// udp-server.js
const udp = require('dgram')
const server = udp.createSocket('udp4')
const fs = require('fs')
server.on('listening', function () {
  var address = server.address()
  var port = address.port
  console.log('Server is listening at port ' + port)
})
server.on('message', function (msg, info) {
  console.log(
    `Data received from ${info.address}:${info.port}: ${msg.toString()}`
  )
  fs.appendFileSync('./out', msg.toString())
})
server.on('error', function (error) {
  console.log('Error: ' + error)
  server.close()
})
server.bind(7788)
// udp-client.js
const udp = require('dgram')
const client = udp.createSocket('udp4')
for (let i = 0; i < 26; i++) {
  const char = String.fromCharCode(0x41 + i)
  client.send(Buffer.from(char), 7788, '********', function (error) {
    if (error) {
      console.log(error)
    }
  })
}

// tcp-server.js
const net = require('net')
const server = net.createServer()
const fs = require('fs')
server.on('connection', function (conn) {
  conn.on('data', (msg) => {
    console.log(
      `Data received from ${conn.address().address}:${
        conn.address().port
      }: ${msg.toString()}`
    )
    fs.appendFileSync('./out', msg.toString())
  })
})
server.listen(8899, () => {
  console.log('server listening to %j', server.address().port)
})
// tcp-client.js
var net = require('net')
var client = new net.Socket()
client.connect(8899, '********', function () {
  for (let i = 0; i < 26; i++) {
    const char = String.fromCharCode(0x41 + i)
    client.write(char)
  }
})

+-------------------------------+
|      64 個(gè)字節(jié)的 UDP 首部       |
+-------------------------------+
|  SEQ(4 個(gè)字節(jié)) |  ACK(4 個(gè)字節(jié)) |
+-------------------------------+
|             Data              |
+-------------------------------+

+---+---+---+---+
| 1 | 2 | 3 | 4 |
+---+---+---+---+

+---+---+---+---+
| 1 | 2 | 3 | 4 |
+---+---+---+---+
// ACK = 4，刪除 1 2 3，并取消掉他們的定時(shí)器
+---+
| 4 |
+---+

// packet.js
class Packet {
  constructor({seq, ack, data = ''}) {
    this.seq = seq // 序列號(hào)
    this.ack = ack // 確認(rèn)號(hào)
    this.data = data // 數(shù)據(jù)
  }
  // 將 Packet 轉(zhuǎn)換成 Buffer，以便通過網(wǎng)絡(luò)傳輸
  toBuffer() {
    const seqBuffer = Buffer.alloc(4)
    seqBuffer.writeUInt32BE(this.seq)
    const ackBuffer = Buffer.alloc(4)
    ackBuffer.writeUInt32BE(this.ack)
    const dataBuffer = Buffer.from(this.data)
    return Buffer.concat([seqBuffer, ackBuffer, dataBuffer])
  }
  // 從 Buffer 中解析出 Packet
  static fromBuffer(buffer) {
    const seq = buffer.readUInt32BE()
    const ack = buffer.readUInt32BE(4)
    const data = buffer.slice(8)
    return new Packet({seq, ack, data})
  }
}
module.exports = Packet
// reliableUDP.js
const dgram = require('dgram')
const Packet = require('./packet')
class ReliableUDP {
  constructor() {
    this.socket = dgram.createSocket('udp4')
    this.socket.on('message', this.handleMessage.bind(this))
    this.sendWindow = [] // 發(fā)送窗口，用于存放待確認(rèn)的數(shù)據(jù)包
    this.receiveWindow = [] // 接收窗口，用于存放已接收的數(shù)據(jù)包
    this.expectedSeq = 1 // 期望接收的數(shù)據(jù)包序列號(hào)
    this.nextSeq = 1 // 下一個(gè)要發(fā)送的數(shù)據(jù)包序列號(hào)
    this.timeout = 100 // 超時(shí)時(shí)間，單位為毫秒
    this.timeoutIds = {} // 用于存放定時(shí)器 ID
  }
  listen(port, address, fn) {
    this.socket.bind(port, address, fn)
  }
  // 發(fā)送數(shù)據(jù)包
  sendPacket(packet, address, port) {
    const buffer = packet.toBuffer()
    this.socket.send(buffer, port, address, (err) => {
      if (err) {
        console.error(err)
      }
    })
    if (packet.ack) return
    if (!this.sendWindow.includes((p) => p.seq === packet.seq))
      this.sendWindow.push(packet)
    // 設(shè)置超時(shí)定時(shí)器
    const timeoutId = setTimeout(() => {
      this.handleTimeout(packet.seq, address, port)
    }, this.timeout)
    this.timeoutIds[packet.seq] = timeoutId
  }
  // 處理接收到的數(shù)據(jù)包
  handleMessage(msg, rinfo) {
    const {address, port} = rinfo
    const packet = Packet.fromBuffer(msg)
    // 收到的是應(yīng)答的包
    if (packet.ack) {
      const ackNum = packet.ack - 1
      // 處理發(fā)送窗口中已經(jīng)確認(rèn)的數(shù)據(jù)包
      while (this.sendWindow.length > 0 && this.sendWindow[0].seq <= ackNum) {
        this.sendWindow.shift()
      }
      // 清除超時(shí)定時(shí)器
      if (this.timeoutIds[ackNum]) {
        clearTimeout(this.timeoutIds[ackNum])
        delete this.timeoutIds[ackNum]
      }
    } else {
      // 如果是重復(fù)的數(shù)據(jù)包，則忽略
      if (packet.seq < this.expectedSeq) {
        return
      }
      // 如果是期望接收的數(shù)據(jù)包
      if (packet.seq === this.expectedSeq) {
        this.receiveWindow.push(packet)
        this.expectedSeq++
        // 處理接收窗口中已經(jīng)確認(rèn)的數(shù)據(jù)包
        while (
          this.receiveWindow.length > 0 &&
          this.receiveWindow[0].seq <= this.expectedSeq
        ) {
          const packet = this.receiveWindow.shift()
          this.onPacketReceived(packet.data)
        }
        const ackPacket = new Packet({
          seq: this.nextSeq++,
          ack: this.expectedSeq,
        })
        this.sendPacket(ackPacket, address, port)
      } else {
        // 如果是未來的數(shù)據(jù)包，暫不做處理，更好的做法是緩存起來
      }
    }
  }
  // 應(yīng)用層調(diào)用該方法發(fā)送數(shù)據(jù)
  send(data, address, port) {
    const packet = new Packet({
      seq: this.nextSeq,
      ack: null,
      data,
    })
    this.sendPacket(packet, address, port)
    this.nextSeq++
  }
  // 應(yīng)用層調(diào)用該方法注冊(cè)回調(diào)函數(shù)，接收數(shù)據(jù)
  onReceive(callback) {
    this.onPacketReceived = callback
  }
  // 處理超時(shí)
  handleTimeout(seq, address, port) {
    // 重傳超時(shí)的數(shù)據(jù)包
    const packet = this.sendWindow.find((p) => p.seq === seq)
    if (packet) {
      this.sendPacket(packet, address, port)
    }
  }
}
module.exports = ReliableUDP
// server.js
const ReliableUDP = require('./reliableUDP')
const server = new ReliableUDP()
server.listen(7788, 'localhost')
server.onReceive((data) => {
  console.log(data.toString())
})
// client.js
const ReliableUDP = require('./reliableUDP')
const client = new ReliableUDP()
for (let i = 0; i < 26; i++) {
  const char = String.fromCharCode(0x41 + i)
  client.send(char, 'localhost', 7788)
}