test(mtproto): cover single-backend DC aliases

Follow up gramsrv PR #17 with boundary coverage and public configuration docs.

Canonical-Telesrv: b4df3e72c24470e4ce09e5fc1d46e0c2944f6d3e

Reviewed-Head: e7eb07b9eb

Co-authored-by: onysd <beatvin128@gmail.com>

internal/config/config.go

@@ -31,12 +31,10 @@ type Config struct {
 	RSAKeyPath string
 	// DC 是本 server 的 DC ID。
 	DC int
-	// StrictDCCheck turns on exact DC-ID validation for the permanent-key
-	// exchange (default off = lenient). See mtprotoedge.Options.StrictDC doc
-	// for the full rationale: telesrv is always a single physical backend, but
-	// many client forks alias dc_id 1..5 to it, so a mismatched client-chosen
-	// dc_id is expected, not an attack — strict mode exists only for a
-	// hypothetical future real multi-DC deployment.
+	// StrictDCCheck enables the default-off key-exchange DC-label diagnostic.
+	// The normal single-backend mode accepts every wire int32 label without
+	// partitioning auth keys, sessions, or business state. See
+	// mtprotoedge.Options.StrictDC for the optional strict behavior.
 	StrictDCCheck bool
 	// MTProtoMaxConnections / PerIP 覆盖 raw Accept、codec sniff、握手到认证 session
 	// 的完整物理连接生命周期；负数关闭对应 admission 上限。

internal/config/config_test.go

@@ -49,6 +49,34 @@ func TestLoadUsesExplicitAdvertiseIP(t *testing.T) {
 	}
 }
 
+func TestLoadStrictDCCheck(t *testing.T) {
+	t.Run("defaults off", func(t *testing.T) {
+		disableDefaultConfigFile(t)
+		t.Setenv("TELESRV_STRICT_DC_CHECK", "")
+
+		cfg, err := Load()
+		if err != nil {
+			t.Fatalf("Load: %v", err)
+		}
+		if cfg.StrictDCCheck {
+			t.Fatal("StrictDCCheck = true, want default false")
+		}
+	})
+
+	t.Run("explicitly enabled", func(t *testing.T) {
+		disableDefaultConfigFile(t)
+		t.Setenv("TELESRV_STRICT_DC_CHECK", "true")
+
+		cfg, err := Load()
+		if err != nil {
+			t.Fatalf("Load: %v", err)
+		}
+		if !cfg.StrictDCCheck {
+			t.Fatal("StrictDCCheck = false, want true")
+		}
+	})
+}
+
 func TestLoadMTProtoAdmissionAndRPCBudgets(t *testing.T) {
 	disableDefaultConfigFile(t)
 	t.Setenv("TELESRV_MTPROTO_MAX_CONNECTIONS", "12345")