Add main business logic of this program

Now we can download torrents like old Python
version does.

domains/fetcher/v1/querier.go

@@ -11,14 +11,23 @@ import (
 	"github.com/PuerkitoBio/goquery"
 )
 
-func setQuerier(pageFile string, pageType string, page int) error {
+func obtainQuerier(pageFile string) (*goquery.Document, error) {
 	f, err := os.Open(pageFile)
 	if err != nil {
-		return err
+		return nil, err
 	}
 	defer f.Close()
 
 	querier, err := goquery.NewDocumentFromReader(f)
+	if err != nil {
+		return nil, err
+	}
+
+	return querier, nil
+}
+
+func setQuerier(pageFile string, pageType string, page int) error {
+	querier, err := obtainQuerier(pageFile)
 	if err != nil {
 		return err
 	}