TCP server/client 如何保持连接？

Question

我编写了一个简单的 TCP 回显服务器来处理多个客户端。它使用 select() 来获得多个连接。

服务器代码：

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


int create_listener(uint16_t port) {

    int listen_fd;
    struct sockaddr_in name;

    listen_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (listen_fd < 0) {
        perror ("socket");
        exit(EXIT_FAILURE);
    }

    bzero(&name, sizeof(name));
    name.sin_family = AF_INET;
    name.sin_addr.s_addr = htonl(INADDR_ANY);
    name.sin_port = htons(port);

    if (bind(listen_fd, (struct sockaddr *) &name, sizeof(name)) < 0) {
        perror ("bind");
        exit(EXIT_FAILURE);
    }


    return listen_fd;
}

int read_from_client(int fd) {
    char buffer[100];
    int nbytes;

    nbytes = read(fd, buffer, 100);
    if (nbytes < 0) {
        perror("read");
        exit(EXIT_FAILURE);
    }
    else if (nbytes == 0) {
        return -1;
    }
    else {
        fprintf(stderr, "Server: got message: %s\n", buffer);
        write(fd, buffer, strlen(buffer) + 1);
        return 0;
    }
}


int main(int argc, char *argv[]) {

    int listen_fd;
    uint16_t port = 22000;

    fd_set active_fd_set, read_fd_set;
    int i;

    struct sockaddr_in servaddr;

    /* Create the socket and set it up to accept connections. */
    listen_fd = create_listener(port);
    if (listen(listen_fd, 10) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    /* Initialize the set of active sockets. */
    FD_ZERO(&active_fd_set);
    FD_SET(listen_fd, &active_fd_set);


    while (1) {

        /* Block until input arrives on one or more active sockets. */
        read_fd_set = active_fd_set;
        if (select(FD_SETSIZE, &read_fd_set, NULL, NULL, 0) < 0) {
            perror("select");
            exit(EXIT_FAILURE);
        }

        /* Service all the sockets with input pending. */
        for (i = 0; i < FD_SETSIZE; ++i) {
            if (FD_ISSET(i, &read_fd_set)) {
                if (i == listen_fd) {
                    /* Connection request on original socket. */
                    int new_fd;
                    new_fd = accept(listen_fd, (struct sockaddr *) NULL, NULL);

                    if (new_fd < 0) {
                        perror ("accept");
                        exit(EXIT_FAILURE);
                    }

                    FD_SET(new_fd, &active_fd_set);
                }
                else {
                    /* Data arriving on an already-connected socket. */
                    if (read_from_client(i) < 0) {
                        close(i);
                        FD_CLR(i, &active_fd_set);
                    }
                }
            }
        }
    }

    return 0;
}

客户代码：

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>

int main(int argc, char *argv[]) {

    int sockfd, n;
    char sendline[100];
    char recvline[100];
    struct sockaddr_in servaddr;

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    bzero(&servaddr, sizeof(servaddr));

    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(22000);

    inet_pton(AF_INET, "127.0.0.1", &(servaddr.sin_addr));

    connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr));


    while (1) {
        bzero(sendline, 100);
        bzero(recvline, 100);
        fgets(sendline, 100, stdin);

        write(sockfd, sendline, strlen(sendline) + 1);
        read(sockfd, recvline, 100);

        printf("%s", recvline);
    }



    return 0;
}

问题是当我运行在一个终端中的服务器和运行在另外两个终端中的两个客户端时。如果我使用 Ctrl+C 终止一个客户端，服务器会自动终止。我想知道为什么服务器会这样。我期待的是服务器运行永远存在。当客户端 1 终止时，服务器仍应与客户端 2 保持实时连接。

Answer 1

您似乎在 read_from_client 中点击了 exit。通常，在为多个客户端提供服务的服务器中，当其中一个客户端连接出现故障时，您可能不想退出。

TCP server/client 如何保持连接？

TCP server/client how to keep connections alive?

c

sockets

tcp

tcpserver