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 FileLike 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 +76,13 @@ type Server struct {
 	debugStream   io.Writer
 	readOnly      bool
 	pktMgr        *packetManager
-	openFiles     map[string]*os.File
+	openFiles     map[string]FileLike
 	openFilesLock sync.RWMutex
 	handleCount   int
 	workDir       string
 }
 
-func (svr *Server) nextHandle(f *os.File) string {
+func (svr *Server) nextHandle(f FileLike) string {
 	svr.openFilesLock.Lock()
 	defer svr.openFilesLock.Unlock()
 	svr.handleCount++
@@ -56,7 +102,7 @@ func (svr *Server) closeHandle(handle string) error {
 	return EBADF
 }
 
-func (svr *Server) getHandle(handle string) (*os.File, bool) {
+func (svr *Server) getHandle(handle string) (FileLike, bool) {
 	svr.openFilesLock.RLock()
 	defer svr.openFilesLock.RUnlock()
 	f, ok := svr.openFiles[handle]
@@ -85,7 +131,7 @@ 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]FileLike),
 	}
 
 	for _, o := range options {
@@ -462,7 +508,7 @@ func (p *sshFxpOpenPacket) respond(svr *Server) responsePacket {
 		osFlags |= os.O_EXCL
 	}
 
-	f, err := os.OpenFile(svr.toLocalPath(p.Path), osFlags, 0o644)
+	f, err := openFileLike(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 openFileLike(path string, flag int, mode fs.FileMode) (FileLike, error) {
+	return os.OpenFile(path, flag, mode)
+}

server_windows.go

@@ -1,8 +1,15 @@
+//go:build go1.18
+
 package sftp
 
 import (
+	"fmt"
+	"io/fs"
+	"os"
 	"path"
 	"path/filepath"
+	"syscall"
+	"time"
 )
 
 func (s *Server) toLocalPath(p string) string {
@@ -37,3 +44,76 @@ func (s *Server) toLocalPath(p string) string {
 
 	return lp
 }
+
+var kernel32, _ = syscall.LoadLibrary("kernel32.dll")
+var getLogicalDrivesHandle, _ = syscall.GetProcAddress(kernel32, "GetLogicalDrives")
+
+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) {
+	if ret, _, callErr := syscall.Syscall(uintptr(getLogicalDrivesHandle), 0, 0, 0, 0); callErr != 0 {
+		return nil, fmt.Errorf("GetLogicalDrives: %w", callErr)
+	} else {
+		drives := bitsToDrives(uint32(ret))
+		return drives, nil
+	}
+}
+
+type dummyDriveStat struct {
+	name string
+}
+
+func (s *dummyDriveStat) Name() string {
+	return s.name
+}
+func (s *dummyDriveStat) Size() int64 {
+	return 1024
+}
+func (s *dummyDriveStat) Mode() os.FileMode {
+	return os.FileMode(0755)
+}
+func (s *dummyDriveStat) ModTime() time.Time {
+	return time.Now()
+}
+func (s *dummyDriveStat) IsDir() bool {
+	return true
+}
+func (s *dummyDriveStat) Sys() any {
+	return nil
+}
+
+type WinRoot struct {
+	dummyFile
+}
+
+func (f *WinRoot) Readdir(int) ([]os.FileInfo, error) {
+	drives, err := getDrives()
+	if err != nil {
+		return nil, err
+	}
+	infos := []os.FileInfo{}
+	for _, drive := range drives {
+		infos = append(infos, &dummyDriveStat{drive})
+	}
+	return nil, os.ErrPermission
+}
+
+func openFileLike(path string, flag int, mode fs.FileMode) (FileLike, error) {
+	if path == "/" {
+		return &WinRoot{}, nil
+	}
+	return os.OpenFile(path, flag, mode)
+}