From 448ff10b9f597366e46a8e45b2ee7a8aa7a2dc66 Mon Sep 17 00:00:00 2001
From: xu91102 <169027046+xu91102@users.noreply.github.com>
Date: Sun, 27 Sep 2026 00:18:05 +0800
Subject: [PATCH] Fix case-insensitive stable sorting of response headers

---
 httpie/output/formatters/headers.py |  2 +-
 tests/test_output.py                | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/httpie/output/formatters/headers.py b/httpie/output/formatters/headers.py
index 2188193902..1b701bee51 100644
--- a/httpie/output/formatters/headers.py
+++ b/httpie/output/formatters/headers.py
@@ -14,5 +14,5 @@ def format_headers(self, headers: str) -> str:
 
         """
         lines = headers.splitlines()
-        headers = sorted(lines[1:], key=lambda h: h.split(':')[0])
+        headers = sorted(lines[1:], key=lambda h: h.split(':')[0].lower())
         return '\r\n'.join(lines[:1] + headers)
diff --git a/tests/test_output.py b/tests/test_output.py
index 2242177dbc..37dae73325 100644
--- a/tests/test_output.py
+++ b/tests/test_output.py
@@ -19,6 +19,7 @@
 from httpie.cli.definition import parser
 from httpie.encoding import UTF8
 from httpie.output.formatters.colors import get_lexer, PIE_STYLE_NAMES, BUNDLED_STYLES
+from httpie.output.formatters.headers import HeadersFormatter
 from httpie.status import ExitStatus
 from .fixtures import XML_DATA_RAW, XML_DATA_FORMATTED
 from .utils import COLOR, CRLF, HTTP_OK, MockEnvironment, http, DUMMY_URL, strip_colors
@@ -378,6 +379,23 @@ def test_CRLF_formatted_request(self, httpbin):
 
 
 class TestFormatOptions:
+    def test_header_sort_retains_order_for_mixed_case_repeated_fields(self):
+        formatter = HeadersFormatter(format_options=PARSED_DEFAULT_FORMAT_OPTIONS)
+        headers = CRLF.join([
+            'HTTP/1.1 200 OK',
+            'set-cookie: first=1',
+            'X-Z: last',
+            'Set-Cookie: second=2',
+            'accept: text/plain',
+        ])
+        assert formatter.format_headers(headers) == CRLF.join([
+            'HTTP/1.1 200 OK',
+            'accept: text/plain',
+            'set-cookie: first=1',
+            'Set-Cookie: second=2',
+            'X-Z: last',
+        ])
+
     def test_header_formatting_options(self):
         def get_headers(sort):
             return http(