Fixed panic when loading spec with Domain on env which do not support…

… custom domains

If Domain is non empty and enable_custom_domains is false, API router
becomes nil, and panics.

This was part of recent change to fix order of API loading. Restored
original behavior when default router picked as fallback.

api_loader.go

@@ -585,6 +585,15 @@ func loadApps(specs []*APISpec, muxer *mux.Router) {
 	for i, spec := range specs {
 		go func(spec *APISpec, i int) {
 			subrouter := hostRouters[spec.Domain]
+			if subrouter == nil {
+				log.WithFields(logrus.Fields{
+					"prefix": "main",
+					"domain": spec.Domain,
+					"api_id": spec.APIID,
+				}).Warning("Trying to load API with Domain when custom domains are disabled.")
+				subrouter = muxer
+			}
+
 			chainObj := processSpec(spec, apisByListen, redisStore, redisOrgStore, healthStore, rpcAuthStore, rpcOrgStore, subrouter)
 			chainObj.Index = i
 			chainChannel <- chainObj

gateway_test.go

@@ -1182,3 +1182,28 @@ func TestMultiTargetProxy(t *testing.T) {
 		}
 	}
 }
+
+func TestCustomDomain(t *testing.T) {
+	t.Run("With custom domain support", func(t *testing.T) {
+		config.Global.EnableCustomDomains = true
+		defer func() {
+			config.Global.EnableCustomDomains = false
+		}()
+
+		buildAndLoadAPI(func(spec *APISpec) {
+			spec.Domain = "localhost"
+		},
+			func(spec *APISpec) {
+				spec.Domain = ""
+			})
+	})
+
+	t.Run("Without custom domain support", func(t *testing.T) {
+		buildAndLoadAPI(func(spec *APISpec) {
+			spec.Domain = "localhost"
+		},
+			func(spec *APISpec) {
+				spec.Domain = ""
+			})
+	})
+}