feat(config): sync make default country configurable

internal/rpc/help.go

@@ -19,7 +19,11 @@ func (r *Router) registerHelp(d *tlprofile.Dispatcher) {
 		return r.onHelpGetConfig(ctx)
 	})
 	registerRPC[*tg.HelpGetNearestDCRequest](d, tlprofile.SemanticMethodHelpGetNearestDC, func(ctx context.Context, layerRequest *tg.HelpGetNearestDCRequest) (any, error) {
-		return tdesktop.NearestDC(r.cfg.DC), nil
+		return &tg.NearestDC{
+			Country:   r.cfg.DefaultCountryCode,
+			ThisDC:    r.cfg.DC,
+			NearestDC: r.cfg.DC,
+		}, nil
 	})
 	registerRPC[*tg.HelpGetInviteTextRequest](d, tlprofile.SemanticMethodHelpGetInviteText, func(ctx context.Context, layerRequest *tg.HelpGetInviteTextRequest) (any, error) {
 		return &tg.HelpInviteText{Message: "Join me on " + branding.ProductName + "."}, nil

internal/rpc/router.go

@@ -52,6 +52,7 @@ var (
 // Config 是 Router 所需的服务端信息。
 type Config struct {
 	DC                  int
+	DefaultCountryCode  string // help.getNearestDc 返回的 ISO 3166-1 alpha-2 国家码。
 	IP                  string // 对外公布的 DC IP（写入 DCOptions）
 	Port                int    // 对外公布的 DC 端口
 	InstanceID          string // 进程内唯一标识，用于跨实例 ephemeral push 去重。

internal/rpc/router_dispatch_test.go

@@ -71,6 +71,31 @@ func TestDispatchUnwrapsWrappers(t *testing.T) {
 	}
 }
 
+func TestDispatchNearestDCUsesConfiguredDefaultCountryCode(t *testing.T) {
+	r := New(Config{
+		DC:                 2,
+		DefaultCountryCode: "US",
+		IP:                 "127.0.0.1",
+		Port:               2398,
+	}, Deps{}, zaptest.NewLogger(t), clock.System)
+
+	var b bin.Buffer
+	if err := (&tg.HelpGetNearestDCRequest{}).Encode(&b); err != nil {
+		t.Fatalf("encode help.getNearestDc: %v", err)
+	}
+	enc, err := r.Dispatch(context.Background(), [8]byte{}, 0, &b)
+	if err != nil {
+		t.Fatalf("dispatch help.getNearestDc: %v", err)
+	}
+	nearest, ok := enc.(*tg.NearestDC)
+	if !ok {
+		t.Fatalf("result type = %T, want *tg.NearestDC", enc)
+	}
+	if nearest.Country != "US" || nearest.ThisDC != 2 || nearest.NearestDC != 2 {
+		t.Fatalf("nearestDc = %+v", nearest)
+	}
+}
+
 func TestDispatchRejectsAuthorizedRPCBeforeLogin(t *testing.T) {
 	r := New(Config{DC: 2, IP: "127.0.0.1", Port: 2398}, Deps{
 		Auth: &captureAuthService{},