udpserver.c

gistfile1.c

#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 *err)
{
  perror(err);
  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()");
    }
    else
    {
      printf("Received packet from %s:%d\nData: %s\n\n",
          inet_ntoa(cli_addr.sin_addr), ntohs(cli_addr.sin_port), buf);
      sendto(sockfd, buf, strlen(buf), 0, (struct sockaddr*)&cli_addr, slen);
//      close(sockfd);
//      return;
    }
  }
}

Simple echo server written in C using UDP as the transport.