redirect /r/:id action

main.go

@@ -175,6 +175,8 @@ func process(_ context.Context, w gemini.ResponseWriter, r *gemini.Request) {
 		renderTag(w, r, client)
 	case regexp.MustCompile(`^/__a/`).MatchString(r.URL.Path):
 		downloadAttachment(w, r, client)
+	case regexp.MustCompile(`^/r/.+`).MatchString(r.URL.Path):
+		redirectAction(w, r, client)
 	default:
 		w.WriteHeader(gemini.StatusNotFound, "Out of space")
 	}
@@ -522,3 +524,26 @@ func renderTag(w gemini.ResponseWriter, r *gemini.Request, client TreeManagerCli
 		return
 	}
 }
+
+func redirectAction(w gemini.ResponseWriter, r *gemini.Request, client TreeManagerClient) {
+	urlParts := strings.Split(r.URL.Path, "/")
+	id := urlParts[1]
+
+	fr := FileRequest{Id: id}
+	file, err := client.GetFile(context.Background(), &fr)
+	if err != nil {
+		log.Fatalf("client.GetFile failed: %v", err)
+		w.WriteHeader(gemini.StatusTemporaryFailure, "Internal server error")
+		return
+	}
+
+	w.WriteHeader(
+		gemini.StatusPermanentRedirect,
+		fmt.Sprintf(
+			"/f/%s/%s/%s",
+			strings.Join(file.File.Category, "/"),
+			file.File.Id,
+			file.File.GmiName(),
+		),
+	)
+}