server.go: "/" for windows

examples/go-sftp-server/main.go

@@ -20,10 +20,13 @@ func main() {
 	var (
 		readOnly    bool
 		debugStderr bool
+		winRoot     bool
 	)
 
 	flag.BoolVar(&readOnly, "R", false, "read-only server")
 	flag.BoolVar(&debugStderr, "e", false, "debug to stderr")
+	flag.BoolVar(&winRoot, "wr", false, "windows root")
+
 	flag.Parse()
 
 	debugStream := io.Discard
@@ -128,6 +131,11 @@ func main() {
 			fmt.Fprintf(debugStream, "Read write server\n")
 		}
 
+		if winRoot {
+			serverOptions = append(serverOptions, sftp.WindowsRootEnumeratesDrives())
+			fmt.Fprintf(debugStream, "Windows root enabled\n")
+		}
+
 		server, err := sftp.NewServer(
 			channel,
 			serverOptions...,

go.mod

@@ -6,4 +6,5 @@ require (
 	github.com/kr/fs v0.1.0
 	github.com/stretchr/testify v1.8.0
 	golang.org/x/crypto v0.31.0
+	golang.org/x/sys v0.28.0 // indirect
 )

server.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"io/fs"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -21,6 +22,18 @@ 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
+}
+
 // 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,
@@ -30,14 +43,15 @@ 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
 	maxTxPacket   uint32
 }
 
-func (svr *Server) nextHandle(f *os.File) string {
+func (svr *Server) nextHandle(f file) string {
 	svr.openFilesLock.Lock()
 	defer svr.openFilesLock.Unlock()
 	svr.handleCount++
@@ -57,7 +71,7 @@ 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]
@@ -86,7 +100,7 @@ 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),
 		maxTxPacket: defaultMaxTxPacket,
 	}
 
@@ -118,6 +132,14 @@ func ReadOnly() ServerOption {
 	}
 }
 
+// WindowsRootEnumeratesDrives configures a Server to serve a virtual '/' for windows that lists all drives
+func WindowsRootEnumeratesDrives() 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.
@@ -215,7 +237,7 @@ func handlePacket(s *Server, p orderedRequest) error {
 		}
 	case *sshFxpLstatPacket:
 		// stat the requested file
-		info, err := os.Lstat(s.toLocalPath(p.Path))
+		info, err := s.lstat(s.toLocalPath(p.Path))
 		rpkt = &sshFxpStatResponse{
 			ID:   p.ID,
 			info: info,
@@ -289,7 +311,7 @@ func handlePacket(s *Server, p orderedRequest) error {
 	case *sshFxpOpendirPacket:
 		lp := s.toLocalPath(p.Path)
 
-		if stat, err := os.Stat(lp); err != nil {
+		if stat, err := s.stat(lp); err != nil {
 			rpkt = statusFromError(p.ID, err)
 		} else if !stat.IsDir() {
 			rpkt = statusFromError(p.ID, &os.PathError{
@@ -493,7 +515,7 @@ func (p *sshFxpOpenPacket) respond(svr *Server) responsePacket {
 		mode = fs.FileMode() & os.ModePerm
 	}
 
-	f, err := os.OpenFile(svr.toLocalPath(p.Path), osFlags, mode)
+	f, err := svr.openfile(svr.toLocalPath(p.Path), osFlags, mode)
 	if err != nil {
 		return statusFromError(p.ID, err)
 	}

server_posix.go

@@ -0,0 +1,21 @@
+//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)
+}
+
+func (s *Server) lstat(name string) (os.FileInfo, error) {
+	return os.Lstat(name)
+}
+
+func (s *Server) stat(name string) (os.FileInfo, error) {
+	return os.Stat(name)
+}

server_windows.go

@@ -1,8 +1,15 @@
 package sftp
 
 import (
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
 	"path"
 	"path/filepath"
+	"time"
+
+	"golang.org/x/sys/windows"
 )
 
 func (s *Server) toLocalPath(p string) string {
@@ -12,7 +19,11 @@ 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 +44,148 @@ 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 {
+	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 (f *winRoot) Stat() (os.FileInfo, error) {
+	return nil, os.ErrPermission
+}
+func (f *winRoot) ReadAt(b []byte, off int64) (int, error) {
+	return 0, os.ErrPermission
+}
+func (f *winRoot) WriteAt(b []byte, off int64) (int, error) {
+	return 0, os.ErrPermission
+}
+func (f *winRoot) Name() string {
+	return "/"
+}
+func (f *winRoot) Truncate(int64) error {
+	return os.ErrPermission
+}
+func (f *winRoot) Chmod(mode fs.FileMode) error {
+	return os.ErrPermission
+}
+func (f *winRoot) Chown(uid, gid int) error {
+	return os.ErrPermission
+}
+func (f *winRoot) Close() error {
+	return 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)
+}
+
+type winRootFileInfo struct {
+	fs.FileInfo
+	name string
+}
+
+func (w winRootFileInfo) Name() string       { return w.name }
+func (w winRootFileInfo) Size() int64        { return 0 }
+func (w winRootFileInfo) Mode() fs.FileMode  { return fs.ModeDir | 0555 } // read+execute for all
+func (w winRootFileInfo) ModTime() time.Time { return time.Time{} }
+func (w winRootFileInfo) IsDir() bool        { return true }
+func (w winRootFileInfo) Sys() interface{}   { return nil }
+
+// Create a new root FileInfo
+var rootFileInfo = winRootFileInfo{
+	name: "/",
+}
+
+func (s *Server) lstat(name string) (os.FileInfo, error) {
+	if name == `\\.\` && s.winRoot {
+		return rootFileInfo, nil
+	}
+	return os.Lstat(name)
+}
+
+func (s *Server) stat(name string) (os.FileInfo, error) {
+	if name == `\\.\` && s.winRoot {
+		return rootFileInfo, nil
+	}
+	return os.Stat(name)
+}