nat.h

#ifndef CURO_NAT_H
#define CURO_NAT_H

#include "icmp.h"
#include "ip.h"
#include "utils.h"
#include <cstdint>

#define NAT_GLOBAL_PORT_MIN 20000
#define NAT_GLOBAL_PORT_MAX 59999

#define NAT_GLOBAL_PORT_SIZE (NAT_GLOBAL_PORT_MAX - NAT_GLOBAL_PORT_MIN + 1)

#define NAT_ICMP_ID_SIZE 0xffff

// NATの方向
enum class nat_direction { outgoing, incoming };

// NATに対応しているプロトコル
enum class nat_protocol { udp, tcp, icmp, icmp_error };

struct nat_packet_head {
    union {
        struct { // tcp, udp
            uint16_t src_port;
            uint16_t dest_port;
            union {
                struct {
                    uint16_t len;
                    uint16_t checksum;
                } udp;
                struct {
                    uint32_t seq;
                    uint32_t ack_seq;
                    uint8_t offset;
                    uint8_t flag;
                    uint16_t window;
                    uint16_t checksum;
                    uint16_t urg_ptr;
                } tcp;
            };
        };
        struct { // icmp
            icmp_header header;
            uint16_t identify;
            uint16_t sequence;
        } icmp;
        struct { // icmp error
            icmp_header header;
            uint32_t unused;
            ip_header error_iph;
            uint16_t src_port;
            uint16_t dest_port;
        } icmp_error;
    };
};

struct nat_entry {
    uint32_t global_addr;
    uint32_t local_addr;
    uint16_t global_port;
    uint16_t local_port;
};

// ICMP, UDP, TCPのNATテーブルのセット
struct nat_entries {
    nat_entry icmp[NAT_ICMP_ID_SIZE];
    nat_entry udp[NAT_GLOBAL_PORT_SIZE];
    nat_entry tcp[NAT_GLOBAL_PORT_SIZE];
};

// NATの内側のip_deviceが持つNATデバイス
struct nat_device {
    uint32_t outside_addr; // 変換先のIPアドレス
    nat_entries *entries;  // NATテーブル
};

void dump_nat_tables();

bool nat_exec(ip_header *ip_packet, size_t len, nat_device *nat_dev,
              nat_protocol proto, nat_direction direction);

nat_entry *get_nat_entry_by_global(nat_entries *entries, nat_protocol proto,
                                   uint32_t addr, uint16_t port);
nat_entry *get_nat_entry_by_local(nat_entries *entries, nat_protocol proto,
                                  uint32_t addr, uint16_t port);
nat_entry *create_nat_entry(nat_entries *entries, nat_protocol proto,
                            uint16_t desired);

#endif // CURO_NAT_H