Question

我正试图找到一种方法让我的服务器打印其TCP端口号和IP地址，但我现在如何生成错误的IP，我得到的输出为0.0.33.32。任何帮助表示赞赏！

#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>
#include <time.h>

#define PORT "21467"  // the port users will be connecting to

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

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

char hname[100];
gethostname(hname, sizeof hname);

if ((rv = getaddrinfo(hname, 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);
}


char host[100];
char service[20];

getnameinfo(p->ai_addr, p->ai_addrlen, host, sizeof host, service, sizeof service, 0);
inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr),
        host, sizeof host);

printf("server: has TCP port number %s and IP address %s\n", service, host); 

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

int numbytes;
char buf[100];

while(1) {  // main accept() loop
    sin_size = sizeof their_addr;
    new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
    if (new_fd == -1) {
        perror("accept");
        continue;
    }

    inet_ntop(their_addr.ss_family,
        get_in_addr((struct sockaddr *)&their_addr),
        s, sizeof s);

    //getnameinfo(get_in_addr((struct sockaddr *)&their_addr), sizeof get_in_addr((struct sockaddr *)&their_addr), NULL, NULL, service, sizeof service, 0);

    if ((numbytes = recv(new_fd, buf, 100, 0)) == -1)
        perror("recv");

    /* if ((numbytes = recv(sockfd, buf, 100, 0)) == -1) {
    perror("recv");
    exit(1);
}*/ 

    struct tm* local;
    char toClient[50];
    printf("server: received '%s'\n",buf);
    time_t curTime = time(0);
    local = localtime(&curTime);
    if(buf[0] == 't'    ){ 
        printf("server: received time request\n", s);
        sprintf(toClient, "Time: %d::%d::%d", local->tm_hour, local->tm_min, local->tm_sec);  //Seg faulting
        printf("Sent the time to the client having IP address %s and port number %s\n", s, service);
    }
    else if(buf[0] == 'd'){
        printf("server: received date request\n", s);
        sprintf(toClient, "Date: %d::%d::%d", 1900+local->tm_year, 1+local->tm_mon, local->tm_mday);
        printf("Sent the date to the client having IP address %s and port number %s\n", s, service);
    }
    else{

    }   

    if ((numbytes = send(new_fd, toClient, sizeof toClient, 0)) == -1) {
    perror("send");
    exit(1);
}
    close(new_fd);
    break; //Temporary
}


close(sockfd);
return 0;
}

Answer 1

您可能需要使用的是getsockname功能：

struct sockaddr_storage my_addr;
socklen_t my_addr_len = sizeof(my_addr);
if (getsockname(sockfd, (struct sockaddr *) &my_addr, &my_addr_len) != -1)
{
#ifndef NI_MAXHOST
# define NI_MAXHOST 1025
#endif
#ifndef NI_MAXSERV
# define NI_MAXSERV 32
#endif

    char host[NI_MAXHOST];
    char serv[NI_MAXSERV];

    if (getnameinfo((const struct sockaddr *) &my_addr, my_addr.ss_len,
                    host, sizeof(host),
                    serv, sizeof(serv), 0) == 0)
    {
        printf("Host address: %s, host service: %s\n", host, serv);
    }
}

Answer 2

问题出在inet_ntop来电：

inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr),
          host, sizeof host);

在这里，您在调用

后使用指针p

freeaddrinfo(servinfo);

您需要在某些变量中复制从sockaddr获得的结构socklen_t和getaddrinfo，或者存储结构addrinfo以供进一步使用。否则，您将导致未定义的行为，就像您现在遇到的那样。记住，Valgrind是你的朋友。

Answer 3

嗯，其他答案（getsockname）可能已经是你需要的了。

我只想强调一下了解网络编程的最佳资源之一：

<强> Beej's guide to network programming

它相当短，你在1小时内完成它
适用于Windows和Linux（以及unix等...）
解释了必要细节背后的概念（没有必要，没有必要）

需要帮助在C中获取TCP端口号和IP地址

3 个答案: