WebHost: Fix: strict suuid converter (#6130)

* WebHost: disallow '=' and whitespace in SUUID and append the correct number of '='

This makes Room IDs unambiguous and avoids breaking if b64decode ever becomes strict.

* Tests, WebHost: add SUUID tests

* Tests, WebHost: add edge cases to SUUID tests

test/webhost/test_suuid.py

@@ -0,0 +1,76 @@
+import math
+from typing import Any, Callable
+from typing_extensions import override
+from uuid import uuid4
+
+from werkzeug.routing import BaseConverter
+
+from . import TestBase
+
+
+class TestSUUID(TestBase):
+    converter: BaseConverter
+    filter: Callable[[Any], str]
+
+    @override
+    def setUp(self) -> None:
+        from werkzeug.routing import Map
+
+        super().setUp()
+        self.converter = self.app.url_map.converters["suuid"](Map())
+        self.filter = self.app.jinja_env.filters["suuid"]  # type: ignore  # defines how we use it, not what it can be
+
+    def test_is_reversible(self) -> None:
+        u = uuid4()
+        self.assertEqual(u, self.converter.to_python(self.converter.to_url(u)))
+        s = "A" * 22  # uuid with all zeros
+        self.assertEqual(s, self.converter.to_url(self.converter.to_python(s)))
+
+    def test_uuid_length(self) -> None:
+        with self.assertRaises(ValueError):
+            self.converter.to_python("AAAA")
+
+    def test_padding(self) -> None:
+        self.converter.to_python("A" * 22)  # check that the correct value works
+        with self.assertRaises(ValueError):
+            self.converter.to_python("A" * 22 + "==")  # converter should not allow padding
+
+    def test_empty(self) -> None:
+        with self.assertRaises(ValueError):
+            self.converter.to_python("")
+
+    def test_stray_equal_signs(self) -> None:
+        self.converter.to_python("A" * 22)  # check that the correct value works
+        with self.assertRaises(ValueError):
+            self.converter.to_python("A" * 22 + "==" + "AA")  # the "==AA" should not be ignored, but error out
+        with self.assertRaises(ValueError):
+            self.converter.to_python("A" * 20 + "==" + "AA")  # the final "A"s should not be appended to the first "A"s
+
+    def test_stray_whitespace(self) -> None:
+        s = "A" * 22
+        self.converter.to_python(s)  # check that the correct value works
+        for char in " \t\r\n\v":
+            for pos in (0, 11, 22):
+                with self.subTest(char=char, pos=pos):
+                    s_with_whitespace = s[0:pos] + char * 4 + s[pos:]  # insert 4 to make padding correct
+                    # check that the constructed s_with_whitespace is correct
+                    self.assertEqual(len(s_with_whitespace), len(s) + 4)
+                    self.assertEqual(s_with_whitespace[pos], char)
+                    # s_with_whitespace should be invalid as SUUID
+                    with self.assertRaises(ValueError):
+                        self.converter.to_python(s_with_whitespace)
+
+    def test_filter_returns_valid_string(self) -> None:
+        u = uuid4()
+        s = self.filter(u)
+        self.assertIsInstance(s, str)
+        self.assertNotIn("=", s)
+        self.assertEqual(len(s), math.ceil(len(u.bytes) * 4 / 3))
+
+    def test_filter_is_same_as_converter(self) -> None:
+        u = uuid4()
+        self.assertEqual(self.filter(u), self.converter.to_url(u))
+
+    def test_filter_bad_type(self) -> None:
+        with self.assertRaises(Exception):  # currently the type is not checked directly, so any exception is valid
+            self.filter(None)