/* vi: set sw=4 ts=4: */
/*
 * Russ Dill <Russ.Dill@asu.edu> July 2001
 *
 * Licensed under GPLv2, see file LICENSE in this source tree.
 */
#include "common.h"
#include "dhcpd.h"

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

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

/* Clear out all leases with matching nonzero chaddr OR yiaddr.
 * If chaddr == NULL, this is a conflict lease.
 */
static void clear_leases(const uint8_t *chaddr, uint32_t yiaddr)
{
        unsigned i;

        for (i = 0; i < server_config.max_leases; i++) {
                if ((chaddr && memcmp(g_leases[i].lease_mac, chaddr, 6) == 0)
                 || (yiaddr && g_leases[i].lease_nip == yiaddr)
                ) {
                        memset(&g_leases[i], 0, sizeof(g_leases[i]));
                }
        }
}

/* Add a lease into the table, clearing out any old ones.
 * If chaddr == NULL, this is a conflict lease.
 */
struct dyn_lease* FAST_FUNC add_lease(
                const uint8_t *chaddr, uint32_t yiaddr,
                leasetime_t leasetime,
                const char *hostname, int hostname_len)
{
        struct dyn_lease *oldest;

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

        oldest = oldest_expired_lease();

        if (oldest) {
                memset(oldest, 0, sizeof(*oldest));
                if (hostname) {
                        char *p;

                        hostname_len++; /* include NUL */
                        if (hostname_len > sizeof(oldest->hostname))
                                hostname_len = sizeof(oldest->hostname);
                        p = safe_strncpy(oldest->hostname, hostname, hostname_len);
                        /*
                         * Sanitization (s/bad_char/./g).
                         * The intent is not to allow only "DNS-valid" hostnames,
                         * but merely make dumpleases output safe for shells to use.
                         * We accept "0-9A-Za-z._-", all other chars turn to dots.
                         */
                        while (*p) {
                                if (!isalnum(*p) && *p != '-' && *p != '_')
                                        *p = '.';
                                p++;
                        }
                }
                if (chaddr)
                        memcpy(oldest->lease_mac, chaddr, 6);
                oldest->lease_nip = yiaddr;
                oldest->expires = time(NULL) + leasetime;
        }

        return oldest;
}

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

/* Find the first lease that matches MAC, NULL if no match */
struct dyn_lease* FAST_FUNC find_lease_by_mac(const uint8_t *mac)
{
        unsigned i;

        for (i = 0; i < server_config.max_leases; i++)
                if (memcmp(g_leases[i].lease_mac, mac, 6) == 0)
                        return &g_leases[i];

        return NULL;
}

/* Find the first lease that matches IP, NULL is no match */
struct dyn_lease* FAST_FUNC find_lease_by_nip(uint32_t nip)
{
        unsigned i;

        for (i = 0; i < server_config.max_leases; i++)
                if (g_leases[i].lease_nip == nip)
                        return &g_leases[i];

        return NULL;
}

/* Check if the IP is taken; if it is, add it to the lease table */
static int nobody_responds_to_arp(uint32_t nip, const uint8_t *safe_mac, unsigned arpping_ms)
{
        struct in_addr temp;
        int r;

        r = arpping(nip, safe_mac,
                        server_config.server_nip,
                        server_config.server_mac,
                        server_config.interface,
                        arpping_ms);
        if (r)
                return r;

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

/* Find a new usable (we think) address */
uint32_t FAST_FUNC find_free_or_expired_nip(const uint8_t *safe_mac, unsigned arpping_ms)
{
        uint32_t addr;
        struct dyn_lease *oldest_lease = NULL;

#if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
        uint32_t stop;
        unsigned i, hash;

        /* hash hwaddr: use the SDBM hashing algorithm.  Seems to give good
         * dispersal even with similarly-valued "strings".
         */
        hash = 0;
        for (i = 0; i < 6; i++)
                hash += safe_mac[i] + (hash << 6) + (hash << 16) - hash;

        /* pick a seed based on hwaddr then iterate until we find a free address. */
        addr = server_config.start_ip
                + (hash % (1 + server_config.end_ip - server_config.start_ip));
        stop = addr;
#else
        addr = server_config.start_ip;
#define stop (server_config.end_ip + 1)
#endif
        do {
                uint32_t nip;
                struct dyn_lease *lease;

                /* ie, 192.168.55.0 */
                if ((addr & 0xff) == 0)
                        goto next_addr;
                /* ie, 192.168.55.255 */
                if ((addr & 0xff) == 0xff)
                        goto next_addr;
                nip = htonl(addr);
                /* skip our own address */
                if (nip == server_config.server_nip)
                        goto next_addr;
                /* is this a static lease addr? */
                if (is_nip_reserved(server_config.static_leases, nip))
                        goto next_addr;

                lease = find_lease_by_nip(nip);
                if (!lease) {
//TODO: DHCP servers do not always sit on the same subnet as clients: should *ping*, not arp-ping!
                        if (nobody_responds_to_arp(nip, safe_mac, arpping_ms))
                                return nip;
                } else {
                        if (!oldest_lease || lease->expires < oldest_lease->expires)
                                oldest_lease = lease;
                }

 next_addr:
                addr++;
#if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
                if (addr > server_config.end_ip)
                        addr = server_config.start_ip;
#endif
        } while (addr != stop);

        if (oldest_lease
         && is_expired_lease(oldest_lease)
         && nobody_responds_to_arp(oldest_lease->lease_nip, safe_mac, arpping_ms)
        ) {
                return oldest_lease->lease_nip;
        }

        return 0;
}