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// Copyright (c) 2022 Johannes Stoelp
//
// dhcp protocol: https://datatracker.ietf.org/doc/html/rfc2131
// dhcp options : https://datatracker.ietf.org/doc/html/rfc2132
#ifndef DHCP_H
#define DHCP_H
#include "types.h"
#include <optional>
// -- Global constants.
constexpr u16 DHCP_SERVER_PORT = 67;
constexpr u16 DHCP_CLIENT_PORT = 68;
constexpr usize DHCP_MESSAGE_LEN = 576;
constexpr usize DHCP_MESSAGE_MIN_LEN = 243;
constexpr u32 DHCP_OPTION_COOKIE = 0x63538263;
enum class dhcp_operation : u8 {
BOOTREQUEST = 1,
BOOTREPLY,
};
enum class dhcp_option : u8 {
PAD = 0,
END = 255,
// Vendor Extensions.
SUBNET_MASK = 1,
ROUTER = 3,
DNS = 6,
// IP Layer Parameters per Interface.
BROADCAST_ADDR = 28,
// DHCP Extensions.
REQUESTED_IP = 50,
IP_ADDRESS_LEASE_TIME,
OPTION_OVERLOAD,
DHCP_MESSAGE_TYPE,
SERVER_IDENTIFIER,
PARAMETER_REQUEST_LIST,
MESSAGE,
MAX_DHCP_MESSAGE_SIZE,
RENEWAL_TIME_T1,
REBINDING_TIME_T2,
CLASS_ID,
CLIENT_ID,
};
// -- DHCP message.
enum class dhcp_message_type : u8 {
DHCP_DISCOVER = 1,
DHCP_OFFER,
DHCP_REQUEST,
DHCP_DECLINE,
DHCP_ACK,
DHCP_NAK,
DHCP_RELEAE,
};
struct dhcp_message {
dhcp_operation op;
u8 htype;
u8 hlen;
u8 hops;
u32 xid;
u16 secs;
u16 flags;
u32 ciaddr;
u32 yiaddr;
u32 siaddr;
u32 giaddr;
u8 chaddr[16];
u8 sname[64];
u8 file[128];
u32 cookie;
u8 options[312 - 4 /* cookie len */];
} __attribute__((packed));
static_assert(DHCP_MESSAGE_MIN_LEN == offsetof(dhcp_message, options) + 3 /* DHCP_MESSAGE_TYPE size */,
"Declare min size as dhcp_message with the DHCP_MESSAGE_TYPE option.");
// -- DHCP Utilities.
struct option_view {
const u8* data;
usize len;
};
// Search for the option with tag 'search_tag' in the options 'opt' of length 'len'.
std::optional<struct option_view> get_option(const u8* opt, usize len, dhcp_option search_tag);
template<typename T>
constexpr T get_opt_val(const u8* opt_data) {
T ret = 0;
for (size_t i = 0; i < sizeof(T); ++i) {
ret = (ret << 8) | *opt_data++;
}
return ret;
}
template<typename T>
u8* put_opt_val(u8* opt_data, T val) {
for (size_t i = sizeof(T); i; --i) {
*opt_data++ = (val >> ((i - 1) * 8)) & 0xff;
}
return opt_data;
}
#endif
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