高可用协议招式：keepalive

• 什么是keepalive
• tcp如何实现keepalive
• http如何实现keepalive
• 自定义协议时该怎样实现keepalive

什么是keepalive

Keepalive是一种技术，它可以帮助保持网络连接活跃，避免链路失效。它可以通过给双方发送定期的探测报文，来确认对侧主机是否仍然处于可用状态，并采取必要的措施保持链路的连接性、可靠性和可用性。

tcp如何实现keepalive

tcp提供了相关函数

客户端TCP keep-alive：
// 设置keep-alive参数
int optval = 1;
setsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE, &optval, sizeof(int));
// 设置keep-alive间隔 
optval = 10; // 10s 
setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPIDLE, &optval, sizeof(int));
// 设置探测次数 
optval = 3; // 每10s探测3次 
setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPCNT, &optval, sizeof(int));
// 设置探测间距 
optval = 2; // 每2s探测一次 
setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPINTVL, &optval, sizeof(int));

http如何实现keepalive

http在1.1版本实现了keepalive
HTTP/1.1实现keep-alive的方法如下：

1. 客户端向服务端发出请求时附带Connection: keep-alive

request = "GET / HTTP/1.1\r\n" + \ 
"Host: example.com\r\n" + \
"Connection: keep-alive\r\n" + \ # 附带此行
"\r\n"

2. 服务端正常回复，并附带上Connection: keep-alive

response = "HTTP/1.1 200 OK\r\n" + \ 
"Connection: keep-alive\r\n" + \ # 附带此行
"Content-Length: {}\r\n".format(len(data)) + \
"\r\n" + data

3. 客户端重用连接，后续请求仍使用此TCP连接

request = "GET /other_url HTTP/1.1\r\n" + \ 
"Host: example.com\r\n" + \
"Connection: keep-alive\r\n" + \ # 仍然附带此行
"\r\n"

自定义协议时该怎样实现keepalive

1.客户端定时发送心跳包：客户端定时发送心跳包，服务端收到后即回复确认码，客户端收到确认码即表示连接状态正常；
2.服务端检测客户端：服务端定时检测客户端是否响应心跳包，若客户端在指定时间内未收到确认码，则关闭该连接；
C++ demo代码：

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
using namespace std;
#define SER_PORT 9999
#define MAX_LEN 1024
#define CLIENT_NUM 10
int main() {int sockfd, client_fd[CLIENT_NUM] = {0}; // 套接字描述符struct sockaddr_in server_addr, client_addr; // 地址信息socklen_t addrlen = sizeof(sockaddr); // 地址信息长度char buf[MAX_LEN]; // 数据缓冲区int opt = 1; // 优化选项// 定义epoll句柄int epfd;struct epoll_event ev, events[CLIENT_NUM];memset(&ev, 0, sizeof(ev));// 初始化服务器地址bzero(&server_addr, sizeof(struct sockaddr_in));server_addr.sin_family = AF_INET;server_addr.sin_port = htons(SER_PORT);server_addr.sin_addr.s_addr = htonl(INADDR_ANY);// 创建套接字if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {cout << "Create Socket failed!" << endl;return -1;}// 设置优化选项setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));// 绑定地址if (bind(sockfd, (struct sockaddr *)&server_addr, sizeof(struct sockaddr_in)) < 0) {cout << "Bind Failed!" << endl;return -1;}// 监听if (listen(sockfd, 5) < 0) {cout << "Listen Failed!" << endl;return -1;}// 创建epollepfd = epoll_create(CLIENT_NUM);ev.events = EPOLLIN;ev.data.fd = sockfd;epoll_ctl(epfd, EPOLL_CTL_ADD, sockfd, &ev);// 循环处理客户端请求while(1){int retval;retval = epoll_wait(epfd, events, CLIENT_NUM, -1); // -1表示永远等待// 遍历retval个就绪事件for (int i = 0; i < retval; ++i){// 客户端连接请求if (events[i].data.fd == sockfd && events[i].events & EPOLLIN){// 接收客户端连接int conn_fd = accept(sockfd, (struct sockaddr*)&client_addr, &addrlen);if (conn_fd < 0){cout << "Accept Failed!" << endl;return -1;}// 设置新的监听事件ev.events = EPOLLIN;ev.data.fd = conn_fd;epoll_ctl(epfd, EPOLL_CTL_ADD, conn_fd, &ev);// 设置客户端socket为非阻塞int flag = fcntl(conn_fd, F_GETFL);flag |= O_NONBLOCK;fcntl(conn_fd, F_SETFL, flag);cout << "A New Client Connection: " << inet_ntoa(client_addr.sin_addr) << endl;}// 客户端消息if (events[i].data.fd > 0 && events[i].events & EPOLLIN){// 遍历已连接描述符for (int j = 0; j < CLIENT_NUM; ++j){// 接收客户端消息if (events[i].data.fd == client_fd[j]){int len = recv(client_fd[j], buf, MAX_LEN, 0);if (len > 0){// 获取消息类型int type = (unsigned int)buf;switch (type){// 处理心跳包case 0x10:// 向客户端发送确认码send(events[i].data.fd, "\x12\x00\x00\x00", 4, 0);break;// 处理客户端数据case 0x11:// 处理客户端发来的数据cout << "Client Data: " << buf << endl;break;default:break;}}}}}}}close(sockfd);return 0;
}