TCP socket心跳包示例程序

在做游戏开发时，经常需要在应用层实现自己的心跳机制，即定时发送一个自定义的结构体（心跳包），让对方知道自己还活着，以确保连接的有效性。

在TCP socket心跳机制中，心跳包可以由服务器发送给客户端，也可以由客户端发送给服务器，不过比较起来，前者开销可能更大。—— 这里实现的是由客户端给服务器发送心跳包，基本思路是：

1） 服务器为每个客户端保存了IP和计数器count，即

map<fd, pair<ip, count>>

。服务端主线程采用 select 实现多路IO复用，监听新连接以及接受数据包（心跳包），子线程用于检测心跳：

如果主线程接收到的是心跳包，将该客户端对应的计数器 count 清零；

在子线程中，每隔3秒遍历一次所有客户端的计数器 count：

若 count 小于 5，将 count 计数器加 1；

若 count 等于 5，说明已经15秒未收到该用户心跳包，判定该用户已经掉线；

2） 客户端则只是开辟子线程，定时给服务器发送心跳包（本示例中定时时间为3秒）。

下面是Linux下一个socket心跳包的简单实现：

/*************************************************************************
> File Name: Server.cpp
> Author: SongLee
> E-mail: lisong.shine@qq.com
> Created Time: 2016年05月05日 星期四 22时50分23秒
> Personal Blog: http://songlee24.github.io/ ************************************************************************/
#include<netinet/in.h>   // sockaddr_in
#include<sys/types.h>    // socket
#include<sys/socket.h>   // socket
#include<arpa/inet.h>
#include<unistd.h>
#include<sys/select.h>   // select
#include<sys/ioctl.h>
#include<sys/time.h>
#include<iostream>
#include<vector>
#include<map>
#include<string>
#include<cstdlib>
#include<cstdio>
#include<cstring>
using namespace std;
#define BUFFER_SIZE 1024

enum Type {HEART, OTHER};

struct PACKET_HEAD
{
Type type;
int length;
};

void* heart_handler(void* arg);

class Server
{
private:
struct sockaddr_in server_addr;
socklen_t server_addr_len;
int listen_fd;    // 监听的fd
int max_fd;       // 最大的fd
fd_set master_set;   // 所有fd集合，包括监听fd和客户端fd
fd_set working_set;  // 工作集合
struct timeval timeout;
map<int, pair<string, int> > mmap;   // 记录连接的客户端fd--><ip, count>
public:
Server(int port);
~Server();
void Bind();
void Listen(int queue_len = 20);
void Accept();
void Run();
void Recv(int nums);
friend void* heart_handler(void* arg);
};

Server::Server(int port)
{
bzero(&server_addr, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = htons(INADDR_ANY);
server_addr.sin_port = htons(port);
// create socket to listen
listen_fd = socket(PF_INET, SOCK_STREAM, 0);
if(listen_fd < 0)
{
cout << "Create Socket Failed!";
exit(1);
}
int opt = 1;
setsockopt(listen_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
}

Server::~Server()
{
for(int fd=0; fd<=max_fd; ++fd)
{
if(FD_ISSET(fd, &master_set))
{
close(fd);
}
}
}

void Server::Bind()
{
if(-1 == (bind(listen_fd, (struct sockaddr*)&server_addr, sizeof(server_addr))))
{
cout << "Server Bind Failed!";
exit(1);
}
cout << "Bind Successfully.\n";
}

void Server::Listen(int queue_len)
{
if(-1 == listen(listen_fd, queue_len))
{
cout << "Server Listen Failed!";
exit(1);
}
cout << "Listen Successfully.\n";
}

void Server::Accept()
{
struct sockaddr_in client_addr;
socklen_t client_addr_len = sizeof(client_addr);

int new_fd = accept(listen_fd, (struct sockaddr*)&client_addr, &client_addr_len);
if(new_fd < 0)
{
cout << "Server Accept Failed!";
exit(1);
}

string ip(inet_ntoa(client_addr.sin_addr));    // 获取客户端IP

cout << ip << " new connection was accepted.\n";

mmap.insert(make_pair(new_fd, make_pair(ip, 0)));

// 将新建立的连接的fd加入master_set
FD_SET(new_fd, &master_set);
if(new_fd > max_fd)
{
max_fd = new_fd;
}
}

void Server::Recv(int nums)
{
for(int fd=0; fd<=max_fd; ++fd)
{
if(FD_ISSET(fd, &working_set))
{
bool close_conn = false;  // 标记当前连接是否断开了

PACKET_HEAD head;
recv(fd, &head, sizeof(head), 0);   // 先接受包头

if(head.type == HEART)
{
mmap[fd].second = 0;        // 每次收到心跳包，count置0
cout << "Received heart-beat from client.\n";
}
else
{
// 数据包，通过head.length确认数据包长度
}

if(close_conn)  // 当前这个连接有问题，关闭它
{
close(fd);
FD_CLR(fd, &master_set);
if(fd == max_fd)  // 需要更新max_fd;
{
while(FD_ISSET(max_fd, &master_set) == false)
--max_fd;
}
}
}
}
}

void Server::Run()
{
pthread_t id;     // 创建心跳检测线程
int ret = pthread_create(&id, NULL, heart_handler, (void*)this);
if(ret != 0)
{
cout << "Can not create heart-beat checking thread.\n";
}

max_fd = listen_fd;   // 初始化max_fd
FD_ZERO(&master_set);
FD_SET(listen_fd, &master_set);  // 添加监听fd

while(1)
{
FD_ZERO(&working_set);
memcpy(&working_set, &master_set, sizeof(master_set));

timeout.tv_sec = 30;
timeout.tv_usec = 0;

int nums = select(max_fd+1, &working_set, NULL, NULL, &timeout);
if(nums < 0)
{
cout << "select() error!";
exit(1);
}

if(nums == 0)
{
//cout << "select() is timeout!";
continue;
}

if(FD_ISSET(listen_fd, &working_set))
Accept();   // 有新的客户端请求
else
Recv(nums); // 接收客户端的消息
}
}

// thread function
void* heart_handler(void* arg)
{
cout << "The heartbeat checking thread started.\n";
Server* s = (Server*)arg;
while(1)
{
map<int, pair<string, int> >::iterator it = s->mmap.begin();
for( ; it!=s->mmap.end(); )
{
if(it->second.second == 5)   // 3s*5没有收到心跳包，判定客户端掉线
{
cout << "The client " << it->second.first << " has be offline.\n";

int fd = it->first;
close(fd);            // 关闭该连接
FD_CLR(fd, &s->master_set);
if(fd == s->max_fd)      // 需要更新max_fd;
{
while(FD_ISSET(s->max_fd, &s->master_set) == false)
s->max_fd--;
}

s->mmap.erase(it++);  // 从map中移除该记录
}
else if(it->second.second < 5 && it->second.second >= 0)
{
it->second.second += 1;
++it;
}
else
{
++it;
}
}
sleep(3);   // 定时三秒
}
}

int main()
{
Server server(15000);
server.Bind();
server.Listen();
server.Run();
return 0;
}

/*************************************************************************
> File Name: Client.cpp
> Author: SongLee
> E-mail: lisong.shine@qq.com
> Created Time: 2016年05月05日 星期四 23时41分56秒
> Personal Blog: http://songlee24.github.io/ ************************************************************************/
#include<netinet/in.h>   // sockaddr_in
#include<sys/types.h>    // socket
#include<sys/socket.h>   // socket
#include<arpa/inet.h>
#include<sys/ioctl.h>
#include<unistd.h>
#include<iostream>
#include<string>
#include<cstdlib>
#include<cstdio>
#include<cstring>
using namespace std;
#define BUFFER_SIZE 1024

enum Type {HEART, OTHER};

struct PACKET_HEAD
{
Type type;
int length;
};

void* send_heart(void* arg);

class Client
{
private:
struct sockaddr_in server_addr;
socklen_t server_addr_len;
int fd;
public:
Client(string ip, int port);
~Client();
void Connect();
void Run();
friend void* send_heart(void* arg);
};

Client::Client(string ip, int port)
{
bzero(&server_addr, sizeof(server_addr));
server_addr.sin_family = AF_INET;
if(inet_pton(AF_INET, ip.c_str(), &server_addr.sin_addr) == 0)
{
cout << "Server IP Address Error!";
exit(1);
}
server_addr.sin_port = htons(port);
server_addr_len = sizeof(server_addr);
// create socket
fd = socket(AF_INET, SOCK_STREAM, 0);
if(fd < 0)
{
cout << "Create Socket Failed!";
exit(1);
}
}

Client::~Client()
{
close(fd);
}

void Client::Connect()
{
cout << "Connecting......" << endl;
if(connect(fd, (struct sockaddr*)&server_addr, server_addr_len) < 0)
{
cout << "Can not Connect to Server IP!";
exit(1);
}
cout << "Connect to Server successfully." << endl;
}

void Client::Run()
{
pthread_t id;
int ret = pthread_create(&id, NULL, send_heart, (void*)this);
if(ret != 0)
{
cout << "Can not create thread!";
exit(1);
}
}

// thread function
void* send_heart(void* arg)
{
cout << "The heartbeat sending thread started.\n";
Client* c = (Client*)arg;
int count = 0;  // 测试
while(1)
{
PACKET_HEAD head;
head.type = HEART;
head.length = 0;
send(c->fd, &head, sizeof(head), 0);
sleep(3);     // 定时3秒

++count;      // 测试：发送15次心跳包就停止发送
if(count > 15)
break;
}
}

int main()
{
Client client("127.0.0.1", 15000);
client.Connect();
client.Run();
while(1)
{
string msg;
getline(cin, msg);
if(msg == "exit")
break;
cout << "msg\n";
}
return 0;
}

可以看出，客户端启动以后发送了15次心跳包，然后停止发送心跳包。在经过一段时间后（3s*5），服务器就判断该客户端掉线，并断开了连接。