Filename normalisation of form-data/multipart file uploads (umlauts on Apple clients) (#2625)

Co-authored-by: L. Karkkainen <tronic@users.noreply.github.com>

sanic/request.py

@@ -27,6 +27,7 @@ if TYPE_CHECKING:
     from sanic.app import Sanic
 
 import email.utils
+import unicodedata
 import uuid
 
 from collections import defaultdict
@@ -1084,6 +1085,16 @@ def parse_multipart_form(body, boundary):
                         form_parameters["filename*"]
                     )
                     file_name = unquote(value, encoding=encoding)
+
+                # Normalize to NFC (Apple MacOS/iOS send NFD)
+                # Notes:
+                # - No effect for Windows, Linux or Android clients which
+                #   already send NFC
+                # - Python open() is tricky (creates files in NFC no matter
+                #   which form you use)
+                if file_name is not None:
+                    file_name = unicodedata.normalize("NFC", file_name)
+
             elif form_header_field == "content-type":
                 content_type = form_header_value
                 content_charset = form_parameters.get("charset", "utf-8")

tests/test_requests.py

@@ -1293,6 +1293,24 @@ async def test_request_string_representation_asgi(app):
             "------sanic--\r\n",
             "filename_\u00A0_test",
         ),
+        # Umlaut using NFC normalization (Windows, Linux, Android)
+        (
+            "------sanic\r\n"
+            'content-disposition: form-data; filename*="utf-8\'\'filename_%C3%A4_test"; name="test"\r\n'
+            "\r\n"
+            "OK\r\n"
+            "------sanic--\r\n",
+            "filename_\u00E4_test",
+        ),
+        # Umlaut using NFD normalization (MacOS client)
+        (
+            "------sanic\r\n"
+            'content-disposition: form-data; filename*="utf-8\'\'filename_a%CC%88_test"; name="test"\r\n'
+            "\r\n"
+            "OK\r\n"
+            "------sanic--\r\n",
+            "filename_\u00E4_test",  # Sanic should normalize to NFC
+        ),
     ],
 )
 def test_request_multipart_files(app, payload, filename):