保持C语言中的套接字开放状态

Question

保持C语言中的套接字开放状态

3

我认为这可能是一个简单的解决方案，我只是想太多了。我正在编写一个非常基本的聊天程序，客户端和服务器轮流发送消息。现在，我让它只发送一次来回的消息，然后客户端关闭套接字。该程序不必同时打开套接字，只要能像秋千一样来回切换即可，而不是像真正的聊天程序那样可以同时从两侧接收多个输入。

在客户端中使用while循环会保持其打开状态，但while循环的条件是什么？

我尝试过几种不同的条件，但它们都没有起作用...它只会让它挂起。我还尝试注释掉服务器代码中的一些close()函数，但也没有用。

我还有一个小问题，就是接收到的输入打印出来是乱码，但我认为这是因为在字符串数组中没有内容时打印了内存地址...我只是想不起如何缩短它。哈哈。

Server.c:

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

#define PORT "3490"  // The port users will be connecting to

#define BACKLOG 10   // How many pending connections queue will hold

char input[20];
char *pointer;

void sigchld_handler(int s)
{
    while(waitpid(-1, NULL, WNOHANG) > 0);
}

// Get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
    if (sa->sa_family == AF_INET) {
        return &(((struct sockaddr_in*)sa)->sin_addr);
    }
    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int main(void)
{
    int sockfd, new_fd;  // Listen on sock_fd, new connection on new_fd
    struct addrinfo hints, *servinfo, *p;
    struct sockaddr_storage their_addr; // Connector's address information
    socklen_t sin_size;
    struct sigaction sa;
    int yes = 1;
    char s[INET6_ADDRSTRLEN];
    int rv;

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE; // use my IP

    if ((rv = getaddrinfo(NULL, PORT, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
        return 1;
    }

    // loop through all the results and bind to the first we can
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,
                             p->ai_protocol)) == -1) {
            perror("server: socket");
            continue;
        }

        if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes,
                       sizeof(int)) == -1) {
            perror("setsockopt");
            exit(1);
        }

        if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
            close(sockfd);
            perror("server: bind");
            continue;
        }

        break;
    }

    if (p == NULL)  {
        fprintf(stderr, "server: failed to bind\n");
        return 2;
    }

    freeaddrinfo(servinfo); // All done with this structure

    if (listen(sockfd, BACKLOG) == -1) {
        perror("listen");
        exit(1);
    }

    sa.sa_handler = sigchld_handler; // Reap all dead processes
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;
    if (sigaction(SIGCHLD, &sa, NULL) == -1) {
        perror("sigaction");
        exit(1);
    }

    printf("server: waiting for connections...\n");

    sin_size = sizeof their_addr;

    while((new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size)) > 0) {  // Main accept() loop

        if (new_fd == -1) {
            perror("accept");
            continue;
        }

        inet_ntop(their_addr.ss_family,
            get_in_addr((struct sockaddr *)&their_addr),
            s, sizeof s);
        printf("server: got connection from %s\n", s);

        if (!fork()) { // this is the child process
            close(sockfd); // child doesn't need the listener

            char input[20];
            char *pointer;
            printf("Type in an server's input: ");
            scanf("%s", input);
            pointer = input;  //Will need to clean this up to be more effcient... later

            if (send(new_fd, pointer, strlen(input), 0) == -1) //Need to change the length to
                                                               //the actual length of the
                                                               //input... later.

                perror("send");
            close(new_fd);
            exit(0);
        }

        char Cinput[20];
        if ((recv(new_fd, Cinput, strlen(Cinput), 0)) == 0) { //NEW LINE ADDED HERE
            printf("No more messages");
        }

        if ((recv(new_fd, Cinput, strlen(Cinput), 0)) == -1) {
                perror("recv");
                exit(1);
        }

        printf("Server: received '%s'\n",Cinput);

        close(new_fd);  // Parent doesn't need this
    }
    return 0;
}

Client.c

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

#include <arpa/inet.h>

#define PORT "3490" // The port client will be connecting to

#define MAXDATASIZE 100 // Max number of bytes we can get at once

// Get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
    if (sa->sa_family == AF_INET) {
        return &(((struct sockaddr_in*)sa)->sin_addr);
    }

    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int main(int argc, char *argv[])
{
    int sockfd, numbytes;
    char buf[MAXDATASIZE];
    struct addrinfo hints, *servinfo, *p;
    /*
        This is what is in the struct

        struct addrinfo {
            int ai_flags; // AI_PASSIVE, AI_CANONNAME, etc.
            int ai_family; // AF_INET, AF_INET6, AF_UNSPEC
            int ai_socktype; // SOCK_STREAM, SOCK_DGRAM
            int ai_protocol; // Use 0 for "any"
            size_t ai_addrlen; // Size of ai_addr in bytes
            struct sockaddr *ai_addr; // struct sockaddr_in or _in6
            char *ai_canonname; // Full canonical hostname
            struct addrinfo *ai_next; // Linked list, next node
        };

        getaddrinfo() will return a pointer to this
    */
    int rv;
    char s[INET6_ADDRSTRLEN];

    if (argc != 2) {
        fprintf(stderr,"usage: client hostname\n");
        exit(1);
    }

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;

    if ((rv = getaddrinfo(argv[1], PORT, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
        return 1;
    }

    // Loop through all the results and connect to the first we can
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,
                             p->ai_protocol)) == -1) {
            perror("client: socket");
            continue;
        }

        if (connect(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
            close(sockfd);
            perror("client: connect");
            continue;
        }

        break;
    }

    if (p == NULL) {
        fprintf(stderr, "client: failed to connect\n");
        return 2;
    }

    inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr),
              s, sizeof s);
    printf("client: connecting to %s\n", s);

    freeaddrinfo(servinfo); // All done with this structure

    while(1)//NEW LINE ADDEDthis is getting the client to repeat asking for the input, but doesn't send it.
    {
        if ((numbytes = recv(sockfd, buf, MAXDATASIZE-1, 0)) == 0) { //NEW LINE ADDED
               printf("Shutdown");
        }

        if ((numbytes = recv(sockfd, buf, MAXDATASIZE-1, 0)) == -1) {
            perror("recv");
            exit(1);
        }

        buf[numbytes] = '\0';

        printf("client: received '%s'\n",buf);

        char Cinput[20];
        char *pointer;
        printf("Type in an client's input: ");
        scanf("%s", Cinput);
        pointer = Cinput;
        if (send(sockfd, pointer, strlen(Cinput), 0) == -1)
        {
            perror("send");
            close(sockfd);
            exit(0);
        }
    }

    close(sockfd); //As soon as the client receives a message, it closes the socket.
    //We probably need a while loop in here in order to keep the socket open,
    //but what are the parameters for the while loop?
    return 0;
}

- Hokerie

您的循环应该在连接存在的同时，执行客户端预期使用该连接进行的任何操作。这不是一个真正的问题。 - user207421

1

好的，我提到过我想保持客户端的连接开放（这样它就可以继续接受消息），我尝试了不同的条件，但都没有成功。我刚刚编辑了客户端的while条件，现在它只是不断地要求输入而不是发送它。 - Hokerie

1个回答

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- Anish Ramaswamy · Accepted Answer

以下伪代码将确保同一个客户端和服务器可以无限发送消息，直到其中一个挂断：

客户端：

创建socket。
连接到它。
接收数据。
如果接收返回0，则表示另一端已执行有序关闭。转到步骤7。
发送响应。
转到步骤3。
停止。

服务器：

创建socket。
绑定套接字到地址。
将套接字标记为监听。
接受连接。
如果接受的连接无效，请转到步骤4。
发送数据。
接收响应。
如果接收返回0，则表示另一端已执行有序关闭。转到步骤4以接受新连接。
转到步骤6。