refactor: extract GetVolumeServerId to util package

Move the volume server ID determination logic to a shared utility function
to avoid code duplication between volume.go and rack.go.

Ref: https://github.com/seaweedfs/seaweedfs/issues/7487

weed/command/volume.go

@@ -256,10 +256,7 @@ func (v VolumeServerOptions) startVolumeServer(volumeFolders, maxVolumeCounts, v
 	}
 
 	// Determine volume server ID: if not specified, use ip:port
-	volumeServerId := strings.TrimSpace(*v.id)
-	if volumeServerId == "" {
-		volumeServerId = util.JoinHostPort(*v.ip, *v.port)
-	}
+	volumeServerId := util.GetVolumeServerId(*v.id, *v.ip, *v.port)
 
 	volumeServer := weed_server.NewVolumeServer(volumeMux, publicVolumeMux,
 		*v.ip, *v.port, *v.portGrpc, *v.publicUrl, volumeServerId,

weed/topology/rack.go

@@ -52,11 +52,7 @@ func (r *Rack) GetOrCreateDataNode(ip string, port int, grpcPort int, publicUrl
 	defer r.Unlock()
 
 	// Determine the node ID: use provided id, or fall back to ip:port for backward compatibility
-	// Trim whitespace to treat " " as empty
-	nodeId := strings.TrimSpace(id)
-	if nodeId == "" {
-		nodeId = util.JoinHostPort(ip, port)
-	}
+	nodeId := util.GetVolumeServerId(id, ip, port)
 
 	// First, try to find by node ID using O(1) map lookup (stable identity)
 	if c, ok := r.children[NodeId(nodeId)]; ok {

weed/util/network.go

@@ -64,3 +64,14 @@ func JoinHostPort(host string, port int) string {
 	}
 	return net.JoinHostPort(host, portStr)
 }
+
+// GetVolumeServerId returns the volume server ID.
+// If id is provided (non-empty after trimming), use it as the identifier.
+// Otherwise, fall back to ip:port for backward compatibility.
+func GetVolumeServerId(id, ip string, port int) string {
+	volumeServerId := strings.TrimSpace(id)
+	if volumeServerId == "" {
+		volumeServerId = JoinHostPort(ip, port)
+	}
+	return volumeServerId
+}