server.go: "/" for windows

server.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"io/fs"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -21,6 +22,51 @@ const (
 	SftpServerWorkerCount = 8
 )
 
+type file interface {
+	Stat() (os.FileInfo, error)
+	ReadAt(b []byte, off int64) (int, error)
+	WriteAt(b []byte, off int64) (int, error)
+	Readdir(int) ([]os.FileInfo, error)
+	Name() string
+	Truncate(int64) error
+	Chmod(mode fs.FileMode) error
+	Chown(uid, gid int) error
+	Close() error
+}
+
+type dummyFile struct {
+}
+
+func (f *dummyFile) Stat() (os.FileInfo, error) {
+	return nil, os.ErrPermission
+}
+func (f *dummyFile) ReadAt(b []byte, off int64) (int, error) {
+	return 0, os.ErrPermission
+}
+func (f *dummyFile) WriteAt(b []byte, off int64) (int, error) {
+	return 0, os.ErrPermission
+}
+func (f *dummyFile) Readdir(int) ([]os.FileInfo, error) {
+	return nil, os.ErrPermission
+}
+func (f *dummyFile) Name() string {
+	return "dummyFile"
+}
+func (f *dummyFile) Truncate(int64) error {
+	return os.ErrPermission
+}
+func (f *dummyFile) Chmod(mode fs.FileMode) error {
+	return os.ErrPermission
+}
+func (f *dummyFile) Chown(uid, gid int) error {
+	return os.ErrPermission
+}
+func (f *dummyFile) Close() error {
+	return os.ErrPermission
+}
+
+var _ = dummyFile{} // ignore unused
+
 // Server is an SSH File Transfer Protocol (sftp) server.
 // This is intended to provide the sftp subsystem to an ssh server daemon.
 // This implementation currently supports most of sftp server protocol version 3,
@@ -30,13 +76,14 @@ type Server struct {
 	debugStream   io.Writer
 	readOnly      bool
 	pktMgr        *packetManager
-	openFiles     map[string]*os.File
+	openFiles     map[string]file
 	openFilesLock sync.RWMutex
 	handleCount   int
 	workDir       string
+	winRoot       bool
 }
 
-func (svr *Server) nextHandle(f *os.File) string {
+func (svr *Server) nextHandle(f file) string {
 	svr.openFilesLock.Lock()
 	defer svr.openFilesLock.Unlock()
 	svr.handleCount++
@@ -56,7 +103,7 @@ func (svr *Server) closeHandle(handle string) error {
 	return EBADF
 }
 
-func (svr *Server) getHandle(handle string) (*os.File, bool) {
+func (svr *Server) getHandle(handle string) (file, bool) {
 	svr.openFilesLock.RLock()
 	defer svr.openFilesLock.RUnlock()
 	f, ok := svr.openFiles[handle]
@@ -85,7 +132,7 @@ func NewServer(rwc io.ReadWriteCloser, options ...ServerOption) (*Server, error)
 		serverConn:  svrConn,
 		debugStream: ioutil.Discard,
 		pktMgr:      newPktMgr(svrConn),
-		openFiles:   make(map[string]*os.File),
+		openFiles:   make(map[string]file),
 	}
 
 	for _, o := range options {
@@ -116,6 +163,14 @@ func ReadOnly() ServerOption {
 	}
 }
 
+// WinRoot configures a Server to serve a virtual '/' for windows that lists all drives
+func WinRoot() ServerOption {
+	return func(s *Server) error {
+		s.winRoot = true
+		return nil
+	}
+}
+
 // WithAllocator enable the allocator.
 // After processing a packet we keep in memory the allocated slices
 // and we reuse them for new packets.
@@ -462,7 +517,7 @@ func (p *sshFxpOpenPacket) respond(svr *Server) responsePacket {
 		osFlags |= os.O_EXCL
 	}
 
-	f, err := os.OpenFile(svr.toLocalPath(p.Path), osFlags, 0o644)
+	f, err := svr.openfile(svr.toLocalPath(p.Path), osFlags, 0o644)
 	if err != nil {
 		return statusFromError(p.ID, err)
 	}

server_posix.go

@@ -0,0 +1,13 @@
+//go:build !windows
+// +build !windows
+
+package sftp
+
+import (
+	"io/fs"
+	"os"
+)
+
+func (s *Server) openfile(path string, flag int, mode fs.FileMode) (file, error) {
+	return os.OpenFile(path, flag, mode)
+}

server_windows.go

@@ -1,8 +1,14 @@
 package sftp
 
 import (
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
 	"path"
 	"path/filepath"
+
+	"golang.org/x/sys/windows"
 )
 
 func (s *Server) toLocalPath(p string) string {
@@ -12,7 +18,11 @@ func (s *Server) toLocalPath(p string) string {
 
 	lp := filepath.FromSlash(p)
 
-	if path.IsAbs(p) {
+	if path.IsAbs(p) { // starts with '/'
+		if len(p) == 1 && s.winRoot {
+			return `\\.\` // for openfile
+		}
+
 		tmp := lp
 		for len(tmp) > 0 && tmp[0] == '\\' {
 			tmp = tmp[1:]
@@ -33,7 +43,93 @@ func (s *Server) toLocalPath(p string) string {
 			// e.g. "/C:" to "C:\\"
 			return tmp
 		}
+
+		if s.winRoot {
+			// Make it so that "/Windows" is not found, and "/c:/Windows" has to be used
+			return `\\.\` + tmp
+		}
 	}
 
 	return lp
 }
+
+func bitsToDrives(bitmap uint32) []string {
+	var drive rune = 'a'
+	var drives []string
+
+	for bitmap != 0 {
+		if bitmap&1 == 1 {
+			drives = append(drives, string(drive)+":")
+		}
+		drive++
+		bitmap >>= 1
+	}
+
+	return drives
+}
+
+func getDrives() ([]string, error) {
+	mask, err := windows.GetLogicalDrives()
+	if err != nil {
+		return nil, fmt.Errorf("GetLogicalDrives: %w", err)
+	}
+	return bitsToDrives(mask), nil
+}
+
+type driveInfo struct {
+	fs.FileInfo
+	name string
+}
+
+func (i *driveInfo) Name() string {
+	return i.name // since the Name() returned from a os.Stat("C:\\") is "\\"
+}
+
+type winRoot struct {
+	dummyFile
+	drives []string
+}
+
+func newWinRoot() (*winRoot, error) {
+	drives, err := getDrives()
+	if err != nil {
+		return nil, err
+	}
+	return &winRoot{
+		drives: drives,
+	}, nil
+}
+
+func (f *winRoot) Readdir(n int) ([]os.FileInfo, error) {
+	drives := f.drives
+	if n > 0 && len(drives) > n {
+		drives = drives[:n]
+	}
+	f.drives = f.drives[len(drives):]
+	if len(drives) == 0 {
+		return nil, io.EOF
+	}
+
+	var infos []os.FileInfo
+	for _, drive := range drives {
+		fi, err := os.Stat(drive + `\`)
+		if err != nil {
+			return nil, err
+		}
+
+		di := &driveInfo{
+			FileInfo: fi,
+			name:     drive,
+		}
+		infos = append(infos, di)
+	}
+
+	return infos, nil
+}
+
+func (s *Server) openfile(path string, flag int, mode fs.FileMode) (file, error) {
+	if path == `\\.\` && s.winRoot {
+		return newWinRoot()
+	}
+	return os.OpenFile(path, flag, mode)
+}