reverse: resolve long names in Open and GetAttr

The last patch added functionality for generating gocryptfs.longname.*
files, this patch adds support for mapping them back to the full
filenames.

Note that resolving a long name needs a full readdir. A cache
will be implemented later on to improve performance.

1 files changed, 61 insertions, 0 deletions

diff --git a/internal/fusefrontend_reverse/reverse_longnames.go b/internal/fusefrontend_reverse/reverse_longnames.go
new file mode 100644
index 0000000..46e1791
--- /dev/null
+++ b/internal/fusefrontend_reverse/reverse_longnames.go
@@ -0,0 +1,61 @@
+package fusefrontend_reverse
+
+import (
+	"os"
+	"path/filepath"
+	"syscall"
+
+	"github.com/hanwen/go-fuse/fuse"
+	"github.com/hanwen/go-fuse/fuse/nodefs"
+
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+)
+
+const (
+	shortNameMax = 176
+)
+
+func (rfs *reverseFS) findLongnameParent(dir string, dirIV []byte, longname string) (string, error) {
+	absDir := filepath.Join(rfs.args.Cipherdir, dir)
+	dirfd, err := os.Open(absDir)
+	if err != nil {
+		return "", err
+	}
+	dirEntries, err := dirfd.Readdirnames(-1)
+	if err != nil {
+		return "", err
+	}
+	for _, e := range dirEntries {
+		if len(e) <= shortNameMax {
+			continue
+		}
+		cName := rfs.nameTransform.EncryptName(e, dirIV)
+		if len(cName) <= syscall.NAME_MAX {
+			panic("logic error or wrong shortNameMax constant?")
+		}
+		hName := nametransform.HashLongName(cName)
+		if longname == hName {
+			return e, nil
+		}
+	}
+	return "", syscall.ENOENT
+}
+
+func (rfs *reverseFS) newNameFile(relPath string) (nodefs.File, fuse.Status) {
+	dotName := filepath.Base(relPath)                                    // gocryptfs.longname.XYZ.name
+	longname := dotName[:len(dotName)-len(nametransform.LongNameSuffix)] // gocryptfs.longname.XYZ
+
+	cDir := saneDir(relPath)
+	pDir, err := rfs.decryptPath(cDir)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	dirIV := deriveDirIV(cDir)
+	e, err := rfs.findLongnameParent(pDir, dirIV, longname)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	content := []byte(rfs.nameTransform.EncryptName(e, dirIV))
+	parentFile := filepath.Join(rfs.args.Cipherdir, pDir)
+	return rfs.NewVirtualFile(content, parentFile)
+}