/* vi: set sw=4 ts=4: */
/* Port to Busybox Copyright (C) 2006 Jesse Dutton <jessedutton@gmail.com>
 *
 * Licensed under GPL v2, see file LICENSE in this tarball for details.
 *
 * DHCP Relay for 'DHCPv4 Configuration of IPSec Tunnel Mode' support
 * Copyright (C) 2002 Mario Strasser <mast@gmx.net>,
 *                   Zuercher Hochschule Winterthur,
 *                   Netbeat AG
 * Upstream has GPL v2 or later
 */

#include "common.h"
#include "options.h"

#define SERVER_PORT      67
#define SELECT_TIMEOUT    5 /* select timeout in sec. */
#define MAX_LIFETIME   2*60 /* lifetime of an xid entry in sec. */

/* This list holds information about clients. The xid_* functions manipulate this list. */
struct xid_item {
        unsigned timestamp;
        int client;
        uint32_t xid;
        struct sockaddr_in ip;
        struct xid_item *next;
};

#define dhcprelay_xid_list (*(struct xid_item*)&bb_common_bufsiz1)

static struct xid_item *xid_add(uint32_t xid, struct sockaddr_in *ip, int client)
{
        struct xid_item *item;

        /* create new xid entry */
        item = xmalloc(sizeof(struct xid_item));

        /* add xid entry */
        item->ip = *ip;
        item->xid = xid;
        item->client = client;
        item->timestamp = monotonic_sec();
        item->next = dhcprelay_xid_list.next;
        dhcprelay_xid_list.next = item;

        return item;
}

static void xid_expire(void)
{
        struct xid_item *item = dhcprelay_xid_list.next;
        struct xid_item *last = &dhcprelay_xid_list;
        unsigned current_time = monotonic_sec();

        while (item != NULL) {
                if ((current_time - item->timestamp) > MAX_LIFETIME) {
                        last->next = item->next;
                        free(item);
                        item = last->next;
                } else {
                        last = item;
                        item = item->next;
                }
        }
}

static struct xid_item *xid_find(uint32_t xid)
{
        struct xid_item *item = dhcprelay_xid_list.next;
        while (item != NULL) {
                if (item->xid == xid) {
                        return item;
                }
                item = item->next;
        }
        return NULL;
}

static void xid_del(uint32_t xid)
{
        struct xid_item *item = dhcprelay_xid_list.next;
        struct xid_item *last = &dhcprelay_xid_list;
        while (item != NULL) {
                if (item->xid == xid) {
                        last->next = item->next;
                        free(item);
                        item = last->next;
                } else {
                        last = item;
                        item = item->next;
                }
        }
}

/**
 * get_dhcp_packet_type - gets the message type of a dhcp packet
 * p - pointer to the dhcp packet
 * returns the message type on success, -1 otherwise
 */
static int get_dhcp_packet_type(struct dhcp_packet *p)
{
        uint8_t *op;

        /* it must be either a BOOTREQUEST or a BOOTREPLY */
        if (p->op != BOOTREQUEST && p->op != BOOTREPLY)
                return -1;
        /* get message type option */
        op = get_option(p, DHCP_MESSAGE_TYPE);
        if (op != NULL)
                return op[0];
        return -1;
}

/**
 * get_client_devices - parses the devices list
 * dev_list - comma separated list of devices
 * returns array
 */
static char **get_client_devices(char *dev_list, int *client_number)
{
        char *s, **client_dev;
        int i, cn;

        /* copy list */
        dev_list = xstrdup(dev_list);

        /* get number of items, replace ',' with NULs */
        s = dev_list;
        cn = 1;
        while (*s) {
                if (*s == ',') {
                        *s = '\0';
                        cn++;
                }
                s++;
        }
        *client_number = cn;

        /* create vector of pointers */
        client_dev = xzalloc(cn * sizeof(*client_dev));
        client_dev[0] = dev_list;
        i = 1;
        while (i != cn) {
                client_dev[i] = client_dev[i - 1] + strlen(client_dev[i - 1]) + 1;
                i++;
        }
        return client_dev;
}


/* Creates listen sockets (in fds) bound to client and server ifaces,
 * and returns numerically max fd.
 */
static int init_sockets(char **client_ifaces, int num_clients,
                        char *server_iface, int *fds)
{
        int i, n;

        /* talk to real server on bootps */
        fds[0] = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT, server_iface);
        n = fds[0];

        for (i = 1; i < num_clients; i++) {
                /* listen for clients on bootps */
                fds[i] = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT, client_ifaces[i-1]);
                if (fds[i] > n)
                        n = fds[i];
        }
        return n;
}


/**
 * pass_to_server() - forwards dhcp packets from client to server
 * p - packet to send
 * client - number of the client
 */
static void pass_to_server(struct dhcp_packet *p, int packet_len, int client, int *fds,
                        struct sockaddr_in *client_addr, struct sockaddr_in *server_addr)
{
        int res, type;
        struct xid_item *item;

        /* check packet_type */
        type = get_dhcp_packet_type(p);
        if (type != DHCPDISCOVER && type != DHCPREQUEST
         && type != DHCPDECLINE && type != DHCPRELEASE
         && type != DHCPINFORM
        ) {
                return;
        }

        /* create new xid entry */
        item = xid_add(p->xid, client_addr, client);

        /* forward request to LAN (server) */
        errno = 0;
        res = sendto(fds[0], p, packet_len, 0, (struct sockaddr*)server_addr,
                        sizeof(struct sockaddr_in));
        if (res != packet_len) {
                bb_perror_msg("sendto");
        }
}

/**
 * pass_to_client() - forwards dhcp packets from server to client
 * p - packet to send
 */
static void pass_to_client(struct dhcp_packet *p, int packet_len, int *fds)
{
        int res, type;
        struct xid_item *item;

        /* check xid */
        item = xid_find(p->xid);
        if (!item) {
                return;
        }

        /* check packet type */
        type = get_dhcp_packet_type(p);
        if (type != DHCPOFFER && type != DHCPACK && type != DHCPNAK) {
                return;
        }

        if (item->ip.sin_addr.s_addr == htonl(INADDR_ANY))
                item->ip.sin_addr.s_addr = htonl(INADDR_BROADCAST);
        errno = 0;
        res = sendto(fds[item->client], p, packet_len, 0, (struct sockaddr*) &(item->ip),
                        sizeof(item->ip));
        if (res != packet_len) {
                bb_perror_msg("sendto");
                return;
        }

        /* remove xid entry */
        xid_del(p->xid);
}

int dhcprelay_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int dhcprelay_main(int argc, char **argv)
{
        struct dhcp_packet dhcp_msg;
        struct sockaddr_in server_addr;
        struct sockaddr_in client_addr;
        fd_set rfds;
        char **client_ifaces;
        int *fds;
        int num_sockets, max_socket;
        uint32_t our_nip;

        server_addr.sin_family = AF_INET;
        server_addr.sin_port = htons(SERVER_PORT);

        /* dhcprelay client_iface1,client_iface2,... server_iface [server_IP] */
        if (argc == 4) {
                if (!inet_aton(argv[3], &server_addr.sin_addr))
                        bb_perror_msg_and_die("bad server IP");
        } else if (argc == 3) {
                server_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
        } else {
                bb_show_usage();
        }

        /* Produce list of client ifaces */
        client_ifaces = get_client_devices(argv[1], &num_sockets);

        num_sockets++; /* for server socket at fds[0] */
        fds = xmalloc(num_sockets * sizeof(fds[0]));

        /* Create sockets and bind one to every iface */
        max_socket = init_sockets(client_ifaces, num_sockets, argv[2], fds);

        /* Get our IP on server_iface */
        if (udhcp_read_interface(argv[2], NULL, &our_nip, NULL))
                return 1;

        /* Main loop */
        while (1) {
//reinit stuff from time to time? go back to get_client_devices
//every N minutes?
                struct timeval tv;
                size_t packlen;
                socklen_t addr_size;
                int i;

                FD_ZERO(&rfds);
                for (i = 0; i < num_sockets; i++)
                        FD_SET(fds[i], &rfds);
                tv.tv_sec = SELECT_TIMEOUT;
                tv.tv_usec = 0;
                if (select(max_socket + 1, &rfds, NULL, NULL, &tv) > 0) {
                        /* server */
                        if (FD_ISSET(fds[0], &rfds)) {
                                packlen = udhcp_recv_kernel_packet(&dhcp_msg, fds[0]);
                                if (packlen > 0) {
                                        pass_to_client(&dhcp_msg, packlen, fds);
                                }
                        }
                        /* clients */
                        for (i = 1; i < num_sockets; i++) {
                                if (!FD_ISSET(fds[i], &rfds))
                                        continue;
                                addr_size = sizeof(struct sockaddr_in);
                                packlen = recvfrom(fds[i], &dhcp_msg, sizeof(dhcp_msg), 0,
                                                (struct sockaddr *)(&client_addr), &addr_size);
                                if (packlen <= 0)
                                        continue;

                                /* Get our IP on corresponding client_iface */
//why? what if server can't route such IP?
                                if (udhcp_read_interface(client_ifaces[i-1], NULL, &dhcp_msg.gateway_nip, NULL)) {
                                        /* Fall back to our server_iface's IP */
//this makes more sense!
                                        dhcp_msg.gateway_nip = our_nip;
                                }
//maybe set dhcp_msg.flags |= BROADCAST_FLAG too?
                                pass_to_server(&dhcp_msg, packlen, i, fds, &client_addr, &server_addr);
                        }
                }
                xid_expire();
        } /* while (1) */

        /* return 0; - not reached */
}