raw_socket.c

#include <arpa/inet.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include "raw_socket.h"

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

void print_ip_header(char *buffer) {
  struct iphdr *iph = (struct iphdr *)buffer;
  struct sockaddr_in source, dest;

  memset(&source, 0, sizeof(source));
  source.sin_addr.s_addr = iph->saddr;

  memset(&dest, 0, sizeof(dest));
  dest.sin_addr.s_addr = iph->daddr;

  printf("\n");
  printf("IP Header\n");
  printf("  Version         : %d\n",(unsigned int)iph->version);
  printf("  Length          : %d\n",((unsigned int)(iph->ihl))*4);
  printf("  Type Of Service : %d\n",(unsigned int)iph->tos);
  printf("  Total Length    : %d\n",ntohs(iph->tot_len));
  printf("  Identification  : %d\n",ntohs(iph->id));
  printf("  Fragment Offset : %d\n",ntohs(iph->frag_off));
  printf("  TTL             : %d\n",(unsigned int)iph->ttl);
  printf("  Protocol        : %d\n",(unsigned int)iph->protocol);
  printf("  Checksum        : %d\n",ntohs(iph->check));
  printf("  Source          : %s\n",inet_ntoa(source.sin_addr));
  printf("  Destination     : %s\n",inet_ntoa(dest.sin_addr));
}

int verify_port(char * buffer) {
  struct iphdr *iph = (struct iphdr *)buffer;
  struct udphdr *udph = (struct udphdr*)(buffer + (iph->ihl*4));
  return (udph->dest == APPPORT);
}

char * get_source_addr(char *buffer) {
  struct iphdr *iph = (struct iphdr *)buffer;
  struct sockaddr_in source;

  memset(&source, 0, sizeof(source));
  source.sin_addr.s_addr = iph->saddr;
  return inet_ntoa(source.sin_addr);
}

char * get_payload(char *buffer) {
  struct iphdr *iph = (struct iphdr *)buffer;
  struct udphdr *udph = (struct udphdr*)(buffer + (iph->ihl*4));
  return (char *)(buffer + (iph->ihl*4) + sizeof(udph) - 4);
}

void do_server(char **source_addr, char **recv_payload) {
  struct sockaddr_in si_me, si_other;
  int s, b, size;
  socklen_t slen=sizeof(si_other);
  char buffer[BUFLEN];

  while(1) {
    s = socket(AF_INET, SOCK_RAW, IPPROTO_UDP);
    if (s<0) fatal("socket");

    memset((char *) &si_me, 0, sizeof(si_me));
    si_me.sin_family = AF_INET;
    si_me.sin_port = htons(APPPORT);
    si_me.sin_addr.s_addr = htonl(INADDR_ANY);

    b = bind(s, (struct sockaddr *) &si_me, sizeof(si_me));
    if (b < 0) fatal("bind");

    size = recvfrom(s, buffer, BUFLEN, 0, (struct sockaddr *) &si_other, &slen);
    if (size < 0) fatal("recvfrom()");

    if (verify_port(buffer)){
      print_ip_header(buffer);
      *source_addr = get_source_addr(buffer);
      *recv_payload = get_payload(buffer);
      break;
    }

    close(s);
  }
}

void do_client(char *dest, char *message) {
  struct sockaddr_in si;
  int s, e, slen=sizeof(si);
  char buf[BUFLEN];

  sleep(2);

  s = socket(AF_INET, SOCK_RAW, IPPROTO_UDP);
  if (s < 0) fatal("socket");

  memset((char *) &si, 0, sizeof(si));
  si.sin_family = AF_INET;
  si.sin_port = htons(APPPORT);
  if (inet_aton(dest, &si.sin_addr)==0) fatal("inet_aton");


  sprintf(buf, "%s", message);
  e = sendto(s, buf, BUFLEN, 0, (struct sockaddr *) &si, slen);
  if (e < 0) fatal("sendto");

  printf("\nPacket Sent\n");
  close(s);
}