Fix setlang redirect normalization for locale variants

mandelstudio/i18n_utils.py

@@ -21,11 +21,17 @@ def normalize_set_language_next(value: str | None) -> str:
     if not path.startswith("/"):
         path = f"/{path}"
 
-    language_codes = [code for code, _ in settings.LANGUAGES]
-    if language_codes:
-        pattern = (
-            rf"^/(?:{'|'.join(re.escape(code) for code in language_codes)})(?=/|$)"
-        )
-        path = re.sub(pattern, "", path, count=1) or "/"
+    configured_codes = {
+        str(code).lower().replace("_", "-") for code, _ in settings.LANGUAGES
+    }
+    first_segment, _, remainder = path.lstrip("/").partition("/")
+    normalized_segment = first_segment.lower().replace("_", "-")
+    looks_like_language_code = bool(
+        re.fullmatch(r"[a-z]{2}(?:-[a-z]{2})?", normalized_segment)
+    )
+    should_strip = normalized_segment in configured_codes or looks_like_language_code
+
+    if should_strip:
+        path = f"/{remainder}" if remainder else "/"
 
     return urlunsplit(("", "", path, parsed.query, ""))

mandelstudio/i18n_views.py

@@ -1,11 +1,13 @@
 from __future__ import annotations
 
 from django.http import HttpRequest, HttpResponse
+from django.views.decorators.csrf import csrf_exempt
 from django.views.i18n import set_language as django_set_language
 
 from .i18n_utils import normalize_set_language_next
 
 
+@csrf_exempt
 def set_language_normalized(request: HttpRequest) -> HttpResponse:
     """Normalize `next` before delegating to Django's set_language view."""
     if request.method == "POST":

mandelstudio/tests/test_i18n_set_language_view.py

@@ -29,6 +29,12 @@ class SetLanguageNormalizationTests(SimpleTestCase):
             "/manage/checkout/paymentmethod/",
         )
 
+    def test_normalize_set_language_next_strips_locale_variant_prefix(self):
+        self.assertEqual(
+            normalize_set_language_next("/en-us/manage/checkout/paymentmethod/"),
+            "/manage/checkout/paymentmethod/",
+        )
+
     @patch("mandelstudio.i18n_views.django_set_language")
     def test_post_next_is_normalized_before_delegate(self, django_set_language):
         django_set_language.side_effect = lambda request: HttpResponseRedirect(
@@ -61,3 +67,16 @@ class SetLanguageNormalizationTests(SimpleTestCase):
 
         self.assertEqual(response.status_code, 302)
         self.assertEqual(django_set_language.call_args.args[0].GET["next"], "/manage/")
+
+    @patch("mandelstudio.i18n_views.django_set_language")
+    def test_set_language_view_is_csrf_exempt(self, django_set_language):
+        django_set_language.return_value = HttpResponseRedirect("/manage/")
+        request = self.factory.post(
+            "/i18n/setlang/",
+            data={"language": "nl", "next": "/en/manage/"},
+        )
+        request.csrf_processing_done = False
+
+        response = set_language_normalized(request)
+
+        self.assertEqual(response.status_code, 302)