Add MaxMind GeoIP2 database service with refreshable interface

internal/service/maxmind/mmdb/mmdb.go

@@ -0,0 +1,187 @@
+package mmdb
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/netip"
+	"os"
+	"sync"
+
+	"git.kor-elf.net/kor-elf-shield/geoip2"
+	"git.kor-elf.net/kor-elf-shield/geoip2/internal/pkg"
+
+	oschwaldGeoip2 "github.com/oschwald/geoip2-golang/v2"
+)
+
+// download is an interface for downloading MaxMind GeoIP2 database.
+type download interface {
+	// Download downloads MaxMind GeoIP2 database.
+	Download(dir string, ctx context.Context) error
+}
+
+type service struct {
+	// download is an interface for downloading MaxMind GeoIP2 database.
+	download download
+	// info is a function that returns information about the IP address.
+	info   info
+	logger geoip2.Logger
+	// dir is a directory for storing MaxMind GeoIP2 database.
+	dir *pkg.Dir
+
+	// isRefreshing is a flag that indicates whether the database is being refreshed.
+	isRefreshing bool
+	// mu is a mutex for synchronizing access to the reader.
+	mu sync.RWMutex
+	// reader is a MaxMind GeoIP2 database reader.
+	reader *oschwaldGeoip2.Reader
+}
+
+// info is a function that returns information about the IP address.
+// @param ip - IP address
+// @param reader - MaxMind GeoIP2 database reader
+// @return geoip2.Info - information about the IP address
+type info func(ip netip.Addr, reader *oschwaldGeoip2.Reader) (geoip2.Info, error)
+
+// NewMMDB creates a new MaxMind GeoIP2 database service.
+// @param download - an interface for downloading MaxMind GeoIP2 database
+// @param info - a function that returns information about the IP address
+// @param logger - a logger
+// @param dir - a directory for storing MaxMind GeoIP2 database
+// @return geoip2.RefreshableGeoIP2 - a MaxMind GeoIP2 database service
+func NewMMDB(download download, info info, logger geoip2.Logger, dir *pkg.Dir) geoip2.RefreshableGeoIP2 {
+	s := &service{
+		download: download,
+		logger:   logger,
+		dir:      dir,
+		info:     info,
+
+		mu: sync.RWMutex{},
+	}
+	s.init()
+	return s
+}
+
+// Info returns information about the IP address.
+// @param ip - IP address
+// @return geoip2.Info - information about the IP address
+// @return error - an error if the IP address could not be found
+func (s *service) Info(ip netip.Addr) (geoip2.Info, error) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	if s.reader == nil {
+		return geoip2.Info{}, errors.New("geoip reader is not ready")
+	}
+
+	return s.info(ip, s.reader)
+}
+
+// Refresh refreshes the MaxMind GeoIP2 database.
+// @param ctx - a context
+// @return error - an error if the database could not be refreshed
+func (s *service) Refresh(ctx context.Context) error {
+	if s.isRefreshing {
+		return fmt.Errorf("process is refreshing")
+	}
+	s.isRefreshing = true
+	defer func() {
+		s.isRefreshing = false
+	}()
+
+	if err := s.fetch(ctx); err != nil {
+		return err
+	}
+
+	newReader, err := s.openReader()
+	if err != nil {
+		return err
+	}
+
+	s.mu.Lock()
+	oldReader := s.reader
+	s.reader = newReader
+	s.mu.Unlock()
+
+	if oldReader != nil {
+		_ = oldReader.Close()
+	}
+
+	return nil
+}
+
+// Close closes the MaxMind GeoIP2 database.
+// @return error - an error if the database could not be closed
+func (s *service) Close() error {
+	if s.reader != nil {
+		return s.reader.Close()
+	}
+	return nil
+}
+
+// init initializes the MaxMind GeoIP2 database service.
+func (s *service) init() {
+	reader, err := s.openReader()
+	if err != nil {
+		go func() {
+			// If there is no data yet, then we try to get the data.
+			if err := s.Refresh(context.Background()); err != nil {
+				s.logger.Error(err)
+			}
+		}()
+		return
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.reader = reader
+}
+
+// openReader opens the MaxMind GeoIP2 database reader.
+// @return (*oschwaldGeoip2.Reader, error) - a MaxMind GeoIP2 database reader and an error if the database could not be opened
+// 1. If the database is already open, then it is returned.
+// 2. If the database is not open, then it is opened and returned.
+func (s *service) openReader() (*oschwaldGeoip2.Reader, error) {
+	path, err := pkg.FindMMDBFile(s.dir.PathCurrentDir)
+	if err != nil {
+		return nil, err
+	}
+	return oschwaldGeoip2.Open(path)
+}
+
+// fetch downloads the MaxMind GeoIP2 database.
+// @param ctx - a context
+// @return error - an error if the database could not be downloaded
+func (s *service) fetch(ctx context.Context) error {
+	tmpDir, err := s.dir.CreateRandomTmpDir()
+	if err != nil {
+		return err
+	}
+	defer func() {
+		if err := os.RemoveAll(tmpDir); err != nil {
+			s.logger.Error(err)
+		}
+	}()
+
+	if err := s.download.Download(tmpDir, ctx); err != nil {
+		return err
+	}
+
+	tmpDirForFiles, err := s.dir.CreateRandomTmpDir()
+	if err != nil {
+		return err
+	}
+	defer func() {
+		if err := os.RemoveAll(tmpDir); err != nil {
+			s.logger.Error(err)
+		}
+	}()
+
+	if err := pkg.MovingFiles(tmpDir, tmpDirForFiles); err != nil {
+		return err
+	}
+
+	if err := s.dir.ReplaceDirToCurrent(tmpDirForFiles); err != nil {
+		return err
+	}
+	return nil
+}