UDP client server programming

[CLearner88]

Hi guys, i`m doing a UDP server program for 2 clients.
My question is how do i differentiate between them?
lets say i have a client alice and bob

i want to differentiate between them

how do i do that?

below are the codes

server

//UDPServer.c

/* 
 *  gcc -o server UDPServer.c
 *  ./server
 */
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdlib.h> 
#include <string.h>
#define BUFLEN 512
#define PORT 9930

void err(char *str)
{
    perror(str);
    exit(1);
}

int main(void)
{
    struct sockaddr_in my_addr, cli_addr;
    int sockfd, i; 
    socklen_t slen=sizeof(cli_addr);
    char buf[BUFLEN];

    if ((sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1)
      err("socket");
    else 
      printf("Server : Socket() successful\n");

    bzero(&my_addr, sizeof(my_addr));
    my_addr.sin_family = AF_INET;
    my_addr.sin_port = htons(PORT);
    my_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    
    if (bind(sockfd, (struct sockaddr* ) &my_addr, sizeof(my_addr))==-1)
      err("bind");
    else
      printf("Server : bind() successful\n");

    while(1)
    {
        if (recvfrom(sockfd, buf, BUFLEN, 0, (struct sockaddr*)&cli_addr, &slen)==-1)
            err("recvfrom()");
        printf("Received packet from %s:%d\nData: %s\n\n",
               inet_ntoa(cli_addr.sin_addr), ntohs(cli_addr.sin_port), buf);
	
    }

    close(sockfd);
    return 0;
}

Client

//UDPClient.c

/*
 * gcc -o client UDPClient.c
 * ./client 
 */

#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdlib.h> 
#include <string.h>
#define BUFLEN 512
#define PORT 9930

void err(char *s)
{
    perror(s);
    exit(1);
}

int main(int argc, char** argv)
{
    struct sockaddr_in serv_addr;
    int sockfd, i, slen=sizeof(serv_addr);
    char buf[BUFLEN];

    if(argc != 2)
    {
      printf("Usage : %s <Server-IP>\n",argv[0]);
      exit(0);
    }

    if ((sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1)
        err("socket");

    bzero(&serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(PORT);
    if (inet_aton(argv[1], &serv_addr.sin_addr)==0)
    {
        fprintf(stderr, "inet_aton() failed\n");
        exit(1);
    }

    while(1)
    {
        printf("\nEnter data to send(Type exit and press enter to exit) : ");
        scanf("%[^\n]",buf);
        getchar();
        if(strcmp(buf,"exit") == 0)
          exit(0);

        if (sendto(sockfd, buf, BUFLEN, 0, (struct sockaddr*)&serv_addr, slen)==-1)
            err("sendto()");
    }

    close(sockfd);
    return 0;
}

Thanks in advance!

[Cubbi]

is cli_addr insufficient? If it is (eg you need to know that two datagrams from the same address are from the same client process), then you have to send sequence numbers or some other identification data from the application.

[CLearner88]

i see, then may i know how do i send sequence numbers over? can i have an example?
i am quite new to c programming

and also in c, how do i store values that i get from the buffer into variables in c? i am quite lost on that!

i`m using this to do a diffie-hellman key exchange and RC4.

[Cubbi]

it's up to you to come up with it. Physically, it would be in buf in addition to the 512 bytes you're already sending. (btw, don't forget to limit your scanf, it's %514[^\n] in this case)

Or you could switch to TCP, That's what it exists for.

for the variables, you could memcpy() from the offset in the buffer to the address of the variable

[CLearner88]

ok thanks alot!
i have to do this in udp as its an assignment requirement!