[downloader/dash] Add testing facility

youtube_dl/downloader/dash.py

@@ -16,12 +16,21 @@ class DashSegmentsFD(FileDownloader):
         base_url = info_dict['url']
         segment_urls = info_dict['segment_urls']
 
+        is_test = self.params.get('test', False)
+        remaining_bytes = self._TEST_FILE_SIZE if is_test else None
         byte_counter = 0
 
-        def append_url_to_file(outf, target_url, target_name):
+        def append_url_to_file(outf, target_url, target_name, remaining_bytes=None):
             self.to_screen('[DashSegments] %s: Downloading %s' % (info_dict['id'], target_name))
             req = compat_urllib_request.Request(target_url)
+            if remaining_bytes is not None:
+                req.add_header('Range', 'bytes=0-%d' % (remaining_bytes - 1))
+
             data = self.ydl.urlopen(req).read()
+
+            if remaining_bytes is not None:
+                data = data[:remaining_bytes]
+
             outf.write(data)
             return len(data)
 
@@ -37,8 +46,13 @@ class DashSegmentsFD(FileDownloader):
             for i, segment_url in enumerate(segment_urls):
                 segment_len = append_url_to_file(
                     outf, combine_url(base_url, segment_url),
-                    'segment %d / %d' % (i + 1, len(segment_urls)))
+                    'segment %d / %d' % (i + 1, len(segment_urls)),
+                    remaining_bytes)
                 byte_counter += segment_len
+                if remaining_bytes is not None:
+                    remaining_bytes -= segment_len
+                    if remaining_bytes <= 0:
+                        break
 
         self.try_rename(tmpfilename, filename)