fix(router/affinity): prevent panic caused by nil return in initialization phase

cluster/router/affinity/router_test.go

@@ -28,6 +28,7 @@ import (
 import (
 	"dubbo.apache.org/dubbo-go/v3/cluster/router/condition"
 	"dubbo.apache.org/dubbo-go/v3/common"
+	"dubbo.apache.org/dubbo-go/v3/common/constant"
 	"dubbo.apache.org/dubbo-go/v3/config_center"
 	"dubbo.apache.org/dubbo-go/v3/protocol/base"
 	"dubbo.apache.org/dubbo-go/v3/protocol/invocation"
@@ -235,3 +236,14 @@ affinityAware:
 	}
 
 }
+
+func Test_newApplicationAffinityRouter(t *testing.T) {
+	u, _ := common.NewURL("condition://0.0.0.0/com.foo.BarService")
+	router := newApplicationAffinityRouter(u)
+	assert.Nil(t, router)
+
+	u.SetParam(constant.ApplicationKey, "test-app")
+	router = newApplicationAffinityRouter(u)
+	assert.NotNil(t, router)
+	assert.Equal(t, "test-app", router.currentApplication)
+}

cluster/router/chain/chain.go

@@ -33,6 +33,7 @@ import (
 import (
 	"dubbo.apache.org/dubbo-go/v3/cluster/router"
 	"dubbo.apache.org/dubbo-go/v3/common"
+	"dubbo.apache.org/dubbo-go/v3/common/constant"
 	"dubbo.apache.org/dubbo-go/v3/common/extension"
 	"dubbo.apache.org/dubbo-go/v3/protocol/base"
 )
@@ -108,6 +109,12 @@ func (c *RouterChain) copyRouters() []router.PriorityRouter {
 // NewRouterChain init router chain
 // Loop routerFactories and call NewRouter method
 func NewRouterChain(url *common.URL) (*RouterChain, error) {
+	if url.SubURL != nil {
+		if appName := url.SubURL.GetParam(constant.ApplicationKey, ""); appName != "" {
+			url.CompareAndSwapParam(constant.ApplicationKey, "", appName)
+		}
+	}
+
 	routerFactories := extension.GetRouterFactories()
 	if len(routerFactories) == 0 {
 		return nil, perrors.Errorf("No routerFactory exits , create one please")

common/url.go

@@ -564,6 +564,22 @@ func (c *URL) SetParam(key string, value string) {
 	c.params.Set(key, value)
 }
 
+// CompareAndSwapParam will set the key-value pair into URL when the current value equals the expected value.
+// It returns true if the value was set successfully, false otherwise.
+// This is a thread-safe compare-and-swap operation.
+func (c *URL) CompareAndSwapParam(key string, expected string, newValue string) bool {
+	c.paramsLock.Lock()
+	defer c.paramsLock.Unlock()
+	if c.params == nil {
+		c.params = url.Values{}
+	}
+	if c.params.Get(key) == expected {
+		c.params.Set(key, newValue)
+		return true
+	}
+	return false
+}
+
 func (c *URL) SetAttribute(key string, value any) {
 	c.attributesLock.Lock()
 	defer c.attributesLock.Unlock()