[mixcloud] Simplify url extraction

On the tracks I tested the server number in the url from the webpage is valid
for the mp3 or the m4a file and any other number is invalid, it's a
waste of time to check them.

youtube_dl/extractor/mixcloud.py

@@ -1,7 +1,6 @@
 from __future__ import unicode_literals
 
 import re
-import itertools
 
 from .common import InfoExtractor
 from ..compat import (
@@ -46,20 +45,16 @@ class MixcloudIE(InfoExtractor):
         },
     }]
 
-    def _get_url(self, track_id, template_url, server_number):
-        boundaries = (1, 30)
-        for nr in server_numbers(server_number, boundaries):
-            url = template_url % nr
+    def _check_url(self, url, track_id, ext):
         try:
             # We only want to know if the request succeed
             # don't download the whole file
             self._request_webpage(
                 HEADRequest(url), track_id,
-                    'Checking URL %d/%d ...' % (nr, boundaries[-1]))
-                return url
+                'Trying %s URL' % ext)
+            return True
         except ExtractorError:
-                pass
-        return None
+            return False
 
     def _real_extract(self, url):
         mobj = re.match(self._VALID_URL, url)
@@ -72,14 +67,9 @@ class MixcloudIE(InfoExtractor):
         preview_url = self._search_regex(
             r'\s(?:data-preview-url|m-preview)="([^"]+)"', webpage, 'preview url')
         song_url = preview_url.replace('/previews/', '/c/originals/')
-        server_number = int(self._search_regex(r'stream(\d+)', song_url, 'server number'))
-        template_url = re.sub(r'(stream\d*)', 'stream%d', song_url)
-        final_song_url = self._get_url(track_id, template_url, server_number)
-        if final_song_url is None:
-            self.to_screen('Trying with m4a extension')
-            template_url = template_url.replace('.mp3', '.m4a').replace('originals/', 'm4a/64/')
-            final_song_url = self._get_url(track_id, template_url, server_number)
-        if final_song_url is None:
+        if not self._check_url(song_url, track_id, 'mp3'):
+            song_url = song_url.replace('.mp3', '.m4a').replace('originals/', 'm4a/64/')
+            if not self._check_url(song_url, track_id, 'm4a'):
                 raise ExtractorError('Unable to extract track url')
 
         PREFIX = (
@@ -107,7 +97,7 @@ class MixcloudIE(InfoExtractor):
         return {
             'id': track_id,
             'title': title,
-            'url': final_song_url,
+            'url': song_url,
             'description': description,
             'thumbnail': thumbnail,
             'uploader': uploader,
@@ -115,35 +105,3 @@ class MixcloudIE(InfoExtractor):
             'view_count': view_count,
             'like_count': like_count,
         }
-
-
-def server_numbers(first, boundaries):
-    """ Server numbers to try in descending order of probable availability.
-    Starting from first (i.e. the number of the server hosting the preview file)
-    and going further and further up to the higher boundary and down to the
-    lower one in an alternating fashion. Namely:
-
-        server_numbers(2, (1, 5))
-
-        # Where the preview server is 2, min number is 1 and max is 5.
-        # Yields: 2, 3, 1, 4, 5
-
-    Why not random numbers or increasing sequences? Since from what I've seen,
-    full length files seem to be hosted on servers whose number is closer to
-    that of the preview; to be confirmed.
-    """
-    zip_longest = getattr(itertools, 'zip_longest', None)
-    if zip_longest is None:
-        # python 2.x
-        zip_longest = itertools.izip_longest
-
-    if len(boundaries) != 2:
-        raise ValueError("boundaries should be a two-element tuple")
-    min, max = boundaries
-    highs = range(first + 1, max + 1)
-    lows = range(first - 1, min - 1, -1)
-    rest = filter(
-        None, itertools.chain.from_iterable(zip_longest(highs, lows)))
-    yield first
-    for n in rest:
-        yield n