util.go

package util

import (
	"bufio"
	"bytes"
	"encoding/gob"
	"encoding/json"
	"errors"
	"fmt"
	"hash/crc32"
	"io"
	"io/fs"
	"math/rand"
	"net"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"strings"
	"text/template"
	"time"

	"github.com/ngoduykhanh/wireguard-ui/store"
	"github.com/ngoduykhanh/wireguard-ui/telegram"
	"github.com/skip2/go-qrcode"
	"golang.org/x/mod/sumdb/dirhash"

	externalip "github.com/glendc/go-external-ip"
	"github.com/labstack/gommon/log"
	"github.com/ngoduykhanh/wireguard-ui/model"
	"github.com/sdomino/scribble"
)

var qrCodeSettings = model.QRCodeSettings{
	Enabled:    true,
	IncludeDNS: true,
	IncludeMTU: true,
}

// BuildClientConfig to create wireguard client config string
func BuildClientConfig(client model.Client, server model.Server, setting model.GlobalSetting) string {
	// Interface section
	clientAddress := fmt.Sprintf("Address = %s\n", strings.Join(client.AllocatedIPs, ","))
	clientPrivateKey := fmt.Sprintf("PrivateKey = %s\n", client.PrivateKey)
	clientDNS := ""
	if client.UseServerDNS {
		clientDNS = fmt.Sprintf("DNS = %s\n", strings.Join(setting.DNSServers, ","))
	}
	clientMTU := ""
	if setting.MTU > 0 {
		clientMTU = fmt.Sprintf("MTU = %d\n", setting.MTU)
	}

	// Peer section
	peerPublicKey := fmt.Sprintf("PublicKey = %s\n", server.KeyPair.PublicKey)
	peerPresharedKey := ""
	if client.PresharedKey != "" {
		peerPresharedKey = fmt.Sprintf("PresharedKey = %s\n", client.PresharedKey)
	}

	peerAllowedIPs := fmt.Sprintf("AllowedIPs = %s\n", strings.Join(client.AllowedIPs, ","))

	desiredHost := setting.EndpointAddress
	desiredPort := server.Interface.ListenPort
	if strings.Contains(desiredHost, ":") {
		split := strings.Split(desiredHost, ":")
		desiredHost = split[0]
		if n, err := strconv.Atoi(split[1]); err == nil {
			desiredPort = n
		} else {
			log.Error("Endpoint appears to be incorrectly formatted: ", err)
		}
	}
	peerEndpoint := fmt.Sprintf("Endpoint = %s:%d\n", desiredHost, desiredPort)

	peerPersistentKeepalive := ""
	if setting.PersistentKeepalive > 0 {
		peerPersistentKeepalive = fmt.Sprintf("PersistentKeepalive = %d\n", setting.PersistentKeepalive)
	}

	// build the config as string
	strConfig := "[Interface]\n" +
		clientAddress +
		clientPrivateKey +
		clientDNS +
		clientMTU +
		"\n[Peer]\n" +
		peerPublicKey +
		peerPresharedKey +
		peerAllowedIPs +
		peerEndpoint +
		peerPersistentKeepalive

	return strConfig
}

// ClientDefaultsFromEnv to read the default values for creating a new client from the environment or use sane defaults
func ClientDefaultsFromEnv() model.ClientDefaults {
	clientDefaults := model.ClientDefaults{}
	clientDefaults.AllowedIps = LookupEnvOrStrings(DefaultClientAllowedIpsEnvVar, []string{"0.0.0.0/0"})
	clientDefaults.ExtraAllowedIps = LookupEnvOrStrings(DefaultClientExtraAllowedIpsEnvVar, []string{})
	clientDefaults.UseServerDNS = LookupEnvOrBool(DefaultClientUseServerDNSEnvVar, true)
	clientDefaults.EnableAfterCreation = LookupEnvOrBool(DefaultClientEnableAfterCreationEnvVar, true)

	return clientDefaults
}

// ContainsCIDR to check if ipnet1 contains ipnet2
// https://stackoverflow.com/a/40406619/6111641
// https://go.dev/play/p/Q4J-JEN3sF
func ContainsCIDR(ipnet1, ipnet2 *net.IPNet) bool {
	ones1, _ := ipnet1.Mask.Size()
	ones2, _ := ipnet2.Mask.Size()
	return ones1 <= ones2 && ipnet1.Contains(ipnet2.IP)
}

// ValidateCIDR to validate a network CIDR
func ValidateCIDR(cidr string) bool {
	_, _, err := net.ParseCIDR(cidr)
	if err != nil {
		return false
	}
	return true
}

// ValidateCIDRList to validate a list of network CIDR
func ValidateCIDRList(cidrs []string, allowEmpty bool) bool {
	for _, cidr := range cidrs {
		if allowEmpty {
			if len(cidr) > 0 {
				if ValidateCIDR(cidr) == false {
					return false
				}
			}
		} else {
			if ValidateCIDR(cidr) == false {
				return false
			}
		}
	}
	return true
}

// ValidateAllowedIPs to validate allowed ip addresses in CIDR format
func ValidateAllowedIPs(cidrs []string) bool {
	if ValidateCIDRList(cidrs, false) == false {
		return false
	}
	return true
}

// ValidateExtraAllowedIPs to validate extra Allowed ip addresses, allowing empty strings
func ValidateExtraAllowedIPs(cidrs []string) bool {
	if ValidateCIDRList(cidrs, true) == false {
		return false
	}
	return true
}

// ValidateServerAddresses to validate allowed ip addresses in CIDR format
func ValidateServerAddresses(cidrs []string) bool {
	if ValidateCIDRList(cidrs, false) == false {
		return false
	}
	return true
}

// ValidateIPAddress to validate the IPv4 and IPv6 address
func ValidateIPAddress(ip string) bool {
	if net.ParseIP(ip) == nil {
		return false
	}
	return true
}

// ValidateIPAddressList to validate a list of IPv4 and IPv6 addresses
func ValidateIPAddressList(ips []string) bool {
	for _, ip := range ips {
		if ValidateIPAddress(ip) == false {
			return false
		}
	}
	return true
}

// GetInterfaceIPs to get local machine's interface ip addresses
func GetInterfaceIPs() ([]model.Interface, error) {
	// get machine's interfaces
	ifaces, err := net.Interfaces()
	if err != nil {
		return nil, err
	}

	var interfaceList []model.Interface

	// get interface's ip addresses
	for _, i := range ifaces {
		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
			}
			if ip == nil || ip.IsLoopback() {
				continue
			}
			ip = ip.To4()
			if ip == nil {
				continue
			}

			iface := model.Interface{}
			iface.Name = i.Name
			iface.IPAddress = ip.String()
			interfaceList = append(interfaceList, iface)
		}
	}
	return interfaceList, err
}

// GetPublicIP to get machine's public ip address
func GetPublicIP() (model.Interface, error) {
	// set time out to 5 seconds
	cfg := externalip.ConsensusConfig{}
	cfg.Timeout = time.Second * 5
	consensus := externalip.NewConsensus(&cfg, nil)

	// add trusted voters
	consensus.AddVoter(externalip.NewHTTPSource("https://checkip.amazonaws.com/"), 1)
	consensus.AddVoter(externalip.NewHTTPSource("http://whatismyip.akamai.com"), 1)
	consensus.AddVoter(externalip.NewHTTPSource("https://ifconfig.top"), 1)

	publicInterface := model.Interface{}
	publicInterface.Name = "Public Address"

	ip, err := consensus.ExternalIP()
	if err != nil {
		publicInterface.IPAddress = "N/A"
	} else {
		publicInterface.IPAddress = ip.String()
	}

	// error handling happened above, no need to pass it through
	return publicInterface, nil
}

// GetIPFromCIDR get ip from CIDR
func GetIPFromCIDR(cidr string) (string, error) {
	ip, _, err := net.ParseCIDR(cidr)
	if err != nil {
		return "", err
	}
	return ip.String(), nil
}

// GetAllocatedIPs to get all ip addresses allocated to clients and server
func GetAllocatedIPs(ignoreClientID string) ([]string, error) {
	allocatedIPs := make([]string, 0)

	// initialize database directory
	dir := "./db"
	db, err := scribble.New(dir, nil)
	if err != nil {
		return nil, err
	}

	// read server information
	serverInterface := model.ServerInterface{}
	if err := db.Read("server", "interfaces", &serverInterface); err != nil {
		return nil, err
	}

	// append server's addresses to the result
	for _, cidr := range serverInterface.Addresses {
		ip, err := GetIPFromCIDR(cidr)
		if err != nil {
			return nil, err
		}
		allocatedIPs = append(allocatedIPs, ip)
	}

	// read client information
	records, err := db.ReadAll("clients")
	if err != nil {
		return nil, err
	}

	// append client's addresses to the result
	for _, f := range records {
		client := model.Client{}
		if err := json.Unmarshal(f, &client); err != nil {
			return nil, err
		}

		if client.ID != ignoreClientID {
			for _, cidr := range client.AllocatedIPs {
				ip, err := GetIPFromCIDR(cidr)
				if err != nil {
					return nil, err
				}
				allocatedIPs = append(allocatedIPs, ip)
			}
		}
	}

	return allocatedIPs, nil
}

// inc from https://play.golang.org/p/m8TNTtygK0
func inc(ip net.IP) {
	for j := len(ip) - 1; j >= 0; j-- {
		ip[j]++
		if ip[j] > 0 {
			break
		}
	}
}

// GetBroadcastIP func to get the broadcast ip address of a network
func GetBroadcastIP(n *net.IPNet) net.IP {
	var broadcast net.IP
	if len(n.IP) == 4 {
		broadcast = net.ParseIP("0.0.0.0").To4()
	} else {
		broadcast = net.ParseIP("::")
	}
	for i := 0; i < len(n.IP); i++ {
		broadcast[i] = n.IP[i] | ^n.Mask[i]
	}
	return broadcast
}

// GetBroadcastAndNetworkAddrsLookup get the ip address that can't be used with current server interfaces
func GetBroadcastAndNetworkAddrsLookup(interfaceAddresses []string) map[string]bool {
	list := make(map[string]bool)
	for _, ifa := range interfaceAddresses {
		_, netAddr, err := net.ParseCIDR(ifa)
		if err != nil {
			continue
		}

		broadcastAddr := GetBroadcastIP(netAddr).String()
		networkAddr := netAddr.IP.String()
		list[broadcastAddr] = true
		list[networkAddr] = true
	}
	return list
}

// GetAvailableIP get the ip address that can be allocated from an CIDR
// We need interfaceAddresses to find real broadcast and network addresses
func GetAvailableIP(cidr string, allocatedList, interfaceAddresses []string) (string, error) {
	ip, netAddr, err := net.ParseCIDR(cidr)
	if err != nil {
		return "", err
	}

	unavailableIPs := GetBroadcastAndNetworkAddrsLookup(interfaceAddresses)

	for ip := ip.Mask(netAddr.Mask); netAddr.Contains(ip); inc(ip) {
		available := true
		suggestedAddr := ip.String()
		for _, allocatedAddr := range allocatedList {
			if suggestedAddr == allocatedAddr {
				available = false
				break
			}
		}
		if available && !unavailableIPs[suggestedAddr] {
			return suggestedAddr, nil
		}
	}

	return "", errors.New("no more available ip address")
}

// ValidateIPAllocation to validate the list of client's ip allocation
// They must have a correct format and available in serverAddresses space
func ValidateIPAllocation(serverAddresses []string, ipAllocatedList []string, ipAllocationList []string) (bool, error) {
	for _, clientCIDR := range ipAllocationList {
		ip, _, _ := net.ParseCIDR(clientCIDR)

		// clientCIDR must be in CIDR format
		if ip == nil {
			return false, fmt.Errorf("invalid ip allocation input %s. Must be in CIDR format", clientCIDR)
		}

		// return false immediately if the ip is already in use (in ipAllocatedList)
		for _, item := range ipAllocatedList {
			if item == ip.String() {
				return false, fmt.Errorf("IP %s already allocated", ip)
			}
		}

		// even if it is not in use, we still need to check if it
		// belongs to a network of the server.
		var isValid = false
		for _, serverCIDR := range serverAddresses {
			_, serverNet, _ := net.ParseCIDR(serverCIDR)
			if serverNet.Contains(ip) {
				isValid = true
				break
			}
		}

		// current ip allocation is valid, check the next one
		if isValid {
			continue
		} else {
			return false, fmt.Errorf("IP %s does not belong to any network addresses of WireGuard server", ip)
		}
	}

	return true, nil
}

// findSubnetRangeForIP to find first SR for IP, and cache the match
func findSubnetRangeForIP(cidr string) (uint16, error) {
	ip, _, err := net.ParseCIDR(cidr)
	if err != nil {
		return 0, err
	}

	if srName, ok := IPToSubnetRange[ip.String()]; ok {
		return srName, nil
	}

	for srIndex, sr := range SubnetRangesOrder {
		for _, srCIDR := range SubnetRanges[sr] {
			if srCIDR.Contains(ip) {
				IPToSubnetRange[ip.String()] = uint16(srIndex)
				return uint16(srIndex), nil
			}
		}
	}
	return 0, fmt.Errorf("subnet range not found for this IP")
}

// FillClientSubnetRange to fill subnet ranges client belongs to, does nothing if SRs are not found
func FillClientSubnetRange(client model.ClientData) model.ClientData {
	cl := *client.Client
	for _, ip := range cl.AllocatedIPs {
		sr, err := findSubnetRangeForIP(ip)
		if err != nil {
			continue
		}
		cl.SubnetRanges = append(cl.SubnetRanges, SubnetRangesOrder[sr])
	}
	return model.ClientData{
		Client: &cl,
		QRCode: client.QRCode,
	}
}

// ValidateAndFixSubnetRanges to check if subnet ranges are valid for the server configuration
// Removes all non-valid CIDRs
func ValidateAndFixSubnetRanges(db store.IStore) error {
	if len(SubnetRangesOrder) == 0 {
		return nil
	}

	server, err := db.GetServer()
	if err != nil {
		return err
	}
	var serverSubnets []*net.IPNet
	for _, addr := range server.Interface.Addresses {
		addr = strings.TrimSpace(addr)
		_, netAddr, err := net.ParseCIDR(addr)
		if err != nil {
			return err
		}
		serverSubnets = append(serverSubnets, netAddr)
	}

	for _, rng := range SubnetRangesOrder {
		cidrs := SubnetRanges[rng]
		if len(cidrs) > 0 {
			newCIDRs := make([]*net.IPNet, 0)
			for _, cidr := range cidrs {
				valid := false

				for _, serverSubnet := range serverSubnets {
					if ContainsCIDR(serverSubnet, cidr) {
						valid = true
						break
					}
				}

				if valid {
					newCIDRs = append(newCIDRs, cidr)
				} else {
					log.Warnf("[%v] CIDR is outside of all server subnets: %v. Removed.", rng, cidr)
				}
			}

			if len(newCIDRs) > 0 {
				SubnetRanges[rng] = newCIDRs
			} else {
				delete(SubnetRanges, rng)
				log.Warnf("[%v] No valid CIDRs in this subnet range. Removed.", rng)
			}
		}
	}

	return nil
}

// GetSubnetRangesString to get a formatted string, representing active subnet ranges
func GetSubnetRangesString() string {
	if len(SubnetRangesOrder) == 0 {
		return ""
	}

	strB := strings.Builder{}

	for _, rng := range SubnetRangesOrder {
		cidrs := SubnetRanges[rng]
		if len(cidrs) > 0 {
			strB.WriteString(rng)
			strB.WriteString(":[")
			first := true
			for _, cidr := range cidrs {
				if !first {
					strB.WriteString(", ")
				}
				strB.WriteString(cidr.String())
				first = false
			}
			strB.WriteString("]  ")
		}
	}

	return strings.TrimSpace(strB.String())
}

// WriteWireGuardServerConfig to write Wireguard server config. e.g. wg0.conf
func WriteWireGuardServerConfig(tmplDir fs.FS, serverConfig model.Server, clientDataList []model.ClientData, usersList []model.User, globalSettings model.GlobalSetting) error {
	var tmplWireguardConf string

	// if set, read wg.conf template from WgConfTemplate
	if len(WgConfTemplate) > 0 {
		fileContentBytes, err := os.ReadFile(WgConfTemplate)
		if err != nil {
			return err
		}
		tmplWireguardConf = string(fileContentBytes)
	} else {
		// read default wg.conf template file to string
		fileContent, err := StringFromEmbedFile(tmplDir, "wg.conf")
		if err != nil {
			return err
		}
		tmplWireguardConf = fileContent
	}

	// escape multiline notes
	escapedClientDataList := []model.ClientData{}
	for _, cd := range clientDataList {
		if cd.Client.AdditionalNotes != "" {
			cd.Client.AdditionalNotes = strings.ReplaceAll(cd.Client.AdditionalNotes, "\n", "\n# ")
		}
		escapedClientDataList = append(escapedClientDataList, cd)
	}

	// parse the template
	t, err := template.New("wg_config").Parse(tmplWireguardConf)
	if err != nil {
		return err
	}

	// write config file to disk
	f, err := os.Create(globalSettings.ConfigFilePath)
	if err != nil {
		return err
	}

	config := map[string]interface{}{
		"serverConfig":   serverConfig,
		"clientDataList": escapedClientDataList,
		"globalSettings": globalSettings,
		"usersList":      usersList,
	}

	err = t.Execute(f, config)
	if err != nil {
		return err
	}
	f.Close()

	return nil
}

// SendRequestedConfigsToTelegram to send client all their configs. Returns failed configs list.
func SendRequestedConfigsToTelegram(db store.IStore, userid int64) []string {
	failedList := make([]string, 0)
	TgUseridToClientIDMutex.RLock()
	if clids, found := TgUseridToClientID[userid]; found && len(clids) > 0 {
		TgUseridToClientIDMutex.RUnlock()

		for _, clid := range clids {
			clientData, err := db.GetClientByID(clid, qrCodeSettings)
			if err != nil {
				// return fmt.Errorf("unable to get client")
				failedList = append(failedList, clid)
				continue
			}

			// build config
			server, _ := db.GetServer()
			globalSettings, _ := db.GetGlobalSettings()
			config := BuildClientConfig(*clientData.Client, server, globalSettings)
			configData := []byte(config)
			var qrData []byte

			if clientData.Client.PrivateKey != "" {
				qrData, err = qrcode.Encode(config, qrcode.Medium, 512)
				if err != nil {
					// return fmt.Errorf("unable to encode qr")
					failedList = append(failedList, clientData.Client.Name)
					continue
				}
			}

			userid, err := strconv.ParseInt(clientData.Client.TgUserid, 10, 64)
			if err != nil {
				// return fmt.Errorf("tg usrid is unreadable")
				failedList = append(failedList, clientData.Client.Name)
				continue
			}

			err = telegram.SendConfig(userid, clientData.Client.Name, configData, qrData, true)
			if err != nil {
				failedList = append(failedList, clientData.Client.Name)
				continue
			}
			time.Sleep(2 * time.Second)
		}
	} else {
		TgUseridToClientIDMutex.RUnlock()
	}
	return failedList
}

func LookupEnvOrString(key string, defaultVal string) string {
	if val, ok := os.LookupEnv(key); ok {
		return val
	}
	return defaultVal
}

func LookupEnvOrBool(key string, defaultVal bool) bool {
	if val, ok := os.LookupEnv(key); ok {
		v, err := strconv.ParseBool(val)
		if err != nil {
			fmt.Fprintf(os.Stderr, "LookupEnvOrBool[%s]: %v\n", key, err)
		}
		return v
	}
	return defaultVal
}

func LookupEnvOrInt(key string, defaultVal int) int {
	if val, ok := os.LookupEnv(key); ok {
		v, err := strconv.Atoi(val)
		if err != nil {
			fmt.Fprintf(os.Stderr, "LookupEnvOrInt[%s]: %v\n", key, err)
		}
		return v
	}
	return defaultVal
}

func LookupEnvOrStrings(key string, defaultVal []string) []string {
	if val, ok := os.LookupEnv(key); ok {
		return strings.Split(val, ",")
	}
	return defaultVal
}

func LookupEnvOrFile(key string, defaultVal string) string {
	if val, ok := os.LookupEnv(key); ok {
		if file, err := os.Open(val); err == nil {
			var content string
			scanner := bufio.NewScanner(file)
			for scanner.Scan() {
				content += scanner.Text()
			}
			return content
		}
	}
	return defaultVal
}

func StringFromEmbedFile(embed fs.FS, filename string) (string, error) {
	file, err := embed.Open(filename)
	if err != nil {
		return "", err
	}
	content, err := io.ReadAll(file)
	if err != nil {
		return "", err
	}
	return string(content), nil
}

func ParseLogLevel(lvl string) (log.Lvl, error) {
	switch strings.ToLower(lvl) {
	case "debug":
		return log.DEBUG, nil
	case "info":
		return log.INFO, nil
	case "warn":
		return log.WARN, nil
	case "error":
		return log.ERROR, nil
	case "off":
		return log.OFF, nil
	default:
		return log.DEBUG, fmt.Errorf("not a valid log level: %s", lvl)
	}
}

// GetCurrentHash returns current hashes
func GetCurrentHash(db store.IStore) (string, string) {
	hashClients, _ := dirhash.HashDir(path.Join(db.GetPath(), "clients"), "prefix", dirhash.Hash1)
	files := append([]string(nil), "prefix/global_settings.json", "prefix/interfaces.json", "prefix/keypair.json")

	osOpen := func(name string) (io.ReadCloser, error) {
		return os.Open(filepath.Join(path.Join(db.GetPath(), "server"), strings.TrimPrefix(name, "prefix")))
	}
	hashServer, _ := dirhash.Hash1(files, osOpen)

	return hashClients, hashServer
}

func HashesChanged(db store.IStore) bool {
	old, _ := db.GetHashes()
	oldClient := old.Client
	oldServer := old.Server
	newClient, newServer := GetCurrentHash(db)

	if oldClient != newClient {
		//fmt.Println("Hash for client differs")
		return true
	}
	if oldServer != newServer {
		//fmt.Println("Hash for server differs")
		return true
	}
	return false
}

func UpdateHashes(db store.IStore) error {
	var clientServerHashes model.ClientServerHashes
	clientServerHashes.Client, clientServerHashes.Server = GetCurrentHash(db)
	return db.SaveHashes(clientServerHashes)
}

func RandomString(length int) string {
	var seededRand = rand.New(rand.NewSource(time.Now().UnixNano()))
	charset := "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	b := make([]byte, length)
	for i := range b {
		b[i] = charset[seededRand.Intn(len(charset))]
	}
	return string(b)
}

func ManagePerms(path string) error {
	err := os.Chmod(path, 0600)
	return err
}

func AddTgToClientID(userid int64, clientID string) {
	TgUseridToClientIDMutex.Lock()
	defer TgUseridToClientIDMutex.Unlock()

	if _, ok := TgUseridToClientID[userid]; ok && TgUseridToClientID[userid] != nil {
		TgUseridToClientID[userid] = append(TgUseridToClientID[userid], clientID)
	} else {
		TgUseridToClientID[userid] = []string{clientID}
	}
}

func UpdateTgToClientID(userid int64, clientID string) {
	TgUseridToClientIDMutex.Lock()
	defer TgUseridToClientIDMutex.Unlock()

	// Detach clientID from any existing userid
	for uid, cls := range TgUseridToClientID {
		if cls != nil {
			filtered := filterStringSlice(cls, clientID)
			if len(filtered) > 0 {
				TgUseridToClientID[uid] = filtered
			} else {
				delete(TgUseridToClientID, uid)
			}
		}
	}

	// Attach it to the new one
	if _, ok := TgUseridToClientID[userid]; ok && TgUseridToClientID[userid] != nil {
		TgUseridToClientID[userid] = append(TgUseridToClientID[userid], clientID)
	} else {
		TgUseridToClientID[userid] = []string{clientID}
	}
}

func RemoveTgToClientID(clientID string) {
	TgUseridToClientIDMutex.Lock()
	defer TgUseridToClientIDMutex.Unlock()

	// Detach clientID from any existing userid
	for uid, cls := range TgUseridToClientID {
		if cls != nil {
			filtered := filterStringSlice(cls, clientID)
			if len(filtered) > 0 {
				TgUseridToClientID[uid] = filtered
			} else {
				delete(TgUseridToClientID, uid)
			}
		}
	}
}

func filterStringSlice(s []string, excludedStr string) []string {
	filtered := s[:0]
	for _, v := range s {
		if v != excludedStr {
			filtered = append(filtered, v)
		}
	}
	return filtered
}

func GetDBUserCRC32(dbuser model.User) uint32 {
	buf := new(bytes.Buffer)
	enc := gob.NewEncoder(buf)
	if err := enc.Encode(dbuser); err != nil {
		panic("model.User is gob-incompatible, session verification is impossible")
	}
	return crc32.ChecksumIEEE(buf.Bytes())
}

func ConcatMultipleSlices(slices ...[]byte) []byte {
	var totalLen int

	for _, s := range slices {
		totalLen += len(s)
	}

	result := make([]byte, totalLen)

	var i int

	for _, s := range slices {
		i += copy(result[i:], s)
	}

	return result
}

func GetCookiePath() string {
	cookiePath := BasePath
	if cookiePath == "" {
		cookiePath = "/"
	}
	return cookiePath
}