/***
  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 <sys/param.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 DHCPLease {
        uint32_t t1;
        uint32_t t2;
        uint32_t lifetime;
        be32_t address;
        be32_t server_address;
        be32_t subnet_mask;
        be32_t router;
        struct in_addr *dns;
        size_t dns_size;
        uint16_t mtu;
        char *domainname;
        char *hostname;
};

typedef struct DHCPLease DHCPLease;

struct sd_dhcp_client {
        DHCPState state;
        sd_event *event;
        sd_event_source *timeout_resend;
        int index;
        int fd;
        union sockaddr_union link;
        sd_event_source *receive_message;
        uint8_t *req_opts;
        size_t req_opts_allocated;
        size_t req_opts_size;
        be32_t last_addr;
        struct ether_addr mac_addr;
        uint32_t xid;
        usec_t start_time;
        unsigned int attempt;
        usec_t request_sent;
        sd_event_source *timeout_t1;
        sd_event_source *timeout_t2;
        sd_event_source *timeout_expire;
        sd_dhcp_client_cb_t cb;
        void *userdata;
        DHCPLease *lease;
};

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,
};

static int client_receive_message(sd_event_source *s, int fd,
                                  uint32_t revents, void *userdata);

int sd_dhcp_client_set_callback(sd_dhcp_client *client, sd_dhcp_client_cb_t cb,
                                void *userdata) {
        assert_return(client, -EINVAL);

        client->cb = cb;
        client->userdata = userdata;

        return 0;
}

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_allocated,
                            client->req_opts_size + 1))
                return -ENOMEM;

        client->req_opts[client->req_opts_size++] = 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;
}

int sd_dhcp_client_get_address(sd_dhcp_client *client, struct in_addr *addr) {
        assert_return(client, -EINVAL);
        assert_return(addr, -EINVAL);

        switch (client->state) {
        case DHCP_STATE_INIT:
        case DHCP_STATE_SELECTING:
        case DHCP_STATE_INIT_REBOOT:
        case DHCP_STATE_REBOOTING:
        case DHCP_STATE_REQUESTING:
                return -EADDRNOTAVAIL;

        case DHCP_STATE_BOUND:
        case DHCP_STATE_RENEWING:
        case DHCP_STATE_REBINDING:
                addr->s_addr = client->lease->address;

                break;
        }

        return 0;
}

int sd_dhcp_client_get_mtu(sd_dhcp_client *client, uint16_t *mtu) {
        assert_return(client, -EINVAL);
        assert_return(mtu, -EINVAL);

        switch (client->state) {
        case DHCP_STATE_INIT:
        case DHCP_STATE_SELECTING:
        case DHCP_STATE_INIT_REBOOT:
        case DHCP_STATE_REBOOTING:
        case DHCP_STATE_REQUESTING:
                return -EADDRNOTAVAIL;

        case DHCP_STATE_BOUND:
        case DHCP_STATE_RENEWING:
        case DHCP_STATE_REBINDING:
                if (client->lease->mtu)
                        *mtu = client->lease->mtu;
                else
                        return -ENOENT;

                break;
        }

        return 0;
}

int sd_dhcp_client_get_dns(sd_dhcp_client *client, struct in_addr **addr, size_t *addr_size) {
        assert_return(client, -EINVAL);
        assert_return(addr, -EINVAL);
        assert_return(addr_size, -EINVAL);

        switch (client->state) {
        case DHCP_STATE_INIT:
        case DHCP_STATE_SELECTING:
        case DHCP_STATE_INIT_REBOOT:
        case DHCP_STATE_REBOOTING:
        case DHCP_STATE_REQUESTING:
                return -EADDRNOTAVAIL;

        case DHCP_STATE_BOUND:
        case DHCP_STATE_RENEWING:
        case DHCP_STATE_REBINDING:
                if (client->lease->dns_size) {
                        *addr_size = client->lease->dns_size;
                        *addr = client->lease->dns;
                } else
                        return -ENOENT;

                break;
        }

        return 0;
}

int sd_dhcp_client_get_domainname(sd_dhcp_client *client, const char **domainname) {
        assert_return(client, -EINVAL);
        assert_return(domainname, -EINVAL);

        switch (client->state) {
        case DHCP_STATE_INIT:
        case DHCP_STATE_SELECTING:
        case DHCP_STATE_INIT_REBOOT:
        case DHCP_STATE_REBOOTING:
        case DHCP_STATE_REQUESTING:
                return -EADDRNOTAVAIL;

        case DHCP_STATE_BOUND:
        case DHCP_STATE_RENEWING:
        case DHCP_STATE_REBINDING:
                if (client->lease->domainname)
                        *domainname = client->lease->domainname;
                else
                        return -ENOENT;

                break;
        }

        return 0;
}

int sd_dhcp_client_get_hostname(sd_dhcp_client *client, const char **hostname) {
        assert_return(client, -EINVAL);
        assert_return(hostname, -EINVAL);

        switch (client->state) {
        case DHCP_STATE_INIT:
        case DHCP_STATE_SELECTING:
        case DHCP_STATE_INIT_REBOOT:
        case DHCP_STATE_REBOOTING:
        case DHCP_STATE_REQUESTING:
                return -EADDRNOTAVAIL;

        case DHCP_STATE_BOUND:
        case DHCP_STATE_RENEWING:
        case DHCP_STATE_REBINDING:
                if (client->lease->hostname)
                        *hostname = client->lease->hostname;
                else
                        return -ENOENT;

                break;
        }

        return 0;
}

int sd_dhcp_client_prefixlen(const struct in_addr *addr) {
        int len = 0;
        uint32_t mask;

        assert_return(addr, -EADDRNOTAVAIL);

        mask = be32toh(addr->s_addr);
        while (mask) {
                len++;
                mask = mask << 1;
        }

        return len;
}

int sd_dhcp_client_get_router(sd_dhcp_client *client, struct in_addr *addr) {
        assert_return(client, -EINVAL);
        assert_return(addr, -EINVAL);

        switch (client->state) {
        case DHCP_STATE_INIT:
        case DHCP_STATE_SELECTING:
        case DHCP_STATE_INIT_REBOOT:
        case DHCP_STATE_REBOOTING:
        case DHCP_STATE_REQUESTING:
                return -EADDRNOTAVAIL;

        case DHCP_STATE_BOUND:
        case DHCP_STATE_RENEWING:
        case DHCP_STATE_REBINDING:
                addr->s_addr = client->lease->router;

                break;
        }

        return 0;
}

int sd_dhcp_client_get_netmask(sd_dhcp_client *client, struct in_addr *addr) {
        assert_return(client, -EINVAL);
        assert_return(addr, -EINVAL);

        switch (client->state) {
        case DHCP_STATE_INIT:
        case DHCP_STATE_SELECTING:
        case DHCP_STATE_INIT_REBOOT:
        case DHCP_STATE_REBOOTING:
        case DHCP_STATE_REQUESTING:
                return -EADDRNOTAVAIL;

        case DHCP_STATE_BOUND:
        case DHCP_STATE_RENEWING:
        case DHCP_STATE_REBINDING:
                addr->s_addr = client->lease->subnet_mask;

                break;
        }

        return 0;
}

static int client_notify(sd_dhcp_client *client, int event) {
        if (client->cb)
                client->cb(client, event, client->userdata);

        return 0;
}

static void lease_free(DHCPLease *lease) {
        if (!lease)
                return;

        free(lease->hostname);
        free(lease->domainname);
        free(lease->dns);
        free(lease);
}

DEFINE_TRIVIAL_CLEANUP_FUNC(DHCPLease*, lease_free);
#define _cleanup_lease_free_ _cleanup_(lease_freep)

static int client_stop(sd_dhcp_client *client, int error) {
        assert_return(client, -EINVAL);

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

        if (client->fd >= 0)
                close(client->fd);
        client->fd = -1;

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

        client->timeout_t1 = sd_event_source_unref(client->timeout_t1);
        client->timeout_t2 = sd_event_source_unref(client->timeout_t2);
        client->timeout_expire = sd_event_source_unref(client->timeout_expire);

        client->attempt = 1;

        client_notify(client, error);

        switch (client->state) {

        case DHCP_STATE_INIT:
        case DHCP_STATE_SELECTING:
        case DHCP_STATE_REQUESTING:
        case DHCP_STATE_BOUND:

                client->start_time = 0;
                client->state = DHCP_STATE_INIT;
                break;

        case DHCP_STATE_INIT_REBOOT:
        case DHCP_STATE_REBOOTING:
        case DHCP_STATE_RENEWING:
        case DHCP_STATE_REBINDING:

                break;
        }

        if (client->lease) {
                lease_free(client->lease);
                client->lease = NULL;
        }

        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;
        be16_t max_size;

        *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);

        if (client->state == DHCP_STATE_RENEWING ||
            client->state == DHCP_STATE_REBINDING)
                message->ciaddr = client->lease->address;

        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;

                /* Some DHCP servers will send bigger DHCP packets than the
                   defined default size unless the Maximum Messge Size option
                   is explicitely set */
                max_size = htobe16(DHCP_IP_UDP_SIZE + DHCP_MESSAGE_SIZE +
                                   DHCP_CLIENT_MIN_OPTIONS_SIZE);
                err = dhcp_option_append(opt, optlen,
                                         DHCP_OPTION_MAXIMUM_MESSAGE_SIZE,
                                         2, &max_size);
                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 - 1];
        }

        while (sum >> 16)
                sum = (sum & 0xffff) + (sum >> 16);

        return ~sum;
}

static void client_append_ip_headers(DHCPPacket *packet, uint16_t len) {
        packet->ip.version = IPVERSION;
        packet->ip.ihl = DHCP_IP_SIZE / 4;
        packet->ip.tot_len = htobe16(len);

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

        packet->udp.source = htobe16(DHCP_PORT_CLIENT);
        packet->udp.dest = htobe16(DHCP_PORT_SERVER);
        packet->udp.len = htobe16(len - DHCP_IP_SIZE);

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

        packet->ip.ttl = IPDEFTTL;
        packet->ip.check = 0;
        packet->ip.check = client_checksum(&packet->ip, DHCP_IP_SIZE);
}

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;

        client_append_ip_headers(discover, len);

        err = dhcp_network_send_raw_socket(client->fd, &client->link,
                                           discover, len);

        return err;
}

static int client_send_request(sd_dhcp_client *client, uint16_t secs) {
        _cleanup_free_ DHCPPacket *request;
        size_t optlen, len;
        int err;
        uint8_t *opt;

        optlen = DHCP_CLIENT_MIN_OPTIONS_SIZE;
        len = DHCP_MESSAGE_SIZE + optlen;

        request = malloc0(len);
        if (!request)
                return -ENOMEM;

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

        if (client->state == DHCP_STATE_REQUESTING) {
                err = dhcp_option_append(&opt, &optlen,
                                         DHCP_OPTION_REQUESTED_IP_ADDRESS,
                                         4, &client->lease->address);
                if (err < 0)
                        return err;

                err = dhcp_option_append(&opt, &optlen,
                                         DHCP_OPTION_SERVER_IDENTIFIER,
                                         4, &client->lease->server_address);
                if (err < 0)
                        return err;
        }

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

        if (client->state == DHCP_STATE_RENEWING) {
                err = dhcp_network_send_udp_socket(client->fd,
                                                   client->lease->server_address,
                                                   &request->dhcp,
                                                   len - DHCP_IP_UDP_SIZE);
        } else {
                client_append_ip_headers(request, len);

                err = dhcp_network_send_raw_socket(client->fd, &client->link,
                                                   request, len);
        }

        return err;
}

static int client_timeout_resend(sd_event_source *s, uint64_t usec,
                                 void *userdata) {
        sd_dhcp_client *client = userdata;
        usec_t next_timeout = 0;
        uint32_t time_left;
        uint16_t secs;
        int err = 0;

        switch (client->state) {
        case DHCP_STATE_RENEWING:

                time_left = (client->lease->t2 - client->lease->t1)/2;
                if (time_left < 60)
                        time_left = 60;

                next_timeout = usec + time_left * USEC_PER_SEC;

                break;

        case DHCP_STATE_REBINDING:

                time_left = (client->lease->lifetime - client->lease->t2)/2;
                if (time_left < 60)
                        time_left = 60;

                next_timeout = usec + time_left * USEC_PER_SEC;
                break;

        case DHCP_STATE_INIT:
        case DHCP_STATE_INIT_REBOOT:
        case DHCP_STATE_REBOOTING:
        case DHCP_STATE_SELECTING:
        case DHCP_STATE_REQUESTING:
        case DHCP_STATE_BOUND:

                if (client->attempt < 64)
                        client->attempt *= 2;

                next_timeout = usec + (client->attempt - 1) * USEC_PER_SEC;

                break;
        }

        next_timeout += (random_u32() & 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;

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

        switch (client->state) {
        case DHCP_STATE_INIT:
                err = client_send_discover(client, secs);
                if (err >= 0) {
                        client->state = DHCP_STATE_SELECTING;
                        client->attempt = 1;
                } else {
                        if (client->attempt >= 64)
                                goto error;
                }

                break;

        case DHCP_STATE_SELECTING:
                err = client_send_discover(client, secs);
                if (err < 0 && client->attempt >= 64)
                        goto error;

                break;

        case DHCP_STATE_REQUESTING:
        case DHCP_STATE_RENEWING:
        case DHCP_STATE_REBINDING:
                err = client_send_request(client, secs);
                if (err < 0 && client->attempt >= 64)
                         goto error;

                client->request_sent = usec;

                break;

        case DHCP_STATE_INIT_REBOOT:
        case DHCP_STATE_REBOOTING:
        case DHCP_STATE_BOUND:

                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;
}

static int client_initialize_events(sd_dhcp_client *client, usec_t usec) {
        int r;

        r = sd_event_add_io(client->event, client->fd, EPOLLIN,
                            client_receive_message, client,
                            &client->receive_message);
        if (r < 0)
                goto error;

        r = sd_event_add_monotonic(client->event, usec, 0,
                                   client_timeout_resend, client,
                                   &client->timeout_resend);

error:
        if (r < 0)
                client_stop(client, r);

        return 0;

}

static int client_timeout_expire(sd_event_source *s, uint64_t usec,
                                 void *userdata) {
        sd_dhcp_client *client = userdata;

        client_stop(client, DHCP_EVENT_EXPIRED);

        return 0;
}

static int client_timeout_t2(sd_event_source *s, uint64_t usec, void *userdata) {
        sd_dhcp_client *client = userdata;
        int r;

        if (client->fd >= 0) {
                client->receive_message =
                        sd_event_source_unref(client->receive_message);
                close(client->fd);
                client->fd = -1;
        }

        client->state = DHCP_STATE_REBINDING;
        client->attempt = 1;

        r = dhcp_network_bind_raw_socket(client->index, &client->link);
        if (r < 0) {
                client_stop(client, r);
                return 0;
        }

        client->fd = r;

        return client_initialize_events(client, usec);
}

static int client_timeout_t1(sd_event_source *s, uint64_t usec, void *userdata) {
        sd_dhcp_client *client = userdata;
        int r;

        client->state = DHCP_STATE_RENEWING;
        client->attempt = 1;

        r = dhcp_network_bind_udp_socket(client->index,
                                         client->lease->address);
        if (r < 0) {
                client_stop(client, r);
                return 0;
        }

        client->fd = r;

        return client_initialize_events(client, usec);
}

static int client_parse_offer(uint8_t code, uint8_t len, const uint8_t *option,
                              void *user_data) {
        DHCPLease *lease = user_data;
        be32_t val;

        switch(code) {

        case DHCP_OPTION_IP_ADDRESS_LEASE_TIME:
                if (len == 4) {
                        memcpy(&val, option, 4);
                        lease->lifetime = be32toh(val);
                }

                break;

        case DHCP_OPTION_SERVER_IDENTIFIER:
                if (len >= 4)
                        memcpy(&lease->server_address, option, 4);

                break;

        case DHCP_OPTION_SUBNET_MASK:
                if (len >= 4)
                        memcpy(&lease->subnet_mask, option, 4);

                break;

        case DHCP_OPTION_ROUTER:
                if (len >= 4)
                        memcpy(&lease->router, option, 4);

                break;

        case DHCP_OPTION_DOMAIN_NAME_SERVER:
                if (len >= 4) {
                        unsigned i;

                        lease->dns_size = len / 4;

                        free(lease->dns);
                        lease->dns = new0(struct in_addr, lease->dns_size);
                        if (!lease->dns)
                                return -ENOMEM;

                        for (i = 0; i < lease->dns_size; i++) {
                                memcpy(&lease->dns[i].s_addr, option + 4 * i, 4);
                        }
                }

                break;

        case DHCP_OPTION_INTERFACE_MTU:
                if (len >= 2) {
                        be16_t mtu;

                        memcpy(&mtu, option, 2);
                        lease->mtu = be16toh(mtu);

                        if (lease->mtu < 68)
                                lease->mtu = 0;
                }

                break;

        case DHCP_OPTION_DOMAIN_NAME:
                if (len >= 1) {
                        free(lease->domainname);
                        lease->domainname = strndup((const char *)option, len);
                }

                break;

        case DHCP_OPTION_HOST_NAME:
                if (len >= 1) {
                        free(lease->hostname);
                        lease->hostname = strndup((const char *)option, len);
                }

                break;

        case DHCP_OPTION_RENEWAL_T1_TIME:
                if (len == 4) {
                        memcpy(&val, option, 4);
                        lease->t1 = be32toh(val);
                }

                break;

        case DHCP_OPTION_REBINDING_T2_TIME:
                if (len == 4) {
                        memcpy(&val, option, 4);
                        lease->t2 = be32toh(val);
                }

                break;
        }

        return 0;
}

static int client_verify_headers(sd_dhcp_client *client, DHCPPacket *message,
                                 size_t len) {
        size_t hdrlen;

        if (len < (DHCP_IP_UDP_SIZE + DHCP_MESSAGE_SIZE))
                return -EINVAL;

        hdrlen = message->ip.ihl * 4;
        if (hdrlen < 20 || hdrlen > len || client_checksum(&message->ip,
                                                           hdrlen))
                return -EINVAL;

        message->ip.check = message->udp.len;
        message->ip.ttl = 0;

        if (hdrlen + be16toh(message->udp.len) > len ||
            client_checksum(&message->ip.ttl, be16toh(message->udp.len) + 12))
                return -EINVAL;

        if (be16toh(message->udp.source) != DHCP_PORT_SERVER ||
            be16toh(message->udp.dest) != DHCP_PORT_CLIENT)
                return -EINVAL;

        if (message->dhcp.op != BOOTREPLY)
                return -EINVAL;

        if (be32toh(message->dhcp.xid) != client->xid)
                return -EINVAL;

        if (memcmp(&message->dhcp.chaddr[0], &client->mac_addr.ether_addr_octet,
                    ETHER_ADDR_LEN))
                return -EINVAL;

        return 0;
}

static int client_receive_offer(sd_dhcp_client *client, DHCPPacket *offer,
                                size_t len) {
        _cleanup_lease_free_ DHCPLease *lease = NULL;
        int r;

        r = client_verify_headers(client, offer, len);
        if (r < 0)
                return r;

        lease = new0(DHCPLease, 1);
        if (!lease)
                return -ENOMEM;

        len = len - DHCP_IP_UDP_SIZE;
        r = dhcp_option_parse(&offer->dhcp, len, client_parse_offer,
                              lease);
        if (r != DHCP_OFFER)
                return -ENOMSG;

        lease->address = offer->dhcp.yiaddr;

        if (lease->address == INADDR_ANY ||
            lease->server_address == INADDR_ANY ||
            lease->subnet_mask == INADDR_ANY ||
            lease->lifetime == 0)
                return -ENOMSG;

        client->lease = lease;
        lease = NULL;

        return 0;
}

static int client_receive_ack(sd_dhcp_client *client, const uint8_t *buf,
                              size_t len) {
        DHCPPacket *ack;
        DHCPMessage *dhcp;
        _cleanup_lease_free_ DHCPLease *lease = NULL;
        int r;

        if (client->state == DHCP_STATE_RENEWING) {
                dhcp = (DHCPMessage *)buf;
        } else {
                ack = (DHCPPacket *)buf;

                r = client_verify_headers(client, ack, len);
                if (r < 0)
                        return r;

                dhcp = &ack->dhcp;
                len -= DHCP_IP_UDP_SIZE;
        }

        lease = new0(DHCPLease, 1);
        if (!lease)
                return -ENOMEM;

        r = dhcp_option_parse(dhcp, len, client_parse_offer, lease);
        if (r == DHCP_NAK)
                return DHCP_EVENT_NO_LEASE;

        if (r != DHCP_ACK)
                return -ENOMSG;

        lease->address = dhcp->yiaddr;

        if (lease->address == INADDR_ANY ||
            lease->server_address == INADDR_ANY ||
            lease->subnet_mask == INADDR_ANY || lease->lifetime == 0)
                return -ENOMSG;

        r = DHCP_EVENT_IP_ACQUIRE;
        if (client->lease) {
                if (client->lease->address != lease->address ||
                    client->lease->subnet_mask != lease->subnet_mask ||
                    client->lease->router != lease->router) {
                        r = DHCP_EVENT_IP_CHANGE;
                }

                lease_free(client->lease);
        }

        client->lease = lease;
        lease = NULL;

        return r;
}

static uint64_t client_compute_timeout(uint64_t request_sent,
                                       uint32_t lifetime) {
        return request_sent + (lifetime - 3) * USEC_PER_SEC +
                + (random_u32() & 0x1fffff);
}

static int client_set_lease_timeouts(sd_dhcp_client *client, uint64_t usec) {
        uint64_t next_timeout;
        int r;

        if (client->lease->lifetime < 10)
                return -EINVAL;

        client->timeout_t1 = sd_event_source_unref(client->timeout_t1);
        client->timeout_t2 = sd_event_source_unref(client->timeout_t2);
        client->timeout_expire = sd_event_source_unref(client->timeout_expire);

        if (!client->lease->t1)
                client->lease->t1 = client->lease->lifetime / 2;

        next_timeout = client_compute_timeout(client->request_sent,
                                              client->lease->t1);
        if (next_timeout < usec)
                return -EINVAL;

        r = sd_event_add_monotonic(client->event, next_timeout,
                                     10 * USEC_PER_MSEC,
                                     client_timeout_t1, client,
                                     &client->timeout_t1);
        if (r < 0)
                return r;

        if (!client->lease->t2)
                client->lease->t2 = client->lease->lifetime * 7 / 8;

        if (client->lease->t2 < client->lease->t1)
                return -EINVAL;

        if (client->lease->lifetime < client->lease->t2)
                return -EINVAL;

        next_timeout = client_compute_timeout(client->request_sent,
                                              client->lease->t2);
        if (next_timeout < usec)
                return -EINVAL;

        r = sd_event_add_monotonic(client->event, next_timeout,
                                     10 * USEC_PER_MSEC,
                                     client_timeout_t2, client,
                                     &client->timeout_t2);
        if (r < 0)
                return r;

        next_timeout = client_compute_timeout(client->request_sent,
                                              client->lease->lifetime);
        if (next_timeout < usec)
                return -EINVAL;

        r = sd_event_add_monotonic(client->event, next_timeout,
                                     10 * USEC_PER_MSEC,
                                     client_timeout_expire, client,
                                     &client->timeout_expire);
        if (r < 0)
                return r;

        return 0;
}

static int client_receive_message(sd_event_source *s, int fd,
                                  uint32_t revents, void *userdata) {
        sd_dhcp_client *client = userdata;
        uint8_t buf[sizeof(DHCPPacket) + DHCP_CLIENT_MIN_OPTIONS_SIZE];
        int buflen = sizeof(buf);
        int len, r = 0, notify_event = 0;
        DHCPPacket *message;
        usec_t time_now;

        len = read(fd, &buf, buflen);
        if (len < 0)
                return 0;

        r = sd_event_get_now_monotonic(client->event, &time_now);
        if (r < 0)
                goto error;

        switch (client->state) {
        case DHCP_STATE_SELECTING:

                message = (DHCPPacket *)&buf;

                if (client_receive_offer(client, message, len) >= 0) {

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

                        client->state = DHCP_STATE_REQUESTING;
                        client->attempt = 1;

                        r = sd_event_add_monotonic(client->event, time_now, 0,
                                                   client_timeout_resend,
                                                   client,
                                                   &client->timeout_resend);
                        if (r < 0)
                                goto error;
                }

                break;

        case DHCP_STATE_REQUESTING:
        case DHCP_STATE_RENEWING:
        case DHCP_STATE_REBINDING:

                r = client_receive_ack(client, buf, len);

                if (r == DHCP_EVENT_NO_LEASE)
                        goto error;

                if (r >= 0) {
                        client->timeout_resend =
                                sd_event_source_unref(client->timeout_resend);

                        if (client->state == DHCP_STATE_REQUESTING)
                                notify_event = DHCP_EVENT_IP_ACQUIRE;
                        else if (r != DHCP_EVENT_IP_ACQUIRE)
                                notify_event = r;

                        client->state = DHCP_STATE_BOUND;
                        client->attempt = 1;

                        client->last_addr = client->lease->address;

                        r = client_set_lease_timeouts(client, time_now);
                        if (r < 0)
                                goto error;

                        if (notify_event)
                                client_notify(client, notify_event);

                        client->receive_message =
                                sd_event_source_unref(client->receive_message);
                        close(client->fd);
                        client->fd = -1;
                }

                r = 0;

                break;

        case DHCP_STATE_INIT:
        case DHCP_STATE_INIT_REBOOT:
        case DHCP_STATE_REBOOTING:
        case DHCP_STATE_BOUND:

                break;
        }

error:
        if (r < 0 || r == DHCP_EVENT_NO_LEASE)
                return client_stop(client, r);

        return 0;
}

int sd_dhcp_client_start(sd_dhcp_client *client) {
        int r;

        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_u32();

        r = dhcp_network_bind_raw_socket(client->index, &client->link);

        if (r < 0) {
                client_stop(client, r);
                return r;
        }

        client->fd = r;
        client->start_time = now(CLOCK_MONOTONIC);

        return client_initialize_events(client, client->start_time);
}

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

sd_dhcp_client *sd_dhcp_client_free(sd_dhcp_client *client) {
        assert_return(client, NULL);

        sd_dhcp_client_stop(client);

        sd_event_unref(client->event);
        free(client->req_opts);
        free(client);

        return NULL;
}

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->fd = -1;
        client->attempt = 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;
}