Linux C Socket 本地回环测试程序：客户端非阻塞重连服务器

以下是一个简单的 socket 本地回环测试程序，包含客户端非阻塞的用 select 重连服务器：

服务器端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define PORT 8888
#define BUFFER_SIZE 1024

int main()
{
    int sockfd, newsockfd, n;
    socklen_t clilen;
    char buffer[BUFFER_SIZE];
    struct sockaddr_in serv_addr, cli_addr;

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
    {
        perror("ERROR opening socket");
        exit(1);
    }

    bzero((char *) &serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = INADDR_ANY;
    serv_addr.sin_port = htons(PORT);

    if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
    {
        perror("ERROR on binding");
        exit(1);
    }

    listen(sockfd, 5);
    clilen = sizeof(cli_addr);

    while (1)
    {
        newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);
        if (newsockfd < 0)
        {
            perror("ERROR on accept");
            exit(1);
        }

        bzero(buffer, BUFFER_SIZE);
        n = read(newsockfd, buffer, BUFFER_SIZE-1);
        if (n < 0)
        {
            perror("ERROR reading from socket");
            exit(1);
        }

        printf("Received message: %s\n", buffer);

        n = write(newsockfd, buffer, strlen(buffer));
        if (n < 0)
        {
            perror("ERROR writing to socket");
            exit(1);
        }

        close(newsockfd);
    }

    close(sockfd);
    return 0;
}

客户端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/select.h>

#define PORT 8888
#define BUFFER_SIZE 1024

int main()
{
    int sockfd, n;
    struct sockaddr_in serv_addr;
    char buffer[BUFFER_SIZE];
    fd_set read_fds;
    struct timeval timeout;
    int fd_flags;

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
    {
        perror("ERROR opening socket");
        exit(1);
    }

    bzero((char *) &serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    serv_addr.sin_port = htons(PORT);

    fd_flags = fcntl(sockfd, F_GETFL, 0);
    fcntl(sockfd, F_SETFL, fd_flags | O_NONBLOCK);

    if (connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
    {
        if (errno != EINPROGRESS)
        {
            perror("ERROR connecting");
            exit(1);
        }
    }

    FD_ZERO(&read_fds);
    FD_SET(sockfd, &read_fds);

    timeout.tv_sec = 5;
    timeout.tv_usec = 0;

    n = select(sockfd+1, NULL, &read_fds, NULL, &timeout);
    if (n < 0)
    {
        perror("ERROR in select");
        exit(1);
    }
    else if (n == 0)
    {
        printf("ERROR: Connection timeout\n");
        exit(1);
    }

    if (!FD_ISSET(sockfd, &read_fds))
    {
        printf("ERROR: Socket not ready for reading\n");
        exit(1);
    }

    bzero(buffer, BUFFER_SIZE);
    n = read(sockfd, buffer, BUFFER_SIZE-1);
    if (n < 0)
    {
        perror("ERROR reading from socket");
        exit(1);
    }

    printf("Received message: %s\n", buffer);

    close(sockfd);

    return 0;
}

在客户端代码中，我们使用了非阻塞连接方式，通过 select 函数来检查连接是否成功建立，并设置了超时时间。如果超时或连接失败，则程序会退出。