From d8025e3d0f7576df227eda665ca58891474aa4e8 Mon Sep 17 00:00:00 2001
From: mdali9821 <mdali9821@users.noreply.github.com>
Date: Fri, 24 Apr 2026 11:01:00 +0530
Subject: [PATCH] Preserve IPv6 zone identifier in prepared URLs

requote_uri percent-encodes the literal '%' zone-id separator to '%25',
which urllib3 then forwards verbatim to getaddrinfo(). The kernel cannot
resolve a zone literally named '%25eth0', so link-local IPv6 URLs such
as https://[fe80::1%ens192]/ fail with [Errno -2] Name or service not
known since requests 2.32.0.

Restore the literal '%' inside the bracketed host after requoting.
urllib3.util.parse_url already normalizes both the literal ('%eth0')
and RFC 6874 ('%25eth0') forms to the literal form, so we only need
to undo the re-encoding that requote_uri performs on the authority.

Fixes #6735.
---
 src/requests/models.py | 10 ++++++++++
 tests/test_requests.py | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/src/requests/models.py b/src/requests/models.py
index e158b6cca2..08dcdb4455 100644
--- a/src/requests/models.py
+++ b/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):
diff --git a/tests/test_requests.py b/tests/test_requests.py
index 6d1bef66e0..a0ad23b464 100644
--- a/tests/test_requests.py
+++ b/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",
         (