dhcp/client.cpp

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stddef.h>
#include <time.h>

#include <fcntl.h>
#include <arpa/inet.h>
#include <linux/if_packet.h>

#include "ip4.h"
#include "udp4.h"
#include "dhcp4.h"
#include "eth.h"
#include "packet.h"
#include "interface.h"
#include "sock.h"

void print_message(packet::packet const& p, dhcp4::options const& options)
{
  printf("dhcp4 op: %d\n", p.dhcp4->op);
  printf("dhcp4 yiaddr: %s\n", ip4::tostr(p.dhcp4->yiaddr));

  printf("message type: %s\n", dhcp4::message_type_tostr(options.message_type));
  printf("subnet mask: %s\n", ip4::tostr(options.subnet_mask));
  printf("router: %s\n", ip4::tostr(options.router));
  printf("domain name server: %s\n", ip4::tostr(options.domain_name_server));
}

int main()
{
  srand(time(NULL));
  uint32_t dhcp_transaction_id = rand();

  int sock = sock::create(68);

  char const * interface_name = "wlp174s0";
  int ifa_index = sock::interface_index(sock, interface_name);
  sock::bind_interface(sock, ifa_index);

  uint8_t eth_source_address[6];
  sock::interface_address(sock, interface_name, eth_source_address);
  uint8_t eth_destination_address[] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff};

  uint32_t ip4_source_address = 0x00000000;
  uint32_t ip4_destination_address = 0xffffffff;

  packet::packet p{};
  dhcp4::options options{};
  static uint8_t recvbuf[65536];
  static uint8_t sendbuf[16384];

  //////////////////////////////////////////////////////////////////////
  // dhcp send discover
  //////////////////////////////////////////////////////////////////////
  {
    dhcp4::message_parameters params = {
    };

    int length = packet::make(sendbuf,
                              dhcp4::op::bootrequest,
                              eth_source_address,
                              eth_destination_address,
                              eth_source_address, // eth_client_address
                              ip4_source_address,
                              ip4_destination_address,
                              68, // udp4_source_port
                              67, // udp4_destination_port
                              dhcp_transaction_id,
                              dhcp4::message_type::dhcpdiscover,
                              &params);

    sock::send(sock, ifa_index, sendbuf, length, eth_destination_address);
  }

  //////////////////////////////////////////////////////////////////////
  // dhcp recv offer
  //////////////////////////////////////////////////////////////////////

  {
    struct sockaddr_ll recv_address;
    int flags = 0;
    socklen_t socklen = (sizeof (struct sockaddr_ll));
    ssize_t rret = recvfrom(sock, recvbuf, (sizeof (recvbuf)), flags,
                            (struct sockaddr *)&recv_address, &socklen);
    if (rret < 0) {
      perror("recvfrom");
      exit(EXIT_FAILURE);
    }

    packet::parse(recvbuf, rret, &p);
    int dhcp4_options_length = rret - (packet::dhcp4_offset + (offsetof (dhcp4::message, options)));
    dhcp4::parse_options(p.dhcp4, dhcp4_options_length, &options);
    print_message(p, options);

    assert(p.dhcp4->op == dhcp4::op::bootreply);
    assert(options.message_type == dhcp4::message_type::dhcpoffer);
  }

  //////////////////////////////////////////////////////////////////////
  // dhcp send request
  //////////////////////////////////////////////////////////////////////

  {
    dhcp4::message_parameters params = {
      .requested_ip_address = p.dhcp4->yiaddr,
    };

    int length = packet::make(sendbuf,
                              dhcp4::op::bootrequest,
                              eth_source_address,
                              eth_destination_address,
                              eth_source_address, // eth_client_address
                              ip4_source_address,
                              ip4_destination_address,
                              68, // udp4_source_port
                              67, // udp4_destination_port
                              dhcp_transaction_id,
                              dhcp4::message_type::dhcprequest,
                              &params);

    sock::send(sock, ifa_index, sendbuf, length, eth_destination_address);
  }

  //////////////////////////////////////////////////////////////////////
  // dhcp recv ack
  //////////////////////////////////////////////////////////////////////

  {
    struct sockaddr_ll recv_address;
    int flags = 0;
    socklen_t socklen = (sizeof (struct sockaddr_ll));
    ssize_t rret = recvfrom(sock, recvbuf, (sizeof (recvbuf)), flags,
                            (struct sockaddr *)&recv_address, &socklen);
    if (rret < 0) {
      perror("recvfrom");
      exit(EXIT_FAILURE);
    }

    packet::parse(recvbuf, rret, &p);
    int dhcp4_options_length = rret - (packet::dhcp4_offset + (offsetof (dhcp4::message, options)));
    dhcp4::parse_options(p.dhcp4, dhcp4_options_length, &options);
    print_message(p, options);

    assert(p.dhcp4->op == dhcp4::op::bootreply);
    assert(options.message_type == dhcp4::message_type::dhcpack);
  }

  //////////////////////////////////////////////////////////////////////
  // interface configure
  //////////////////////////////////////////////////////////////////////

  uint32_t mask = ntohl(options.subnet_mask);
  uint8_t prefix_length = 32 - __builtin_ctz(mask);
  printf("prefix_length %d\n", prefix_length);

  interface::configure(ifa_index,
                       prefix_length,
                       p.dhcp4->yiaddr,
                       options.router);

  //////////////////////////////////////////////////////////////////////
  // dns configure
  //////////////////////////////////////////////////////////////////////

  int dfd = open("/etc/resolv.conf", O_CREAT | O_WRONLY | O_TRUNC);
  if (dfd < 0) {
    perror("open");
    exit(EXIT_FAILURE);
  }

  char dbuf[1024];
  int dbuflen = snprintf(dbuf, (sizeof (dbuf)), "nameserver %s\n",
                         ip4::tostr(options.domain_name_server));
  if (dbuflen < 0) {
    perror("snprintf");
    exit(EXIT_FAILURE);
  }

  ssize_t dret = write(dfd, dbuf, dbuflen);
  if (dret < 0) {
    perror("write");
    exit(EXIT_FAILURE);
  }

  //////////////////////////////////////////////////////////////////////
  // exit
  //////////////////////////////////////////////////////////////////////

  close(dfd);
  close(sock);
  exit(EXIT_SUCCESS);
}