Server 端

go run main.go

package main

import (
    "encoding/json"
    "log"
    "net"
    "sync"
)

type User struct {
    Uid  string
    Name string
    conn *ConnInfo
}

type ConnInfo struct {
    conn net.Conn
    user *User
}

type SessionManager struct {
    sync.RWMutex
    users map[string]*User
}

func NewSessionManager() *SessionManager {
    return &SessionManager{
        users: make(map[string]*User),
    }
}

func (s *SessionManager) User(uid string) (*User, bool) {
    s.RLock()
    defer s.RUnlock()
    u, ok := s.users[uid]
    return u, ok
}

func (s *SessionManager) AddUser(u *User) {
    s.Lock()
    s.users[u.Uid] = u
    s.Unlock()
}

func (s *SessionManager) RemoveUser(uid string) {
    s.Lock()
    delete(s.users, uid)
    s.Unlock()
}

var manager = NewSessionManager()

func Start() {
    listener, err := net.Listen("tcp", ":8099")
    if err != nil {
        panic(err)
    }
    for {
        conn, err := listener.Accept()
        if err != nil {
            break
        }
        log.Printf("remote conn:%s", conn.RemoteAddr())
        go handleConn(conn)
    }
}

type LoginProto struct {
    Uid  string `json:"uid"`
    Name string `json:"name"`
}

type MessageDataProto struct {
    To      string `json:"to"`
    Message string `json:"message"`
}

type CommandProto struct {
    Command string `json:"command"`
    Content string `json:"content"`
}

func handleConn(conn net.Conn) {
    connInfo := &ConnInfo{
        conn: conn,
    }
    buf := make([]byte, 1024)
    for {
        n, err := conn.Read(buf)
        if err != nil {
            log.Printf("conn %s read err:%s", conn.RemoteAddr(), err.Error())
            if connInfo.user != nil {
                manager.RemoveUser(connInfo.user.Uid)
                log.Printf("uid %s is offline", connInfo.user.Uid)
            }
            break
        }
        var cmd CommandProto
        if err := json.Unmarshal(buf[:n], &cmd); err != nil {
            log.Printf("failed to unmarshal buf data:%s", buf[:n])
            continue
        }
        switch cmd.Command {
        case "Login":
            var login LoginProto
            if err := json.Unmarshal([]byte(cmd.Content), &login); err != nil {
                log.Printf("failed to unmarshal content data:%s", cmd.Content)
                continue
            }
            u := &User{
                Uid:  login.Uid,
                Name: login.Name,
                conn: connInfo,
            }
            connInfo.user = u
            manager.AddUser(u)
            log.Printf("uid %s,name:%s login successfully", u.Uid, u.Name)
        case "Send":
            if connInfo.user == nil {
                log.Println("user doesn't login")
                continue
            }
            var msg MessageDataProto
            if err := json.Unmarshal([]byte(cmd.Content), &msg); err != nil {
                log.Printf("failed to unmarshal content data:%s", cmd.Content)
                continue
            }
            toUser, exist := manager.User(msg.To)
            if !exist {
                log.Printf("peer user %s is offline", msg.To)
                continue
            }
            data := struct {
                From    string
                Message string
            }{
                From:    connInfo.user.Uid,
                Message: msg.Message,
            }
            if err := json.NewEncoder(toUser.conn.conn).Encode(data); err != nil {
                log.Printf("send data from %s to %s err:%s", connInfo.user.Uid, msg.To, err.Error())
                continue
            }
        default:
            log.Printf("unknown command:%s", cmd.Command)
        }
    }
}

func main() {
    log.SetFlags(log.LstdFlags | log.Lshortfile)
    Start()
}

client 端

通过telnet连接Server

telnet localhost 8099

然后再发送登录uid:001指令

{
    "command":"Login",
    "content":" { \"uid\":\"001\", \"name\":\"Tom\" } "
}

再起一个窗口，也通过telnet连接Server

telnet localhost 8099

然后再发送登录uid:002指令

{
    "command":"Login",
    "content":" { \"uid\":\"002\", \"name\":\"Jack\" } "
}

然后在之前的uid:001窗口给对端uid:002发送消息指令

{
    "command":"Send",
    "content":" { \"to\":\"002\", \"message\":\"Hello Jack\" } "
}

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