update writefile code. changed the way usetemp works to make sure file permissions/owner/attributes are kept on original file

pkg/packet/packet.go

@@ -422,6 +422,7 @@ type FileInfo struct {
 	ModTs    int64  `json:"modts"`
 	IsDir    bool   `json:"isdir,omitempty"`
 	Perm     int    `json:"perm"`
+	NotFound bool   `json:"notfound,omitempty"` // when NotFound is set, Perm will be set to permission for directory
 }
 
 type StreamFileResponseType struct {

pkg/server/server.go

@@ -272,6 +272,58 @@ func makeTemp(path string, mode fs.FileMode) (*os.File, error) {
 	return writeFd, nil
 }
 
+func checkFileWritable(path string) error {
+	finfo, err := os.Stat(path) // ok to follow symlinks
+	if errors.Is(err, fs.ErrNotExist) {
+		dirName := filepath.Dir(path)
+		dirInfo, err := os.Stat(dirName)
+		if err != nil {
+			return fmt.Errorf("file does not exist, error trying to stat parent directory: %w", err)
+		}
+		if !dirInfo.IsDir() {
+			return fmt.Errorf("file does not exist, parent path [%s] is not a directory", dirName)
+		}
+		return nil
+	} else {
+		if err != nil {
+			return fmt.Errorf("cannot stat: %w", err)
+		}
+		if finfo.IsDir() {
+			return fmt.Errorf("invalid path, cannot write a directory")
+		}
+		if (finfo.Mode() & fs.ModeSymlink) != 0 {
+			return fmt.Errorf("writefile does not support symlinks") // note this shouldn't happen because we're using Stat (not Lstat)
+		}
+		if (finfo.Mode() & (fs.ModeNamedPipe | fs.ModeSocket | fs.ModeDevice)) != 0 {
+			return fmt.Errorf("writefile does not support special files (named pipes, sockets, devices): mode=%v", finfo.Mode())
+		}
+		writePerm := (finfo.Mode().Perm() & 0o222)
+		if writePerm == 0 {
+			return fmt.Errorf("file is not writable, perms: %v", finfo.Mode().Perm())
+		}
+		return nil
+	}
+}
+
+func copyFile(dstName string, srcName string) error {
+	srcFd, err := os.Open(srcName)
+	if err != nil {
+		return err
+	}
+	defer srcFd.Close()
+	dstFd, err := os.OpenFile(dstName, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o777) // use 777 because OpenFile respects umask
+	if err != nil {
+		return err
+	}
+	// we don't defer dstFd.Close() so we can return an error if dstFd.Close() returns an error
+	_, err = io.Copy(dstFd, srcFd)
+	if err != nil {
+		dstFd.Close()
+		return err
+	}
+	return dstFd.Close()
+}
+
 func (m *MServer) writeFile(pk *packet.WriteFilePacketType, wfc *WriteFileContext) {
 	defer wfc.setDone()
 	if pk.Path == "" {
@@ -280,55 +332,19 @@ func (m *MServer) writeFile(pk *packet.WriteFilePacketType, wfc *WriteFileContex
 		m.Sender.SendPacket(resp)
 		return
 	}
-	var finfo fs.FileInfo
-	var err error
-	if pk.UseTemp {
-		finfo, err = os.Lstat(pk.Path)
-	} else {
-		finfo, err = os.Stat(pk.Path)
-	}
-	if err == nil && finfo.IsDir() {
-		err = fmt.Errorf("invalid path, cannot write a directory")
-	}
-	if err == nil && ((finfo.Mode() & fs.ModeSymlink) != 0) {
-		err = fmt.Errorf("writefile (with usetemp) does not support symlinks")
-	}
-	if err == nil && ((finfo.Mode() & (fs.ModeNamedPipe | fs.ModeSocket | fs.ModeDevice | fs.ModeSetuid | fs.ModeSetgid)) != 0) {
-		err = fmt.Errorf("writefile does not support special files (named pipes, sockets, devices, setuid, or setgid): mode=%v", finfo.Mode())
-	}
-	if err == nil {
-		writePerm := (finfo.Mode().Perm() & 0o222)
-		if writePerm == 0 {
-			err = fmt.Errorf("file is not writable, perms: %v", finfo.Mode().Perm())
-		}
-	}
+	err := checkFileWritable(pk.Path)
 	if err != nil {
 		resp := packet.MakeWriteFileReadyPacket(pk.ReqId)
 		resp.Error = err.Error()
 		m.Sender.SendPacket(resp)
 		return
 	}
-
 	var writeFd *os.File
 	if pk.UseTemp {
-		dirName := filepath.Dir(pk.Path)
-		dirFInfo, err := os.Stat(dirName)
-		if err == nil {
-			writePerm := (dirFInfo.Mode().Perm() & 0o222)
-			if writePerm == 0 {
-				err = fmt.Errorf("file-write tempmode is set, but parent directory is not writeable, perms: %v", dirFInfo.Mode().Perm())
-			}
-		}
+		writeFd, err = os.CreateTemp("", "mshell.writefile.*") // "" means make this file in standard TempDir
 		if err != nil {
 			resp := packet.MakeWriteFileReadyPacket(pk.ReqId)
-			resp.Error = err.Error()
-			m.Sender.SendPacket(resp)
-			return
-		}
-		writeFd, err = makeTemp(pk.Path, finfo.Mode().Perm())
-		if err != nil {
-			resp := packet.MakeWriteFileReadyPacket(pk.ReqId)
-			resp.Error = fmt.Sprintf("write-file could not open tempfile: %v", err)
+			resp.Error = fmt.Sprintf("cannot create temp file: %v", err)
 			m.Sender.SendPacket(resp)
 			return
 		}
@@ -388,12 +404,12 @@ func (m *MServer) writeFile(pk *packet.WriteFilePacketType, wfc *WriteFileContex
 		if doneErr != nil {
 			os.Remove(writeFd.Name())
 		} else {
-			renameErr := os.Rename(writeFd.Name(), pk.Path)
-			if renameErr != nil {
-				doneErr = fmt.Errorf("error renaming temp file: %v", renameErr)
-				// rename failed, try to remove temp file still
-				os.Remove(writeFd.Name())
+			// copy file between writeFd.Name() and pk.Path
+			copyErr := copyFile(pk.Path, writeFd.Name())
+			if err != nil {
+				doneErr = fmt.Errorf("error writing file: %v", copyErr)
 			}
+			os.Remove(writeFd.Name())
 		}
 	}
 	donePk := packet.MakeWriteFileDonePacket(pk.ReqId)
@@ -403,9 +419,44 @@ func (m *MServer) writeFile(pk *packet.WriteFilePacketType, wfc *WriteFileContex
 	m.Sender.SendPacket(donePk)
 }
 
+func (m *MServer) returnStreamFileNewFileResponse(pk *packet.StreamFilePacketType) {
+	// ok, file doesn't exist, so try to check the directory at least to see if we can write a file here
+	resp := packet.MakeStreamFileResponse(pk.ReqId)
+	defer func() {
+		if resp.Error == "" {
+			resp.Done = true
+		}
+		m.Sender.SendPacket(resp)
+	}()
+	dirName := filepath.Dir(pk.Path)
+	dirInfo, err := os.Stat(dirName)
+	if err != nil {
+		resp.Error = fmt.Sprintf("file does not exist, error trying to stat parent directory: %v", err)
+		return
+	}
+	if !dirInfo.IsDir() {
+		resp.Error = fmt.Sprintf("file does not exist, parent path [%s] is not a directory", dirName)
+		return
+	}
+	resp.Info = &packet.FileInfo{
+		Name:     pk.Path,
+		Size:     0,
+		ModTs:    0,
+		IsDir:    false,
+		Perm:     int(dirInfo.Mode().Perm()),
+		NotFound: true,
+	}
+	return
+}
+
 func (m *MServer) streamFile(pk *packet.StreamFilePacketType) {
 	resp := packet.MakeStreamFileResponse(pk.ReqId)
 	finfo, err := os.Stat(pk.Path)
+	if errors.Is(err, fs.ErrNotExist) {
+		// special return
+		m.returnStreamFileNewFileResponse(pk)
+		return
+	}
 	if err != nil {
 		resp.Error = fmt.Sprintf("cannot stat file %q: %v", pk.Path, err)
 		m.Sender.SendPacket(resp)