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, 26 insertions, 0 deletions

diff --git a/internal/fusefrontend_reverse/reverse_diriv.go b/internal/fusefrontend_reverse/reverse_diriv.go
new file mode 100644
index 0000000..df3a4d1
--- /dev/null
+++ b/internal/fusefrontend_reverse/reverse_diriv.go
@@ -0,0 +1,26 @@
+package fusefrontend_reverse
+
+import (
+	"crypto/sha256"
+
+	"github.com/hanwen/go-fuse/fuse"
+	"github.com/hanwen/go-fuse/fuse/nodefs"
+
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+)
+
+// deriveDirIV derives the DirIV from the encrypted directory path by
+// hashing it
+func deriveDirIV(dirPath string) []byte {
+	hash := sha256.Sum256([]byte(dirPath))
+	return hash[:nametransform.DirIVLen]
+}
+
+func (rfs *reverseFS) newDirIVFile(cRelPath string) (nodefs.File, fuse.Status) {
+	cDir := saneDir(cRelPath)
+	absDir, err := rfs.abs(rfs.decryptPath(cDir))
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	return rfs.NewVirtualFile(deriveDirIV(cDir), absDir)
+}