feat(outbounds): support custom subscription user agents (#6398)

Some subscription providers require a client-specific User-Agent before returning outbound links. Persist an optional value per subscription and use it for refreshes and previews while preserving the existing default for blank values.

internal/web/service/outbound_subscription_test.go

@@ -3,6 +3,8 @@ package service
 import (
 	"bytes"
 	"errors"
+	"net/http"
+	"net/http/httptest"
 	"slices"
 	"testing"
 
@@ -40,7 +42,7 @@ func TestOutboundSubscriptionCreatePropagatesAllocationDatabaseFailures(t *testi
 		{name: "priority count query", tagPrefix: "custom-", operation: "priority allocation"},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
-			created, err := (&OutboundSubscriptionService{}).Create("test", "https://1.1.1.1/sub", tc.tagPrefix, true, 600, false, false, false)
+			created, err := (&OutboundSubscriptionService{}).Create("test", "https://1.1.1.1/sub", tc.tagPrefix, "", true, 600, false, false, false)
 			if !errors.Is(err, errInjected) {
 				t.Fatalf("Create error = %v, want injected %s query failure", err, tc.operation)
 			}
@@ -83,7 +85,7 @@ func TestOutboundSubscriptionUpdatePropagatesPrefixQueryFailureWithoutMutation(t
 	})
 
 	err := (&OutboundSubscriptionService{}).Update(
-		original.Id, "after", "https://1.1.1.1/changed", "", false, 1200, false, false, false,
+		original.Id, "after", "https://1.1.1.1/changed", "", "", false, 1200, false, false, false,
 	)
 	if !errors.Is(err, errInjected) {
 		t.Fatalf("Update error = %v, want injected prefix query failure", err)
@@ -102,6 +104,30 @@ func TestOutboundSubscriptionUpdatePropagatesPrefixQueryFailureWithoutMutation(t
 	}
 }
 
+func TestOutboundSubscriptionRefreshUsesCustomUserAgent(t *testing.T) {
+	setupSettingTestDB(t)
+	const wantUserAgent = "ClashMetaForAndroid/2.11.13"
+	var gotUserAgent string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotUserAgent = r.UserAgent()
+		_, _ = w.Write([]byte("vless://00000000-0000-4000-8000-000000000000@1.1.1.1:443?security=tls&type=tcp#node"))
+	}))
+	t.Cleanup(server.Close)
+
+	sub := &model.OutboundSubscription{
+		Url: server.URL, AllowPrivate: true, UserAgent: wantUserAgent, TagPrefix: "test-",
+	}
+	if err := database.GetDB().Create(sub).Error; err != nil {
+		t.Fatalf("seed subscription: %v", err)
+	}
+	if _, err := (&OutboundSubscriptionService{}).Refresh(sub.Id); err != nil {
+		t.Fatalf("Refresh: %v", err)
+	}
+	if gotUserAgent != wantUserAgent {
+		t.Fatalf("User-Agent = %q, want %q", gotUserAgent, wantUserAgent)
+	}
+}
+
 func TestReadBoundedOutboundSubscriptionBody(t *testing.T) {
 	t.Run("accepts body at the limit", func(t *testing.T) {
 		want := bytes.Repeat([]byte("a"), int(maxOutboundSubscriptionBytes))