feat: include If-Modified-Since

Author: G-Rath

pkg/database/smart.go

@@ -153,14 +153,18 @@ func (db *SmartDB) fetchModifiedIDs(since time.Time) ([]modifiedIDRow, error) {
 		return nil, err
 	}
 
+	req.Header.Add("If-Modified-Since", since.Format(http.TimeFormat))
+
 	resp, err := http.DefaultClient.Do(req)
 	if err != nil {
 		return nil, err
 	}
 
 	defer resp.Body.Close()
 
-	if resp.StatusCode != http.StatusOK {
+	if resp.StatusCode == http.StatusNotModified {
+		return []modifiedIDRow{}, nil
+	} else if resp.StatusCode != http.StatusOK {
 		return nil, fmt.Errorf("%w (%s)", ErrUnexpectedStatusCode, resp.Status)
 	}