sftpd: add support for some SSH commands

md5sum, sha1sum are used by rclone.
cd, pwd improve the support for RemoteFiles mobile app.

These commands are all implemented inside SFTPGo so they work even
if the matching system commands are not available, for example on Windows

sftpd/scp.go

@@ -14,7 +14,6 @@ import (
 	"github.com/drakkan/sftpgo/dataprovider"
 	"github.com/drakkan/sftpgo/logger"
 	"github.com/drakkan/sftpgo/utils"
-	"golang.org/x/crypto/ssh"
 )
 
 var (
@@ -24,13 +23,8 @@ var (
 	newLine = []byte{0x0A}
 )
 
-type execMsg struct {
-	Command string
-}
-
 type scpCommand struct {
-	connection Connection
-	args       []string
+	sshCommand
 }
 
 func (c *scpCommand) handle() error {
@@ -494,16 +488,6 @@ func (c *scpCommand) handleDownload(filePath string) error {
 	return err
 }
 
-// returns the SCP destination path.
-// We ensure that the path is absolute and in SFTP (UNIX) format
-func (c *scpCommand) getDestPath() string {
-	destPath := filepath.ToSlash(c.args[len(c.args)-1])
-	if !filepath.IsAbs(destPath) {
-		destPath = "/" + destPath
-	}
-	return destPath
-}
-
 func (c *scpCommand) getCommandType() string {
 	return c.args[len(c.args)-2]
 }
@@ -597,21 +581,6 @@ func (c *scpCommand) sendProtocolMessage(message string) error {
 	return err
 }
 
-// sends the SCP command exit status
-func (c *scpCommand) sendExitStatus(err error) {
-	status := uint32(0)
-	if err != nil {
-		status = uint32(1)
-	}
-	exitStatus := sshSubsystemExitStatus{
-		Status: status,
-	}
-	c.connection.Log(logger.LevelDebug, logSenderSCP, "send exit status for command with args: %v user: %v err: %v",
-		c.args, c.connection.User.Username, err)
-	c.connection.channel.SendRequest("exit-status", false, ssh.Marshal(&exitStatus))
-	c.connection.channel.Close()
-}
-
 // get the next upload protocol message ignoring T command if any
 // we use our own user setting for permissions
 func (c *scpCommand) getNextUploadProtocolMessage() (string, error) {