feat: sub file as sublink fallback

Author: st0nie

common/subscription/subscription.go

@@ -154,13 +154,20 @@ func ResolveSubscription(log *logrus.Logger, client *http.Client, configDir stri
 		req  *http.Request
 		resp *http.Response
 	)
+
+	var save_to_file bool = false
+
 	switch u.Scheme {
 	case "file":
 		b, err = ResolveFile(u, configDir)
 		if err != nil {
 			return "", nil, err
 		}
 		goto resolve
+	case "http-file", "https-file":
+		save_to_file = true
+		subscription = strings.Replace(subscription, "-file", "", 1)
+		break
 	default:
 	}
 	req, err = http.NewRequest("GET", subscription, nil)
@@ -170,13 +177,39 @@ func ResolveSubscription(log *logrus.Logger, client *http.Client, configDir stri
 	req.Header.Set("User-Agent", fmt.Sprintf("dae/%v (like v2rayA/1.0 WebRequestHelper) (like v2rayN/1.0 WebRequestHelper)", config.Version))
 	resp, err = client.Do(req)
 	if err != nil {
+		if save_to_file {
+			// fail to fetch, try to read from file
+			u.Host = tag + ".sub"
+			u.Path = ""
+			b, err = ResolveFile(u, configDir)
+
+			if err != nil {
+				return "", nil, err
+			}
+			goto resolve
+		}
+
 		return "", nil, err
 	}
 	defer resp.Body.Close()
 	b, err = io.ReadAll(resp.Body)
 	if err != nil {
 		return "", nil, err
 	}
+
+	if save_to_file {
+		path := filepath.Join(configDir, tag+".sub")
+		file, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0600)
+		if err != nil {
+			return "", nil, err
+		}
+		defer file.Close()
+
+		_, err = file.Write(b)
+		if err != nil {
+			return "", nil, err
+		}
+	}
 resolve:
 	if nodes, err = ResolveSubscriptionAsSIP008(log, b); err == nil {
 		return tag, nodes, nil