fusefrontend: Utimens: ugly band-aid for nil pointer crash in go-fuse

Crash is described at https://github.com/rfjakob/gocryptfs/issues/48 .
Revert this once https://github.com/hanwen/go-fuse/pull/131 is merged.

internal/fusefrontend/file.go

@@ -386,7 +386,19 @@ func (f *file) GetAttr(a *fuse.Attr) fuse.Status {
 	return fuse.OK
 }
 
+// TODO drop this once https://github.com/hanwen/go-fuse/pull/131 is
+// merged
+const BrokenAtimeOmit = true
+
 func (f *file) Utimens(a *time.Time, m *time.Time) fuse.Status {
+	if a == nil && BrokenAtimeOmit {
+		// Band-aid for a nil pointer crash, described in
+		// https://github.com/rfjakob/gocryptfs/issues/48
+		//
+		// TODO drop this once https://github.com/hanwen/go-fuse/pull/131 is
+		// merged
+		a = m
+	}
 	f.fdLock.RLock()
 	defer f.fdLock.RUnlock()
 	return f.loopbackFile.Utimens(a, m)

tests/matrix/matrix_test.go

@@ -25,6 +25,7 @@ import (
 	"testing"
 
 	"github.com/rfjakob/gocryptfs/internal/cryptocore"
+	"github.com/rfjakob/gocryptfs/internal/fusefrontend"
 	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
 	"github.com/rfjakob/gocryptfs/tests/test_helpers"
 )
@@ -698,6 +699,11 @@ func doTestUtimesNano(t *testing.T, path string) {
 			out: [2]syscall.Timespec{{Sec: 1, Nsec: 2}, {Sec: 5, Nsec: 6}},
 		},
 	}
+	if fusefrontend.BrokenAtimeOmit {
+		// TODO remove this once the pull request is merged:
+		// https://github.com/hanwen/go-fuse/pull/131
+		utimeTestcases = utimeTestcases[:1]
+	}
 	for i, tc := range utimeTestcases {
 		err := syscall.UtimesNano(path, tc.in[:])
 		if err != nil {