C套接字编程 - 连接外部源

Question

我正在尝试使用C进行套接字编程，我的问题是，无论我尝试什么，我都无法让我的客户端 - 服务器模型通过互联网连接，除非通过登录我的路由器和端口转发我正在输入的端口我的节目。基本上我的server.c阻塞并等待连接，然后它连接后将服务器的时间发送到客户端。我试图在我的两台机器上打开端口，如下所示：

sudo iptables -A INPUT -p tcp --dport 20001 -j ACCEPT

我下载了iptables-persistent软件包，确保规则保持重启状态。 iptables -L告诉我两台机器上的端口都是打开的，但连接仍然超时。我知道这是可能的，因为Steam和Discord不需要向前移动任何东西而且它们仍然可以实现。我家里有一台服务器，所以如果解决方案需要一个“中间人”服务器来促进两个客户端之间的连接，那么对我来说这不是问题。此外，我在两个独立的网络上，所以这不是问题。

server.c：

/* --- server.c --- */
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <time.h>

int main(int argc, char *argv[])
{
    int listenfd = 0, connfd = 0;
    struct sockaddr_in serv_addr;

    char sendBuff[1025];
    time_t ticks;

    /* creates an UN-named socket inside the kernel and returns
     * an integer known as socket descriptor
     * This function takes domain/family as its first argument.
     * For Internet family of IPv4 addresses we use AF_INET
     */
    listenfd = socket(AF_INET, SOCK_STREAM, 0);
    memset(&serv_addr, '0', sizeof(serv_addr));
    memset(sendBuff, '0', sizeof(sendBuff));

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(20001);

    /* The call to the function "bind()" assigns the details specified
     * in the structure 『serv_addr' to the socket created in the step above
     */
    bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr));

    /* The call to the function "listen()" with second argument as 10 specifies
     * maximum number of client connections that server will queue for this listening
     * socket.
     */
    listen(listenfd, 10);

    while(1)
    {
        /* In the call to accept(), the server is put to sleep and when for an incoming
         * client request, the three way TCP handshake* is complete, the function accept()
         * wakes up and returns the socket descriptor representing the client socket.
         */
        connfd = accept(listenfd, (struct sockaddr*)NULL, NULL);

        /* As soon as server gets a request from client, it prepares the date and time and
         * writes on the client socket through the descriptor returned by accept()
         */
        ticks = time(NULL);
        snprintf(sendBuff, sizeof(sendBuff), "%.24s\r\n", ctime(&ticks));
        write(connfd, sendBuff, strlen(sendBuff));

        close(connfd);
        sleep(1);
    }
}

和client.c：

/* --- client.c --- */
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <arpa/inet.h>

int main(int argc, char *argv[])
{
    int sockfd = 0, n = 0;
    char recvBuff[1024];
    struct sockaddr_in serv_addr;

    if(argc != 2)
    {
        printf("\n Usage: %s <ip of server> \n",argv[0]);
        return 1;
    }

    memset(recvBuff, '0',sizeof(recvBuff));

    /* a socket is created through call to socket() function */
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf("\n Error : Could not create socket \n");
        return 1;
    }

    memset(&serv_addr, '0', sizeof(serv_addr));

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(20001);

    if(inet_pton(AF_INET, argv[1], &serv_addr.sin_addr)<=0)
    {
        printf("\n inet_pton error occured\n");
        return 1;
    }

    /* Information like IP address of the remote host and its port is
     * bundled up in a structure and a call to function connect() is made
     * which tries to connect this socket with the socket (IP address and port)
     * of the remote host
     */
    if( connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
    {
        printf("\n Error : Connect Failed \n");
        return 1;
    }

    /* Once the sockets are connected, the server sends the data (date+time)
     * on clients socket through clients socket descriptor and client can read it
     * through normal read call on the its socket descriptor.
     */
    while ( (n = read(sockfd, recvBuff, sizeof(recvBuff)-1)) > 0)
    {
        recvBuff[n] = 0;
        if(fputs(recvBuff, stdout) == EOF)
        {
            printf("\n Error : Fputs error\n");
        }
    }

    if(n < 0)
    {
        printf("\n Read error \n");
    }

    return 0;
}

Answer 1

这一行说明了您在服务器上连接的端口

serv_addr.sin_port = htons(42020);

将它更改为与服务器相同的端口号，它应该可以正常工作。

serv_addr.sin_port = htons(20001);