configfile: use map[flagIota] for feature flags

This should make things saner and more extensible. It prepares
the infrastructure for "required feature flags" that will be used
to deprecate old gocryptfs version.

internal/configfile/config_file.go

@@ -4,7 +4,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
-	"log"
 
 	"github.com/rfjakob/gocryptfs/internal/contentenc"
 	"github.com/rfjakob/gocryptfs/internal/cryptocore"
@@ -55,13 +54,13 @@ func CreateConfFile(filename string, password string, plaintextNames bool, logN
 	cf.EncryptKey(key, password, logN)
 
 	// Set feature flags
-	cf.FeatureFlags = append(cf.FeatureFlags, FlagGCMIV128)
+	cf.FeatureFlags = append(cf.FeatureFlags, knownFlags[FlagGCMIV128])
 	if plaintextNames {
-		cf.FeatureFlags = append(cf.FeatureFlags, FlagPlaintextNames)
+		cf.FeatureFlags = append(cf.FeatureFlags, knownFlags[FlagPlaintextNames])
 	} else {
-		cf.FeatureFlags = append(cf.FeatureFlags, FlagDirIV)
-		cf.FeatureFlags = append(cf.FeatureFlags, FlagEMENames)
-		cf.FeatureFlags = append(cf.FeatureFlags, FlagLongNames)
+		cf.FeatureFlags = append(cf.FeatureFlags, knownFlags[FlagDirIV])
+		cf.FeatureFlags = append(cf.FeatureFlags, knownFlags[FlagEMENames])
+		cf.FeatureFlags = append(cf.FeatureFlags, knownFlags[FlagLongNames])
 	}
 
 	// Write file to disk
@@ -166,37 +165,3 @@ func (cf *ConfFile) WriteFile() error {
 
 	return nil
 }
-
-const (
-	// Understood Feature Flags.
-	// Also teach isFeatureFlagKnown() about any additions and
-	// add it to CreateConfFile() if you want to have it enabled by default.
-	FlagPlaintextNames = "PlaintextNames"
-	FlagDirIV          = "DirIV"
-	FlagEMENames       = "EMENames"
-	FlagGCMIV128       = "GCMIV128"
-	FlagLongNames      = "LongNames"
-)
-
-// Verify that we understand a feature flag
-func (cf *ConfFile) isFeatureFlagKnown(flag string) bool {
-	switch flag {
-	case FlagPlaintextNames, FlagDirIV, FlagEMENames, FlagGCMIV128, FlagLongNames:
-		return true
-	default:
-		return false
-	}
-}
-
-// isFeatureFlagSet - is the feature flag "flagWant" enabled?
-func (cf *ConfFile) IsFeatureFlagSet(flagWant string) bool {
-	if !cf.isFeatureFlagKnown(flagWant) {
-		log.Panicf("BUG: Tried to use unsupported feature flag %s", flagWant)
-	}
-	for _, flag := range cf.FeatureFlags {
-		if flag == flagWant {
-			return true
-		}
-	}
-	return false
-}

internal/configfile/config_test.go

@@ -72,14 +72,23 @@ func TestCreateConfFile(t *testing.T) {
 }
 
 func TestIsFeatureFlagKnown(t *testing.T) {
+	// Test a few hardcoded values
+	testKnownFlags := []string{"DirIV", "PlaintextNames", "EMENames", "GCMIV128", "LongNames"}
+	// And also everything in knownFlags (yes, it is likely that we end up with
+	// some duplicates. Does not matter.)
+	for _, f := range knownFlags {
+		testKnownFlags = append(testKnownFlags, f)
+	}
+
 	var cf ConfFile
-	if !cf.isFeatureFlagKnown(FlagDirIV) {
-		t.Errorf("This flag should be known")
+	for _, f := range testKnownFlags {
+		if !cf.isFeatureFlagKnown(f) {
+			t.Errorf("flag %q should be known", f)
+		}
 	}
-	if !cf.isFeatureFlagKnown(FlagPlaintextNames) {
-		t.Errorf("This flag should be known")
-	}
-	if cf.isFeatureFlagKnown("StrangeFeatureFlag") {
-		t.Errorf("This flag should be NOT known")
+
+	f := "StrangeFeatureFlag"
+	if cf.isFeatureFlagKnown(f) {
+		t.Errorf("flag %q should be NOT known", f)
 	}
 }

internal/configfile/feature_flags.go

@@ -0,0 +1,41 @@
+package configfile
+
+type flagIota int
+
+const (
+	FlagPlaintextNames flagIota = iota
+	FlagDirIV
+	FlagEMENames
+	FlagGCMIV128
+	FlagLongNames
+)
+
+// knownFlags stores the known feature flags and their string representation
+var knownFlags map[flagIota]string = map[flagIota]string{
+	FlagPlaintextNames: "PlaintextNames",
+	FlagDirIV:          "DirIV",
+	FlagEMENames:       "EMENames",
+	FlagGCMIV128:       "GCMIV128",
+	FlagLongNames:      "LongNames",
+}
+
+// isFeatureFlagKnown verifies that we understand a feature flag
+func (cf *ConfFile) isFeatureFlagKnown(flag string) bool {
+	for _, knownFlag := range knownFlags {
+		if knownFlag == flag {
+			return true
+		}
+	}
+	return false
+}
+
+// isFeatureFlagSet - is the feature flag "flagWant" enabled?
+func (cf *ConfFile) IsFeatureFlagSet(flagWant flagIota) bool {
+	flagString := knownFlags[flagWant]
+	for _, flag := range cf.FeatureFlags {
+		if flag == flagString {
+			return true
+		}
+	}
+	return false
+}