什么是TCP粘包問題以及為什么會產(chǎn)生TCP粘包，本文不加討論。本文使用golang的bufio.Scanner來實(shí)現(xiàn)自定義協(xié)議解包。

協(xié)議數(shù)據(jù)包定義

本文模擬一個日志服務(wù)器，該服務(wù)器接收客戶端傳到的數(shù)據(jù)包并顯示出來

type Package struct {Version [2]byte // 協(xié)議版本，暫定V1Length int16 // 數(shù)據(jù)部分長度Timestamp int64 // 時間戳HostnameLength int16 // 主機(jī)名長度Hostname []byte // 主機(jī)名TagLength int16 // 標(biāo)簽長度Tag []byte // 標(biāo)簽Msg []byte // 日志數(shù)據(jù) }

協(xié)議定義部分沒有什么好講的，根據(jù)具體的業(yè)務(wù)邏輯定義即可。

數(shù)據(jù)打包

由于TCP協(xié)議是語言無關(guān)的協(xié)議，所以直接把協(xié)議數(shù)據(jù)包結(jié)構(gòu)體發(fā)送到TCP連接中也是不可能的，只能發(fā)送字節(jié)流數(shù)據(jù)，所以需要自己實(shí)現(xiàn)數(shù)據(jù)編碼。所幸golang提供了binary來幫助我們實(shí)現(xiàn)網(wǎng)絡(luò)字節(jié)編碼。

func (p *Package) Pack(writer io.Writer) error {var err errorerr = 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(biāo)為io.Writer，有利于接口擴(kuò)展，只要實(shí)現(xiàn)了該接口即可編碼數(shù)據(jù)寫入。binary.BigEndian是字節(jié)序，本文暫時不討論，有需要的讀者可以自行查找資料研究。

數(shù)據(jù)解包

解包需要將TCP數(shù)據(jù)包解析到結(jié)構(gòu)體中，接下來會講為什么需要添加幾個數(shù)據(jù)無關(guān)的長度字段。

func (p *Package) Unpack(reader io.Reader) error {var err errorerr = 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 }

由于主機(jī)名、標(biāo)簽這種數(shù)據(jù)是不固定長度的，所以需要兩個字節(jié)來標(biāo)識數(shù)據(jù)長度，否則讀取的時候只知道一個總的數(shù)據(jù)長度是無法區(qū)分主機(jī)名、標(biāo)簽名、日志數(shù)據(jù)的。

數(shù)據(jù)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(shù)據(jù)包沒有產(chǎn)生粘包問題，解決粘包就是要正確分割字節(jié)流中的數(shù)據(jù)。一般有以下做法：

定長分隔(每個數(shù)據(jù)包最大為該長度) 缺點(diǎn)是數(shù)據(jù)不足時會浪費(fèi)傳輸資源

特定字符分隔(如rn) 缺點(diǎn)是如果正文中有rn就會導(dǎo)致問題

在數(shù)據(jù)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。

scanner := bufio.NewScanner(reader) // reader為實(shí)現(xiàn)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' { // 由于我們定義的數(shù)據(jù)包頭最開始為兩個字節(jié)的版本號，所以只有以V開頭的數(shù)據(jù)包才處理if len(data) > 4 { // 如果收到的數(shù)據(jù)>4個字節(jié)(2字節(jié)版本號+2字節(jié)數(shù)據(jù)包長度)length := int16(0)binary.Read(bytes.NewReader(data[2:4]), binary.BigEndian, &length) // 讀取數(shù)據(jù)包第3-4字節(jié)(int16)=>數(shù)據(jù)部分長度if int(length)+4 <= len(data) { // 如果讀取到的數(shù)據(jù)正文長度+2字節(jié)版本號+2字節(jié)數(shù)據(jù)長度不超過讀到的數(shù)據(jù)(實(shí)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(shù)據(jù)包 for scanner.Scan() {scannedPack := new(Package)scannedPack.Unpack(bytes.NewReader(scanner.Bytes()))log.Println(scannedPack) }

本文的核心就在于scanner.Split方法，該方法用來解析TCP數(shù)據(jù)包

完整源碼

package mainimport ("bufio""bytes""encoding/binary""fmt""io""log""os""time" )type Package struct {Version [2]byte // 協(xié)議版本Length int16 // 數(shù)據(jù)部分長度Timestamp int64 // 時間戳HostnameLength int16 // 主機(jī)名長度Hostname []byte // 主機(jī)名TagLength int16 // Tag長度Tag []byte // TagMsg []byte // 數(shù)據(jù)部分長度 }func (p *Package) Pack(writer io.Writer) error {var err errorerr = 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 errorerr = 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(("現(xiàn)在時間是:" + 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)// scannerscanner := 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(shù)據(jù)包")} }

寫在最后

golang作為一門強(qiáng)大的網(wǎng)絡(luò)編程語言，實(shí)現(xiàn)自定義協(xié)議是非常重要的，實(shí)際上實(shí)現(xiàn)自定義協(xié)議也不是很難，以下幾個步驟：

數(shù)據(jù)包編碼

數(shù)據(jù)包解碼

處理TCP粘包問題

斷線重連(可以使用心跳實(shí)現(xiàn))(非必須)

本文引用自我自己的博客golang解決TCP粘包問題

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