200行代码实现blockchain 区块链实例详解

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

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

<span style="font-family:arial, helvetica, sans-serif;">'use strict';</span> 
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(); 

总结

以上所述是小编给大家介绍的200行代码实现blockchain 区块链实例详解，希望对大家有所帮助