在C中保持套接字打开

Question

我认为这可能是一个简单的解决方案，我只是在思考。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。现在我有它只来回发送一次消息，客户端关闭套接字。该程序不必同时打开套接字，只要它可以像摇摆一样来回切换，而不是真正的聊天程序，它可以同时从双方进行多次输入。

客户端中的while循环是否会保持打开状态以及while循环的条件是什么？

我尝试了几种不同的条件，但没有一种工作......它只是让它挂起来。我也试过在服务器代码中注释掉一些close()函数，但这也没有用。

我也有一个小问题收到输入打印乱码，但我认为这是因为它打印字符串数组的内存地址，当它什么都没有...我只是不记得如何缩短它。洛尔。

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;
}

Answer 1

以下伪代码将确保相同的客户端和服务器可以无限地向对方发送消息，直到其中一个挂起：

客户端：

1. 创建socket。
2. connect。
3. recv数据。
4. 如果recv返回0，则表示另一端已执行有序关机。转到第7步。
5. send回复。
6. 转到第3步。
7. 停止。

服务器：

1. 创建socket。
2. bind套接字到地址。
3. 将套接字标记为listen ing。
4. accept一个连接。
5. 如果接受的连接无效，请转到步骤4.
6. send数据。
7. recv回复。
8. 如果recv返回0，则表示另一端已执行有序关机。转到步骤4以接受新连接。
9. 转到第6步。