linux socket 判断连接是否断开 send和recv函数

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文章目录

前言
一、如何判断连接是否断开 send和recv函数？
二、代码示例
总结

前言

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介绍linux socket 判断连接是否断开 send和recv函数
提供示例代码： ser端 3秒发送一个命令给 cli端，然后cli端处理命令

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一、如何判断连接是否断开 send和recv函数？

send:
send() 或 sendto() 函数发送数据时，当尝试向一个已经关闭的套接字发送数据时，默认情况下会生成 SIGPIPE 信号给你的进程，导致进程退出
可以使用 MSG_NOSIGNAL 标志来避免生成 SIGPIPE 信号。

 ssize_t send_received = send(clifd, cmd_buf, sizeof(cmd_buf) - 1, MSG_NOSIGNAL);printf("send_received = %d\n", send_received);if (send_received == -1) {if (errno == EPIPE) {printf("Client disconnected.\n");} else {perror("Send failed");}close(clifd);return -1;}

recv:

可以判断返回值 recv返回 0表述对端关闭

ssize_t bytes_received = recv(sockfd, cmd_buf, sizeof(cmd_buf) - 1, 0);if (bytes_received < 0) {perror("recv failed");close(sockfd);return -1;} else if (bytes_received == 0) {printf("ser closed\n");close(sockfd);return 0;}

二、代码示例

socket_cmd.h

#ifndef __SOCKET_CMD_H__
#define __SOCKET_CMD_H__typedef enum {CMD_TYPE_TEST = 0x1100,CMD_TYPE_EXEC,CMD_TYPE_DOWNLOAD,CMD_TYPE_UPLOAD,CMD_TYPE_MAX,
} cmd_type_t;typedef enum {OP_TYPE_TEST = 0x2100,OP_TYPE_REQ,OP_TYPE_ACK,OP_TYPE_FAIL,OP_TYPE_MAX,
} op_type_t;struct s_cmd
{int cmd;int op;char msg[256];
};#endif

socket_cmd_ser.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>#include "socket_cmd.h"#define SERVER_IP "127.0.0.1" // 服务器的 IP 地址
#define SERVER_PORT 8080       // 服务器的端口号int ser_sock_create(char * addr, int port, int listen_num)
{char s_ip[16] = {0};int sockfd;int clifd;struct sockaddr_in server_addr = {0}; struct sockaddr_in client_addr = {0};char cmd_buf[512] = {0};int ret = 0;int addr_len = 0;if(addr == NULL || port > 65535 || port < 0 || listen_num <= 0 || listen_num > 1024){return -1;}printf("addr = %s, port = %d, listen_num = %d\n", addr, port, listen_num);memcpy(s_ip, addr, strnlen(addr, 16));// 创建套接字sockfd = socket(AF_INET, SOCK_STREAM, 0);if (sockfd < 0) {perror("socket creation failed");return -1;}// Set the SO_REUSEADDR optionint optval = 1;if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval)) == -1) {perror("Setsockopt failed");close(sockfd);return 1;}// 设置客户端地址信息server_addr.sin_family = AF_INET;server_addr.sin_port = htons(port); // 客户端绑定的端口号server_addr.sin_addr.s_addr = inet_addr(s_ip); // 绑定所有可用接口// 绑定套接字到客户端地址if (bind(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {perror("bind failed");close(sockfd);return -1;}addr_len = sizeof(client_addr);// 获取并打印绑定的 IP 地址和端口号if (getsockname(sockfd, (struct sockaddr *)&server_addr, &addr_len) == -1) {perror("getsockname failed");close(sockfd);return -1;}char ip_str[INET_ADDRSTRLEN];inet_ntop(AF_INET, &server_addr.sin_addr, ip_str, sizeof(ip_str));printf("ser bind %s:%d\n", ip_str, ntohs(server_addr.sin_port));// 开始监听连接if (listen(sockfd, listen_num) < 0) {perror("Listen failed");return -1;}clifd = accept(sockfd, NULL, NULL);if (clifd < 0) {perror("Accept failed");return -1;}// 这里可以添加发送和接收数据的代码while(1){memset(cmd_buf, 0, sizeof(cmd_buf));struct s_cmd cmd = {0};cmd.cmd = CMD_TYPE_TEST;cmd.op = OP_TYPE_TEST;memcpy(cmd.msg, "hello cmd", strnlen( "hello cmd", 128));memcpy(cmd_buf, &cmd, sizeof(cmd));ssize_t send_received = send(clifd, cmd_buf, sizeof(cmd) , MSG_NOSIGNAL);//ssize_t send_received = write(clifd, cmd_buf, sizeof(cmd_buf) - 1);printf("send_received = %d\n", send_received);if (send_received == -1) {if (errno == EPIPE) {printf("Client disconnected.\n");} else {perror("Send failed");}close(clifd);return -1;}usleep(3* 1000 * 1000);}// 关闭套接字close(sockfd);
}int main() {int sockfd;ser_sock_create("0.0.0.0", 9090, 1);return 0;
}

socket_cmd_cli.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>#include "socket_cmd.h"#define SERVER_IP "127.0.0.1" // 服务器的 IP 地址
#define SERVER_PORT 8080       // 服务器的端口号
#define CLIENT_PORT 19091       // 客户端绑定的端口号int cli_cmd_dispatch(struct s_cmd * cmd)
{struct s_cmd* tmp_cmd = NULL;if(cmd == NULL){return -1;}tmp_cmd = malloc(sizeof(struct s_cmd));if(tmp_cmd == NULL){return -1;}memcpy(tmp_cmd, cmd, sizeof(struct s_cmd));switch(tmp_cmd->cmd){case CMD_TYPE_TEST:break;default:break;}free(tmp_cmd);return 0;
}int cli_check_cmd_valid(struct s_cmd * cmd)
{if(cmd == NULL){return -1;}return 0;
}int cli_sock_create(char * seraddr, int serport, char * cliaddr, int cliport)
{char s_ip[16] = {0};char c_ip[16] = {0};int sockfd;struct sockaddr_in server_addr = {0}; struct sockaddr_in client_addr = {0};char cmd_buf[512] = {0};int ret = 0;int addr_len = 0;if(seraddr == NULL || serport > 65535 || serport < 0 || cliport < 0 || cliport > 65535){return -1;}if(cliaddr == NULL){memcpy(c_ip, "0.0.0.0", strnlen("0.0.0.0", 16));}else{memcpy(c_ip, cliaddr, strnlen(cliaddr, 16));}memcpy(s_ip, seraddr, strnlen(seraddr, 16));// 创建套接字sockfd = socket(AF_INET, SOCK_STREAM, 0);if (sockfd < 0) {perror("socket creation failed");exit(EXIT_FAILURE);}// 设置客户端地址信息client_addr.sin_family = AF_INET;client_addr.sin_port = htons(CLIENT_PORT); // 客户端绑定的端口号client_addr.sin_addr.s_addr = inet_addr(c_ip); // 绑定所有可用接口// 绑定套接字到客户端地址if (bind(sockfd, (struct sockaddr *)&client_addr, sizeof(client_addr)) < 0) {perror("bind failed");close(sockfd);exit(EXIT_FAILURE);}addr_len = sizeof(client_addr);// 获取并打印绑定的 IP 地址和端口号if (getsockname(sockfd, (struct sockaddr *)&client_addr, &addr_len) == -1) {perror("getsockname failed");close(sockfd);exit(EXIT_FAILURE);}char ip_str[INET_ADDRSTRLEN];inet_ntop(AF_INET, &client_addr.sin_addr, ip_str, sizeof(ip_str));printf("cli bind %s:%d\n", ip_str, ntohs(client_addr.sin_port));// 设置服务器地址信息memset(&server_addr, 0, sizeof(server_addr));server_addr.sin_family = AF_INET;server_addr.sin_port = htons(serport);server_addr.sin_addr.s_addr = inet_addr(s_ip);// 连接到服务器if (connect(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {perror("connection to server failed");close(sockfd);exit(EXIT_FAILURE);}printf("connetct to ser %s:%d\n", s_ip, serport);// 这里可以添加发送和接收数据的代码while(1){struct s_cmd cmd = {0};memset(cmd_buf, 0, sizeof(cmd_buf));ssize_t bytes_received = recv(sockfd, cmd_buf, sizeof(struct s_cmd), 0);if (bytes_received < 0) {perror("recv failed");close(sockfd);return -1;} else if (bytes_received == 0) {printf("ser closed\n");close(sockfd);return 0;}memcpy(&cmd, cmd_buf, sizeof(struct s_cmd));printf("bytes_received = %d, cmd.cmd = 0x%x, cmd.op = 0x%x, cmd.msg = %s\n", bytes_received, cmd.cmd, cmd.op, cmd.msg);if(cli_check_cmd_valid(&cmd) == 0){cli_cmd_dispatch(&cmd);}}// 关闭套接字close(sockfd);
}int main() {int sockfd;cli_sock_create("127.0.0.1", 9090, NULL, 0);return 0;
}

总结

socket通信 ser端 3秒发送一个命令给 cli端，然后cli端处理命令的代码和如何判断socket对端断开连接。