clarify objectType handling in List, ListElements

fake.go

@@ -157,6 +157,11 @@ func (fake *Fake) ListAll(_ context.Context) (map[string][]string, error) {
 
 // List is part of Interface.
 func (fake *Fake) List(_ context.Context, objectType string) ([]string, error) {
+	objectType = canonicalObjectType(objectType)
+	if _, ok := listableTypes[objectType]; !ok {
+		return nil, fmt.Errorf("can't List() type %q", objectType)
+	}
+
 	fake.RLock()
 	defer fake.RUnlock()
 	if fake.Table == nil {
@@ -166,29 +171,29 @@ func (fake *Fake) List(_ context.Context, objectType string) ([]string, error) {
 	var result []string
 
 	switch objectType {
-	case "flowtable", "flowtables":
+	case "flowtable":
 		for name := range fake.Table.Flowtables {
 			result = append(result, name)
 		}
-	case "chain", "chains":
+	case "chain":
 		for name := range fake.Table.Chains {
 			result = append(result, name)
 		}
-	case "set", "sets":
+	case "set":
 		for name := range fake.Table.Sets {
 			result = append(result, name)
 		}
-	case "map", "maps":
+	case "map":
 		for name := range fake.Table.Maps {
 			result = append(result, name)
 		}
-	case "counter", "counters":
+	case "counter":
 		for name := range fake.Table.Counters {
 			result = append(result, name)
 		}
 
 	default:
-		return nil, fmt.Errorf("unsupported object type %q", objectType)
+		return nil, fmt.Errorf("internal error: missing List() support for %q", objectType)
 	}
 
 	return result, nil
@@ -220,6 +225,10 @@ func (fake *Fake) ListRules(_ context.Context, chain string) ([]*Rule, error) {
 
 // ListElements is part of Interface
 func (fake *Fake) ListElements(_ context.Context, objectType, name string) ([]*Element, error) {
+	if objectType != "set" && objectType != "map" {
+		return nil, fmt.Errorf("invalid objectType %q", objectType)
+	}
+
 	fake.RLock()
 	defer fake.RUnlock()
 	if fake.Table == nil {

nftables.go

@@ -46,8 +46,8 @@ type Interface interface {
 	ListAll(ctx context.Context) (map[string][]string, error)
 
 	// List returns a list of the names of the objects of objectType ("chain", "set",
-	// "map" or "counter") in the table. If there are no such objects, this will
-	// return an empty list and no error.
+	// "map", "counter", or "flowtable" in the table. If there are no such objects,
+	// this will return an empty list and no error.
 	List(ctx context.Context, objectType string) ([]string, error)
 
 	// ListRules returns a list of the rules in a chain, in order. If no chain name is
@@ -412,17 +412,33 @@ func (nft *realNFTables) ListAll(ctx context.Context) (map[string][]string, erro
 	return result, nil
 }
 
+// Takes objectType, which can be either singular or plural, and returns the singular
+// form.
+func canonicalObjectType(objectType string) string {
+	// All currently-existing nftables object types have plural forms that are just
+	// the singular form plus 's', and none have singular forms ending in 's'.
+	if objectType[len(objectType)-1] == 's' {
+		objectType = objectType[:len(objectType)-1]
+	}
+	return objectType
+}
+
+var listableTypes = map[string]bool{
+	"chain":     true,
+	"set":       true,
+	"map":       true,
+	"counter":   true,
+	"flowtable": true,
+}
+
 // List is part of Interface.
 func (nft *realNFTables) List(ctx context.Context, objectType string) ([]string, error) {
 	if nft.table == "" {
 		return nil, fmt.Errorf("can't use List() on a knftables.Interface with no associated family/table")
 	}
-
-	// objectType is allowed to be either singular or plural. All currently-existing
-	// nftables object types have plural forms that are just the singular form plus 's',
-	// and none have singular forms ending in 's'.
-	if objectType[len(objectType)-1] == 's' {
-		objectType = objectType[:len(objectType)-1]
+	objectType = canonicalObjectType(objectType)
+	if _, ok := listableTypes[objectType]; !ok {
+		return nil, fmt.Errorf("can't List() type %q", objectType)
 	}
 
 	// We want to restrict nft to looking only at our table, so we have to do "list table"
@@ -501,6 +517,9 @@ func (nft *realNFTables) ListElements(ctx context.Context, objectType, name stri
 	if nft.table == "" {
 		return nil, fmt.Errorf("can't use ListElements() on a knftables.Interface with no associated family/table")
 	}
+	if objectType != "set" && objectType != "map" {
+		return nil, fmt.Errorf("invalid objectType %q", objectType)
+	}
 
 	cmd := exec.CommandContext(ctx, nft.path, "--json", "list", objectType, string(nft.family), nft.table, name)
 	out, err := nft.exec.Run(cmd)