Preserve IPv6 zone identifier in prepared URLs (#6735)

src/requests/models.py

@@ -480,6 +480,16 @@ def prepare_url(self, url, params):
                 query = enc_params
 
         url = requote_uri(urlunparse([scheme, netloc, path, None, query, fragment]))
+
+        # Preserve the IPv6 zone identifier separator ('%') inside a bracketed
+        # host. ``requote_uri`` percent-encodes a literal '%' to '%25', but
+        # ``urllib3`` forwards the (already-parsed) host to ``getaddrinfo()``
+        # verbatim, so an encoded zone identifier like ``%25eth0`` cannot be
+        # resolved by the OS. See https://github.com/psf/requests/issues/6735.
+        if host and "%" in host:
+            encoded_host = host.replace("%", "%25", 1)
+            url = url.replace(encoded_host, host, 1)
+
         self.url = url
 
     def prepare_headers(self, headers):

tests/test_requests.py

@@ -147,6 +147,39 @@ def test_path_is_not_double_encoded(self):
 
         assert request.path_url == "/get/test%20case"
 
+    @pytest.mark.parametrize(
+        "url, expected",
+        (
+            (
+                # Literal '%' zone-id separator must be preserved, otherwise
+                # urllib3 will forward '%25ens192' to getaddrinfo() which the
+                # OS cannot resolve. Regression test for #6735.
+                "https://[fe80::1%ens192]/redfish/v1",
+                "https://[fe80::1%ens192]/redfish/v1",
+            ),
+            (
+                # RFC 6874 form ('%25') must be normalized back to the literal
+                # form expected by getaddrinfo() / urllib3.
+                "https://[fe80::1%25ens192]/redfish/v1",
+                "https://[fe80::1%ens192]/redfish/v1",
+            ),
+            (
+                # Zone-id preserved alongside port/query/fragment.
+                "https://[fe80::5eed:8cff:fe00:0da4%ens192]:8443/api?x=1#f",
+                "https://[fe80::5eed:8cff:fe00:0da4%ens192]:8443/api?x=1#f",
+            ),
+            (
+                # Plain IPv6 (no zone id) must be unaffected.
+                "https://[::1]/",
+                "https://[::1]/",
+            ),
+        ),
+    )
+    def test_ipv6_zone_id_is_preserved(self, url, expected):
+        """See: https://github.com/psf/requests/issues/6735"""
+        request = requests.Request("GET", url).prepare()
+        assert request.url == expected
+
     @pytest.mark.parametrize(
         "url, expected",
         (