UDP

<server_udp.c>

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

#include <signal.h>

void error(char *msg)
{

 perror(msg);
 exit(0);

}

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

 int sock, length, fromlen, n;
 struct sockaddr_in server;
 struct sockaddr_in from;

 char buf[1024];

 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]));
 server.sin_port  = htons(8024);
 
 if( bind(sock, (struct sockaddr *)&server, length) < 0 )
  error("Binding");
 fromlen = sizeof(struct sockaddr_in);

 while (1)
 {

  n = recvfrom(sock, buf, 256, 0, (struct sockaddr *)&from, &fromlen);

  if(n <0)
  { 

   error("recvfrom");
   printf("Receive size 0\n");
   exit(-1);

  }
  
  write( 1, "Received a datagram: ", 21);
  buf[n] = '\0';
  write( 1, buf, n);

  n = sendto(sock,"Got your msg\n",13, 0, (struct sockaddr *)&from, sizeof(from));

  if(n <0) error("sendto");

 }

}

---

<client_udp.c>

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

#include <signal.h>

void error(char *);

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

 int sock, length, n;
 struct sockaddr_in server, from;
 struct hostent *hp;

 char buffer[256];
 
 if(argc != 3)
 {

  printf("Usage: server port \n");
  exit(1);

 }

 sock = (AF_INET, SOCK_DGRAM, 0);
 if(sock <0) error("Socket\n");

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

 bcopy((char *)hp->h_addr, (char *)&server.sin_addr, hp->h_length);
 //server.sin_port = htons(atoi(argv[2]));
 server.sin_port = htons(8024);
 length = sizeof(struct sockaddr_in);
 printf("Please enter the message");

 bzero(buffer, 256);
 fgets(buffer, 255, stdin);

 n = sendto(sock, buffer, strlen(buffer), 0,(struct sockaddr *)&server, sizeof(server));
 if(n < 0) error("Sendto\n");

 n = recvfrom(sock, buffer, 256, 0, (struct sockaddr *)&server, &length);
 if(n < 0) error("recvfrom\n");

 buffer[n] = '\0';

 write(1, "Got an ack: ",12);
 write(1, buffer,n);

}

void error(char *msg)
{ 

 perror(msg);
 exit(0);

}