6行代碼解決golang TCP粘包

時間 2019-11-07

標籤代碼解決 golang tcp 欄目 Go 简体版

原文原文鏈接

什麼是TCP粘包問題以及爲何會產生TCP粘包，本文不加討論。本文使用golang的bufio.Scanner來實現自定義協議解包。html

協議數據包定義

本文模擬一個日誌服務器，該服務器接收客戶端傳到的數據包並顯示出來golang

type Package struct {
    Version        [2]byte // 協議版本，暫定V1
    Length         int16   // 數據部分長度
    Timestamp      int64   // 時間戳
    HostnameLength int16   // 主機名長度
    Hostname       []byte  // 主機名
    TagLength      int16   // 標籤長度
    Tag            []byte  // 標籤
    Msg            []byte  // 日誌數據
}

協議定義部分沒有什麼好講的，根據具體的業務邏輯定義便可。編程

數據打包

因爲TCP協議是語言無關的協議，因此直接把協議數據包結構體發送到TCP鏈接中也是不可能的，只能發送字節流數據，因此須要本身實現數據編碼。所幸golang提供了binary來幫助咱們實現網絡字節編碼。服務器

func (p *Package) Pack(writer io.Writer) error {
    var err error
    err = binary.Write(writer, binary.BigEndian, &p.Version)
    err = binary.Write(writer, binary.BigEndian, &p.Length)
    err = binary.Write(writer, binary.BigEndian, &p.Timestamp)
    err = binary.Write(writer, binary.BigEndian, &p.HostnameLength)
    err = binary.Write(writer, binary.BigEndian, &p.Hostname)
    err = binary.Write(writer, binary.BigEndian, &p.TagLength)
    err = binary.Write(writer, binary.BigEndian, &p.Tag)
    err = binary.Write(writer, binary.BigEndian, &p.Msg)
    return err
}

Pack方法的輸出目標爲io.Writer，有利於接口擴展，只要實現了該接口便可編碼數據寫入。binary.BigEndian是字節序，本文暫時不討論，有須要的讀者能夠自行查找資料研究。網絡

數據解包

解包須要將TCP數據包解析到結構體中，接下來會講爲何須要添加幾個數據無關的長度字段。tcp

func (p *Package) Unpack(reader io.Reader) error {
    var err error
    err = binary.Read(reader, binary.BigEndian, &p.Version)
    err = binary.Read(reader, binary.BigEndian, &p.Length)
    err = binary.Read(reader, binary.BigEndian, &p.Timestamp)
    err = binary.Read(reader, binary.BigEndian, &p.HostnameLength)
    p.Hostname = make([]byte, p.HostnameLength)
    err = binary.Read(reader, binary.BigEndian, &p.Hostname)
    err = binary.Read(reader, binary.BigEndian, &p.TagLength)
    p.Tag = make([]byte, p.TagLength)
    err = binary.Read(reader, binary.BigEndian, &p.Tag)
    p.Msg = make([]byte, p.Length-8-2-p.HostnameLength-2-p.TagLength)
    err = binary.Read(reader, binary.BigEndian, &p.Msg)
    return err
}

因爲主機名、標籤這種數據是不固定長度的，因此須要兩個字節來標識數據長度，不然讀取的時候只知道一個總的數據長度是沒法區分主機名、標籤名、日誌數據的。編程語言

數據包的粘包問題解決

上文只是解決了編碼/解碼問題，前提是收到的數據包沒有產生粘包問題，解決粘包就是要正確分割字節流中的數據。通常有如下作法：編碼

定長分隔(每一個數據包最大爲該長度) 缺點是數據不足時會浪費傳輸資源
特定字符分隔(如rn) 缺點是若是正文中有rn就會致使問題
在數據包中添加長度字段(本文采用的)

golang提供了bufio.Scanner來解決粘包問題。日誌

scanner := bufio.NewScanner(reader) // reader爲實現了io.Reader接口的對象，如net.Conn
scanner.Split(func(data []byte, atEOF bool) (advance int, token []byte, err error) {
    if !atEOF && data[0] == 'V' { // 因爲咱們定義的數據包頭最開始爲兩個字節的版本號，因此只有以V開頭的數據包才處理
        if len(data) > 4 { // 若是收到的數據>4個字節(2字節版本號+2字節數據包長度)
            length := int16(0)
            binary.Read(bytes.NewReader(data[2:4]), binary.BigEndian, &length) // 讀取數據包第3-4字節(int16)=>數據部分長度
            if int(length)+4 <= len(data) { // 若是讀取到的數據正文長度+2字節版本號+2字節數據長度不超過讀到的數據(實際上就是成功完整的解析出了一個包)
                return int(length) + 4, data[:int(length)+4], nil
            }
        }
    }
    return
})
// 打印接收到的數據包
for scanner.Scan() {
    scannedPack := new(Package)
    scannedPack.Unpack(bytes.NewReader(scanner.Bytes()))
    log.Println(scannedPack)
}

本文的核心就在於scanner.Split方法，該方法用來解析TCP數據包code

完整源碼

package main

import (
    "bufio"
    "bytes"
    "encoding/binary"
    "fmt"
    "io"
    "log"
    "os"
    "time"
)

type Package struct {
    Version        [2]byte // 協議版本
    Length         int16   // 數據部分長度
    Timestamp      int64   // 時間戳
    HostnameLength int16   // 主機名長度
    Hostname       []byte  // 主機名
    TagLength      int16   // Tag長度
    Tag            []byte  // Tag
    Msg            []byte  // 數據部分長度
}

func (p *Package) Pack(writer io.Writer) error {
    var err error
    err = binary.Write(writer, binary.BigEndian, &p.Version)
    err = binary.Write(writer, binary.BigEndian, &p.Length)
    err = binary.Write(writer, binary.BigEndian, &p.Timestamp)
    err = binary.Write(writer, binary.BigEndian, &p.HostnameLength)
    err = binary.Write(writer, binary.BigEndian, &p.Hostname)
    err = binary.Write(writer, binary.BigEndian, &p.TagLength)
    err = binary.Write(writer, binary.BigEndian, &p.Tag)
    err = binary.Write(writer, binary.BigEndian, &p.Msg)
    return err
}
func (p *Package) Unpack(reader io.Reader) error {
    var err error
    err = binary.Read(reader, binary.BigEndian, &p.Version)
    err = binary.Read(reader, binary.BigEndian, &p.Length)
    err = binary.Read(reader, binary.BigEndian, &p.Timestamp)
    err = binary.Read(reader, binary.BigEndian, &p.HostnameLength)
    p.Hostname = make([]byte, p.HostnameLength)
    err = binary.Read(reader, binary.BigEndian, &p.Hostname)
    err = binary.Read(reader, binary.BigEndian, &p.TagLength)
    p.Tag = make([]byte, p.TagLength)
    err = binary.Read(reader, binary.BigEndian, &p.Tag)
    p.Msg = make([]byte, p.Length-8-2-p.HostnameLength-2-p.TagLength)
    err = binary.Read(reader, binary.BigEndian, &p.Msg)
    return err
}

func (p *Package) String() string {
    return fmt.Sprintf("version:%s length:%d timestamp:%d hostname:%s tag:%s msg:%s",
        p.Version,
        p.Length,
        p.Timestamp,
        p.Hostname,
        p.Tag,
        p.Msg,
    )
}

func main() {
    hostname, err := os.Hostname()
    if err != nil {
        log.Fatal(err)
    }

    pack := &Package{
        Version:        [2]byte{'V', '1'},
        Timestamp:      time.Now().Unix(),
        HostnameLength: int16(len(hostname)),
        Hostname:       []byte(hostname),
        TagLength:      4,
        Tag:            []byte("demo"),
        Msg:            []byte(("如今時間是:" + time.Now().Format("2006-01-02 15:04:05"))),
    }
    pack.Length = 8 + 2 + pack.HostnameLength + 2 + pack.TagLength + int16(len(pack.Msg))

    buf := new(bytes.Buffer)
    // 寫入四次，模擬TCP粘包效果
    pack.Pack(buf)
    pack.Pack(buf)
    pack.Pack(buf)
    pack.Pack(buf)
    // scanner
    scanner := bufio.NewScanner(buf)
    scanner.Split(func(data []byte, atEOF bool) (advance int, token []byte, err error) {
        if !atEOF && data[0] == 'V' {
            if len(data) > 4 {
                length := int16(0)
                binary.Read(bytes.NewReader(data[2:4]), binary.BigEndian, &length)
                if int(length)+4 <= len(data) {
                    return int(length) + 4, data[:int(length)+4], nil
                }
            }
        }
        return
    })
    for scanner.Scan() {
        scannedPack := new(Package)
        scannedPack.Unpack(bytes.NewReader(scanner.Bytes()))
        log.Println(scannedPack)
    }
    if err := scanner.Err(); err != nil {
        log.Fatal("無效數據包")
    }
}