[downloader/fragment] Set final file's mtime according to last fragment's Last-Modified header (closes #11718, closes #18384, closes #27138)

youtube_dl/downloader/fragment.py

@@ -97,12 +97,15 @@ class FragmentFD(FileDownloader):
 
     def _download_fragment(self, ctx, frag_url, info_dict, headers=None):
         fragment_filename = '%s-Frag%d' % (ctx['tmpfilename'], ctx['fragment_index'])
-        success = ctx['dl'].download(fragment_filename, {
+        fragment_info_dict = {
             'url': frag_url,
             'http_headers': headers or info_dict.get('http_headers'),
-        })
+        }
+        success = ctx['dl'].download(fragment_filename, fragment_info_dict)
         if not success:
             return False, None
+        if fragment_info_dict.get('filetime'):
+            ctx['fragment_filetime'] = fragment_info_dict.get('filetime')
         down, frag_sanitized = sanitize_open(fragment_filename, 'rb')
         ctx['fragment_filename_sanitized'] = frag_sanitized
         frag_content = down.read()
@@ -258,6 +261,13 @@ class FragmentFD(FileDownloader):
             downloaded_bytes = ctx['complete_frags_downloaded_bytes']
         else:
             self.try_rename(ctx['tmpfilename'], ctx['filename'])
+            if self.params.get('updatetime', True):
+                filetime = ctx.get('fragment_filetime')
+                if filetime:
+                    try:
+                        os.utime(ctx['filename'], (time.time(), filetime))
+                    except Exception:
+                        pass
             downloaded_bytes = os.path.getsize(encodeFilename(ctx['filename']))
 
         self._hook_progress({