feat(inbounds): add Port-with-Fallback inbound type

Adds a new "portfallback" protocol that emits as a VLESS-TLS inbound
under the hood but is paired with a sidecar table of child inbounds.
Panel auto-builds settings.fallbacks at Xray-config-gen time from the
sidecar — each child's listen+port becomes the fallback dest, with
SNI/ALPN/path/xver match criteria pulled from the row. No more typing
loopback ports by hand or keeping settings.fallbacks in sync.

Backend: new FallbackService (Get/SetChildren, BuildFallbacksJSON);
two new routes (GET/POST /panel/api/inbounds/:id/fallbackChildren);
xray.GetXrayConfig injects fallbacks for PortFallback inbounds; the
inbound model emits protocol="vless" so Xray accepts the config.

Frontend: PORTFALLBACK joins the protocol dropdown; selecting it
shows the standard VLESS controls plus a Fallback Children table
(inbound picker + per-row SNI/ALPN/path/xver). Children are loaded
on edit and replaced atomically on save.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/service/fallback.go

@@ -0,0 +1,122 @@
+package service
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/mhsanaei/3x-ui/v3/database"
+	"github.com/mhsanaei/3x-ui/v3/database/model"
+
+	"gorm.io/gorm"
+)
+
+type FallbackService struct{}
+
+type FallbackChildInput struct {
+	ChildId   int    `json:"childId"`
+	Name      string `json:"name"`
+	Alpn      string `json:"alpn"`
+	Path      string `json:"path"`
+	Xver      int    `json:"xver"`
+	SortOrder int    `json:"sortOrder"`
+}
+
+func (s *FallbackService) GetChildren(masterId int) ([]model.InboundFallbackChild, error) {
+	var rows []model.InboundFallbackChild
+	err := database.GetDB().
+		Where("master_id = ?", masterId).
+		Order("sort_order ASC, id ASC").
+		Find(&rows).Error
+	if err != nil {
+		return nil, err
+	}
+	return rows, nil
+}
+
+func (s *FallbackService) SetChildren(masterId int, children []FallbackChildInput) error {
+	db := database.GetDB()
+	return db.Transaction(func(tx *gorm.DB) error {
+		if err := tx.Where("master_id = ?", masterId).Delete(&model.InboundFallbackChild{}).Error; err != nil {
+			return err
+		}
+		for i, c := range children {
+			if c.ChildId <= 0 || c.ChildId == masterId {
+				continue
+			}
+			row := model.InboundFallbackChild{
+				MasterId:  masterId,
+				ChildId:   c.ChildId,
+				Name:      c.Name,
+				Alpn:      c.Alpn,
+				Path:      c.Path,
+				Xver:      c.Xver,
+				SortOrder: c.SortOrder,
+			}
+			if row.SortOrder == 0 {
+				row.SortOrder = i
+			}
+			if err := tx.Create(&row).Error; err != nil {
+				return err
+			}
+		}
+		return nil
+	})
+}
+
+func (s *FallbackService) BuildFallbacksJSON(tx *gorm.DB, masterId int) ([]map[string]any, error) {
+	if tx == nil {
+		tx = database.GetDB()
+	}
+	var rows []model.InboundFallbackChild
+	err := tx.Where("master_id = ?", masterId).
+		Order("sort_order ASC, id ASC").
+		Find(&rows).Error
+	if err != nil {
+		return nil, err
+	}
+	if len(rows) == 0 {
+		return nil, nil
+	}
+
+	childIds := make([]int, 0, len(rows))
+	for i := range rows {
+		childIds = append(childIds, rows[i].ChildId)
+	}
+	var children []model.Inbound
+	if err := tx.Where("id IN ?", childIds).Find(&children).Error; err != nil {
+		return nil, err
+	}
+	byId := make(map[int]*model.Inbound, len(children))
+	for i := range children {
+		byId[children[i].Id] = &children[i]
+	}
+
+	out := make([]map[string]any, 0, len(rows))
+	for _, r := range rows {
+		child, ok := byId[r.ChildId]
+		if !ok {
+			continue
+		}
+		listen := strings.TrimSpace(child.Listen)
+		if listen == "" || listen == "0.0.0.0" || listen == "::" || listen == "::0" {
+			listen = "127.0.0.1"
+		}
+		entry := map[string]any{
+			"dest": fmt.Sprintf("%s:%d", listen, child.Port),
+		}
+		if r.Name != "" {
+			entry["name"] = r.Name
+		}
+		if r.Alpn != "" {
+			entry["alpn"] = r.Alpn
+		}
+		if r.Path != "" {
+			entry["path"] = r.Path
+		}
+		if r.Xver > 0 {
+			entry["xver"] = r.Xver
+		}
+		out = append(out, entry)
+	}
+	return out, nil
+}

web/service/inbound.go

@@ -24,8 +24,9 @@ import (
 )
 
 type InboundService struct {
-	xrayApi       xray.XrayAPI
-	clientService ClientService
+	xrayApi         xray.XrayAPI
+	clientService   ClientService
+	fallbackService FallbackService
 }
 
 func (s *InboundService) runtimeFor(ib *model.Inbound) (runtime.Runtime, error) {

web/service/xray.go

@@ -6,6 +6,7 @@ import (
 	"runtime"
 	"sync"
 
+	"github.com/mhsanaei/3x-ui/v3/database/model"
 	"github.com/mhsanaei/3x-ui/v3/logger"
 	"github.com/mhsanaei/3x-ui/v3/xray"
 
@@ -166,8 +167,29 @@ func (s *XrayService) GetXrayConfig() (*xray.Config, error) {
 			finalClients = append(finalClients, entry)
 		}
 
-		if _, hadClients := settings["clients"]; hadClients || len(finalClients) > 0 {
+		_, hadClients := settings["clients"]
+		mutated := hadClients || len(finalClients) > 0
+		if mutated {
 			settings["clients"] = finalClients
+		}
+
+		if inbound.Protocol == model.PortFallback {
+			fallbacks, fbErr := s.inboundService.fallbackService.BuildFallbacksJSON(nil, inbound.Id)
+			if fbErr != nil {
+				return nil, fbErr
+			}
+			generic := make([]any, 0, len(fallbacks))
+			for _, f := range fallbacks {
+				generic = append(generic, f)
+			}
+			settings["fallbacks"] = generic
+			if _, ok := settings["decryption"]; !ok {
+				settings["decryption"] = "none"
+			}
+			mutated = true
+		}
+
+		if mutated {
 			modifiedSettings, err := json.MarshalIndent(settings, "", "  ")
 			if err != nil {
 				return nil, err