server.go - third_party/pkg/sftp - Git at Google

 package sftp

 // sftp server counterpart

 import (
 	"encoding"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strconv"
 	"sync"
 	"syscall"
 	"time"

 	"github.com/pkg/errors"
 )

 const (
 	sftpServerWorkerCount = 8
 )

 // 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,
 // as specified at http://tools.ietf.org/html/draft-ietf-secsh-filexfer-02
 type Server struct {
 	serverConn
 	debugStream   io.Writer
 	readOnly      bool
 	pktChan       chan rxPacket
 	openFiles     map[string]*os.File
 	openFilesLock sync.RWMutex
 	handleCount   int
 	maxTxPacket   uint32
 }

 func (svr *Server) nextHandle(f *os.File) string {
 	svr.openFilesLock.Lock()
 	defer svr.openFilesLock.Unlock()
 	svr.handleCount++
 	handle := strconv.Itoa(svr.handleCount)
 	svr.openFiles[handle] = f
 	return handle
 }

 func (svr *Server) closeHandle(handle string) error {
 	svr.openFilesLock.Lock()
 	defer svr.openFilesLock.Unlock()
 	if f, ok := svr.openFiles[handle]; ok {
 		delete(svr.openFiles, handle)
 		return f.Close()
 	}

 	return syscall.EBADF
 }

 func (svr *Server) getHandle(handle string) (*os.File, bool) {
 	svr.openFilesLock.RLock()
 	defer svr.openFilesLock.RUnlock()
 	f, ok := svr.openFiles[handle]
 	return f, ok
 }

 type serverRespondablePacket interface {
 	encoding.BinaryUnmarshaler
 	id() uint32
 	respond(svr *Server) error
 }

 // NewServer creates a new Server instance around the provided streams, serving
 // content from the root of the filesystem.  Optionally, ServerOption
 // functions may be specified to further configure the Server.
 //
 // A subsequent call to Serve() is required to begin serving files over SFTP.
 func NewServer(rwc io.ReadWriteCloser, options ...ServerOption) (*Server, error) {
 	s := &Server{
 		serverConn: serverConn{
 			conn: conn{
 				Reader:      rwc,
 				WriteCloser: rwc,
 			},
 		},
 		debugStream: ioutil.Discard,
 		pktChan:     make(chan rxPacket, sftpServerWorkerCount),
 		openFiles:   make(map[string]*os.File),
 		maxTxPacket: 1 << 15,
 	}

 	for _, o := range options {
 		if err := o(s); err != nil {
 			return nil, err
 		}
 	}

 	return s, nil
 }

 // A ServerOption is a function which applies configuration to a Server.
 type ServerOption func(*Server) error

 // WithDebug enables Server debugging output to the supplied io.Writer.
 func WithDebug(w io.Writer) ServerOption {
 	return func(s *Server) error {
 		s.debugStream = w
 		return nil
 	}
 }

 // ReadOnly configures a Server to serve files in read-only mode.
 func ReadOnly() ServerOption {
 	return func(s *Server) error {
 		s.readOnly = true
 		return nil
 	}
 }

 type rxPacket struct {
 	pktType  fxp
 	pktBytes []byte
 }

 // Up to N parallel servers
 func (svr *Server) sftpServerWorker() error {
 	for p := range svr.pktChan {
 		var pkt interface {
 			encoding.BinaryUnmarshaler
 			id() uint32
 		}
 		var readonly = true
 		switch p.pktType {
 		case ssh_FXP_INIT:
 			pkt = &sshFxInitPacket{}
 		case ssh_FXP_LSTAT:
 			pkt = &sshFxpLstatPacket{}
 		case ssh_FXP_OPEN:
 			pkt = &sshFxpOpenPacket{}
 			// readonly handled specially below
 		case ssh_FXP_CLOSE:
 			pkt = &sshFxpClosePacket{}
 		case ssh_FXP_READ:
 			pkt = &sshFxpReadPacket{}
 		case ssh_FXP_WRITE:
 			pkt = &sshFxpWritePacket{}
 			readonly = false
 		case ssh_FXP_FSTAT:
 			pkt = &sshFxpFstatPacket{}
 		case ssh_FXP_SETSTAT:
 			pkt = &sshFxpSetstatPacket{}
 			readonly = false
 		case ssh_FXP_FSETSTAT:
 			pkt = &sshFxpFsetstatPacket{}
 			readonly = false
 		case ssh_FXP_OPENDIR:
 			pkt = &sshFxpOpendirPacket{}
 		case ssh_FXP_READDIR:
 			pkt = &sshFxpReaddirPacket{}
 		case ssh_FXP_REMOVE:
 			pkt = &sshFxpRemovePacket{}
 			readonly = false
 		case ssh_FXP_MKDIR:
 			pkt = &sshFxpMkdirPacket{}
 			readonly = false
 		case ssh_FXP_RMDIR:
 			pkt = &sshFxpRmdirPacket{}
 			readonly = false
 		case ssh_FXP_REALPATH:
 			pkt = &sshFxpRealpathPacket{}
 		case ssh_FXP_STAT:
 			pkt = &sshFxpStatPacket{}
 		case ssh_FXP_RENAME:
 			pkt = &sshFxpRenamePacket{}
 			readonly = false
 		case ssh_FXP_READLINK:
 			pkt = &sshFxpReadlinkPacket{}
 		case ssh_FXP_SYMLINK:
 			pkt = &sshFxpSymlinkPacket{}
 			readonly = false
 		case ssh_FXP_EXTENDED:
 			pkt = &sshFxpExtendedPacket{}
 		default:
 			return errors.Errorf("unhandled packet type: %s", p.pktType)
 		}
 		if err := pkt.UnmarshalBinary(p.pktBytes); err != nil {
 			return err
 		}

 		// handle FXP_OPENDIR specially
 		switch pkt := pkt.(type) {
 		case *sshFxpOpenPacket:
 			readonly = pkt.readonly()
 		case *sshFxpExtendedPacket:
 			readonly = pkt.SpecificPacket.readonly()
 		}

 		// If server is operating read-only and a write operation is requested,
 		// return permission denied
 		if !readonly && svr.readOnly {
 			if err := svr.sendError(pkt, syscall.EPERM); err != nil {
 				return errors.Wrap(err, "failed to send read only packet response")
 			}
 			continue
 		}

 		if err := handlePacket(svr, pkt); err != nil {
 			return err
 		}
 	}
 	return nil
 }

 func handlePacket(s *Server, p interface{}) error {
 	switch p := p.(type) {
 	case *sshFxInitPacket:
 		return s.sendPacket(sshFxVersionPacket{sftpProtocolVersion, nil})
 	case *sshFxpStatPacket:
 		// stat the requested file
 		info, err := os.Stat(p.Path)
 		if err != nil {
 			return s.sendError(p, err)
 		}
 		return s.sendPacket(sshFxpStatResponse{
 			ID:   p.ID,
 			info: info,
 		})
 	case *sshFxpLstatPacket:
 		// stat the requested file
 		info, err := os.Lstat(p.Path)
 		if err != nil {
 			return s.sendError(p, err)
 		}
 		return s.sendPacket(sshFxpStatResponse{
 			ID:   p.ID,
 			info: info,
 		})
 	case *sshFxpFstatPacket:
 		f, ok := s.getHandle(p.Handle)
 		if !ok {
 			return s.sendError(p, syscall.EBADF)
 		}

 		info, err := f.Stat()
 		if err != nil {
 			return s.sendError(p, err)
 		}

 		return s.sendPacket(sshFxpStatResponse{
 			ID:   p.ID,
 			info: info,
 		})
 	case *sshFxpMkdirPacket:
 		// TODO FIXME: ignore flags field
 		err := os.Mkdir(p.Path, 0755)
 		return s.sendError(p, err)
 	case *sshFxpRmdirPacket:
 		err := os.Remove(p.Path)
 		return s.sendError(p, err)
 	case *sshFxpRemovePacket:
 		err := os.Remove(p.Filename)
 		return s.sendError(p, err)
 	case *sshFxpRenamePacket:
 		err := os.Rename(p.Oldpath, p.Newpath)
 		return s.sendError(p, err)
 	case *sshFxpSymlinkPacket:
 		err := os.Symlink(p.Targetpath, p.Linkpath)
 		return s.sendError(p, err)
 	case *sshFxpClosePacket:
 		return s.sendError(p, s.closeHandle(p.Handle))
 	case *sshFxpReadlinkPacket:
 		f, err := os.Readlink(p.Path)
 		if err != nil {
 			return s.sendError(p, err)
 		}

 		return s.sendPacket(sshFxpNamePacket{
 			ID: p.ID,
 			NameAttrs: []sshFxpNameAttr{{
 				Name:     f,
 				LongName: f,
 				Attrs:    emptyFileStat,
 			}},
 		})

 	case *sshFxpRealpathPacket:
 		f, err := filepath.Abs(p.Path)
 		if err != nil {
 			return s.sendError(p, err)
 		}
 		f = filepath.Clean(f)
 		f = filepath.ToSlash(f) // make path more Unix like on windows servers
 		return s.sendPacket(sshFxpNamePacket{
 			ID: p.ID,
 			NameAttrs: []sshFxpNameAttr{{
 				Name:     f,
 				LongName: f,
 				Attrs:    emptyFileStat,
 			}},
 		})
 	case *sshFxpOpendirPacket:
 		return sshFxpOpenPacket{
 			ID:     p.ID,
 			Path:   p.Path,
 			Pflags: ssh_FXF_READ,
 		}.respond(s)
 	case *sshFxpReadPacket:
 		f, ok := s.getHandle(p.Handle)
 		if !ok {
 			return s.sendError(p, syscall.EBADF)
 		}

 		data := make([]byte, clamp(p.Len, s.maxTxPacket))
 		n, err := f.ReadAt(data, int64(p.Offset))
 		if err != nil && (err != io.EOF || n == 0) {
 			return s.sendError(p, err)
 		}
 		return s.sendPacket(sshFxpDataPacket{
 			ID:     p.ID,
 			Length: uint32(n),
 			Data:   data[:n],
 		})
 	case *sshFxpWritePacket:
 		f, ok := s.getHandle(p.Handle)
 		if !ok {
 			return s.sendError(p, syscall.EBADF)
 		}

 		_, err := f.WriteAt(p.Data, int64(p.Offset))
 		return s.sendError(p, err)
 	case serverRespondablePacket:
 		err := p.respond(s)
 		return errors.Wrap(err, "pkt.respond failed")
 	default:
 		return errors.Errorf("unexpected packet type %T", p)
 	}
 }

 // Serve serves SFTP connections until the streams stop or the SFTP subsystem
 // is stopped.
 func (svr *Server) Serve() error {
 	var wg sync.WaitGroup
 	wg.Add(sftpServerWorkerCount)
 	for i := 0; i < sftpServerWorkerCount; i++ {
 		go func() {
 			defer wg.Done()
 			if err := svr.sftpServerWorker(); err != nil {
 				svr.conn.Close() // shuts down recvPacket
 			}
 		}()
 	}

 	var err error
 	var pktType uint8
 	var pktBytes []byte
 	for {
 		pktType, pktBytes, err = svr.recvPacket()
 		if err != nil {
 			break
 		}
 		svr.pktChan <- rxPacket{fxp(pktType), pktBytes}
 	}

 	close(svr.pktChan) // shuts down sftpServerWorkers
 	wg.Wait()          // wait for all workers to exit

 	// close any still-open files
 	for handle, file := range svr.openFiles {
 		fmt.Fprintf(svr.debugStream, "sftp server file with handle %q left open: %v\n", handle, file.Name())
 		file.Close()
 	}
 	return err // error from recvPacket
 }

 type id interface {
 	id() uint32
 }

 // The init packet has no ID, so we just return a zero-value ID
 func (p sshFxInitPacket) id() uint32 { return 0 }

 type sshFxpStatResponse struct {
 	ID   uint32
 	info os.FileInfo
 }

 func (p sshFxpStatResponse) MarshalBinary() ([]byte, error) {
 	b := []byte{ssh_FXP_ATTRS}
 	b = marshalUint32(b, p.ID)
 	b = marshalFileInfo(b, p.info)
 	return b, nil
 }

 var emptyFileStat = []interface{}{uint32(0)}

 func (p sshFxpOpenPacket) readonly() bool {
 	return !p.hasPflags(ssh_FXF_WRITE)
 }

 func (p sshFxpOpenPacket) hasPflags(flags ...uint32) bool {
 	for _, f := range flags {
 		if p.Pflags&f == 0 {
 			return false
 		}
 	}
 	return true
 }

 func (p sshFxpOpenPacket) respond(svr *Server) error {
 	var osFlags int
 	if p.hasPflags(ssh_FXF_READ, ssh_FXF_WRITE) {
 		osFlags |= os.O_RDWR
 	} else if p.hasPflags(ssh_FXF_WRITE) {
 		osFlags |= os.O_WRONLY
 	} else if p.hasPflags(ssh_FXF_READ) {
 		osFlags |= os.O_RDONLY
 	} else {
 		// how are they opening?
 		return svr.sendError(p, syscall.EINVAL)
 	}

 	if p.hasPflags(ssh_FXF_APPEND) {
 		osFlags |= os.O_APPEND
 	}
 	if p.hasPflags(ssh_FXF_CREAT) {
 		osFlags |= os.O_CREATE
 	}
 	if p.hasPflags(ssh_FXF_TRUNC) {
 		osFlags |= os.O_TRUNC
 	}
 	if p.hasPflags(ssh_FXF_EXCL) {
 		osFlags |= os.O_EXCL
 	}

 	f, err := os.OpenFile(p.Path, osFlags, 0644)
 	if err != nil {
 		return svr.sendError(p, err)
 	}

 	handle := svr.nextHandle(f)
 	return svr.sendPacket(sshFxpHandlePacket{p.ID, handle})
 }

 func (p sshFxpReaddirPacket) respond(svr *Server) error {
 	f, ok := svr.getHandle(p.Handle)
 	if !ok {
 		return svr.sendError(p, syscall.EBADF)
 	}

 	dirname := f.Name()
 	dirents, err := f.Readdir(128)
 	if err != nil {
 		return svr.sendError(p, err)
 	}

 	ret := sshFxpNamePacket{ID: p.ID}
 	for _, dirent := range dirents {
 		ret.NameAttrs = append(ret.NameAttrs, sshFxpNameAttr{
 			Name:     dirent.Name(),
 			LongName: runLs(dirname, dirent),
 			Attrs:    []interface{}{dirent},
 		})
 	}
 	return svr.sendPacket(ret)
 }

 func (p sshFxpSetstatPacket) respond(svr *Server) error {
 	// additional unmarshalling is required for each possibility here
 	b := p.Attrs.([]byte)
 	var err error

 	debug("setstat name \"%s\"", p.Path)
 	if (p.Flags & ssh_FILEXFER_ATTR_SIZE) != 0 {
 		var size uint64
 		if size, b, err = unmarshalUint64Safe(b); err == nil {
 			err = os.Truncate(p.Path, int64(size))
 		}
 	}
 	if (p.Flags & ssh_FILEXFER_ATTR_PERMISSIONS) != 0 {
 		var mode uint32
 		if mode, b, err = unmarshalUint32Safe(b); err == nil {
 			err = os.Chmod(p.Path, os.FileMode(mode))
 		}
 	}
 	if (p.Flags & ssh_FILEXFER_ATTR_ACMODTIME) != 0 {
 		var atime uint32
 		var mtime uint32
 		if atime, b, err = unmarshalUint32Safe(b); err != nil {
 		} else if mtime, b, err = unmarshalUint32Safe(b); err != nil {
 		} else {
 			atimeT := time.Unix(int64(atime), 0)
 			mtimeT := time.Unix(int64(mtime), 0)
 			err = os.Chtimes(p.Path, atimeT, mtimeT)
 		}
 	}
 	if (p.Flags & ssh_FILEXFER_ATTR_UIDGID) != 0 {
 		var uid uint32
 		var gid uint32
 		if uid, b, err = unmarshalUint32Safe(b); err != nil {
 		} else if gid, b, err = unmarshalUint32Safe(b); err != nil {
 		} else {
 			err = os.Chown(p.Path, int(uid), int(gid))
 		}
 	}

 	return svr.sendError(p, err)
 }

 func (p sshFxpFsetstatPacket) respond(svr *Server) error {
 	f, ok := svr.getHandle(p.Handle)
 	if !ok {
 		return svr.sendError(p, syscall.EBADF)
 	}

 	// additional unmarshalling is required for each possibility here
 	b := p.Attrs.([]byte)
 	var err error

 	debug("fsetstat name \"%s\"", f.Name())
 	if (p.Flags & ssh_FILEXFER_ATTR_SIZE) != 0 {
 		var size uint64
 		if size, b, err = unmarshalUint64Safe(b); err == nil {
 			err = f.Truncate(int64(size))
 		}
 	}
 	if (p.Flags & ssh_FILEXFER_ATTR_PERMISSIONS) != 0 {
 		var mode uint32
 		if mode, b, err = unmarshalUint32Safe(b); err == nil {
 			err = f.Chmod(os.FileMode(mode))
 		}
 	}
 	if (p.Flags & ssh_FILEXFER_ATTR_ACMODTIME) != 0 {
 		var atime uint32
 		var mtime uint32
 		if atime, b, err = unmarshalUint32Safe(b); err != nil {
 		} else if mtime, b, err = unmarshalUint32Safe(b); err != nil {
 		} else {
 			atimeT := time.Unix(int64(atime), 0)
 			mtimeT := time.Unix(int64(mtime), 0)
 			err = os.Chtimes(f.Name(), atimeT, mtimeT)
 		}
 	}
 	if (p.Flags & ssh_FILEXFER_ATTR_UIDGID) != 0 {
 		var uid uint32
 		var gid uint32
 		if uid, b, err = unmarshalUint32Safe(b); err != nil {
 		} else if gid, b, err = unmarshalUint32Safe(b); err != nil {
 		} else {
 			err = f.Chown(int(uid), int(gid))
 		}
 	}

 	return svr.sendError(p, err)
 }

 // translateErrno translates a syscall error number to a SFTP error code.
 func translateErrno(errno syscall.Errno) uint32 {
 	switch errno {
 	case 0:
 		return ssh_FX_OK
 	case syscall.ENOENT:
 		return ssh_FX_NO_SUCH_FILE
 	case syscall.EPERM:
 		return ssh_FX_PERMISSION_DENIED
 	}

 	return ssh_FX_FAILURE
 }

 func statusFromError(p id, err error) sshFxpStatusPacket {
 	ret := sshFxpStatusPacket{
 		ID: p.id(),
 		StatusError: StatusError{
 			// ssh_FX_OK                = 0
 			// ssh_FX_EOF               = 1
 			// ssh_FX_NO_SUCH_FILE      = 2 ENOENT
 			// ssh_FX_PERMISSION_DENIED = 3
 			// ssh_FX_FAILURE           = 4
 			// ssh_FX_BAD_MESSAGE       = 5
 			// ssh_FX_NO_CONNECTION     = 6
 			// ssh_FX_CONNECTION_LOST   = 7
 			// ssh_FX_OP_UNSUPPORTED    = 8
 			Code: ssh_FX_OK,
 		},
 	}
 	if err != nil {
 		debug("statusFromError: error is %T %#v", err, err)
 		ret.StatusError.Code = ssh_FX_FAILURE
 		ret.StatusError.msg = err.Error()
 		if err == io.EOF {
 			ret.StatusError.Code = ssh_FX_EOF
 		} else if errno, ok := err.(syscall.Errno); ok {
 			ret.StatusError.Code = translateErrno(errno)
 		} else if pathError, ok := err.(*os.PathError); ok {
 			debug("statusFromError: error is %T %#v", pathError.Err, pathError.Err)
 			if errno, ok := pathError.Err.(syscall.Errno); ok {
 				ret.StatusError.Code = translateErrno(errno)
 			}
 		}
 	}
 	return ret
 }

 func clamp(v, max uint32) uint32 {
 	if v > max {
 		return max
 	}
 	return v
 }
	package sftp

	// sftp server counterpart

	import (
	"encoding"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"
	"strconv"
	"sync"
	"syscall"
	"time"

	"github.com/pkg/errors"
	)

	const (
	sftpServerWorkerCount = 8
	)

	// 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,
	// as specified at http://tools.ietf.org/html/draft-ietf-secsh-filexfer-02
	type Server struct {
	serverConn
	debugStream io.Writer
	readOnly bool
	pktChan chan rxPacket
	openFiles map[string]*os.File
	openFilesLock sync.RWMutex
	handleCount int
	maxTxPacket uint32
	}

	func (svr Server) nextHandle(f os.File) string {
	svr.openFilesLock.Lock()
	defer svr.openFilesLock.Unlock()
	svr.handleCount++
	handle := strconv.Itoa(svr.handleCount)
	svr.openFiles[handle] = f
	return handle
	}

	func (svr *Server) closeHandle(handle string) error {
	svr.openFilesLock.Lock()
	defer svr.openFilesLock.Unlock()
	if f, ok := svr.openFiles[handle]; ok {
	delete(svr.openFiles, handle)
	return f.Close()
	}

	return syscall.EBADF
	}

	func (svr Server) getHandle(handle string) (os.File, bool) {
	svr.openFilesLock.RLock()
	defer svr.openFilesLock.RUnlock()
	f, ok := svr.openFiles[handle]
	return f, ok
	}

	type serverRespondablePacket interface {
	encoding.BinaryUnmarshaler
	id() uint32
	respond(svr *Server) error
	}

	// NewServer creates a new Server instance around the provided streams, serving
	// content from the root of the filesystem. Optionally, ServerOption
	// functions may be specified to further configure the Server.
	//
	// A subsequent call to Serve() is required to begin serving files over SFTP.
	func NewServer(rwc io.ReadWriteCloser, options ...ServerOption) (*Server, error) {
	s := &Server{
	serverConn: serverConn{
	conn: conn{
	Reader: rwc,
	WriteCloser: rwc,
	},
	},
	debugStream: ioutil.Discard,
	pktChan: make(chan rxPacket, sftpServerWorkerCount),
	openFiles: make(map[string]*os.File),
	maxTxPacket: 1 << 15,
	}

	for _, o := range options {
	if err := o(s); err != nil {
	return nil, err
	}
	}

	return s, nil
	}

	// A ServerOption is a function which applies configuration to a Server.
	type ServerOption func(*Server) error

	// WithDebug enables Server debugging output to the supplied io.Writer.
	func WithDebug(w io.Writer) ServerOption {
	return func(s *Server) error {
	s.debugStream = w
	return nil
	}
	}

	// ReadOnly configures a Server to serve files in read-only mode.
	func ReadOnly() ServerOption {
	return func(s *Server) error {
	s.readOnly = true
	return nil
	}
	}

	type rxPacket struct {
	pktType fxp
	pktBytes []byte
	}

	// Up to N parallel servers
	func (svr *Server) sftpServerWorker() error {
	for p := range svr.pktChan {
	var pkt interface {
	encoding.BinaryUnmarshaler
	id() uint32
	}
	var readonly = true
	switch p.pktType {
	case ssh_FXP_INIT:
	pkt = &sshFxInitPacket{}
	case ssh_FXP_LSTAT:
	pkt = &sshFxpLstatPacket{}
	case ssh_FXP_OPEN:
	pkt = &sshFxpOpenPacket{}
	// readonly handled specially below
	case ssh_FXP_CLOSE:
	pkt = &sshFxpClosePacket{}
	case ssh_FXP_READ:
	pkt = &sshFxpReadPacket{}
	case ssh_FXP_WRITE:
	pkt = &sshFxpWritePacket{}
	readonly = false
	case ssh_FXP_FSTAT:
	pkt = &sshFxpFstatPacket{}
	case ssh_FXP_SETSTAT:
	pkt = &sshFxpSetstatPacket{}
	readonly = false
	case ssh_FXP_FSETSTAT:
	pkt = &sshFxpFsetstatPacket{}
	readonly = false
	case ssh_FXP_OPENDIR:
	pkt = &sshFxpOpendirPacket{}
	case ssh_FXP_READDIR:
	pkt = &sshFxpReaddirPacket{}
	case ssh_FXP_REMOVE:
	pkt = &sshFxpRemovePacket{}
	readonly = false
	case ssh_FXP_MKDIR:
	pkt = &sshFxpMkdirPacket{}
	readonly = false
	case ssh_FXP_RMDIR:
	pkt = &sshFxpRmdirPacket{}
	readonly = false
	case ssh_FXP_REALPATH:
	pkt = &sshFxpRealpathPacket{}
	case ssh_FXP_STAT:
	pkt = &sshFxpStatPacket{}
	case ssh_FXP_RENAME:
	pkt = &sshFxpRenamePacket{}
	readonly = false
	case ssh_FXP_READLINK:
	pkt = &sshFxpReadlinkPacket{}
	case ssh_FXP_SYMLINK:
	pkt = &sshFxpSymlinkPacket{}
	readonly = false
	case ssh_FXP_EXTENDED:
	pkt = &sshFxpExtendedPacket{}
	default:
	return errors.Errorf("unhandled packet type: %s", p.pktType)
	}
	if err := pkt.UnmarshalBinary(p.pktBytes); err != nil {
	return err
	}

	// handle FXP_OPENDIR specially
	switch pkt := pkt.(type) {
	case *sshFxpOpenPacket:
	readonly = pkt.readonly()
	case *sshFxpExtendedPacket:
	readonly = pkt.SpecificPacket.readonly()
	}

	// If server is operating read-only and a write operation is requested,
	// return permission denied
	if !readonly && svr.readOnly {
	if err := svr.sendError(pkt, syscall.EPERM); err != nil {
	return errors.Wrap(err, "failed to send read only packet response")
	}
	continue
	}

	if err := handlePacket(svr, pkt); err != nil {
	return err
	}
	}
	return nil
	}

	func handlePacket(s *Server, p interface{}) error {
	switch p := p.(type) {
	case *sshFxInitPacket:
	return s.sendPacket(sshFxVersionPacket{sftpProtocolVersion, nil})
	case *sshFxpStatPacket:
	// stat the requested file
	info, err := os.Stat(p.Path)
	if err != nil {
	return s.sendError(p, err)
	}
	return s.sendPacket(sshFxpStatResponse{
	ID: p.ID,
	info: info,
	})
	case *sshFxpLstatPacket:
	// stat the requested file
	info, err := os.Lstat(p.Path)
	if err != nil {
	return s.sendError(p, err)
	}
	return s.sendPacket(sshFxpStatResponse{
	ID: p.ID,
	info: info,
	})
	case *sshFxpFstatPacket:
	f, ok := s.getHandle(p.Handle)
	if !ok {
	return s.sendError(p, syscall.EBADF)
	}

	info, err := f.Stat()
	if err != nil {
	return s.sendError(p, err)
	}

	return s.sendPacket(sshFxpStatResponse{
	ID: p.ID,
	info: info,
	})
	case *sshFxpMkdirPacket:
	// TODO FIXME: ignore flags field
	err := os.Mkdir(p.Path, 0755)
	return s.sendError(p, err)
	case *sshFxpRmdirPacket:
	err := os.Remove(p.Path)
	return s.sendError(p, err)
	case *sshFxpRemovePacket:
	err := os.Remove(p.Filename)
	return s.sendError(p, err)
	case *sshFxpRenamePacket:
	err := os.Rename(p.Oldpath, p.Newpath)
	return s.sendError(p, err)
	case *sshFxpSymlinkPacket:
	err := os.Symlink(p.Targetpath, p.Linkpath)
	return s.sendError(p, err)
	case *sshFxpClosePacket:
	return s.sendError(p, s.closeHandle(p.Handle))
	case *sshFxpReadlinkPacket:
	f, err := os.Readlink(p.Path)
	if err != nil {
	return s.sendError(p, err)
	}

	return s.sendPacket(sshFxpNamePacket{
	ID: p.ID,
	NameAttrs: []sshFxpNameAttr{{
	Name: f,
	LongName: f,
	Attrs: emptyFileStat,
	}},
	})

	case *sshFxpRealpathPacket:
	f, err := filepath.Abs(p.Path)
	if err != nil {
	return s.sendError(p, err)
	}
	f = filepath.Clean(f)
	f = filepath.ToSlash(f) // make path more Unix like on windows servers
	return s.sendPacket(sshFxpNamePacket{
	ID: p.ID,
	NameAttrs: []sshFxpNameAttr{{
	Name: f,
	LongName: f,
	Attrs: emptyFileStat,
	}},
	})
	case *sshFxpOpendirPacket:
	return sshFxpOpenPacket{
	ID: p.ID,
	Path: p.Path,
	Pflags: ssh_FXF_READ,
	}.respond(s)
	case *sshFxpReadPacket:
	f, ok := s.getHandle(p.Handle)
	if !ok {
	return s.sendError(p, syscall.EBADF)
	}

	data := make([]byte, clamp(p.Len, s.maxTxPacket))
	n, err := f.ReadAt(data, int64(p.Offset))
	if err != nil && (err != io.EOF \|\| n == 0) {
	return s.sendError(p, err)
	}
	return s.sendPacket(sshFxpDataPacket{
	ID: p.ID,
	Length: uint32(n),
	Data: data[:n],
	})
	case *sshFxpWritePacket:
	f, ok := s.getHandle(p.Handle)
	if !ok {
	return s.sendError(p, syscall.EBADF)
	}

	_, err := f.WriteAt(p.Data, int64(p.Offset))
	return s.sendError(p, err)
	case serverRespondablePacket:
	err := p.respond(s)
	return errors.Wrap(err, "pkt.respond failed")
	default:
	return errors.Errorf("unexpected packet type %T", p)
	}
	}

	// Serve serves SFTP connections until the streams stop or the SFTP subsystem
	// is stopped.
	func (svr *Server) Serve() error {
	var wg sync.WaitGroup
	wg.Add(sftpServerWorkerCount)
	for i := 0; i < sftpServerWorkerCount; i++ {
	go func() {
	defer wg.Done()
	if err := svr.sftpServerWorker(); err != nil {
	svr.conn.Close() // shuts down recvPacket
	}
	}()
	}

	var err error
	var pktType uint8
	var pktBytes []byte
	for {
	pktType, pktBytes, err = svr.recvPacket()
	if err != nil {
	break
	}
	svr.pktChan <- rxPacket{fxp(pktType), pktBytes}
	}

	close(svr.pktChan) // shuts down sftpServerWorkers
	wg.Wait() // wait for all workers to exit

	// close any still-open files
	for handle, file := range svr.openFiles {
	fmt.Fprintf(svr.debugStream, "sftp server file with handle %q left open: %v\n", handle, file.Name())
	file.Close()
	}
	return err // error from recvPacket
	}

	type id interface {
	id() uint32
	}

	// The init packet has no ID, so we just return a zero-value ID
	func (p sshFxInitPacket) id() uint32 { return 0 }

	type sshFxpStatResponse struct {
	ID uint32
	info os.FileInfo
	}

	func (p sshFxpStatResponse) MarshalBinary() ([]byte, error) {
	b := []byte{ssh_FXP_ATTRS}
	b = marshalUint32(b, p.ID)
	b = marshalFileInfo(b, p.info)
	return b, nil
	}

	var emptyFileStat = []interface{}{uint32(0)}

	func (p sshFxpOpenPacket) readonly() bool {
	return !p.hasPflags(ssh_FXF_WRITE)
	}

	func (p sshFxpOpenPacket) hasPflags(flags ...uint32) bool {
	for _, f := range flags {
	if p.Pflags&f == 0 {
	return false
	}
	}
	return true
	}

	func (p sshFxpOpenPacket) respond(svr *Server) error {
	var osFlags int
	if p.hasPflags(ssh_FXF_READ, ssh_FXF_WRITE) {
	osFlags \|= os.O_RDWR
	} else if p.hasPflags(ssh_FXF_WRITE) {
	osFlags \|= os.O_WRONLY
	} else if p.hasPflags(ssh_FXF_READ) {
	osFlags \|= os.O_RDONLY
	} else {
	// how are they opening?
	return svr.sendError(p, syscall.EINVAL)
	}

	if p.hasPflags(ssh_FXF_APPEND) {
	osFlags \|= os.O_APPEND
	}
	if p.hasPflags(ssh_FXF_CREAT) {
	osFlags \|= os.O_CREATE
	}
	if p.hasPflags(ssh_FXF_TRUNC) {
	osFlags \|= os.O_TRUNC
	}
	if p.hasPflags(ssh_FXF_EXCL) {
	osFlags \|= os.O_EXCL
	}

	f, err := os.OpenFile(p.Path, osFlags, 0644)
	if err != nil {
	return svr.sendError(p, err)
	}

	handle := svr.nextHandle(f)
	return svr.sendPacket(sshFxpHandlePacket{p.ID, handle})
	}

	func (p sshFxpReaddirPacket) respond(svr *Server) error {
	f, ok := svr.getHandle(p.Handle)
	if !ok {
	return svr.sendError(p, syscall.EBADF)
	}

	dirname := f.Name()
	dirents, err := f.Readdir(128)
	if err != nil {
	return svr.sendError(p, err)
	}

	ret := sshFxpNamePacket{ID: p.ID}
	for _, dirent := range dirents {
	ret.NameAttrs = append(ret.NameAttrs, sshFxpNameAttr{
	Name: dirent.Name(),
	LongName: runLs(dirname, dirent),
	Attrs: []interface{}{dirent},
	})
	}
	return svr.sendPacket(ret)
	}

	func (p sshFxpSetstatPacket) respond(svr *Server) error {
	// additional unmarshalling is required for each possibility here
	b := p.Attrs.([]byte)
	var err error

	debug("setstat name \"%s\"", p.Path)
	if (p.Flags & ssh_FILEXFER_ATTR_SIZE) != 0 {
	var size uint64
	if size, b, err = unmarshalUint64Safe(b); err == nil {
	err = os.Truncate(p.Path, int64(size))
	}
	}
	if (p.Flags & ssh_FILEXFER_ATTR_PERMISSIONS) != 0 {
	var mode uint32
	if mode, b, err = unmarshalUint32Safe(b); err == nil {
	err = os.Chmod(p.Path, os.FileMode(mode))
	}
	}
	if (p.Flags & ssh_FILEXFER_ATTR_ACMODTIME) != 0 {
	var atime uint32
	var mtime uint32
	if atime, b, err = unmarshalUint32Safe(b); err != nil {
	} else if mtime, b, err = unmarshalUint32Safe(b); err != nil {
	} else {
	atimeT := time.Unix(int64(atime), 0)
	mtimeT := time.Unix(int64(mtime), 0)
	err = os.Chtimes(p.Path, atimeT, mtimeT)
	}
	}
	if (p.Flags & ssh_FILEXFER_ATTR_UIDGID) != 0 {
	var uid uint32
	var gid uint32
	if uid, b, err = unmarshalUint32Safe(b); err != nil {
	} else if gid, b, err = unmarshalUint32Safe(b); err != nil {
	} else {
	err = os.Chown(p.Path, int(uid), int(gid))
	}
	}

	return svr.sendError(p, err)
	}

	func (p sshFxpFsetstatPacket) respond(svr *Server) error {
	f, ok := svr.getHandle(p.Handle)
	if !ok {
	return svr.sendError(p, syscall.EBADF)
	}

	// additional unmarshalling is required for each possibility here
	b := p.Attrs.([]byte)
	var err error

	debug("fsetstat name \"%s\"", f.Name())
	if (p.Flags & ssh_FILEXFER_ATTR_SIZE) != 0 {
	var size uint64
	if size, b, err = unmarshalUint64Safe(b); err == nil {
	err = f.Truncate(int64(size))
	}
	}
	if (p.Flags & ssh_FILEXFER_ATTR_PERMISSIONS) != 0 {
	var mode uint32
	if mode, b, err = unmarshalUint32Safe(b); err == nil {
	err = f.Chmod(os.FileMode(mode))
	}
	}
	if (p.Flags & ssh_FILEXFER_ATTR_ACMODTIME) != 0 {
	var atime uint32
	var mtime uint32
	if atime, b, err = unmarshalUint32Safe(b); err != nil {
	} else if mtime, b, err = unmarshalUint32Safe(b); err != nil {
	} else {
	atimeT := time.Unix(int64(atime), 0)
	mtimeT := time.Unix(int64(mtime), 0)
	err = os.Chtimes(f.Name(), atimeT, mtimeT)
	}
	}
	if (p.Flags & ssh_FILEXFER_ATTR_UIDGID) != 0 {
	var uid uint32
	var gid uint32
	if uid, b, err = unmarshalUint32Safe(b); err != nil {
	} else if gid, b, err = unmarshalUint32Safe(b); err != nil {
	} else {
	err = f.Chown(int(uid), int(gid))
	}
	}

	return svr.sendError(p, err)
	}

	// translateErrno translates a syscall error number to a SFTP error code.
	func translateErrno(errno syscall.Errno) uint32 {
	switch errno {
	case 0:
	return ssh_FX_OK
	case syscall.ENOENT:
	return ssh_FX_NO_SUCH_FILE
	case syscall.EPERM:
	return ssh_FX_PERMISSION_DENIED
	}

	return ssh_FX_FAILURE
	}

	func statusFromError(p id, err error) sshFxpStatusPacket {
	ret := sshFxpStatusPacket{
	ID: p.id(),
	StatusError: StatusError{
	// ssh_FX_OK = 0
	// ssh_FX_EOF = 1
	// ssh_FX_NO_SUCH_FILE = 2 ENOENT
	// ssh_FX_PERMISSION_DENIED = 3
	// ssh_FX_FAILURE = 4
	// ssh_FX_BAD_MESSAGE = 5
	// ssh_FX_NO_CONNECTION = 6
	// ssh_FX_CONNECTION_LOST = 7
	// ssh_FX_OP_UNSUPPORTED = 8
	Code: ssh_FX_OK,
	},
	}
	if err != nil {
	debug("statusFromError: error is %T %#v", err, err)
	ret.StatusError.Code = ssh_FX_FAILURE
	ret.StatusError.msg = err.Error()
	if err == io.EOF {
	ret.StatusError.Code = ssh_FX_EOF
	} else if errno, ok := err.(syscall.Errno); ok {
	ret.StatusError.Code = translateErrno(errno)
	} else if pathError, ok := err.(*os.PathError); ok {
	debug("statusFromError: error is %T %#v", pathError.Err, pathError.Err)
	if errno, ok := pathError.Err.(syscall.Errno); ok {
	ret.StatusError.Code = translateErrno(errno)
	}
	}
	}
	return ret
	}

	func clamp(v, max uint32) uint32 {
	if v > max {
	return max
	}
	return v
	}