一.概述

• 点对点通信就是客户端A发送消息给服务端,再由服务端把消息传递给客户端B.相同道理客户端B想给客户端A发送消息也需要把消息传递给服务端,再由服务端把消息传递给A
• 正常情况下客户端A和客户端B可以通过用户名、IP等唯一身份标识区分每个用户.在本功能练习中要求客户端先注册用户名,然后告诉服务端给谁发消息.如果用户名存在不允许注册

• 在本功能练习中用户信息存储到临时容器map中,没有进行持久化操作.

  二.代码实现

• 项目结构如下

  --项目名
    --src
        --client
            client.go
        --server
            server.go
    main.go

• 在server.go中编写代码 ```go package main

import ( “net” “fmt” “strings” )

type User struct { Username string OtherUsername string Msg string ServerMsg string }

var ( userMap = make(map[string]net.Conn) user = new(User) )

func main() { addr, := net.ResolveTCPAddr(“tcp4”, “:9999”) lis, := net.ListenTCP(“tcp4”, addr)

for {
    conn, _ := lis.Accept()
    go func() {
        for {
            b := make([]byte, 512)
            //读取数据
            count, _ := conn.Read(b)
            arrStr := strings.Split(string(b[:count]), "-")
            user.Username = arrStr[0]
            user.OtherUsername = arrStr[1]
            user.Msg = arrStr[2]
            user.ServerMsg = arrStr[3]
            userMap[user.Username] = conn
            if v, ok := userMap[user.OtherUsername]; ok && v != nil {
                user.ServerMsg = ""
                n, e := v.Write([]byte(fmt.Sprintf("%s-%s-%s-%s", user.Username, user.OtherUsername, user.Msg, user.ServerMsg)))
                if n == 0 || e != nil {
                    conn.Close()
                    delete(userMap, user.OtherUsername)
                    break
                }
            } else {
                user.ServerMsg = "对方不在线"
                n, e := conn.Write([]byte(fmt.Sprintf("%s-%s-%s-%s", user.Username, user.OtherUsername, user.Msg, user.ServerMsg)))
            }
        }
    }()
}

}

- 在client.go中编写代码
```go
package main
import (
    "net"
    "fmt"
    "sync"
    "os"
    "strings"
)
type User struct {
    Username      string
    OtherUsername string
    Msg           string
    ServerMsg     string
}
var (
    user = new(User)
    wg   sync.WaitGroup
)
func main() {
    wg.Add(1)
    fmt.Println("请登录,输入用户名：")
    fmt.Scanln(&user.Username)
    fmt.Println("请输入要给谁发送消息")
    fmt.Scanln(&user.OtherUsername)
    addr, _ := net.ResolveTCPAddr("tcp4", ":9999")
    conn, _ := net.DialTCP("tcp4", nil, addr)
    go func() {
        fmt.Print("请输入:(只提示一次,以后直接输入即可)")
        for {
            fmt.Scanln(&user.Msg)
            if user.Msg == "exit" {
                conn.Close()
                wg.Done()
                os.Exit(0)
            }
            conn.Write([]byte(fmt.Sprintf("%s-%s-%s-%s", user.Username, user.OtherUsername, user.Msg, user.ServerMsg)))
        }
    }()
    go func() {
        for {
            rb := make([]byte, 512)
            c, _ := conn.Read(rb)
            user2 := new(User)
            arrStr := strings.Split(string(rb[:c]), "-")
            user2.Username = arrStr[0]
            user2.OtherUsername = arrStr[1]
            user2.Msg = arrStr[2]
            user2.ServerMsg = arrStr[3]
            if user2.ServerMsg != "" {
                fmt.Println("\t\t\t服务器消息:", user2.ServerMsg)
            } else {
                fmt.Println("\t\t\t", user2.Username, ":", user2.Msg)
            }
        }
    }()
    wg.Wait()
}