How to run UDP client and server (in C) on two remote hosts?

Question

I am new to socket programming. I wrote codes for UDP Client and Server which work fine on my computer. I want to run these programs on two different hosts, i.e. the Server on my computer and Client on my friend' computer. How do I do it without a router? Please mention if any specific changes are to be made in the code for the purpose.

Here's the code:

Receiver

#include<stdio.h>

#include<stdlib.h>

#include<sys/socket.h>

#include<sys/types.h>

#include<netinet/in.h>

#include<netinet/ip.h>

#include<string.h>

#include<unistd.h>

int main() {
  int ret = socket(AF_INET, SOCK_DGRAM, 0);
  if (ret == -1) {
    printf("socket creation fails\n");
    exit(0);
  } else
    printf("socket creation succeeds\n");

  struct sockaddr_in sender;
  int port;
  printf("Enter port:");
  scanf("%d", & port);
  sender.sin_family = AF_INET;
  sender.sin_port = htons(port);
  sender.sin_addr.s_addr = INADDR_ANY;

  int ret1;
  ret1 = bind(ret, (struct sockaddr * ) & sender, sizeof(sender));

  if (ret1 == -1) {
    printf("socket binding fails\n");
    exit(0);
  }

  printf("socket binding succeeds\n");

  struct sockaddr_in receiver;
  char str[15], str2[15];
  int addrlen = sizeof(receiver);

  while (1) {
    int rec = recvfrom(ret, str, sizeof(str), 0, (struct sockaddr * ) & receiver, & addrlen);
    printf("Received:");
    str[rec] = '\0';
    if (strcmp(str, "exit") == 0)
      break;

    if (rec == -1) {
      printf("recvfrom fails\n");
      exit(0);
    }

    printf("%s\n", str);

    printf("Enter :");
    scanf("%s", str2);

    int recsend = sendto(ret, str2, strlen(str2), 0, (struct sockaddr * ) & receiver, sizeof(receiver));

    if (recsend == -1) {
      printf("sendto fails");
      exit(0);
    }

    if (strcmp(str2, "exit") == 0)
      break;
  }

  close(ret);
  return 0;
}

Sender

#include<stdio.h>

#include<stdlib.h>

#include<sys/socket.h>

#include<sys/types.h>

#include<netinet/in.h>

#include<netinet/ip.h>

#include<string.h>

#include<unistd.h>

int main() {
  int ret = socket(AF_INET, SOCK_DGRAM, 0);
  if (ret == -1) {
    printf("\nsocket creation fails");
    exit(0);
  } else
    printf("\nsocket creation succeeds");

  struct sockaddr_in receiver;
  int port;
  printf("\nEnter port:");
  scanf("%d", & port);
  receiver.sin_family = AF_INET;
  receiver.sin_port = htons(port);
  receiver.sin_addr.s_addr = INADDR_ANY;
  char str[15], str2[15];

  int addrlen1 = sizeof(receiver);
  struct sockaddr_in sender;
  int addrlen = sizeof(sender);
  while (1) {
    printf("Enter:");
    scanf("%s", str);

    int send = sendto(ret, str, strlen(str), 0, (struct sockaddr * ) & receiver, addrlen1);
    if (send == -1) {
      printf("sendto fails");
      exit(0);
    }

    if (strcmp(str, "exit") == 0)
      break;

    int senrec = recvfrom(ret, str2, sizeof(str2), 0, (struct sockaddr * ) & sender, & addrlen);
    printf("\n");
    printf("Received:");
    str2[senrec] = '\0';
    if (strcmp(str2, "exit") == 0)
      break;

    if (senrec == -1) {
      printf("recvfrom fails\n");
      exit(0);
    }

    printf("%s\n", str2);
  }
  close(ret);
  return 0;
}

Let your client know the ip address and the listening port of your server. They have to be connected to a network, what do you mean without router? — my tshirt is cicili bicili
Somewhere on the internet it that said I need to do something called port forwarding using a router to achieve this. — jenny jenkins
And also, what kind of network do the computers have to be in? Please excuse me if the questions seem dumb, I am fairly new to network programming and I don't have the slightest clue how these things are done. — jenny jenkins
Any sort of internet connection will do it for you. Your client has to know the ip address of the server, and the port it listens to. You can quickly learn your ip address by googling "what is my ip". Just connect one of your computers to a mobile hotspot so they will be running on different networks. — my tshirt is cicili bicili

my tshirt is cicili bicili my tshirt is cicili bicili · Accepted Answer · 2020-08-13T10:23:41

Connect both to different networks and get your server's ip address.

Change your client's receiver ip and port to:

receiver.sin_addr.s_addr = inet_addr("8.8.8.8"); // Ip address of your server.
receiver.sin_port=htons(port); // Whatever port your server is listening to

How to run UDP client and server (in C) on two remote hosts?

1 Answers