Fix error with "invalid link" on torrent renaming

Now it uses custom trick instead of os.Rename().

domains/fetcher/v1/fetcher.go

@@ -1,6 +1,6 @@
 // NNM-Club torrent filess mass downloader
 // Created for Uploaders group
-// Copyright (c) 2012-2019 Vladimir "fat0troll" Hodakov
+// Copyright (c) 2012-2020 Vladimir "fat0troll" Hodakov
 
 package fetcherv1
 
@@ -65,7 +65,7 @@ func download(topic *forumTopic) {
 
 	result := outputDirPath + "/" + lastModified + "-" + sanitize.BaseName(topic.Name) + ".torrent"
 
-	err = os.Rename(tempF, result)
+	err = moveFile(tempF, result)
 	if err != nil {
 		dlog.Warn().Err(err).Str("название топика", topic.Name).Str("ссылка на топик", topic.Link).
 			Msg("Не удалось сохранить торрент-файл. Пропуск")

domains/fetcher/v1/mover.go

@@ -0,0 +1,42 @@
+// NNM-Club torrent filess mass downloader
+// Created for Uploaders group
+// Copyright (c) 2012-2020 Vladimir "fat0troll" Hodakov
+
+package fetcherv1
+
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+// Source: https://gist.github.com/var23rav/23ae5d0d4d830aff886c3c970b8f6c6b
+
+/*
+   GoLang: os.Rename() give error "invalid cross-device link" for Docker container with Volumes.
+   moveFile(source, destination) will work moving file between folders
+*/
+
+func moveFile(sourcePath, destPath string) error {
+	inputFile, err := os.Open(sourcePath)
+	if err != nil {
+		return fmt.Errorf("couldn't open source file: %s", err)
+	}
+	outputFile, err := os.Create(destPath)
+	if err != nil {
+		inputFile.Close()
+		return fmt.Errorf("couldn't open destination file: %s", err)
+	}
+	defer outputFile.Close()
+	_, err = io.Copy(outputFile, inputFile)
+	inputFile.Close()
+	if err != nil {
+		return fmt.Errorf("writing to output file failed: %s", err)
+	}
+	// The copy was successful, so now delete the original file
+	err = os.Remove(sourcePath)
+	if err != nil {
+		return fmt.Errorf("failed removing original file: %s", err)
+	}
+	return nil
+}