fix(ipip-476): wire dht router to composableRouter

server.go

@@ -194,9 +194,18 @@ func start(ctx context.Context, cfg *config) error {
 	}
 
 	// Combine HTTP routers with DHT and additional routers
-	crRouters := combineRouters(dhtRouting, cachedAddrBook, providerHTTPRouters, blockProviderRouters)
-	prRouters := combineRouters(dhtRouting, cachedAddrBook, peerHTTPRouters, nil)
-	ipnsRouters := combineRouters(dhtRouting, cachedAddrBook, ipnsHTTPRouters, nil)
+	crRouters := combineRouters(h, dhtRouting, cachedAddrBook, providerHTTPRouters, blockProviderRouters)
+	prRouters := combineRouters(h, dhtRouting, cachedAddrBook, peerHTTPRouters, nil)
+	ipnsRouters := combineRouters(h, dhtRouting, cachedAddrBook, ipnsHTTPRouters, nil)
+
+	// Create DHT router for GetClosestPeers endpoint
+	var dhtRouters router
+	if cachedAddrBook != nil && dhtRouting != nil {
+		cachedRouter := NewCachedRouter(libp2pRouter{host: h, routing: dhtRouting}, cachedAddrBook)
+		dhtRouters = sanitizeRouter{cachedRouter}
+	} else if dhtRouting != nil {
+		dhtRouters = sanitizeRouter{libp2pRouter{host: h, routing: dhtRouting}}
+	}
 
 	_, port, err := net.SplitHostPort(cfg.listenAddress)
 	if err != nil {
@@ -220,6 +229,7 @@ func start(ctx context.Context, cfg *config) error {
 		providers: crRouters,
 		peers:     prRouters,
 		ipns:      ipnsRouters,
+		dht:       dhtRouters,
 	}, handlerOpts...)
 
 	// Add CORS.
@@ -325,14 +335,14 @@ func newHost(cfg *config) (host.Host, error) {
 
 // combineRouters combines delegated HTTP routers with DHT and additional routers.
 // It no longer creates HTTP clients (that's done in createDelegatedHTTPRouters).
-func combineRouters(dht routing.Routing, cachedAddrBook *cachedAddrBook, delegatedRouters, additionalRouters []router) router {
+func combineRouters(h host.Host, dht routing.Routing, cachedAddrBook *cachedAddrBook, delegatedRouters, additionalRouters []router) router {
 	var dhtRouter router
 
 	if cachedAddrBook != nil {
-		cachedRouter := NewCachedRouter(libp2pRouter{routing: dht}, cachedAddrBook)
+		cachedRouter := NewCachedRouter(libp2pRouter{host: h, routing: dht}, cachedAddrBook)
 		dhtRouter = sanitizeRouter{cachedRouter}
 	} else if dht != nil {
-		dhtRouter = sanitizeRouter{libp2pRouter{routing: dht}}
+		dhtRouter = sanitizeRouter{libp2pRouter{host: h, routing: dht}}
 	}
 
 	if len(delegatedRouters) == 0 && len(additionalRouters) == 0 {

server_dht_test.go

@@ -351,6 +351,32 @@ func TestGetClosestPeersEndpoint(t *testing.T) {
 		require.Equal(t, http.StatusOK, resp.StatusCode)
 		require.Equal(t, mediaTypeJSON, resp.Header.Get("Content-Type"))
 	})
+
+	t.Run("GET /routing/v1/dht/closest/peers/{cid} returns 500 when DHT is disabled", func(t *testing.T) {
+		t.Parallel()
+
+		_, pid := makeEd25519PeerID(t)
+		key := peer.ToCid(pid)
+
+		// Pass nil router to simulate DHT disabled via --dht=disabled
+		handler := server.Handler(&composableRouter{dht: nil})
+		srv := httptest.NewServer(handler)
+		t.Cleanup(srv.Close)
+
+		urlStr := fmt.Sprintf("http://%s/routing/v1/dht/closest/peers/%s", srv.Listener.Addr().String(), key.String())
+		req, err := http.NewRequest(http.MethodGet, urlStr, nil)
+		require.NoError(t, err)
+		req.Header.Set("Accept", mediaTypeJSON)
+
+		resp, err := http.DefaultClient.Do(req)
+		require.NoError(t, err)
+
+		// Returns 500 Internal Server Error instead of misleading 200 with empty results
+		require.Equal(t, http.StatusInternalServerError, resp.StatusCode)
+		body, err := io.ReadAll(resp.Body)
+		require.NoError(t, err)
+		require.Contains(t, string(body), "not supported")
+	})
 }
 
 // mockDHTRouter implements the router interface for testing

server_routers.go

@@ -71,7 +71,9 @@ func (r composableRouter) FindPeers(ctx context.Context, pid peer.ID, limit int)
 
 func (r composableRouter) GetClosestPeers(ctx context.Context, key cid.Cid) (iter.ResultIter[*types.PeerRecord], error) {
 	if r.dht == nil {
-		return iter.ToResultIter(iter.FromSlice([]*types.PeerRecord{})), nil
+		// Return ErrNotSupported when no DHT is available (e.g., disabled via --dht=disabled CLI param).
+		// This returns HTTP 501 Not Implemented instead of misleading HTTP 200 with empty results.
+		return nil, routing.ErrNotSupported
 	}
 	return r.dht.GetClosestPeers(ctx, key)
 }

server_test.go

@@ -13,14 +13,14 @@ func TestCombineRouters(t *testing.T) {
 	mockRouter := composableRouter{}
 
 	// Check that combineRouters with DHT only returns sanitizeRouter
-	v := combineRouters(&bundledDHT{}, nil, nil, nil)
+	v := combineRouters(nil, &bundledDHT{}, nil, nil, nil)
 	require.IsType(t, sanitizeRouter{}, v)
 
 	// Check that combineRouters with delegated routers only returns parallelRouter
-	v = combineRouters(nil, nil, []router{mockRouter}, nil)
+	v = combineRouters(nil, nil, nil, []router{mockRouter}, nil)
 	require.IsType(t, parallelRouter{}, v)
 
 	// Check that combineRouters with both DHT and delegated routers returns parallelRouter
-	v = combineRouters(&bundledDHT{}, nil, []router{mockRouter}, nil)
+	v = combineRouters(nil, &bundledDHT{}, nil, []router{mockRouter}, nil)
 	require.IsType(t, parallelRouter{}, v)
 }