Remove Reddit's share-tracking query params

tildes/tests/test_url_transform.py

@@ -34,3 +34,11 @@ def test_other_mobile_subdomain_not_removed():
     cleaned_url = apply_url_transformations(url)
 
     assert cleaned_url == url
+
+
+def test_reddit_tracking_removed():
+    """Ensure that Reddit's "share tracking" query params are removed."""
+    url = "https://www.reddit.com/r/tildes/comments/8k14is/_/?sort=new&st=abcdefgh&sh=1234asd"
+    cleaned_url = apply_url_transformations(url)
+
+    assert cleaned_url == "https://www.reddit.com/r/tildes/comments/8k14is/_/?sort=new"

tildes/tildes/lib/url_transform.py

@@ -129,3 +129,22 @@ class TwitterMobileConverter(UrlTransformer):
     def apply_transformation(cls, parsed_url: ParseResult) -> ParseResult:
         """Apply the actual transformation process to the url."""
         return parsed_url._replace(netloc="twitter.com")
+
+
+class RedditTrackingRemover(UrlTransformer):
+    """Remove Reddit's "share tracking" query parameters (st and sh)."""
+
+    @classmethod
+    def is_applicable(cls, parsed_url: ParseResult) -> bool:
+        """Return whether this transformation should be applied to the url."""
+        return parsed_url.hostname == "www.reddit.com"
+
+    @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.pop("st", None)
+        query_params.pop("sh", None)
+
+        return parsed_url._replace(query=urlencode(query_params, doseq=True))