Add preferred_by route rule item

route/rule/rule_default.go

@@ -117,7 +117,7 @@ func NewDefaultRule(ctx context.Context, logger log.ContextLogger, options optio
 	if len(options.DomainRegex) > 0 {
 		item, err := NewDomainRegexItem(options.DomainRegex)
 		if err != nil {
-			return nil, E.Cause(err, "domain_regex")
+			return nil, err
 		}
 		rule.destinationAddressItems = append(rule.destinationAddressItems, item)
 		rule.allItems = append(rule.allItems, item)
@@ -261,6 +261,11 @@ func NewDefaultRule(ctx context.Context, logger log.ContextLogger, options optio
 		rule.items = append(rule.items, item)
 		rule.allItems = append(rule.allItems, item)
 	}
+	if len(options.PreferredBy) > 0 {
+		item := NewPreferredByItem(ctx, options.PreferredBy)
+		rule.items = append(rule.items, item)
+		rule.allItems = append(rule.allItems, item)
+	}
 	if len(options.RuleSet) > 0 {
 		var matchSource bool
 		if options.RuleSetIPCIDRMatchSource {

route/rule/rule_item_preferred_by.go

@@ -0,0 +1,86 @@
+package rule
+
+import (
+	"context"
+	"strings"
+
+	"github.com/sagernet/sing-box/adapter"
+	E "github.com/sagernet/sing/common/exceptions"
+	F "github.com/sagernet/sing/common/format"
+	"github.com/sagernet/sing/service"
+)
+
+var _ RuleItem = (*PreferredByItem)(nil)
+
+type PreferredByItem struct {
+	ctx          context.Context
+	outboundTags []string
+	outbounds    []adapter.OutboundWithPreferredRoutes
+}
+
+func NewPreferredByItem(ctx context.Context, outboundTags []string) *PreferredByItem {
+	return &PreferredByItem{
+		ctx:          ctx,
+		outboundTags: outboundTags,
+	}
+}
+
+func (r *PreferredByItem) Start() error {
+	outboundManager := service.FromContext[adapter.OutboundManager](r.ctx)
+	for _, outboundTag := range r.outboundTags {
+		rawOutbound, loaded := outboundManager.Outbound(outboundTag)
+		if !loaded {
+			return E.New("outbound not found: ", outboundTag)
+		}
+		outboundWithPreferredRoutes, withRoutes := rawOutbound.(adapter.OutboundWithPreferredRoutes)
+		if !withRoutes {
+			return E.New("outbound type does not support preferred routes: ", rawOutbound.Type())
+		}
+		r.outbounds = append(r.outbounds, outboundWithPreferredRoutes)
+	}
+	return nil
+}
+
+func (r *PreferredByItem) Match(metadata *adapter.InboundContext) bool {
+	var domainHost string
+	if metadata.Domain != "" {
+		domainHost = metadata.Domain
+	} else {
+		domainHost = metadata.Destination.Fqdn
+	}
+	if domainHost != "" {
+		for _, outbound := range r.outbounds {
+			if outbound.PreferredDomain(domainHost) {
+				return true
+			}
+		}
+	}
+	if metadata.Destination.IsIP() {
+		for _, outbound := range r.outbounds {
+			if outbound.PreferredAddress(metadata.Destination.Addr) {
+				return true
+			}
+		}
+	}
+	if len(metadata.DestinationAddresses) > 0 {
+		for _, address := range metadata.DestinationAddresses {
+			for _, outbound := range r.outbounds {
+				if outbound.PreferredAddress(address) {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+func (r *PreferredByItem) String() string {
+	description := "preferred_by="
+	pLen := len(r.outboundTags)
+	if pLen == 1 {
+		description += F.ToString(r.outboundTags[0])
+	} else {
+		description += "[" + strings.Join(F.MapToString(r.outboundTags), " ") + "]"
+	}
+	return description
+}