configfile: add Validate() function, support FlagXChaCha20Poly1305

We used to do validation using lists of mandatory feature flags.

With the introduction of XChaCha20Poly1305, this became too
simplistic, as it uses a different IV length, hence disabling
GCMIV128.

Add a dedicated function, Validate(), with open-coded validation
logic.

The validation and creation logic also gets XChaCha20Poly1305
support, and gocryptfs -init -xchacha now writes the flag into
gocryptfs.conf.

1 files changed, 2 insertions, 3 deletions

diff --git a/internal/configfile/config_test.go b/internal/configfile/config_test.go
index 6986888..021b6c1 100644
--- a/internal/configfile/config_test.go
+++ b/internal/configfile/config_test.go
@@ -152,15 +152,14 @@ func TestIsFeatureFlagKnown(t *testing.T) {
 		testKnownFlags = append(testKnownFlags, f)
 	}
 
-	var cf ConfFile
 	for _, f := range testKnownFlags {
-		if !cf.isFeatureFlagKnown(f) {
+		if !isFeatureFlagKnown(f) {
 			t.Errorf("flag %q should be known", f)
 		}
 	}
 
 	f := "StrangeFeatureFlag"
-	if cf.isFeatureFlagKnown(f) {
+	if isFeatureFlagKnown(f) {
 		t.Errorf("flag %q should be NOT known", f)
 	}
 }