fix(inbounds): reject incompatible VLESS fallbacks and prevent Xray crashes (#7003)

Xray refuses a VLESS inbound with server decryption whenever fallbacks is non-nil, even an empty list, so an API or imported inbound with decryption and fallbacks: [] took every inbound down. Empty fallback arrays are now normalized away on add, update, config build and node push; non-empty ones are refused with decryption, enabling decryption over stored fallback rules is refused, and a legacy conflicting row holds back the running core instead of stopping it. The form, API docs and locales follow. Closes #7001.

internal/web/service/inbound_vless_fallback.go

@@ -0,0 +1,78 @@
+package service
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+
+	"github.com/xtls/xray-core/infra/conf"
+	"gorm.io/gorm"
+
+	"github.com/mhsanaei/3x-ui/v3/internal/database/model"
+)
+
+func vlessDecryptionEnabled(settings string) bool {
+	var s struct {
+		Decryption string `json:"decryption"`
+	}
+	return json.Unmarshal([]byte(settings), &s) == nil && vlessEncValueSet(s.Decryption)
+}
+
+// normalizeVlessFallbacks also protects API/import callers that bypass the form adapter.
+func normalizeVlessFallbacks(inbound *model.Inbound) error {
+	if inbound.Protocol != model.VLESS {
+		return nil
+	}
+	var settings map[string]json.RawMessage
+	if err := json.Unmarshal([]byte(inbound.Settings), &settings); err != nil {
+		return fmt.Errorf("inbound %d: invalid VLESS settings: %w", inbound.Id, err)
+	}
+	raw, exists := settings["fallbacks"]
+	if !exists || bytes.Equal(bytes.TrimSpace(raw), []byte("null")) {
+		return nil
+	}
+	var fallbacks []*conf.VLessInboundFallback
+	if err := json.Unmarshal(raw, &fallbacks); err != nil {
+		return fmt.Errorf("inbound %d: invalid VLESS fallbacks: %w", inbound.Id, err)
+	}
+	if len(fallbacks) == 0 {
+		delete(settings, "fallbacks")
+		normalized, err := json.Marshal(settings)
+		if err != nil {
+			return err
+		}
+		inbound.Settings = string(normalized)
+		return nil
+	}
+	if vlessDecryptionEnabled(inbound.Settings) {
+		return vlessFallbackConflict(inbound.Id)
+	}
+	for _, fallback := range fallbacks {
+		if fallback == nil {
+			return fmt.Errorf("inbound %d: VLESS fallback entries must be objects", inbound.Id)
+		}
+	}
+	candidate := conf.VLessInboundConfig{Decryption: "none", Fallbacks: fallbacks}
+	if _, err := candidate.Build(); err != nil {
+		return fmt.Errorf("inbound %d: invalid VLESS fallbacks: %w", inbound.Id, err)
+	}
+	return nil
+}
+
+func vlessFallbackConflict(id int) error {
+	return fmt.Errorf("inbound %d: VLESS fallbacks cannot be used with active server decryption; remove fallback rules before enabling decryption", id)
+}
+
+func validateVlessManagedFallbacks(tx *gorm.DB, inbound *model.Inbound) error {
+	if inbound.Protocol != model.VLESS || !vlessDecryptionEnabled(inbound.Settings) || inbound.Id == 0 {
+		return nil
+	}
+	fallbacks, err := (&FallbackService{}).BuildFallbacksJSON(tx, inbound.Id)
+	if err != nil {
+		return err
+	}
+	if len(fallbacks) > 0 {
+		return vlessFallbackConflict(inbound.Id)
+	}
+	return nil
+}