C Socket Programming - Connecting to an External Source - c

Question

I'm trying to get into socket programming with C and my problem is that no matter what I try I cannot get my client-server model to connect over the internet except through logging into my router and port forwarding the port I'm inputting in my program. Basically my server.c blocks and waits for a connection, then it sends the time of the server to the client once it connects. I've tried to open ports on both my machines like this:
sudo iptables -A INPUT -p tcp --dport 20001 -j ACCEPT
and I downloaded the iptables-persistent package that makes sure the rules stay on a reboot. iptables -L shows me that the ports are open on both machines, but the connection still times out. I know that somehow this is possible because Steam and Discord don't have to port forward anything and they still make it happen. I have a server at home so if the solution requires a 'middle man' server to facilitate a connection between two clients, then it won't be a problem for me. Also I am on two separate networks, so that's not the problem.
The 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);
}
}
and 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

This line is saying what port you're connecting to on the server
serv_addr.sin_port = htons(42020);
change it to the same port number as the server and it should work just fine.
serv_addr.sin_port = htons(20001);

Answer 2

#include <stdio.h>
#include "http.h"
#define MAX 4096
int main()
{
char s_msg[MAX], c_msg[MAX];
printf("%d", strlen(s_msg));
// Clean buffers:
memset(s_msg,'\0',sizeof(s_msg));
memset(c_msg,'\0',sizeof(c_msg));
char *msg = "GET / HTTP/1.1\r\nUser-Agent: Hellothere\r\nHost: HOSTNAME\r\n\r\n";
int soc = init_client();
int con = connection("HOSTNAME",80);
if(send(socket_desc, msg, strlen(msg), 0) < 0){
printf("Unable to send message\n");
return -1;
}
if (recv(socket_desc, c_msg , MAX, 0)<0)
{
printf("Failed to read from server\n");
return -1;
}
printf("Recieved from server : %s\n",c_msg);
return 0;
}
Using ngrok you need to use Host header