add support for build tag to allow to disable some features

The following build tags are available:

- "nogcs", disable Google Cloud Storage backend
- "nos3", disable S3 Compabible Object Storage backends
- "nobolt", disable Bolt data provider
- "nomysql", disable MySQL data provider
- "nopgsql", disable PostgreSQL data provider
- "nosqlite", disable SQLite data provider
- "noportable", disable portable mode

service/service_portable.go

@@ -0,0 +1,126 @@
+// +build !noportable
+
+package service
+
+import (
+	"fmt"
+	"math/rand"
+	"os"
+	"os/signal"
+	"path/filepath"
+	"strings"
+	"syscall"
+	"time"
+
+	"github.com/grandcat/zeroconf"
+
+	"github.com/drakkan/sftpgo/config"
+	"github.com/drakkan/sftpgo/dataprovider"
+	"github.com/drakkan/sftpgo/logger"
+	"github.com/drakkan/sftpgo/sftpd"
+	"github.com/drakkan/sftpgo/utils"
+)
+
+// StartPortableMode starts the service in portable mode
+func (s *Service) StartPortableMode(sftpdPort int, enabledSSHCommands []string, advertiseService, advertiseCredentials bool) error {
+	if s.PortableMode != 1 {
+		return fmt.Errorf("service is not configured for portable mode")
+	}
+	var err error
+	rand.Seed(time.Now().UnixNano())
+	if len(s.PortableUser.Username) == 0 {
+		s.PortableUser.Username = "user"
+	}
+	if len(s.PortableUser.PublicKeys) == 0 && len(s.PortableUser.Password) == 0 {
+		var b strings.Builder
+		for i := 0; i < 8; i++ {
+			b.WriteRune(chars[rand.Intn(len(chars))])
+		}
+		s.PortableUser.Password = b.String()
+	}
+	dataProviderConf := config.GetProviderConf()
+	dataProviderConf.Driver = dataprovider.MemoryDataProviderName
+	dataProviderConf.Name = ""
+	dataProviderConf.CredentialsPath = filepath.Join(os.TempDir(), "credentials")
+	config.SetProviderConf(dataProviderConf)
+	httpdConf := config.GetHTTPDConfig()
+	httpdConf.BindPort = 0
+	config.SetHTTPDConfig(httpdConf)
+	sftpdConf := config.GetSFTPDConfig()
+	sftpdConf.MaxAuthTries = 12
+	if sftpdPort > 0 {
+		sftpdConf.BindPort = sftpdPort
+	} else {
+		// dynamic ports starts from 49152
+		sftpdConf.BindPort = 49152 + rand.Intn(15000)
+	}
+	if utils.IsStringInSlice("*", enabledSSHCommands) {
+		sftpdConf.EnabledSSHCommands = sftpd.GetSupportedSSHCommands()
+	} else {
+		sftpdConf.EnabledSSHCommands = enabledSSHCommands
+	}
+	config.SetSFTPDConfig(sftpdConf)
+
+	err = s.Start()
+	if err != nil {
+		return err
+	}
+	var mDNSService *zeroconf.Server
+	if advertiseService {
+		version := utils.GetAppVersion()
+		meta := []string{
+			fmt.Sprintf("version=%v", version.GetVersionAsString()),
+		}
+		if advertiseCredentials {
+			logger.InfoToConsole("Advertising credentials via multicast DNS")
+			meta = append(meta, fmt.Sprintf("user=%v", s.PortableUser.Username))
+			if len(s.PortableUser.Password) > 0 {
+				meta = append(meta, fmt.Sprintf("password=%v", s.PortableUser.Password))
+			} else {
+				logger.InfoToConsole("Unable to advertise key based credentials via multicast DNS, we don't have the private key")
+			}
+		}
+		mDNSService, err = zeroconf.Register(
+			fmt.Sprintf("SFTPGo portable %v", sftpdConf.BindPort), // service instance name
+			"_sftp-ssh._tcp",   // service type and protocol
+			"local.",           // service domain
+			sftpdConf.BindPort, // service port
+			meta,               // service metadata
+			nil,                // register on all network interfaces
+		)
+		if err != nil {
+			mDNSService = nil
+			logger.WarnToConsole("Unable to advertise SFTP service via multicast DNS: %v", err)
+		} else {
+			logger.InfoToConsole("SFTP service advertised via multicast DNS")
+		}
+	}
+	sig := make(chan os.Signal, 1)
+	signal.Notify(sig, os.Interrupt, syscall.SIGTERM)
+	go func() {
+		<-sig
+		if mDNSService != nil {
+			logger.InfoToConsole("unregistering multicast DNS service")
+			mDNSService.Shutdown()
+		}
+		s.Stop()
+	}()
+
+	logger.InfoToConsole("Portable mode ready, SFTP port: %v, user: %#v, password: %#v, public keys: %v, directory: %#v, "+
+		"permissions: %+v, enabled ssh commands: %v file extensions filters: %+v", sftpdConf.BindPort, s.PortableUser.Username,
+		s.PortableUser.Password, s.PortableUser.PublicKeys, s.getPortableDirToServe(), s.PortableUser.Permissions,
+		sftpdConf.EnabledSSHCommands, s.PortableUser.Filters.FileExtensions)
+	return nil
+}
+
+func (s *Service) getPortableDirToServe() string {
+	var dirToServe string
+	if s.PortableUser.FsConfig.Provider == 1 {
+		dirToServe = s.PortableUser.FsConfig.S3Config.KeyPrefix
+	} else if s.PortableUser.FsConfig.Provider == 2 {
+		dirToServe = s.PortableUser.FsConfig.GCSConfig.KeyPrefix
+	} else {
+		dirToServe = s.PortableUser.HomeDir
+	}
+	return dirToServe
+}