<p>什么是TCP粘包问题以及为什么会产生TCP粘包，本文不加讨论。本文使用golang的 bufio.Scanner 来实现自定义协议解包。</p>    <h2>协议数据包定义</h2>    <p>本文模拟一个日志服务器，该服务器接收客户端传到的数据包并显示出来</p>    <pre>  <code class="language-go">type Package struct {      Version        [2]byte // 协议版本，暂定V1      Length         int16   // 数据部分长度      Timestamp      int64   // 时间戳      HostnameLength int16   // 主机名长度      Hostname       []byte  // 主机名      TagLength      int16   // 标签长度      Tag            []byte  // 标签      Msg            []byte  // 日志数据  }</code></pre>    <p>协议定义部分没有什么好讲的，根据具体的业务逻辑定义即可。</p>    <h2>数据打包</h2>    <p>由于TCP协议是语言无关的协议，所以直接把协议数据包结构体发送到TCP连接中也是不可能的，只能发送字节流数据，所以需要自己实现数据编码。所幸golang提供了 binary 来帮助我们实现网络字节编码。</p>    <pre>  <code class="language-go">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  }</code></pre>    <p>Pack方法的输出目标为 io.Writer ，有利于接口扩展，只要实现了该接口即可编码数据写入。 binary.BigEndian 是字节序，本文暂时不讨论，有需要的读者可以自行查找资料研究。</p>    <h2>数据解包</h2>    <p>解包需要将TCP数据包解析到结构体中，接下来会讲为什么需要添加几个 数据无关 的长度字段。</p>    <pre>  <code class="language-go">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  }</code></pre>    <p>由于主机名、标签这种数据是不固定长度的，所以需要两个字节来标识数据长度，否则读取的时候只知道一个总的数据长度是无法区分主机名、标签名、日志数据的。</p>    <h2>数据包的粘包问题解决</h2>    <p>上文只是解决了 编码/解码 问题，前提是收到的数据包没有产生粘包问题，解决粘包就是要正确分割字节流中的数据。一般有以下做法：</p>    <ol>     <li>定长分隔(每个数据包最大为该长度) 缺点是数据不足时会浪费传输资源</li>     <li>特定字符分隔(如rn) 缺点是如果正文中有rn就会导致问题</li>     <li>在数据包中添加长度字段(本文采用的)</li>    </ol>    <p>golang提供了 bufio.Scanner 来解决粘包问题。</p>    <pre>  <code class="language-go">scanner := bufio.NewScanner(reader) // reader为实现了io.Reader接口的对象，如net.Conn  scanner.Split(func(data []byte, atEOF bool) (advance int, token []byte, err error) {      if !atEOF && data[0] == 'V' { // 由于我们定义的数据包头最开始为两个字节的版本号，所以只有以V开头的数据包才处理          if len(data) > 4 { // 如果收到的数据>4个字节(2字节版本号+2字节数据包长度)              length := int16(0)              binary.Read(bytes.NewReader(data[2:4]), binary.BigEndian, &length) // 读取数据包第3-4字节(int16)=>数据部分长度              if int(length)+4 <= len(data) { // 如果读取到的数据正文长度+2字节版本号+2字节数据长度不超过读到的数据(实际上就是成功完整的解析出了一个包)                  return int(length) + 4, data[:int(length)+4], nil              }          }      }      return  })  // 打印接收到的数据包  for scanner.Scan() {      scannedPack := new(Package)      scannedPack.Unpack(bytes.NewReader(scanner.Bytes()))      log.Println(scannedPack)  }</code></pre>    <p>本文的核心就在于 scanner.Split 方法，该方法用来解析TCP数据包</p>    <h2>完整源码</h2>    <pre>  <code class="language-go">package main    import (      "bufio"      "bytes"      "encoding/binary"      "fmt"      "io"      "log"      "os"      "time"  )    type Package struct {      Version        [2]byte // 协议版本      Length         int16   // 数据部分长度      Timestamp      int64   // 时间戳      HostnameLength int16   // 主机名长度      Hostname       []byte  // 主机名      TagLength      int16   // Tag长度      Tag            []byte  // Tag      Msg            []byte  // 数据部分长度  }    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(("现在时间是:" + 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)      // 写入四次，模拟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("无效数据包")      }  }</code></pre>    <h2>写在最后</h2>    <p>golang作为一门强大的网络编程语言，实现自定义协议是非常重要的，实际上实现自定义协议也不是很难，以下几个步骤：</p>    <ol>     <li>数据包编码</li>     <li>数据包解码</li>     <li>处理TCP粘包问题</li>     <li>断线重连(可以使用心跳实现)(非必须)</li>    </ol>    <p>本文引用自我自己的博客 <a href="/misc/goto?guid=4959757315798234546" rel="nofollow,noindex">golang解决TCP粘包问题</a></p>    <p> </p>    <p>来自：https://segmentfault.com/a/1190000013493942</p>    <p> </p>