/***
  This file is part of systemd.

  Copyright (C) 2013 Intel Corporation. All rights reserved.

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd 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
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/

#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <net/ethernet.h>

#include "util.h"
#include "list.h"

#include "dhcp-protocol.h"
#include "dhcp-internal.h"
#include "sd-dhcp-client.h"

#define DHCP_CLIENT_MIN_OPTIONS_SIZE            312

struct sd_dhcp_client {
        DHCPState state;
        sd_event *event;
        sd_event_source *timeout_resend;
        int index;
        uint8_t *req_opts;
        size_t req_opts_size;
        uint32_t last_addr;
        struct ether_addr mac_addr;
        uint32_t xid;
        usec_t start_time;
};

static const uint8_t default_req_opts[] = {
        DHCP_OPTION_SUBNET_MASK,
        DHCP_OPTION_ROUTER,
        DHCP_OPTION_HOST_NAME,
        DHCP_OPTION_DOMAIN_NAME,
        DHCP_OPTION_DOMAIN_NAME_SERVER,
        DHCP_OPTION_NTP_SERVER,
};

int sd_dhcp_client_set_request_option(sd_dhcp_client *client, uint8_t option)
{
        size_t i;

        assert_return(client, -EINVAL);
        assert_return (client->state == DHCP_STATE_INIT, -EBUSY);

        switch(option) {
        case DHCP_OPTION_PAD:
        case DHCP_OPTION_OVERLOAD:
        case DHCP_OPTION_MESSAGE_TYPE:
        case DHCP_OPTION_PARAMETER_REQUEST_LIST:
        case DHCP_OPTION_END:
                return -EINVAL;

        default:
                break;
        }

        for (i = 0; i < client->req_opts_size; i++)
                if (client->req_opts[i] == option)
                        return -EEXIST;

        if (!GREEDY_REALLOC(client->req_opts, client->req_opts_size,
                            client->req_opts_size + 1))
                return -ENOMEM;

        client->req_opts[client->req_opts_size - 1] = option;

        return 0;
}

int sd_dhcp_client_set_request_address(sd_dhcp_client *client,
                                       const struct in_addr *last_addr)
{
        assert_return(client, -EINVAL);
        assert_return(client->state == DHCP_STATE_INIT, -EBUSY);

        if (last_addr)
                client->last_addr = last_addr->s_addr;
        else
                client->last_addr = INADDR_ANY;

        return 0;
}

int sd_dhcp_client_set_index(sd_dhcp_client *client, int interface_index)
{
        assert_return(client, -EINVAL);
        assert_return(client->state == DHCP_STATE_INIT, -EBUSY);
        assert_return(interface_index >= -1, -EINVAL);

        client->index = interface_index;

        return 0;
}

int sd_dhcp_client_set_mac(sd_dhcp_client *client,
                           const struct ether_addr *addr)
{
        assert_return(client, -EINVAL);
        assert_return(client->state == DHCP_STATE_INIT, -EBUSY);

        memcpy(&client->mac_addr, addr, ETH_ALEN);

        return 0;
}

static int client_stop(sd_dhcp_client *client, int error)
{
        assert_return(client, -EINVAL);
        assert_return(client->state != DHCP_STATE_INIT &&
                      client->state != DHCP_STATE_INIT_REBOOT, -EALREADY);

        client->timeout_resend = sd_event_source_unref(client->timeout_resend);

        switch (client->state) {

        case DHCP_STATE_INIT:
        case DHCP_STATE_SELECTING:

                client->state = DHCP_STATE_INIT;
                break;

        case DHCP_STATE_INIT_REBOOT:
        case DHCP_STATE_REBOOTING:
        case DHCP_STATE_REQUESTING:
        case DHCP_STATE_BOUND:
        case DHCP_STATE_RENEWING:
        case DHCP_STATE_REBINDING:

                break;
        }

        return 0;
}

static int client_packet_init(sd_dhcp_client *client, uint8_t type,
                              DHCPMessage *message, uint16_t secs,
                              uint8_t **opt, size_t *optlen)
{
        int err;

        *opt = (uint8_t *)(message + 1);

        if (*optlen < 4)
                return -ENOBUFS;
        *optlen -= 4;

        message->op = BOOTREQUEST;
        message->htype = 1;
        message->hlen = ETHER_ADDR_LEN;
        message->xid = htobe32(client->xid);

        /* Although 'secs' field is a SHOULD in RFC 2131, certain DHCP servers
           refuse to issue an DHCP lease if 'secs' is set to zero */
        message->secs = htobe16(secs);

        memcpy(&message->chaddr, &client->mac_addr, ETH_ALEN);
        (*opt)[0] = 0x63;
        (*opt)[1] = 0x82;
        (*opt)[2] = 0x53;
        (*opt)[3] = 0x63;

        *opt += 4;

        err = dhcp_option_append(opt, optlen, DHCP_OPTION_MESSAGE_TYPE, 1,
                                 &type);
        if (err < 0)
                return err;

        /* Some DHCP servers will refuse to issue an DHCP lease if the Cliient
           Identifier option is not set */
        err = dhcp_option_append(opt, optlen, DHCP_OPTION_CLIENT_IDENTIFIER,
                                 ETH_ALEN, &client->mac_addr);
        if (err < 0)
                return err;

        if (type == DHCP_DISCOVER || type == DHCP_REQUEST) {
                err = dhcp_option_append(opt, optlen,
                                         DHCP_OPTION_PARAMETER_REQUEST_LIST,
                                         client->req_opts_size,
                                         client->req_opts);
                if (err < 0)
                        return err;
        }

        return 0;
}

static uint16_t client_checksum(void *buf, int len)
{
        uint32_t sum;
        uint16_t *check;
        int i;
        uint8_t *odd;

        sum = 0;
        check = buf;

        for (i = 0; i < len / 2 ; i++)
                sum += check[i];

        if (len & 0x01) {
                odd = buf;
                sum += odd[len];
        }

        return ~((sum & 0xffff) + (sum >> 16));
}

static int client_send_discover(sd_dhcp_client *client, uint16_t secs)
{
        int err = 0;
        _cleanup_free_ DHCPPacket *discover;
        size_t optlen, len;
        uint8_t *opt;

        optlen = DHCP_CLIENT_MIN_OPTIONS_SIZE;
        len = sizeof(DHCPPacket) + optlen;

        discover = malloc0(len);

        if (!discover)
                return -ENOMEM;

        err = client_packet_init(client, DHCP_DISCOVER, &discover->dhcp,
                                 secs, &opt, &optlen);
        if (err < 0)
                return err;

        if (client->last_addr != INADDR_ANY) {
                err = dhcp_option_append(&opt, &optlen,
                                         DHCP_OPTION_REQUESTED_IP_ADDRESS,
                                         4, &client->last_addr);
                if (err < 0)
                        return err;
        }

        err = dhcp_option_append(&opt, &optlen, DHCP_OPTION_END, 0, NULL);
        if (err < 0)
                return err;

        discover->ip.version = IPVERSION;
        discover->ip.ihl = sizeof(discover->ip) >> 2;
        discover->ip.tot_len = htobe16(len);

        discover->ip.protocol = IPPROTO_UDP;
        discover->ip.saddr = INADDR_ANY;
        discover->ip.daddr = INADDR_BROADCAST;

        discover->udp.source = htobe16(DHCP_PORT_CLIENT);
        discover->udp.dest = htobe16(DHCP_PORT_SERVER);
        discover->udp.len = htobe16(len - sizeof(discover->ip));

        discover->ip.check = discover->udp.len;
        discover->udp.check = client_checksum(&discover->ip.ttl,
                                              len - 8);

        discover->ip.ttl = IPDEFTTL;
        discover->ip.check = 0;
        discover->ip.check = client_checksum(&discover->ip,
                                             sizeof(discover->ip));

        err = dhcp_network_send_raw_packet(client->index, discover, len);

        return 0;
}

static int client_timeout_resend(sd_event_source *s, uint64_t usec,
                                 void *userdata)
{
        sd_dhcp_client *client = userdata;
        usec_t next_timeout;
        uint16_t secs;
        int err = 0;

        switch (client->state) {
        case DHCP_STATE_INIT:
        case DHCP_STATE_SELECTING:

                if (!client->start_time)
                        client->start_time = usec;

                secs = (usec - client->start_time) / USEC_PER_SEC;

                next_timeout = usec + 2 * USEC_PER_SEC + (random() & 0x1fffff);

                err = sd_event_add_monotonic(client->event, next_timeout,
                                             10 * USEC_PER_MSEC,
                                             client_timeout_resend, client,
                                             &client->timeout_resend);
                if (err < 0)
                        goto error;

                if (client_send_discover(client, secs) >= 0)
                        client->state = DHCP_STATE_SELECTING;

                break;

        case DHCP_STATE_INIT_REBOOT:
        case DHCP_STATE_REBOOTING:
        case DHCP_STATE_REQUESTING:
        case DHCP_STATE_BOUND:
        case DHCP_STATE_RENEWING:
        case DHCP_STATE_REBINDING:

                break;
        }

        return 0;

error:
        client_stop(client, err);

        /* Errors were dealt with when stopping the client, don't spill
           errors into the event loop handler */
        return 0;
}

int sd_dhcp_client_start(sd_dhcp_client *client)
{
        int err;

        assert_return(client, -EINVAL);
        assert_return(client->index >= 0, -EINVAL);
        assert_return(client->state == DHCP_STATE_INIT ||
                      client->state == DHCP_STATE_INIT_REBOOT, -EBUSY);

        client->xid = random_u();

        err = sd_event_add_monotonic(client->event, now(CLOCK_MONOTONIC), 0,
                                     client_timeout_resend, client,
                                     &client->timeout_resend);
        if (err < 0)
                goto error;

        return 0;

error:
        client_stop(client, err);

        return err;
}

int sd_dhcp_client_stop(sd_dhcp_client *client)
{
        return client_stop(client, 0);
}

sd_dhcp_client *sd_dhcp_client_new(sd_event *event)
{
        sd_dhcp_client *client;

        assert_return(event, NULL);

        client = new0(sd_dhcp_client, 1);
        if (!client)
                return NULL;

        client->event = sd_event_ref(event);
        client->state = DHCP_STATE_INIT;
        client->index = -1;

        client->req_opts_size = ELEMENTSOF(default_req_opts);

        client->req_opts = memdup(default_req_opts, client->req_opts_size);
        if (!client->req_opts) {
                free(client);
                return NULL;
        }

        return client;
}