/* vi: set sw=4 ts=4: */
/*
 * leases.c -- tools to manage DHCP leases
 * Russ Dill <Russ.Dill@asu.edu> July 2001
 *
 * Licensed under GPLv2, see file LICENSE in this tarball for details.
 */

#include "common.h"
#include "dhcpd.h"


/* Find the oldest expired lease, NULL if there are no expired leases */
static struct dhcpOfferedAddr *oldest_expired_lease(void)
{
        struct dhcpOfferedAddr *oldest_lease = NULL;
        leasetime_t oldest_time = time(NULL);
        unsigned i;

        /* Unexpired leases have leases[i].expires >= current time
         * and therefore can't ever match */
        for (i = 0; i < server_config.max_leases; i++) {
                if (leases[i].expires < oldest_time) {
                        oldest_time = leases[i].expires;
                        oldest_lease = &(leases[i]);
                }
        }
        return oldest_lease;
}


/* Clear every lease out that chaddr OR yiaddr matches and is nonzero */
static void clear_lease(const uint8_t *chaddr, uint32_t yiaddr)
{
        unsigned i, j;

        for (j = 0; j < 16 && !chaddr[j]; j++)
                continue;

        for (i = 0; i < server_config.max_leases; i++) {
                if ((j != 16 && memcmp(leases[i].chaddr, chaddr, 16) == 0)
                 || (yiaddr && leases[i].yiaddr == yiaddr)
                ) {
                        memset(&(leases[i]), 0, sizeof(leases[i]));
                }
        }
}


/* Add a lease into the table, clearing out any old ones */
struct dhcpOfferedAddr* FAST_FUNC add_lease(
                const uint8_t *chaddr, uint32_t yiaddr,
                leasetime_t leasetime, uint8_t *hostname)
{
        struct dhcpOfferedAddr *oldest;
        uint8_t hostname_length;

        /* clean out any old ones */
        clear_lease(chaddr, yiaddr);

        oldest = oldest_expired_lease();

        if (oldest) {
                oldest->hostname[0] = '\0';
                if (hostname) {
                        /* option size byte, + 1 for NUL */
                        hostname_length = hostname[-1] + 1;
                        if (hostname_length > sizeof(oldest->hostname))
                                hostname_length = sizeof(oldest->hostname);
                        hostname = (uint8_t*) safe_strncpy((char*)oldest->hostname, (char*)hostname, hostname_length);
                        /* sanitization (s/non-ASCII/^/g) */
                        while (*hostname) {
                                if (*hostname < ' ' || *hostname > 126)
                                        *hostname = '^';
                                hostname++;
                        }
                }
                memcpy(oldest->chaddr, chaddr, 16);
                oldest->yiaddr = yiaddr;
                oldest->expires = time(NULL) + leasetime;
        }

        return oldest;
}


/* True if a lease has expired */
int FAST_FUNC lease_expired(struct dhcpOfferedAddr *lease)
{
        return (lease->expires < (leasetime_t) time(NULL));
}


/* Find the first lease that matches chaddr, NULL if no match */
struct dhcpOfferedAddr* FAST_FUNC find_lease_by_chaddr(const uint8_t *chaddr)
{
        unsigned i;

        for (i = 0; i < server_config.max_leases; i++)
                if (!memcmp(leases[i].chaddr, chaddr, 16))
                        return &(leases[i]);

        return NULL;
}


/* Find the first lease that matches yiaddr, NULL is no match */
struct dhcpOfferedAddr* FAST_FUNC find_lease_by_yiaddr(uint32_t yiaddr)
{
        unsigned i;

        for (i = 0; i < server_config.max_leases; i++)
                if (leases[i].yiaddr == yiaddr)
                        return &(leases[i]);

        return NULL;
}


/* check is an IP is taken, if it is, add it to the lease table */
static int nobody_responds_to_arp(uint32_t addr)
{
        /* 16 zero bytes */
        static const uint8_t blank_chaddr[16] = { 0 };
        /* = { 0 } helps gcc to put it in rodata, not bss */

        struct in_addr temp;
        int r;

        r = arpping(addr, server_config.server, server_config.arp, server_config.interface);
        if (r)
                return r;

        temp.s_addr = addr;
        bb_info_msg("%s belongs to someone, reserving it for %u seconds",
                inet_ntoa(temp), (unsigned)server_config.conflict_time);
        add_lease(blank_chaddr, addr, server_config.conflict_time, NULL);
        return 0;
}


/* Find a new usable (we think) address. */
uint32_t FAST_FUNC find_free_or_expired_address(void)
{
        uint32_t addr;
        struct dhcpOfferedAddr *oldest_lease = NULL;

        addr = server_config.start_ip; /* addr is in host order here */
        for (; addr <= server_config.end_ip; addr++) {
                uint32_t net_addr;
                struct dhcpOfferedAddr *lease;

                /* ie, 192.168.55.0 */
                if ((addr & 0xff) == 0)
                        continue;
                /* ie, 192.168.55.255 */
                if ((addr & 0xff) == 0xff)
                        continue;
                net_addr = htonl(addr);
                /* addr has a static lease? */
                if (reservedIp(server_config.static_leases, net_addr))
                        continue;

                lease = find_lease_by_yiaddr(net_addr);
                if (!lease) {
                        if (nobody_responds_to_arp(net_addr))
                                return net_addr;
                } else {
                        if (!oldest_lease || lease->expires < oldest_lease->expires)
                                oldest_lease = lease;
                }
        }

        if (oldest_lease && lease_expired(oldest_lease)
         && nobody_responds_to_arp(oldest_lease->yiaddr)
        ) {
                return oldest_lease->yiaddr;
        }

        return 0;
}