Retain blank query params in url transformations

tildes/tests/test_url_transform.py

@@ -4,6 +4,18 @@
 from tildes.lib.url_transform import apply_url_transformations
 
 
+def test_blank_query_params_kept():
+    """Ensure that query params with no value make it through the process.
+
+    Some sites treat the presence of blank params different from their absence, so
+    we don't want to remove them (which urllib's parse_qs and parse_qsl do by default).
+    """
+    url = "http://example.com/path?one=1&two=2&blank=&three=3"
+    transformed_url = apply_url_transformations(url)
+
+    assert transformed_url == url
+
+
 def test_remove_utm_query_params():
     """Ensure that utm query params are removed but others are left."""
     url = "http://example.com/path?utm_source=tildes&utm_campaign=test&something=ok"

tildes/tildes/lib/url_transform.py

@@ -118,7 +118,7 @@ class UtmQueryParamRemover(UrlTransformer):
     @classmethod
     def apply_transformation(cls, parsed_url: ParseResult) -> ParseResult:
         """Apply the actual transformation process to the url."""
-        query_params = parse_qs(parsed_url.query)
+        query_params = parse_qs(parsed_url.query, keep_blank_values=True)
 
         cleaned_params = {
             param: value
@@ -154,7 +154,7 @@ class RedditTrackingRemover(UrlTransformer):
     @classmethod
     def apply_transformation(cls, parsed_url: ParseResult) -> ParseResult:
         """Apply the actual transformation process to the url."""
-        query_params = parse_qs(parsed_url.query)
+        query_params = parse_qs(parsed_url.query, keep_blank_values=True)
 
         query_params.pop("st", None)
         query_params.pop("sh", None)
@@ -195,7 +195,7 @@ class YoutubeUnshortener(UrlTransformer):
         video_id = parsed_url.path.strip("/")
 
         # use parse_qsl() and insert() here so the v= is always the first query param
-        query_params = parse_qsl(parsed_url.query)
+        query_params = parse_qsl(parsed_url.query, keep_blank_values=True)
         query_params.insert(0, ("v", video_id))
 
         return parsed_url._replace(