feat: Add WithFxOption

config/config.go

@@ -142,6 +142,8 @@ type Config struct {
 	CustomUDPBlackHoleSuccessCounter  bool
 	IPv6BlackHoleSuccessCounter       *swarm.BlackHoleSuccessCounter
 	CustomIPv6BlackHoleSuccessCounter bool
+
+	UserFxOptions []fx.Option
 }
 
 func (cfg *Config) makeSwarm(eventBus event.Bus, enableMetrics bool) (*swarm.Swarm, error) {
@@ -556,6 +558,8 @@ func (cfg *Config) NewNode() (host.Host, error) {
 		fxopts = append(fxopts, fx.Invoke(func(bho *routed.RoutedHost) { rh = bho }))
 	}
 
+	fxopts = append(fxopts, cfg.UserFxOptions...)
+
 	app := fx.New(fxopts...)
 	if err := app.Start(context.Background()); err != nil {
 		return nil, err

fx_options_test.go

@@ -0,0 +1,61 @@
+package libp2p
+
+import (
+	"testing"
+
+	"github.com/libp2p/go-libp2p/core/event"
+	"github.com/libp2p/go-libp2p/core/host"
+	"github.com/libp2p/go-libp2p/core/peer"
+	"github.com/stretchr/testify/require"
+	"go.uber.org/fx"
+)
+
+func TestGetPeerID(t *testing.T) {
+	var id peer.ID
+	host, err := New(
+		WithFxOption(fx.Invoke(
+			func(myid peer.ID) {
+				id = myid
+			})))
+	require.NoError(t, err)
+	defer host.Close()
+
+	require.Equal(t, host.ID(), id)
+
+}
+
+func TestGetEventBus(t *testing.T) {
+	var eb event.Bus
+	host, err := New(
+		NoTransports,
+		WithFxOption(
+			fx.Invoke(
+				func(e event.Bus) {
+					eb = e
+				},
+			),
+		),
+	)
+	require.NoError(t, err)
+	defer host.Close()
+
+	require.NotNil(t, eb)
+}
+
+func TestGetHost(t *testing.T) {
+	var h host.Host
+	host, err := New(
+		NoTransports,
+		WithFxOption(
+			fx.Invoke(
+				func(hostFromInvoke host.Host) {
+					h = hostFromInvoke
+				},
+			),
+		),
+	)
+	require.NoError(t, err)
+	defer host.Close()
+
+	require.NotNil(t, h)
+}

options.go

@@ -635,3 +635,12 @@ func IPv6BlackHoleSuccessCounter(f *swarm.BlackHoleSuccessCounter) Option {
 		return nil
 	}
 }
+
+// WithFxOption adds a user provided fx.Option to the libp2p constructor.
+// Experimental: This option is subject to change or removal.
+func WithFxOption(opts ...fx.Option) Option {
+	return func(cfg *Config) error {
+		cfg.UserFxOptions = append(cfg.UserFxOptions, opts...)
+		return nil
+	}
+}