bpo-46075: Store localhost cookies in CookieJar (#30108)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Lib/http/cookiejar.py

@@ -1043,12 +1043,13 @@ class DefaultCookiePolicy(CookiePolicy):
             else:
                 undotted_domain = domain
             embedded_dots = (undotted_domain.find(".") >= 0)
-            if not embedded_dots and domain != ".local":
+            if not embedded_dots and not erhn.endswith(".local"):
                 _debug("   non-local domain %s contains no embedded dot",
                        domain)
                 return False
             if cookie.version == 0:
-                if (not erhn.endswith(domain) and
+                if (not (erhn.endswith(domain) or
+                         erhn.endswith(f"{undotted_domain}.local")) and
                     (not erhn.startswith(".") and
                      not ("."+erhn).endswith(domain))):
                     _debug("   effective request-host %s (even with added "

Lib/test/test_http_cookiejar.py

@@ -920,6 +920,48 @@ class CookieTests(unittest.TestCase):
 ##         self.assertEqual(len(c), 2)
         self.assertEqual(len(c), 4)
 
+    def test_localhost_domain(self):
+        c = CookieJar()
+
+        interact_netscape(c, "http://localhost", "foo=bar; domain=localhost;")
+
+        self.assertEqual(len(c), 1)
+
+    def test_localhost_domain_contents(self):
+        c = CookieJar()
+
+        interact_netscape(c, "http://localhost", "foo=bar; domain=localhost;")
+
+        self.assertEqual(c._cookies[".localhost"]["/"]["foo"].value, "bar")
+
+    def test_localhost_domain_contents_2(self):
+        c = CookieJar()
+
+        interact_netscape(c, "http://localhost", "foo=bar;")
+
+        self.assertEqual(c._cookies["localhost.local"]["/"]["foo"].value, "bar")
+
+    def test_evil_nonlocal_domain(self):
+        c = CookieJar()
+
+        interact_netscape(c, "http://evil.com", "foo=bar; domain=.localhost")
+
+        self.assertEqual(len(c), 0)
+
+    def test_evil_local_domain(self):
+        c = CookieJar()
+
+        interact_netscape(c, "http://localhost", "foo=bar; domain=.evil.com")
+
+        self.assertEqual(len(c), 0)
+
+    def test_evil_local_domain_2(self):
+        c = CookieJar()
+
+        interact_netscape(c, "http://localhost", "foo=bar; domain=.someother.local")
+
+        self.assertEqual(len(c), 0)
+
     def test_two_component_domain_rfc2965(self):
         pol = DefaultCookiePolicy(rfc2965=True)
         c = CookieJar(pol)

Misc/NEWS.d/next/Library/2021-12-14-21-19-04.bpo-46075.KDtcU-.rst

@@ -0,0 +1 @@
+``CookieJar`` with ``DefaultCookiePolicy`` now can process cookies from localhost with domain=localhost explicitly specified in Set-Cookie header.