nettools/net/ip.go

package net_utils

import (
	"encoding/binary"
	"errors"
	"io"
	"net"
	"net/http"

	common_utils "nettools/common"
)

var (
	ErrInitializingRequest = errors.New("error while initializing the request")
	ErrReadingBody         = errors.New("err while reading the body")
	ErrDialingServ         = errors.New("err while dealing the server")
	ErrInterfaceNotFound   = errors.New("provided network interface name wasn't found")
)

const (
	DEFAULT_HTTP_PORT  = 80
	DEFAULT_WS_PORT    = 80
	DEFAULT_WSS_PORT   = 443
	DEFAULT_HTTPS_PORT = 443
	DEFAULT_GRPC_PORT  = 9090
)

const (
	// network masks
	MASK8  uint32 = 0b11111111_00000000_00000000_00000000
	MASK12 uint32 = 0b11111111_11110000_00000000_00000000
	MASK16 uint32 = 0b11111111_11111111_00000000_00000000
	MASK24 uint32 = 0b11111111_11111111_11111111_00000000
	MASK32 uint32 = 0b11111111_11111111_11111111_11111111
	// reserved IP adresses
	IP_192_168_0_0 uint32 = 0b11000000_10101000_00000000_00000000
	IP_172_16_0_0  uint32 = 0b10101100_00010000_00000000_00000000
	IP_10_0_0_0    uint32 = 0b00001010_00000000_00000000_00000000
	// reserved for Local Network IP addresses
	PRESERVED_IP_RANGE_192 uint32 = IP_192_168_0_0 & MASK16
	PRESERVED_IP_RANGE_172 uint32 = IP_172_16_0_0 & MASK12
	PRESERVED_IP_RANGE_10  uint32 = IP_10_0_0_0 & MASK8
)

func MaskToBytes[T common_utils.Int](mask T) [4]uint8 {
	if mask > 32 {
		panic("mask is invalid: value out of range")
	}
	var out [4]uint8
	for i := 0; i < 4; i++ {
		if mask >= 8 {
			out[i] = 0b11111111
			mask -= 8
		} else {
			out[i] = 1<<mask - 1
			out[i] = out[i] << (8 - mask)
			break
		}
	}
	return out
}

func BytesToUint32(in []uint8) (uint32, error) {
	bytes := make([]uint8, 4)
	if len(bytes) > 4 {
		return 0, errors.New("bad input value length, expected up to 4 bytes")
	}
	copy(in, bytes)
	return uint32(
		bytes[0])<<24 |
		uint32(bytes[1])<<16 |
		uint32(bytes[2])<<8 |
		uint32(bytes[3]), nil
}

type NetInterfaceNamesT = map[string]struct{}

// Those are ones I have on my machine, so they are default, lol
var DefaultNetInterfaceNames = NetInterfaceNamesT{
	"eth0":  {},
	"wlan0": {},
}

// Converts IP which is a byte array to an integer
// So it can be used with the bitmasks or be compared fast
func IpToInt(ip net.IP) uint32 {
	if len(ip) == 16 {
		return binary.BigEndian.Uint32(ip[12:16])
	}
	return binary.BigEndian.Uint32(ip)
}

func GetWanIP(ipv4 bool) (net.IP, error) {
	url := "http://4.ident.me"
	if !ipv4 {
		url = "http://6.ident.me"
	}

	req, err := http.Get(url)
	if err != nil {
		return nil, errors.Join(ErrInitializingRequest, err)
	}
	defer req.Body.Close()

	body, err := io.ReadAll(req.Body)
	if err != nil {
		return nil, errors.Join(ErrReadingBody, err)
	}
	return net.ParseIP(string(body)), err
}

func GetLanIP(interfaceNames NetInterfaceNamesT) (net.IP, error) {
	if interfaceNames == nil {
		interfaceNames = DefaultNetInterfaceNames
	}

	ifaces, err := net.Interfaces()
	if err != nil {
		return nil, err
	}

	for _, i := range ifaces {
		if i.Name != "" {
			_, whitelisted := interfaceNames[i.Name]
			if !whitelisted {
				continue
			}
		}
		addrs, err := i.Addrs()
		if err != nil {
			return nil, err
		}

		for _, addr := range addrs {
			var ip net.IP
			switch v := addr.(type) {
			case *net.IPNet:
				ip = v.IP
			case *net.IPAddr:
				ip = v.IP
			}

			intIP := IpToInt(ip)
			if intIP&MASK16 == PRESERVED_IP_RANGE_192 ||
				intIP&MASK12 == PRESERVED_IP_RANGE_172 ||
				intIP&MASK8 == PRESERVED_IP_RANGE_10 {
				return ip, nil
			}
		}
	}
	return nil, ErrInterfaceNotFound
}