Simple ping

ping.c

#include <stdio.h>
#include <stdlib.h>

#include <sys/socket.h>
#include <netinet/in.h>

#include <string.h>

#include <netdb.h>

#include <sys/time.h>

const char *TYPE_STRING[256] = {
  [0] = "Echo Reply",
  [3] = "Destination Unreachable",
  [4] = "Source Quench",
  [8] = "Echo Request",
};

int main(int argc, char **argv)
{
  char *dest=0;

  for (int i = 1; i < argc; i++) {
    if (dest) {
      fprintf(stderr,"Error: Multiple destinations.\n");
      exit(1);
    }
    dest = argv[i];
  }

  if (!dest) {
    fprintf(stderr,"Usage: (sudo) ping DESTINATION\n");
    exit(1);
  }
  struct hostent *he = gethostbyname(dest);
  if (!he) {
    fprintf(stderr, "Error while looking up host %s\n", dest);
    exit(1);
  }

  // ---------------------------------------------------------

  int raw_socket = socket(AF_INET, SOCK_RAW, 1 /* ICMP */);

  if (raw_socket == -1) {
    perror("socket");
    exit(1);
  }

#define BUFFER_SIZE 100
  unsigned char buf[BUFFER_SIZE] = {
    8, 0,
    0, 0, /* checksum */
    0x71, 0x44, /* ID */
    0, 1, /* seq. number */
    'A','B','C','D', /* payload */
  };
  int size = 8 + 4;

  struct sockaddr_in addr;
  memset(&addr, 0, sizeof(struct sockaddr_in));
  addr.sin_family = AF_INET;
  addr.sin_addr.s_addr = *(uint32_t*)he->h_addr;

  int sum = 0;
  for (int i = 0; i < size; i += 2) {
    sum += *(unsigned short*)(buf+i);
    if (sum >= 0x10000) {
      sum &= 0xffff;
      sum += 1;
    }
  }

  /* set checksum */
  buf[2] = ~sum;
  buf[3] = ~sum >> 8;

  struct timeval start;
  gettimeofday(&start, NULL);

  int r;
  r = sendto(raw_socket, buf, size, 0, (struct sockaddr*)&addr, sizeof(struct sockaddr_in));
  printf("%d bytes sent\n", r);

  struct sockaddr_in addr2;
  int addrlen;
  r = recvfrom(raw_socket, buf, sizeof(buf), 0,
               (struct sockaddr*)&addr2, &addrlen);
  printf("%d bytes read (including 20-byte IP header)\n", r);

  struct timeval end;
  gettimeofday(&end, NULL);

  const int type = buf[20];
  const int code = buf[21];
  printf("Type: %d (%s)\n", type, TYPE_STRING[type]);
  printf("Code: %d\n", code);

  if (type == 0 && code == 0) {
    printf("Round-trip time: %.03f ms\n",
           ((end.tv_sec + end.tv_usec/1000000.0) -
            (start.tv_sec + start.tv_usec/1000000.0)) * 1000);
  }

  return 0;
}