[utils] Introduce url_or_none

test/test_utils.py

@@ -78,6 +78,7 @@ from youtube_dl.utils import (
     uppercase_escape,
     lowercase_escape,
     url_basename,
+    url_or_none,
     base_url,
     urljoin,
     urlencode_postdata,
@@ -507,6 +508,16 @@ class TestUtil(unittest.TestCase):
         self.assertEqual(urljoin('http://foo.de/', ['foobar']), None)
         self.assertEqual(urljoin('http://foo.de/a/b/c.txt', '.././../d.txt'), 'http://foo.de/d.txt')
 
+    def test_url_or_none(self):
+        self.assertEqual(url_or_none(None), None)
+        self.assertEqual(url_or_none(''), None)
+        self.assertEqual(url_or_none('foo'), None)
+        self.assertEqual(url_or_none('http://foo.de'), 'http://foo.de')
+        self.assertEqual(url_or_none('https://foo.de'), 'https://foo.de')
+        self.assertEqual(url_or_none('http$://foo.de'), None)
+        self.assertEqual(url_or_none('http://foo.de'), 'http://foo.de')
+        self.assertEqual(url_or_none('//foo.de'), '//foo.de')
+
     def test_parse_age_limit(self):
         self.assertEqual(parse_age_limit(None), None)
         self.assertEqual(parse_age_limit(False), None)

youtube_dl/utils.py

@@ -1866,6 +1866,13 @@ def strip_or_none(v):
     return None if v is None else v.strip()
 
 
+def url_or_none(url):
+    if not url or not isinstance(url, compat_str):
+        return None
+    url = url.strip()
+    return url if re.match(r'^(?:[a-zA-Z][\da-zA-Z.+-]*:)?//', url) else None
+
+
 def parse_duration(s):
     if not isinstance(s, compat_basestring):
         return None