Add relayServerIP field to signal for foreign-relay fallback dial

shared/relay/client/manager_fallback_test.go

@@ -0,0 +1,146 @@
+package client
+
+import (
+	"context"
+	"net/netip"
+	"testing"
+	"time"
+
+	"github.com/netbirdio/netbird/client/iface"
+	"github.com/netbirdio/netbird/relay/server"
+)
+
+// TestManager_ForeignRelayFallbackIP exercises the foreign-relay path
+// end-to-end through Manager.OpenConn. Alice and Bob register on different
+// relay servers; Alice dials Bob's foreign relay using an unresolvable
+// FQDN. Without a fallback IP the dial fails; with Bob's advertised IP it
+// recovers and a payload round-trips between the peers.
+func TestManager_ForeignRelayFallbackIP(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
+	defer cancel()
+
+	// Alice's home relay
+	homeCfg := server.ListenerConfig{Address: "127.0.0.1:52401"}
+	homeSrv, err := server.NewServer(newManagerTestServerConfig(homeCfg.Address))
+	if err != nil {
+		t.Fatalf("create home server: %s", err)
+	}
+	homeErr := make(chan error, 1)
+	go func() {
+		if err := homeSrv.Listen(homeCfg); err != nil {
+			homeErr <- err
+		}
+	}()
+	t.Cleanup(func() { _ = homeSrv.Shutdown(context.Background()) })
+	if err := waitForServerToStart(homeErr); err != nil {
+		t.Fatalf("home server: %s", err)
+	}
+
+	// Bob's foreign relay
+	foreignCfg := server.ListenerConfig{Address: "127.0.0.1:52402"}
+	foreignSrv, err := server.NewServer(newManagerTestServerConfig(foreignCfg.Address))
+	if err != nil {
+		t.Fatalf("create foreign server: %s", err)
+	}
+	foreignErr := make(chan error, 1)
+	go func() {
+		if err := foreignSrv.Listen(foreignCfg); err != nil {
+			foreignErr <- err
+		}
+	}()
+	t.Cleanup(func() { _ = foreignSrv.Shutdown(context.Background()) })
+	if err := waitForServerToStart(foreignErr); err != nil {
+		t.Fatalf("foreign server: %s", err)
+	}
+
+	mCtx, mCancel := context.WithCancel(ctx)
+	t.Cleanup(mCancel)
+
+	mgrAlice := NewManager(mCtx, toURL(homeCfg), "alice", iface.DefaultMTU)
+	if err := mgrAlice.Serve(); err != nil {
+		t.Fatalf("alice manager serve: %s", err)
+	}
+
+	mgrBob := NewManager(mCtx, toURL(foreignCfg), "bob", iface.DefaultMTU)
+	if err := mgrBob.Serve(); err != nil {
+		t.Fatalf("bob manager serve: %s", err)
+	}
+
+	// Bob's real relay URL (what mgrBob.RelayInstanceAddress returns).
+	bobRealAddr, err := mgrBob.RelayInstanceAddress()
+	if err != nil {
+		t.Fatalf("bob relay address: %s", err)
+	}
+	// What Bob's RelayInstanceIP() reports — this is the field that
+	// would ride along in signal as relayServerIP.
+	bobAdvertisedIP := mgrBob.RelayInstanceIP()
+	if !bobAdvertisedIP.IsValid() {
+		t.Fatalf("expected valid RelayInstanceIP for bob, got zero")
+	}
+
+	// .invalid is reserved (RFC 2606), so DNS resolution always fails.
+	const brokenFQDN = "rel://relay-bob-instance.invalid:52402"
+	if brokenFQDN == bobRealAddr {
+		t.Fatalf("broken FQDN must differ from bob's real address (%s)", bobRealAddr)
+	}
+
+	t.Run("no fallback IP, dial fails", func(t *testing.T) {
+		dialCtx, dialCancel := context.WithTimeout(ctx, 5*time.Second)
+		defer dialCancel()
+		_, err := mgrAlice.OpenConn(dialCtx, brokenFQDN, "bob", netip.Addr{})
+		if err == nil {
+			t.Fatalf("expected OpenConn to fail without fallback IP, got success")
+		}
+	})
+
+	t.Run("fallback IP recovers", func(t *testing.T) {
+		// Bob waits for Alice's incoming peer connection on his side.
+		bobSideCh := make(chan error, 1)
+		go func() {
+			conn, err := mgrBob.OpenConn(ctx, bobRealAddr, "alice", netip.Addr{})
+			if err != nil {
+				bobSideCh <- err
+				return
+			}
+			buf := make([]byte, 1024)
+			n, err := conn.Read(buf)
+			if err != nil {
+				bobSideCh <- err
+				return
+			}
+			if _, err := conn.Write(buf[:n]); err != nil {
+				bobSideCh <- err
+				return
+			}
+			bobSideCh <- nil
+		}()
+
+		aliceConn, err := mgrAlice.OpenConn(ctx, brokenFQDN, "bob", bobAdvertisedIP)
+		if err != nil {
+			t.Fatalf("alice OpenConn with fallback IP: %s", err)
+		}
+		t.Cleanup(func() { _ = aliceConn.Close() })
+
+		payload := []byte("alice-to-bob")
+		if _, err := aliceConn.Write(payload); err != nil {
+			t.Fatalf("alice write: %s", err)
+		}
+
+		buf := make([]byte, len(payload))
+		if _, err := aliceConn.Read(buf); err != nil {
+			t.Fatalf("alice read echo: %s", err)
+		}
+		if string(buf) != string(payload) {
+			t.Fatalf("echo mismatch: got %q want %q", buf, payload)
+		}
+
+		select {
+		case err := <-bobSideCh:
+			if err != nil {
+				t.Fatalf("bob side: %s", err)
+			}
+		case <-time.After(5 * time.Second):
+			t.Fatalf("timed out waiting for bob side")
+		}
+	})
+}