/*  Copyright (C) 2011-2015  P.D. Buchan (pdbuchan@yahoo.com)

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

// Send an IPv4 ICMP echo request packet via raw socket at the link layer (ethernet frame),
// and receive echo reply packet (i.e., ping). Includes some ICMP data.
// Need to have destination MAC address.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>           // close()
#include <string.h>           // strcpy, memset(), and memcpy()

#include <netdb.h>            // struct addrinfo
#include <sys/types.h>        // needed for socket(), uint8_t, uint16_t, uint32_t
#include <sys/socket.h>       // needed for socket()
#include <netinet/in.h>       // IPPROTO_ICMP, INET_ADDRSTRLEN
#include <netinet/ip.h>       // struct ip and IP_MAXPACKET (which is 65535)
#include <netinet/ip_icmp.h>  // struct icmp, ICMP_ECHO
#include <arpa/inet.h>        // inet_pton() and inet_ntop()
#include <sys/ioctl.h>        // macro ioctl is defined
#include <bits/ioctls.h>      // defines values for argument "request" of ioctl.
#include <net/if.h>           // struct ifreq
#include <linux/if_ether.h>   // ETH_P_IP = 0x0800, ETH_P_IPV6 = 0x86DD
#include <linux/if_packet.h>  // struct sockaddr_ll (see man 7 packet)
#include <net/ethernet.h>
#include <sys/time.h>         // gettimeofday()

#include <errno.h>            // errno, perror()

// Define some constants.
#define ETH_HDRLEN 14  // Ethernet header length
#define IP4_HDRLEN 20  // IPv4 header length
#define ICMP_HDRLEN 8  // ICMP header length for echo request, excludes data

// Function prototypes
uint16_t checksum (uint16_t *, int);
uint16_t icmp4_checksum (struct icmp, uint8_t *, int);
char *allocate_strmem (int);
uint8_t *allocate_ustrmem (int);
int *allocate_intmem (int);

int
main (int argc, char **argv)
{
  int i, status, datalen, frame_length, sendsd, recvsd, bytes, *ip_flags, timeout, trycount, trylim, done;
  char *interface, *target, *src_ip, *dst_ip, *rec_ip;
  struct ip send_iphdr, *recv_iphdr;
  struct icmp send_icmphdr, *recv_icmphdr;
  uint8_t *data, *src_mac, *dst_mac, *send_ether_frame, *recv_ether_frame;
  struct addrinfo hints, *res;
  struct sockaddr_in *ipv4;
  struct sockaddr_ll device;
  struct ifreq ifr;
  struct sockaddr from;
  socklen_t fromlen;
  struct timeval wait, t1, t2;
  struct timezone tz;
  double dt;
  void *tmp;

  // Allocate memory for various arrays.
  src_mac = allocate_ustrmem (6);
  dst_mac = allocate_ustrmem (6);
  data = allocate_ustrmem (IP_MAXPACKET);
  send_ether_frame = allocate_ustrmem (IP_MAXPACKET);
  recv_ether_frame = allocate_ustrmem (IP_MAXPACKET);
  interface = allocate_strmem (40);
  target = allocate_strmem (40);
  src_ip = allocate_strmem (INET_ADDRSTRLEN);
  dst_ip = allocate_strmem (INET_ADDRSTRLEN);
  rec_ip = allocate_strmem (INET_ADDRSTRLEN);
  ip_flags = allocate_intmem (4);

  // Interface to send packet through.
  strcpy (interface, "eth0");

  // Submit request for a socket descriptor to look up interface.
  // We'll use it to send packets as well, so we leave it open.
  if ((sendsd = socket (PF_PACKET, SOCK_RAW, htons (ETH_P_ALL))) < 0) {
    perror ("socket() failed to get socket descriptor for using ioctl() ");
    exit (EXIT_FAILURE);
  }

  // Use ioctl() to look up interface name and get its MAC address.
  memset (&ifr, 0, sizeof (ifr));
  snprintf (ifr.ifr_name, sizeof (ifr.ifr_name), "%s", interface);
  if (ioctl (sendsd, SIOCGIFHWADDR, &ifr) < 0) {
    perror ("ioctl() failed to get source MAC address ");
    return (EXIT_FAILURE);
  }

  // Copy source MAC address.
  memcpy (src_mac, ifr.ifr_hwaddr.sa_data, 6);

  // Report source MAC address to stdout.
  printf ("MAC address for interface %s is ", interface);
  for (i=0; i<5; i++) {
    printf ("%02x:", src_mac[i]);
  }
  printf ("%02x\n", src_mac[5]);

  // Find interface index from interface name and store index in
  // struct sockaddr_ll device, which will be used as an argument of sendto().
  memset (&device, 0, sizeof (device));
  if ((device.sll_ifindex = if_nametoindex (interface)) == 0) {
    perror ("if_nametoindex() failed to obtain interface index ");
    exit (EXIT_FAILURE);
  }
  printf ("Index for interface %s is %i\n", interface, device.sll_ifindex);

  // Set destination MAC address: you need to fill these out
  dst_mac[0] = 0xff;
  dst_mac[1] = 0xff;
  dst_mac[2] = 0xff;
  dst_mac[3] = 0xff;
  dst_mac[4] = 0xff;
  dst_mac[5] = 0xff;

  // Source IPv4 address: you need to fill this out
  strcpy (src_ip, "192.168.1.132");

  // Destination URL or IPv4 address: you need to fill this out
  strcpy (target, "www.google.com");

  // Fill out hints for getaddrinfo().
  memset (&hints, 0, sizeof (struct addrinfo));
  hints.ai_family = AF_INET;
  hints.ai_socktype = SOCK_STREAM;
  hints.ai_flags = hints.ai_flags | AI_CANONNAME;

  // Resolve target using getaddrinfo().
  if ((status = getaddrinfo (target, NULL, &hints, &res)) != 0) {
    fprintf (stderr, "getaddrinfo() failed: %s\n", gai_strerror (status));
    exit (EXIT_FAILURE);
  }
  ipv4 = (struct sockaddr_in *) res->ai_addr;
  tmp = &(ipv4->sin_addr);
  if (inet_ntop (AF_INET, tmp, dst_ip, INET_ADDRSTRLEN) == NULL) {
    status = errno;
    fprintf (stderr, "inet_ntop() failed.\nError message: %s", strerror (status));
    exit (EXIT_FAILURE);
  }
  freeaddrinfo (res);

  // Fill out sockaddr_ll.
  device.sll_family = AF_PACKET;
  memcpy (device.sll_addr, src_mac, 6);
  device.sll_halen = 6;

  // ICMP data
  datalen = 4;
  data[0] = 'T';
  data[1] = 'e';
  data[2] = 's';
  data[3] = 't';

  // IPv4 header

  // IPv4 header length (4 bits): Number of 32-bit words in header = 5
  send_iphdr.ip_hl = IP4_HDRLEN / sizeof (uint32_t);

  // Internet Protocol version (4 bits): IPv4
  send_iphdr.ip_v = 4;

  // Type of service (8 bits)
  send_iphdr.ip_tos = 0;

  // Total length of datagram (16 bits): IP header + ICMP header + ICMP data
  send_iphdr.ip_len = htons (IP4_HDRLEN + ICMP_HDRLEN + datalen);

  // ID sequence number (16 bits): unused, since single datagram
  send_iphdr.ip_id = htons (0);

  // Flags, and Fragmentation offset (3, 13 bits): 0 since single datagram

  // Zero (1 bit)
  ip_flags[0] = 0;

  // Do not fragment flag (1 bit)
  ip_flags[1] = 0;

  // More fragments following flag (1 bit)
  ip_flags[2] = 0;

  // Fragmentation offset (13 bits)
  ip_flags[3] = 0;

  send_iphdr.ip_off = htons ((ip_flags[0] << 15)
                      + (ip_flags[1] << 14)
                      + (ip_flags[2] << 13)
                      +  ip_flags[3]);

  // Time-to-Live (8 bits): default to maximum value
  send_iphdr.ip_ttl = 255;

  // Transport layer protocol (8 bits): 1 for ICMP
  send_iphdr.ip_p = IPPROTO_ICMP;

  // Source IPv4 address (32 bits)
  if ((status = inet_pton (AF_INET, src_ip, &(send_iphdr.ip_src))) != 1) {
    fprintf (stderr, "inet_pton() failed.\nError message: %s", strerror (status));
    exit (EXIT_FAILURE);
  }

  // Destination IPv4 address (32 bits)
  if ((status = inet_pton (AF_INET, dst_ip, &(send_iphdr.ip_dst))) != 1) {
    fprintf (stderr, "inet_pton() failed.\nError message: %s", strerror (status));
    exit (EXIT_FAILURE);
  }

  // IPv4 header checksum (16 bits): set to 0 when calculating checksum
  send_iphdr.ip_sum = 0;
  send_iphdr.ip_sum = checksum ((uint16_t *) &send_iphdr, IP4_HDRLEN);

  // ICMP header

  // Message Type (8 bits): echo request
  send_icmphdr.icmp_type = ICMP_ECHO;

  // Message Code (8 bits): echo request
  send_icmphdr.icmp_code = 0;

  // Identifier (16 bits): usually pid of sending process - pick a number
  send_icmphdr.icmp_id = htons (1000);

  // Sequence Number (16 bits): starts at 0
  send_icmphdr.icmp_seq = htons (0);

  // ICMP header checksum (16 bits): set to 0 when calculating checksum
  send_icmphdr.icmp_cksum = icmp4_checksum (send_icmphdr, data, datalen);

  // Fill out ethernet frame header.

  // Ethernet frame length = ethernet header (MAC + MAC + ethernet type) + ethernet data (IP header + ICMP header + ICMP data)
  frame_length = 6 + 6 + 2 + IP4_HDRLEN + ICMP_HDRLEN + datalen;

  // Destination and Source MAC addresses
  memcpy (send_ether_frame, dst_mac, 6);
  memcpy (send_ether_frame + 6, src_mac, 6);

  // Next is ethernet type code (ETH_P_IP for IPv4).
  // http://www.iana.org/assignments/ethernet-numbers
  send_ether_frame[12] = ETH_P_IP / 256;
  send_ether_frame[13] = ETH_P_IP % 256;

  // Next is ethernet frame data (IPv4 header + ICMP header + ICMP data).

  // IPv4 header
  memcpy (send_ether_frame + ETH_HDRLEN, &send_iphdr, IP4_HDRLEN);

  // ICMP header
  memcpy (send_ether_frame + ETH_HDRLEN + IP4_HDRLEN, &send_icmphdr, ICMP_HDRLEN);

  // ICMP data
  memcpy (send_ether_frame + ETH_HDRLEN + IP4_HDRLEN + ICMP_HDRLEN, data, datalen);

  // Submit request for a raw socket descriptor to receive packets.
  if ((recvsd = socket (PF_PACKET, SOCK_RAW, htons (ETH_P_ALL))) < 0) {
    perror ("socket() failed to obtain a receive socket descriptor ");
    exit (EXIT_FAILURE);
  }

  // Set maximum number of tries to ping remote host before giving up.
  trylim = 3;
  trycount = 0;

  // Cast recv_iphdr as pointer to IPv4 header within received ethernet frame.
  recv_iphdr = (struct ip *) (recv_ether_frame + ETH_HDRLEN);

  // Cast recv_icmphdr as pointer to ICMP header within received ethernet frame.
  recv_icmphdr = (struct icmp *) (recv_ether_frame + ETH_HDRLEN + IP4_HDRLEN);

  done = 0;
  for (;;) {

    // SEND

    // Send ethernet frame to socket.
    if ((bytes = sendto (sendsd, send_ether_frame, frame_length, 0, (struct sockaddr *) &device, sizeof (device))) <= 0) {
      perror ("sendto() failed ");
      exit (EXIT_FAILURE);
    }

    // Start timer.
    (void) gettimeofday (&t1, &tz);

    // Set time for the socket to timeout and give up waiting for a reply.
    timeout = 2;
    wait.tv_sec  = timeout;
    wait.tv_usec = 0;
    setsockopt (recvsd, SOL_SOCKET, SO_RCVTIMEO, (char *) &wait, sizeof (struct timeval));

    // Listen for incoming ethernet frame from socket recvsd.
    // We expect an ICMP ethernet frame of the form:
    //     MAC (6 bytes) + MAC (6 bytes) + ethernet type (2 bytes)
    //     + ethernet data (IPv4 header + ICMP header)
    // Keep at it for 'timeout' seconds, or until we get an ICMP reply.

    // RECEIVE LOOP
    for (;;) {

      memset (recv_ether_frame, 0, IP_MAXPACKET * sizeof (uint8_t));
      memset (&from, 0, sizeof (from));
      fromlen = sizeof (from);
      if ((bytes = recvfrom (recvsd, recv_ether_frame, IP_MAXPACKET, 0, (struct sockaddr *) &from, &fromlen)) < 0) {

        status = errno;

        // Deal with error conditions first.
        if (status == EAGAIN) {  // EAGAIN = 11
          printf ("No reply within %i seconds.\n", timeout);
          trycount++;
          break;  // Break out of Receive loop.
        } else if (status == EINTR) {  // EINTR = 4
          continue;  // Something weird happened, but let's keep listening.
        } else {
          perror ("recvfrom() failed ");
          exit (EXIT_FAILURE);
        }
      }  // End of error handling conditionals.

      // Check for an IP ethernet frame, carrying ICMP echo reply. If not, ignore and keep listening.
      if ((((recv_ether_frame[12] << 8) + recv_ether_frame[13]) == ETH_P_IP) &&
         (recv_iphdr->ip_p == IPPROTO_ICMP) && (recv_icmphdr->icmp_type == ICMP_ECHOREPLY) && (recv_icmphdr->icmp_code == 0)) {

        // Stop timer and calculate how long it took to get a reply.
        (void) gettimeofday (&t2, &tz);
        dt = (double) (t2.tv_sec - t1.tv_sec) * 1000.0 + (double) (t2.tv_usec - t1.tv_usec) / 1000.0;

        // Extract source IP address from received ethernet frame.
        if (inet_ntop (AF_INET, &(recv_iphdr->ip_src.s_addr), rec_ip, INET_ADDRSTRLEN) == NULL) {
          status = errno;
          fprintf (stderr, "inet_ntop() failed.\nError message: %s", strerror (status));
          exit (EXIT_FAILURE);
        }

        // Report source IPv4 address and time for reply.
        printf ("%s  %g ms (%i bytes received)\n", rec_ip, dt, bytes);
        done = 1;
        break;  // Break out of Receive loop.
      }  // End if IP ethernet frame carrying ICMP_ECHOREPLY
    }  // End of Receive loop.

    // The 'done' flag was set because an echo reply was received; break out of send loop.
    if (done == 1) {
      break;  // Break out of Send loop.
    }

    // We ran out of tries, so let's give up.
    if (trycount == trylim) {
      printf ("Recognized no echo replies from remote host after %i tries.\n", trylim);
      break;
    }

  }  // End of Send loop.

  // Close socket descriptors.
  close (sendsd);
  close (recvsd);

  // Free allocated memory.
  free (src_mac);
  free (dst_mac);
  free (data);
  free (send_ether_frame);
  free (recv_ether_frame);
  free (interface);
  free (target);
  free (src_ip);
  free (dst_ip);
  free (rec_ip);
  free (ip_flags);

  return (EXIT_SUCCESS);
}

// Build IPv4 ICMP pseudo-header and call checksum function.
uint16_t
icmp4_checksum (struct icmp icmphdr, uint8_t *payload, int payloadlen)
{
  char buf[IP_MAXPACKET];
  char *ptr;
  int chksumlen = 0;
  int i;

  ptr = &buf[0];  // ptr points to beginning of buffer buf

  // Copy Message Type to buf (8 bits)
  memcpy (ptr, &icmphdr.icmp_type, sizeof (icmphdr.icmp_type));
  ptr += sizeof (icmphdr.icmp_type);
  chksumlen += sizeof (icmphdr.icmp_type);

  // Copy Message Code to buf (8 bits)
  memcpy (ptr, &icmphdr.icmp_code, sizeof (icmphdr.icmp_code));
  ptr += sizeof (icmphdr.icmp_code);
  chksumlen += sizeof (icmphdr.icmp_code);

  // Copy ICMP checksum to buf (16 bits)
  // Zero, since we don't know it yet
  *ptr = 0; ptr++;
  *ptr = 0; ptr++;
  chksumlen += 2;

  // Copy Identifier to buf (16 bits)
  memcpy (ptr, &icmphdr.icmp_id, sizeof (icmphdr.icmp_id));
  ptr += sizeof (icmphdr.icmp_id);
  chksumlen += sizeof (icmphdr.icmp_id);

  // Copy Sequence Number to buf (16 bits)
  memcpy (ptr, &icmphdr.icmp_seq, sizeof (icmphdr.icmp_seq));
  ptr += sizeof (icmphdr.icmp_seq);
  chksumlen += sizeof (icmphdr.icmp_seq);

  // Copy payload to buf
  memcpy (ptr, payload, payloadlen);
  ptr += payloadlen;
  chksumlen += payloadlen;

  // Pad to the next 16-bit boundary
  for (i=0; i<payloadlen%2; i++, ptr++) {
    *ptr = 0;
    ptr++;
    chksumlen++;
  }

  return checksum ((uint16_t *) buf, chksumlen);
}

// Computing the internet checksum (RFC 1071).
// Note that the internet checksum does not preclude collisions.
uint16_t
checksum (uint16_t *addr, int len)
{
  int count = len;
  register uint32_t sum = 0;
  uint16_t answer = 0;

  // Sum up 2-byte values until none or only one byte left.
  while (count > 1) {
    sum += *(addr++);
    count -= 2;
  }

  // Add left-over byte, if any.
  if (count > 0) {
    sum += *(uint8_t *) addr;
  }

  // Fold 32-bit sum into 16 bits; we lose information by doing this,
  // increasing the chances of a collision.
  // sum = (lower 16 bits) + (upper 16 bits shifted right 16 bits)
  while (sum >> 16) {
    sum = (sum & 0xffff) + (sum >> 16);
  }

  // Checksum is one's compliment of sum.
  answer = ~sum;

  return (answer);
}

// Allocate memory for an array of chars.
char *
allocate_strmem (int len)
{
  void *tmp;

  if (len <= 0) {
    fprintf (stderr, "ERROR: Cannot allocate memory because len = %i in allocate_strmem().\n", len);
    exit (EXIT_FAILURE);
  }

  tmp = (char *) malloc (len * sizeof (char));
  if (tmp != NULL) {
    memset (tmp, 0, len * sizeof (char));
    return (tmp);
  } else {
    fprintf (stderr, "ERROR: Cannot allocate memory for array allocate_strmem().\n");
    exit (EXIT_FAILURE);
  }
}

// Allocate memory for an array of unsigned chars.
uint8_t *
allocate_ustrmem (int len)
{
  void *tmp;

  if (len <= 0) {
    fprintf (stderr, "ERROR: Cannot allocate memory because len = %i in allocate_ustrmem().\n", len);
    exit (EXIT_FAILURE);
  }

  tmp = (uint8_t *) malloc (len * sizeof (uint8_t));
  if (tmp != NULL) {
    memset (tmp, 0, len * sizeof (uint8_t));
    return (tmp);
  } else {
    fprintf (stderr, "ERROR: Cannot allocate memory for array allocate_ustrmem().\n");
    exit (EXIT_FAILURE);
  }
}

// Allocate memory for an array of ints.
int *
allocate_intmem (int len)
{
  void *tmp;

  if (len <= 0) {
    fprintf (stderr, "ERROR: Cannot allocate memory because len = %i in allocate_intmem().\n", len);
    exit (EXIT_FAILURE);
  }

  tmp = (int *) malloc (len * sizeof (int));
  if (tmp != NULL) {
    memset (tmp, 0, len * sizeof (int));
    return (tmp);
  } else {
    fprintf (stderr, "ERROR: Cannot allocate memory for array allocate_intmem().\n");
    exit (EXIT_FAILURE);
  }
}