utils.c

/*
 * The ARP Scanner (arp-scan) is Copyright (C) 2005-2013 Roy Hills,
 * NTA Monitor Ltd.
 *
 * This file is part of arp-scan.
 * 
 * arp-scan 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.
 * 
 * arp-scan 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 arp-scan.  If not, see <http://www.gnu.org/licenses/>.
 *
 * You are encouraged to send comments, improvements or suggestions
 * at the github repository https://github.com/royhills/arp-scan
 *
 * Author: Roy Hills
 * Date: 5 April 2004
 *
 * This file contains various utility functions used by arp-scan.
 */

#include "arp-scan.h"

/*
 *	timeval_diff -- Calculates the difference between two timevals
 *	and returns this difference in a third timeval.
 *
 *	Inputs:
 *
 *	a       = First timeval
 *	b       = Second timeval
 *	diff    = Difference between timevals (a - b).
 *
 *	Returns:
 *
 *	None.
 */
void
timeval_diff(const struct timeval *a, const struct timeval *b,
             struct timeval *diff) {
   struct timeval temp;

   temp.tv_sec = b->tv_sec;
   temp.tv_usec = b->tv_usec;

   /* Perform the carry for the later subtraction by updating b. */
   if (a->tv_usec < temp.tv_usec) {
     int nsec = (temp.tv_usec - a->tv_usec) / 1000000 + 1;
     temp.tv_usec -= 1000000 * nsec;
     temp.tv_sec += nsec;
   }
   if (a->tv_usec - temp.tv_usec > 1000000) {
     int nsec = (a->tv_usec - temp.tv_usec) / 1000000;
     temp.tv_usec += 1000000 * nsec;
     temp.tv_sec -= nsec;
   }
 
   /* Compute the time difference
      tv_usec is certainly positive. */
   diff->tv_sec = a->tv_sec - temp.tv_sec;
   diff->tv_usec = a->tv_usec - temp.tv_usec;
}

/*
 *	hstr_i -- Convert two-digit hex string to unsigned integer
 *
 *	Inputs:
 *
 *	cptr	Two-digit hex string
 *
 *	Returns:
 *
 *	Number corresponding to input hex value.
 *
 *	An input of "0A" or "0a" would return 10.
 *	Note that this function does no sanity checking, it's up to the
 *	caller to ensure that *cptr points to at least two hex digits.
 *
 *	This function is a modified version of hstr_i at www.snippets.org.
 */
unsigned int
hstr_i(const char *cptr)
{
      unsigned int i;
      unsigned int j = 0;
      int k;

      for (k=0; k<2; k++) {
            i = *cptr++ - '0';
            if (9 < i)
                  i -= 7;
            j <<= 4;
            j |= (i & 0x0f);
      }
      return j;
}

/*
 *	hex2data -- Convert hex string to binary data
 *
 *	Inputs:
 *
 *	string		The string to convert
 *	data_len	(output) The length of the resultant binary data
 *
 *	Returns:
 *
 *	Pointer to the binary data.
 *
 *	The returned pointer points to malloc'ed storage which should be
 *	free'ed by the caller when it's no longer needed.  If the length of
 *	the input string is not even, the function will return NULL and
 *	set data_len to 0.
 */
unsigned char *
hex2data(const char *string, size_t *data_len) {
   unsigned char *data;
   unsigned char *cp;
   unsigned i;
   size_t len;

   if (strlen(string) %2 ) {	/* Length is odd */
      *data_len = 0;
      return NULL;
   }

   len = strlen(string) / 2;
   data = Malloc(len);
   cp = data;
   for (i=0; i<len; i++)
      *cp++=hstr_i(&string[i*2]);
   *data_len = len;
   return data;
}

/*
 * make_message -- allocate a sufficiently large string and print into it.
 *
 * Inputs:
 *
 * Format and variable number of arguments.
 *
 * Outputs:
 *
 * Pointer to the string,
 *
 * The code for this function is from the Debian Linux "woody" sprintf man
 * page.  Modified slightly to use wrapper functions for malloc and realloc.
 */
char *
make_message(const char *fmt, ...) {
   int n;
   /* Guess we need no more than 100 bytes. */
   size_t size = 100;
   char *p;
   va_list ap;
   p = Malloc (size);
   while (1) {
      /* Try to print in the allocated space. */
      va_start(ap, fmt);
      n = vsnprintf (p, size, fmt, ap);
      va_end(ap);
      /* If that worked, return the string. */
      if (n > -1 && n < (int) size)
         return p;
      /* Else try again with more space. */
      if (n > -1)    /* glibc 2.1 */
         size = n+1; /* precisely what is needed */
      else           /* glibc 2.0 */
         size *= 2;  /* twice the old size */
      p = Realloc (p, size);
   }
}

/*
 *	hexstring -- Convert data to printable hex string form
 *
 *	Inputs:
 *
 *	string	Pointer to input data.
 *	size	Size of input data.
 *
 *	Returns:
 *
 *	Pointer to the printable hex string.
 *
 *	Each byte in the input data will be represented by two hex digits
 *	in the output string.  Therefore the output string will be twice
 *	as long as the input data plus one extra byte for the trailing NULL.
 *
 *	The pointer returned points to malloc'ed storage which should be
 *	free'ed by the caller when it's no longer needed.
 */
char *
hexstring(const unsigned char *data, size_t size) {
   char *result;
   char *r;
   const unsigned char *cp;
   unsigned i;
/*
 *	If the input data is NULL, return an empty string.
 */
   if (data == NULL) {
      result = Malloc(1);
      result[0] = '\0';
      return result;
   }
/*
 *	Create and return hex string.
 */
   result = Malloc(2*size + 1);
   cp = data;
   r = result;
   for (i=0; i<size; i++) {
      snprintf(r, 3, "%.2x", *cp++);
      r += 2;
   }
   *r = '\0';

   return result;
}

/*
 * get_ether_addr -- Get Ethernet hardware address from text string
 *
 * Inputs:
 *
 * address_string	The text string containing the address
 * ether_addr		(output) The Ethernet hardware address
 *
 * Returns:
 *
 * Zero on success or -1 on failure.
 *
 * The address_string should contain an Ethernet hardware address in one
 * of the following formats:
 *
 * 01-23-45-67-89-ab
 * 01:23:45:67:89:ab
 *
 * The hex characters [a-z] may be specified in either upper or lower case.
 */
int
get_ether_addr(const char *address_string, unsigned char *ether_addr) {
   unsigned mac_b0, mac_b1, mac_b2, mac_b3, mac_b4, mac_b5;
   int result;

   result = sscanf(address_string, "%x:%x:%x:%x:%x:%x",
                   &mac_b0, &mac_b1, &mac_b2, &mac_b3, &mac_b4, &mac_b5);
   if (result !=6 ) {
      result = sscanf(address_string, "%x-%x-%x-%x-%x-%x",
                      &mac_b0, &mac_b1, &mac_b2, &mac_b3, &mac_b4, &mac_b5);
   }
   if (result !=6 ) {
      return -1;
   }
   ether_addr[0] = mac_b0;
   ether_addr[1] = mac_b1;
   ether_addr[2] = mac_b2;
   ether_addr[3] = mac_b3;
   ether_addr[4] = mac_b4;
   ether_addr[5] = mac_b5;

   return 0;
}

/*
 *	str_to_bandwidth -- Convert a bandwidth string to unsigned integer
 *
 *	Inputs:
 *
 *	bandwidth_string	The bandwidth string to convert
 *
 *	Returns:
 *
 *	The bandwidth in bits per second as an unsigned integer
 */
unsigned
str_to_bandwidth(const char *bandwidth_string) {
   char *bandwidth_str;
   size_t bandwidth_len;
   unsigned value;
   int multiplier=1;
   int end_char;

   bandwidth_str=dupstr(bandwidth_string);	/* Writable copy */
   bandwidth_len=strlen(bandwidth_str);
   end_char = bandwidth_str[bandwidth_len-1];
   if (!isdigit(end_char)) {	/* End character is not a digit */
      bandwidth_str[bandwidth_len-1] = '\0';	/* Remove last character */
      switch (end_char) {
         case 'M':
         case 'm':
            multiplier = 1000000;
            break;
         case 'K':
         case 'k':
            multiplier = 1000;
            break;
         default:
            err_msg("ERROR: Unknown bandwidth multiplier character: \"%c\"",
                    end_char);
            break;
      }
   }
   value=Strtoul(bandwidth_str, 10);
   free(bandwidth_str);
   return multiplier * value;
}

/*
 *	str_to_interval -- Convert an interval string to unsigned integer
 *
 *	Inputs:
 *
 *	interval_string		The interval string to convert
 *
 *	Returns:
 *
 *	The interval in microsecons as an unsigned integer
 */
unsigned
str_to_interval(const char *interval_string) {
   char *interval_str;
   size_t interval_len;
   unsigned value;
   int multiplier=1000;
   int end_char;

   interval_str=dupstr(interval_string);	/* Writable copy */
   interval_len=strlen(interval_str);
   end_char = interval_str[interval_len-1];
   if (!isdigit(end_char)) {	/* End character is not a digit */
      interval_str[interval_len-1] = '\0';	/* Remove last character */
      switch (end_char) {
         case 'U':
         case 'u':
            multiplier = 1;
            break;
         case 'S':
         case 's':
            multiplier = 1000000;
            break;
         default:
            err_msg("ERROR: Unknown interval multiplier character: \"%c\"",
                    end_char);
            break;
      }
   }
   value=Strtoul(interval_str, 10);
   free(interval_str);
   return multiplier * value;
}

/*
 *	dupstr -- duplicate a string
 *
 *	Inputs:
 *
 *	str	The string to duplcate
 *
 *	Returns:
 *
 *	A pointer to the duplicate string.
 *
 *	This is a replacement for the common but non-standard "strdup"
 *	function.
 *
 *	The returned pointer points to Malloc'ed memory, which must be
 *	free'ed by the caller.
 */
char *
dupstr(const char *str) {
   char *cp;
   size_t len;

   len = strlen(str) + 1;	/* Allow space for terminating NULL */
   cp = Malloc(len);
   strlcpy(cp, str, len);
   return cp;
}