C > Programs

C UDP socket example Server and Client program

// Server

/* Creates a datagram server. The port
number is passed as an argument. This
server runs forever */

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>

#include <arpa/inet.h>
#include <assert.h>
#include <errno.h>
#include <signal.h>
#include <string.h>
#include <sys/wait.h>
#include <netdb.h>
#include <unistd.h>

void error(char *msg)
{
    perror(msg);
    exit(0);
}

struct Test {
char name[20];
int num;
} test_t;

int main(int argc, char *argv[])
{
   int sock, length, fromlen, n;
   struct sockaddr_in server;
   struct sockaddr_in from;
   char buf[1024];
   struct Test test_name;

   if (argc < 2) {
      fprintf(stderr, "ERROR, no port provided\n");
      exit(0);
   }

   sock=socket(AF_INET, SOCK_DGRAM, 0);
   if (sock < 0) error("Opening socket");
   length = sizeof(server);
   bzero(&server,length);
   server.sin_family=AF_INET;
   server.sin_addr.s_addr=INADDR_ANY;
   server.sin_port=htons(atoi(argv[1]));
   if (bind(sock,(struct sockaddr *)&server,length)<0)
       error("binding");
   fromlen = sizeof(struct sockaddr_in);
   while (1) {
       n = recvfrom(sock,&test_name,1024,0,(struct sockaddr *)&from,&fromlen);
       if (n < 0) error("recvfrom");
       write(1,"Received a datagram: ",21);
       write(1,test_name.name,strlen(test_name.name));
       printf("Received value: %d\n", test_name.num);
       n = sendto(sock,"Got your message\n",17,
                  0,(struct sockaddr *)&from,fromlen);
       if (n  < 0) error("sendto");
   }
}

// Client

/* UDP client in the internet domain */
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>

#include <arpa/inet.h>
#include <assert.h>
#include <errno.h>
#include <signal.h>
#include <string.h>
#include <sys/wait.h>
#include <netdb.h>
#include <unistd.h>

struct Test {
char name[20];
int num;
} test_t;

void error(char *);
int main(int argc, char *argv[])
{
   int sock, length, n;
   struct sockaddr_in server, from;
   struct hostent *hp;
   char buffer[256];
   struct Test test_name;

   test_name.num = 10;

   if (argc != 3) { printf("Usage: server port\n");
                    exit(1);
   }
   sock= socket(AF_INET, SOCK_DGRAM, 0);
   if (sock < 0) error("socket");

   server.sin_family = AF_INET;
   hp = gethostbyname(argv[1]);
   if (hp==0) error("Unknown host");

   bcopy((char *)hp->h_addr,
        (char *)&server.sin_addr,
         hp->h_length);
   server.sin_port = htons(atoi(argv[2]));
   length=sizeof(struct sockaddr_in);
   printf("Please enter the message: ");
   bzero(buffer,256);
   fgets(test_name.name,255,stdin);
   n=sendto(sock,&test_name, 255,0,&server,length);
   if (n < 0) error("Sendto");
   n = recvfrom(sock,buffer,256,0,&from, &length);
   if (n < 0) error("recvfrom");
   write(1,"Got an ack: ",12);
   write(1,buffer,n);
}

void error(char *msg)
{
    perror(msg);
    exit(0);
}