Fallback to another DC if given is unknown

mtglib/internal/telegram/address_pool.go

@@ -7,6 +7,14 @@ type addressPool struct {
 	v6 [][]tgAddr
 }
 
+func (a addressPool) isValidDC(dc int) bool {
+	return dc > 0 && dc <= len(a.v4) && dc <= len(a.v6)
+}
+
+func (a addressPool) getRandomDC() int {
+	return 1 + rand.Intn(len(a.v4))
+}
+
 func (a addressPool) getV4(dc int) []tgAddr {
 	return a.get(a.v4, dc-1)
 }

mtglib/internal/telegram/telegram.go

@@ -42,6 +42,14 @@ func (t Telegram) Dial(ctx context.Context, dc int) (net.Conn, error) {
 	return nil, fmt.Errorf("cannot dial to %d dc: %w", dc, err)
 }
 
+func (t Telegram) IsKnownDC(dc int) bool {
+	return t.pool.isValidDC(dc)
+}
+
+func (t Telegram) GetFallbackDC() int {
+	return t.pool.getRandomDC()
+}
+
 func New(dialer Dialer, ipPreference string, useTestDCs bool) (*Telegram, error) {
 	var pref preferIP
 

mtglib/internal/telegram/telegram_internal_test.go

@@ -44,6 +44,7 @@ func (suite *TelegramTestSuite) TestUnknownDC() {
 		suite.T().Run(strconv.Itoa(value), func(t *testing.T) {
 			_, err := suite.t.Dial(context.Background(), value)
 			assert.Error(t, err)
+			assert.False(t, suite.t.IsKnownDC(value))
 		})
 	}
 }
@@ -71,6 +72,7 @@ func (suite *TelegramTestSuite) TestDialToCorrectIPs() {
 
 			_, err := suite.t.Dial(context.Background(), idx)
 			assert.True(t, errors.Is(err, io.EOF))
+			assert.True(t, suite.t.IsKnownDC(idx))
 		})
 	}
 }
@@ -135,6 +137,22 @@ func (suite *TelegramTestSuite) TestUnknownPreferIP() {
 	suite.Error(err)
 }
 
+func (suite *TelegramTestSuite) TestFallbackDC() {
+	dcs := make([]int, 10)
+
+	for i := 0; i < len(dcs); i++ {
+		dcs[i] = suite.t.GetFallbackDC()
+	}
+
+	for _, v := range dcs {
+		value := v
+
+		suite.T().Run(strconv.Itoa(value), func(t *testing.T) {
+			assert.True(t, suite.t.IsKnownDC(value))
+		})
+	}
+}
+
 func TestTelegram(t *testing.T) {
 	t.Parallel()
 	suite.Run(t, &TelegramTestSuite{})

mtglib/proxy.go

@@ -207,7 +207,16 @@ func (p *Proxy) doObfuscated2Handshake(ctx *streamContext) error {
 }
 
 func (p *Proxy) doTelegramCall(ctx *streamContext) error {
-	conn, err := p.telegram.Dial(ctx, ctx.dc)
+	dc := ctx.dc
+
+	if !p.telegram.IsKnownDC(dc) {
+		dc = p.telegram.GetFallbackDC()
+		ctx.logger = ctx.logger.BindInt("fallback_dc", dc)
+
+		ctx.logger.Warning("unknown DC, fallbacks")
+	}
+
+	conn, err := p.telegram.Dial(ctx, dc)
 	if err != nil {
 		return fmt.Errorf("cannot dial to Telegram: %w", err)
 	}