/*
 * getif.c : get an interface structure
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>

#if defined(SUNOS) || defined(SVR4)
#include <sys/sockio.h>
#endif
#ifdef  SVR4
#include <sys/stropts.h>
#endif

#include <sys/time.h>           /* for struct timeval in net/if.h */    
#include <net/if.h>                             /* for struct ifreq */
#include <netinet/in.h>

#ifndef NO_UNISTD
#include <unistd.h>
#endif
#include <syslog.h>
#include <errno.h>
#include <assert.h>

#include "getif.h"
#include "report.h"

#ifdef  __bsdi__
#define BSD 43
#endif

static struct ifreq ifreq[10];  /* Holds interface configuration */
static struct ifconf ifconf;    /* points to ifreq */

static int nmatch(u_char *ca, u_char *cb);

/* Return a pointer to the interface struct for the passed address. */
struct ifreq *
getif(int s, struct in_addr *addrp)
{
        int maxmatch;
        int len, m, incr;
        struct ifreq *ifrq, *ifrmax;
        struct sockaddr_in *sip;
        char *p;

        /* If no address was supplied, just return NULL. */
        if (!addrp)
                return (struct ifreq *) 0;

        /* Get the interface config if not done already. */
        if (ifconf.ifc_len == 0) {
#ifdef  SVR4
                /*
                 * SysVr4 returns garbage if you do this the obvious way!
                 * This one took a while to figure out... -gwr
                 */
                struct strioctl ioc;
                ioc.ic_cmd = SIOCGIFCONF;
                ioc.ic_timout = 0;
                ioc.ic_len = sizeof(ifreq);
                ioc.ic_dp = (char *) ifreq;
                m = ioctl(s, I_STR, (char *) &ioc);
                ifconf.ifc_len = ioc.ic_len;
                ifconf.ifc_req = ifreq;
#else   /* SVR4 */
                ifconf.ifc_len = sizeof(ifreq);
                ifconf.ifc_req = ifreq;
                m = ioctl(s, SIOCGIFCONF, (caddr_t) & ifconf);
#endif  /* SVR4 */
                if ((m < 0) || (ifconf.ifc_len <= 0)) {
                        report(LOG_ERR, "ioctl SIOCGIFCONF");
                        return (struct ifreq *) 0;
                }
        }
        maxmatch = 7;                           /* this many bits or less... */
        ifrmax = (struct ifreq *) 0;/* ... is not a valid match  */
        p = (char *) ifreq;
        len = ifconf.ifc_len;
        while (len > 0) {
                ifrq = (struct ifreq *) p;
                sip = (struct sockaddr_in *) &ifrq->ifr_addr;
                m = nmatch((u_char *)addrp, (u_char *)&(sip->sin_addr));
                if (m > maxmatch) {
                        maxmatch = m;
                        ifrmax = ifrq;
                }
#ifndef IFNAMSIZ
                /* BSD not defined or earlier than 4.3 */
                incr = sizeof(*ifrq);
#else
                incr = ifrq->ifr_addr.sa_len + IFNAMSIZ;
#endif

                p += incr;
                len -= incr;
        }

        return ifrmax;
}

/*
 * Return the number of leading bits matching in the
 * internet addresses supplied.
 */
static int
nmatch(u_char *ca, u_char *cb)
{
        u_int m = 0;                            /* count of matching bits */
        u_int n = 4;                            /* bytes left, then bitmask */

        /* Count matching bytes. */
        while (n && (*ca == *cb)) {
                ca++;
                cb++;
                m += 8;
                n--;
        }
        /* Now count matching bits. */
        if (n) {
                n = 0x80;
                while (n && ((*ca & n) == (*cb & n))) {
                        m++;
                        n >>= 1;
                }
        }
        return (m);
}

/*
 * Local Variables:
 * tab-width: 4
 * c-indent-level: 4
 * c-argdecl-indent: 4
 * c-continued-statement-offset: 4
 * c-continued-brace-offset: -4
 * c-label-offset: -4
 * c-brace-offset: 0
 * End:
 */