How to connect to a server using only its IP?

Question

I'm kind of new to sockets. So I setup a server and I want to connect a client to it through the internet. I don't understand what I'm doing wrong because the following example works with the loopback address (127.0.0.1) but not when someone else tries to connect to my server using my external IP address. Is it just not that simple or am I doing something wrong in my code?

Edit: (The client specifically gets stuck when it reaches connect() giving a connect: Connection timed out error)

Edit2: I tried using my broadcast address inet_addr("192.168.1.255") instead of INADDR_ANY in the server code. No change.

This is my server code:

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

int main(void) {

    int temp;
    struct sockaddr_in my_addr;
    struct sockaddr_in their_addr;
    int sin_size;
    int numbytes;
    char buf[100];
    int sock_fd; // server file descriptor
    int new_fd; // client file descriptor

    sock_fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (sock_fd == -1) { perror("socket"); exit(1); }

    my_addr.sin_family = AF_INET;
    my_addr.sin_port = htons(9000);
    my_addr.sin_addr.s_addr = INADDR_ANY;
    bzero(&(my_addr.sin_zero), 8);

    temp = bind(sock_fd, (struct sockaddr*)&my_addr, sizeof(struct sockaddr));
    if (temp == -1) { perror("bind"); exit(1); }

    temp = listen(sock_fd, 5);
    if (temp == -1) { perror("listen"); exit(1); }

    printf("\nListening for new connections on port %d ...\n\n", 9000);

    while (1) {
        sin_size = sizeof(struct sockaddr_in);
        new_fd = accept(sock_fd, (struct sockaddr*)&their_addr, &sin_size);
        if (new_fd == -1) { perror("accept"); continue; }
        printf("Got connection from IP (%s)\n", inet_ntoa(their_addr.sin_addr));
        close(new_fd);
    }
}

This is my client code:

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

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

    int temp;
    struct hostent *host_info;
    struct sockaddr_in serv_addr;
    char ip_addr[100];
    int numbytes;
    char buf[100];
    int sock_fd;

    inet_pton(AF_INET, argv[5], &serv_addr.sin_addr);
    host_info = gethostbyaddr(&serv_addr.sin_addr, sizeof serv_addr.sin_addr, AF_INET);
    if (host_info == NULL) { herror("gethostbyname"); exit(1); }

    printf("\nServer: '%s' (IP: %s , Port: %d)\n\n", argv[1], inet_ntop(AF_INET, host_info->h_addr, ip_addr, 100), 9000);

    sock_fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (sock_fd == -1) { perror("socket"); exit(1); }

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(9000);
    serv_addr.sin_addr = *((struct in_addr *)host_info->h_addr);
    bzero(&(serv_addr.sin_zero), 8);

    temp = connect(sock_fd, (struct sockaddr*)&serv_addr, sizeof(struct sockaddr));
    if (temp == -1) { perror("connect"); exit(1); }

    close(sock_fd);
    exit(0);
}

Answer 1

Posting an answer here so I can accept my overall solution. The problem was that I had not forwarded a port on my router as @AdamRosenfield indicated, then after I did that I changed my server's address to:

my_addr.sin_addr.s_addr = inet_addr("192.168.1.2");

which is MY local IP address according to ifconfig (I am using Ubuntu). Now my only problem is that anyone else can connect to my server except me from my own pc, but that might be a problem specific to my router according to @nos.

If anyone has an answer on how to fix that please update me (I tried connecting a client using the loopback address, my external IP, my local IP and a few more, nothing worked).

Answer 2

the client.c should be as below

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

int temp;
struct hostent *host_info;
struct sockaddr_in serv_addr;
char ip_addr[100];
int numbytes;
char buf[100];
int sock_fd;

unsigned long inaddr;

//inet_pton(AF_INET, argv[5], &serv_addr.sin_addr);
//host_info = gethostbyaddr(&serv_addr.sin_addr, sizeof serv_addr.sin_addr, AF_INET);
//if (host_info == NULL) { herror("gethostbyname"); exit(1); }

printf("\nServer: '%s' (IP: %s , Port: %d)\n\n", argv[0], argv[1], 9000);

inaddr = inet_addr(argv[1]);

sock_fd = socket(AF_INET, SOCK_STREAM, 0);
if (sock_fd == -1) { perror("socket"); exit(1); }

serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(9000);
memcpy(&serv_addr.sin_addr, &inaddr, sizeof(inaddr));
//bzero(&(serv_addr.sin_zero), 8);

temp = connect(sock_fd, (struct sockaddr*)&serv_addr, sizeof(struct sockaddr));
if (temp == -1) { perror("connect"); exit(1); }

close(sock_fd);
exit(0);

}

then use g++ compile it:g++ client.c -o client.

use client like this:./client yourserverIP

Answer 3

when set the server address in client code, you can do like this:

serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");//your server's ip address