标题：[实践成功]go tcp tcpclient编码
出处：向东博客 专注WEB应用 构架之美 --- 构架之美，在于尽态极妍 | 应用之美，在于药到病除
时间：Wed, 30 Dec 2020 16:55:50 +0000
作者：jackxiang
地址：http://jackxiang.com/post/10815/

内容：
Server：echoServer.go

/**
 * File: echoServer.go
 * Author: 蛇叔
 * 公众号: 蛇叔编程心法(snakeCodeHeart)
 */
package main

import (
  "fmt"
  "net"
  "os"
  "syscall"
)

const (
  PORT = 8888
  ADDR = "127.0.0.1"
  SIZE = 100
)

func main() {
  // 1. create socketfd
  socketFd, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_STREAM, 0)
  if err != nil || socketFd < 0 {
    fmt.Println("socket create err: ", err)
    os.Exit(-1)
  }

  // 2. bind addr and port
  ip4 := net.ParseIP(ADDR).To4()
  if ip4 == nil {
    fmt.Println("net.ParseIP err")
    os.Exit(-1)
  }
  sa := &syscall.SockaddrInet4{Port: PORT}
  copy(sa.Addr[:], ip4)

  err = syscall.Bind(socketFd, sa)
  if err != nil {
    fmt.Println("socket bind err: ", err)
    os.Exit(-1)
  }

  // 3. listen
  err = syscall.Listen(socketFd, 128)
  if err != nil {
    fmt.Println("socket listen err: ", err)
    os.Exit(-1)
  }

  // 4. accept
  acceptFd, _, err := syscall.Accept(socketFd)
  if err != nil {
    fmt.Println("socket accept err: ", err)
    os.Exit(-1)
  }

  var (
    buf = make([]byte, SIZE)
    readn int
    err2 error
  )

  for {
    // 5. read data
    readn, err2 = syscall.Read(acceptFd, buf)
    if err2 != nil {
      break
    }

    if readn > 0 {
      // 6. write data
      writen, _ := syscall.Write(acceptFd, buf[:readn])
      if writen < 0 {
        fmt.Println("socket write err: ", err)
        break
      }
    } else if readn == 0 {
      fmt.Println("客户端已关闭")
      break
    } else if readn < 0 && err2 != nil {
      fmt.Println("socket read err: ", err2.Error())
      break
    }
  }

  // 7. close
  _ = syscall.Close(acceptFd)
  _ = syscall.Close(socketFd)
}



Client：echoClient.go

/**
 * File: echoClient.go
 * Author: 蛇叔
 * 公众号: 蛇叔编程心法
 */
package main

import (
    "bufio"
    "fmt"
    "net"
    "os"
    "syscall"
)

const (
    PORT = 8888
    ADDR = "127.0.0.1"
    SIZE = 100
)

func main() {

    // 1. 建立socket
    socketFd, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_STREAM, 0)
    if err != nil || socketFd < 0 {
        fmt.Println("socket create err: ", err)
        os.Exit(-1)
    }

    ip4 := net.ParseIP(ADDR).To4()
    if ip4 == nil {
        fmt.Println("net.ParseIP err")
        os.Exit(-1)
    }

    sa := &syscall.SockaddrInet4{Port:PORT}
    copy(sa.Addr[:], ip4)

    // 2. 发起主动连接
    err = syscall.Connect(socketFd, sa)
    if err != nil {
        fmt.Println("socket connect err: ", err)
        os.Exit(-1)
    }

    var (
        bufReader = bufio.NewReader(os.Stdin)
        buf = make([]byte, SIZE)
        writen int
        readn int
        err2 error
    )

    for {
        // 3. 从标准输入读取数据
        line, _, err := bufReader.ReadLine()
        if err != nil {
            fmt.Println("bufReader.ReadLine err: ", err)
            break
        }
        buf = line[:]

        // 4. 向socket对端写入数据
        writen, err2 = syscall.Write(socketFd, buf)
        if writen > 0 {
            readn, err2 =syscall.Read(socketFd, buf)
            if readn > 0 {
                fmt.Println("read from socket: ")
                fmt.Println(string(buf[:readn]))
            } else {
                break
            }
        } else if writen <= 0 && err2 != nil {
            fmt.Printf("socket write; writen:%d,  err: %s\n", writen, err2)
            break
        }
    }

    // 5. close socketFd
    _ = syscall.Close(socketFd)
}



jackXiang@localhost  ~/golearning  ./echoClient
jack
read from socket:
jack
xiang
read from socket:
xiang

Q:果然Ok，两个问题探讨下：
1）        ip4 := net.ParseIP(ADDR).To4()
        sa := &syscall.SockaddrInet4{Port: PORT}
        copy(sa.Addr[:], ip4)  #这个sa.Addr[:] 冒号啥写法呢？

2）for { 这里面是epoll 吗？}

A:
1. 
copy(sa.Addr[:], ip4)  #这个sa.Addr[:] 冒号啥写法呢？

sa.Addr 是一个数组，
sa.Addr[:] 将这个数组临时转为切片，底层数组指向sa.Addr数组
方便copy进行切片复制

2. 就是个for{}死循环，防止代码往下执行

来自：
https://mp.weixin.qq.com/s/dRADQ5kUCT80dX7oEAAXyA
https://mp.weixin.qq.com/s/kFHw73w_IIqjKeicesCpZw


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