gh-61366: Write session cookies in the curl and Wget format (GH-155602)

Write 0 in the expiration time field for session cookies.
curl and Wget ignore the line if this field is empty.

Author: serhiy-storchaka

Lib/http/cookiejar.py

@@ -2109,7 +2109,9 @@ def save(self, filename=None, ignore_discard=False, ignore_expires=False):
                 if cookie.expires is not None:
                     expires = str(cookie.expires)
                 else:
-                    expires = ""
+                    # curl and Wget use 0 for session cookies, and ignore
+                    # the line if this field is empty.
+                    expires = "0"
                 if cookie.value is None:
                     # cookies.txt regards 'Set-Cookie: foo' as a cookie
                     # with no name, whereas http.cookiejar regards it as a

Lib/test/test_http_cookiejar.py

@@ -2048,6 +2048,35 @@ def test_session_cookies(self):
             # we didn't have session cookies in the first place
         self.assertNotEqual(counter["session_before"], 0)
 
+    def test_save_session_cookies(self):
+        # Session cookies are saved with 0 in the expiration time field,
+        # as curl and Wget do (gh-61366).
+        filename = os_helper.TESTFN
+        self.addCleanup(os_helper.unlink, filename)
+        expires = int(time.time() + 3600)
+        c = MozillaCookieJar()
+        c.set_cookie(Cookie(0, "perm", "bar", None, False,
+                            "www.foo.com", True, False, "/", False, False,
+                            expires, False, None, None, {}))
+        c.set_cookie(Cookie(0, "session", "bar", None, False,
+                            "www.foo.com", True, False, "/", False, False,
+                            None, True, None, None, {}))
+        c.save(filename, ignore_discard=True)
+
+        saved = {}
+        with open(filename) as f:
+            for line in f:
+                if line.strip() and not line.startswith("#"):
+                    fields = line.split("\t")
+                    saved[fields[5]] = fields[4]
+        self.assertEqual(saved, {"perm": str(expires), "session": "0"})
+
+        # The saved file can be read back.
+        c = MozillaCookieJar()
+        c.revert(filename, ignore_discard=True)
+        self.assertEqual(sorted(cookie.name for cookie in c),
+                         ["perm", "session"])
+
     def test_load_session_cookies(self):
         # curl and Wget write 0 in the expires field for session cookies,
         # while we write an empty field.  Both should be read (gh-61366).

Misc/NEWS.d/next/Library/2026-08-12-09-30-00.gh-issue-61366.Wr7cKm.rst

@@ -0,0 +1,3 @@
+:meth:`!http.cookiejar.MozillaCookieJar.save` now writes ``0`` in the
+expiration time field for session cookies, as curl and Wget do.  Previously
+this field was left empty, and such lines were ignored by curl and Wget.