高可用协议招式：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：
- 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"
- 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
- 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 <iostream>
#include <string>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <cstring>
#include <fcntl.h>
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epoll
epfd = 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;
}