feat: Add support for legacy markers in ParseManagedBlock to ensure backward compatibility

hostfile/managed_test.go

@@ -159,6 +159,134 @@ func TestParseManagedBlock_CorruptDuplicateMarkers(t *testing.T) {
 	}
 }
 
+// ---------------------------------------------------------------------------
+// ParseManagedBlock — legacy marker tests
+// ---------------------------------------------------------------------------
+
+func TestParseManagedBlock_LegacyMarkers(t *testing.T) {
+	lines := []string{
+		"127.0.0.1 localhost",
+		hostfile.LegacyStartMarker,
+		"1.1.1.1\thost1",
+		"2.2.2.2\thost2",
+		hostfile.LegacyEndMarker,
+		"# trailing comment",
+	}
+	prefix, managed, postfix, has, err := hostfile.ParseManagedBlock(lines)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !has {
+		t.Fatal("expected HasManagedBlock=true for legacy markers")
+	}
+	if len(prefix) != 1 || prefix[0] != "127.0.0.1 localhost" {
+		t.Errorf("unexpected prefix: %v", prefix)
+	}
+	if len(managed) != 2 {
+		t.Errorf("expected 2 managed lines, got %v", managed)
+	}
+	if len(postfix) != 1 || postfix[0] != "# trailing comment" {
+		t.Errorf("unexpected postfix: %v", postfix)
+	}
+}
+
+func TestParseManagedBlock_LegacyStartMarkerAtLine0(t *testing.T) {
+	lines := []string{
+		hostfile.LegacyStartMarker,
+		"1.1.1.1\thost1",
+		hostfile.LegacyEndMarker,
+	}
+	prefix, managed, postfix, has, err := hostfile.ParseManagedBlock(lines)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !has {
+		t.Fatal("expected HasManagedBlock=true")
+	}
+	if len(prefix) != 0 {
+		t.Errorf("expected empty prefix, got %v", prefix)
+	}
+	if len(managed) != 1 || managed[0] != "1.1.1.1\thost1" {
+		t.Errorf("unexpected managed: %v", managed)
+	}
+	if len(postfix) != 0 {
+		t.Errorf("expected empty postfix, got %v", postfix)
+	}
+}
+
+func TestParseManagedBlock_LegacyCorruptStartWithoutEnd(t *testing.T) {
+	lines := []string{
+		"127.0.0.1 localhost",
+		hostfile.LegacyStartMarker,
+		"1.1.1.1\thost1",
+	}
+	_, _, _, _, err := hostfile.ParseManagedBlock(lines)
+	if err == nil {
+		t.Fatal("expected error for legacy start marker without end marker")
+	}
+}
+
+func TestParseManagedBlock_LegacyCorruptEndWithoutStart(t *testing.T) {
+	lines := []string{
+		"127.0.0.1 localhost",
+		"1.1.1.1\thost1",
+		hostfile.LegacyEndMarker,
+	}
+	_, _, _, _, err := hostfile.ParseManagedBlock(lines)
+	if err == nil {
+		t.Fatal("expected error for legacy end marker without start marker")
+	}
+}
+
+func TestParseManagedBlock_MixedOldStartNewEnd(t *testing.T) {
+	// Legacy start with current end — still a valid block (both substrings match).
+	lines := []string{
+		"127.0.0.1 localhost",
+		hostfile.LegacyStartMarker,
+		"1.1.1.1\thost1",
+		hostfile.EndMarker,
+	}
+	_, managed, _, has, err := hostfile.ParseManagedBlock(lines)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !has {
+		t.Fatal("expected HasManagedBlock=true for mixed markers")
+	}
+	if len(managed) != 1 {
+		t.Errorf("expected 1 managed line, got %v", managed)
+	}
+}
+
+func TestParseManagedBlock_LegacyUpgradedOnWrite(t *testing.T) {
+	// Verify that a legacy block is parsed and then reassembled with current markers.
+	lines := []string{
+		"127.0.0.1 localhost",
+		hostfile.LegacyStartMarker,
+		"1.1.1.1\thost1",
+		hostfile.LegacyEndMarker,
+		"# trailing",
+	}
+	prefix, managed, postfix, _, err := hostfile.ParseManagedBlock(lines)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	result := hostfile.AssembleContent(prefix, managed, postfix)
+	// The reassembled output should use the current markers, not legacy.
+	found := false
+	for _, l := range result {
+		if l == hostfile.StartMarker {
+			found = true
+		}
+		if l == hostfile.LegacyStartMarker {
+			t.Fatal("reassembled content should not contain legacy start marker")
+		}
+	}
+	if !found {
+		t.Fatal("reassembled content should contain current start marker")
+	}
+}
+
 // ---------------------------------------------------------------------------
 // AddEntries tests
 // ---------------------------------------------------------------------------