fusefronted: report plaintext size on symlink creation

gocryptfs 2.0 introduced the regression that the size
reported at symlink creation was the ciphertext size,
which is wrong.

Report the plaintext size.

Fixes #574

internal/fusefrontend/node.go

@@ -354,6 +354,9 @@ func (n *Node) Symlink(ctx context.Context, target, name string, out *fuse.Entry
 		errno = fs.ToErrno(err)
 		return
 	}
+	// Report the plaintext size, not the encrypted blob size
+	st.Size = int64(len(target))
+
 	inode = n.newChild(ctx, st, out)
 	return inode, 0
 }

internal/fusefrontend/node_helpers.go

@@ -58,6 +58,8 @@ func (n *Node) readlink(dirfd int, cName string) (out []byte, errno syscall.Errn
 }
 
 // translateSize translates the ciphertext size in `out` into plaintext size.
+// Handles regular files & symlinks (and finds out what is what by looking at
+// `out.Mode`).
 func (n *Node) translateSize(dirfd int, cName string, out *fuse.Attr) {
 	if out.IsRegular() {
 		rn := n.rootNode()

tests/matrix/matrix_test.go

@@ -19,6 +19,7 @@ import (
 	"math/rand"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"runtime"
 	"sync"
 	"syscall"
@@ -882,3 +883,21 @@ func TestStatfs(t *testing.T) {
 		t.Errorf("statfs reports size zero: %#v", st)
 	}
 }
+
+// gocryptfs 2.0 reported the ciphertext size on symlink creation, causing
+// confusion: https://github.com/rfjakob/gocryptfs/issues/574
+func TestSymlinkSize(t *testing.T) {
+	p := filepath.Join(test_helpers.DefaultPlainDir, t.Name())
+	// SYMLINK reports the size to the kernel
+	if err := syscall.Symlink("foo", p); err != nil {
+		t.Fatal(err)
+	}
+	// Kernel serves us this value from the attr cache
+	var st syscall.Stat_t
+	if err := syscall.Lstat(p, &st); err != nil {
+		t.Fatal(err)
+	}
+	if st.Size != 3 {
+		t.Errorf("wrong size: have %d, want %d", st.Size, 3)
+	}
+}