calculateHash(nextIndex, previousBlock.hash, nextTimestamp, blockData);return new Block(nextIndex, previousBlock.hash, nextTimestamp, blockData, nextHash);
};var calculateHashForBlock = (block) => {return calculateHash(block.index, block.previousHash, block.timestamp, block.data);
};var calculateHash = (index, previousHash, timestamp, data) => {return CryptoJS.SHA256(index + previousHash + timestamp + data).toString();
};var addBlock = (newBlock) => {if (isValidNewBlock(newBlock, getLatestBlock())) {blockchain.push(newBlock);}
};var isValidNewBlock = (newBlock, previousBlock) => {if (previousBlock.index + 1 !== newBlock.index) {console.log('invalid index');return false;} else if (previousBlock.hash !== newBlock.previousHash) {console.log('invalid previoushash');return false;} else if (calculateHashForBlock(newBlock) !== newBlock.hash) {console.log(typeof (newBlock.hash) + ' ' + typeof calculateHashForBlock(newBlock));console.log('invalid hash: ' + calculateHashForBlock(newBlock) + ' ' + newBlock.hash);return false;}return true;
};var connectToPeers = (newPeers) => {newPeers.forEach((peer) => {var ws = new WebSocket(peer);ws.on('open', () => initConnection(ws));ws.on('error', () => {console.log('connection failed')});});
};var handleBlockchainResponse = (message) => {var receivedBlocks = JSON.parse(message.data).sort((b1, b2) => (b1.index - b2.index));var latestBlockReceived = receivedBlocks[receivedBlocks.length - 1];var latestBlockHeld = getLatestBlock();if (latestBlockReceived.index > latestBlockHeld.index) {console.log('blockchain possibly behind. We got: ' + latestBlockHeld.index + ' Peer got: ' + latestBlockReceived.index);if (latestBlockHeld.hash === latestBlockReceived.previousHash) {console.log("We can append the received block to our chain");blockchain.push(latestBlockReceived);broadcast(responseLatestMsg());} else if (receivedBlocks.length === 1) {console.log("We have to query the chain from our peer");broadcast(queryAllMsg());} else {console.log("Received blockchain is longer than current blockchain");replaceChain(receivedBlocks);}} else {console.log('received blockchain is not longer than received blockchain. Do nothing');}
};var replaceChain = (newBlocks) => {if (isValidChain(newBlocks) && newBlocks.length > blockchain.length) {console.log('Received blockchain is valid. Replacing current blockchain with received blockchain');blockchain = newBlocks;broadcast(responseLatestMsg());} else {console.log('Received blockchain invalid');}
};var isValidChain = (blockchainToValidate) => {if (JSON.stringify(blockchainToValidate[0]) !== JSON.stringify(getGenesisBlock())) {return false;}var tempBlocks = [blockchainToValidate[0]];for (var i = 1; i < blockchainToValidate.length; i++) {if (isValidNewBlock(blockchainToValidate[i], tempBlocks[i - 1])) {tempBlocks.push(blockchainToValidate[i]);} else {return false;}}return true;
};var getLatestBlock = () => blockchain[blockchain.length - 1];
var queryChainLengthMsg = () => ({'type': MessageType.QUERY_LATEST});
var queryAllMsg = () => ({'type': MessageType.QUERY_ALL});
var responseChainMsg = () =>({'type': MessageType.RESPONSE_BLOCKCHAIN, 'data': JSON.stringify(blockchain)
});
var responseLatestMsg = () => ({'type': MessageType.RESPONSE_BLOCKCHAIN,'data': JSON.stringify([getLatestBlock()])
});var write = (ws, message) => ws.send(JSON.stringify(message));
var broadcast = (message) => sockets.forEach(socket => write(socket, message));connectToPeers(initialPeers);
initHttpServer();
initP2PServer();