From 4c118559cabb5bdbdf57f4bba90b5f2bc748dfd5 Mon Sep 17 00:00:00 2001
From: Andrew Chen <48723787+chuenchen309@users.noreply.github.com>
Date: Sun, 19 Jul 2026 05:15:18 +0800
Subject: [PATCH 1/2] Match header field names case-insensitively in the
 default header_matcher

HTTP header names are case-insensitive and requests stores request.headers
as a CaseInsensitiveDict, but the default (strict_match=False) path rebuilt
them into a plain dict keyed by the request's original casing with a
case-sensitive `k in headers` filter. Any casing difference dropped the
header, so header_matcher({"X-Custom": ...}) failed to match a request
sending "x-custom" (and vice versa), with a misleading "{} doesn't match"
reason. strict_match=True kept the CaseInsensitiveDict and already matched
case-insensitively, so the default path was the outlier.

Key the filtered dict by the matcher's names using CaseInsensitiveDict
membership so the case-insensitive lookup survives.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 responses/matchers.py            |  8 ++++++--
 responses/tests/test_matchers.py | 20 ++++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/responses/matchers.py b/responses/matchers.py
index d61decc1..5c2e0fb3 100644
--- a/responses/matchers.py
+++ b/responses/matchers.py
@@ -432,8 +432,12 @@ def match(request: PreparedRequest) -> Tuple[bool, str]:
         request_headers: Union[Mapping[Any, Any], Any] = request.headers or {}
 
         if not strict_match:
-            # filter down to just the headers specified in the matcher
-            request_headers = {k: v for k, v in request_headers.items() if k in headers}
+            # Filter to the matcher's headers, keyed by the matcher's names, so
+            # the case-insensitive lookup on request.headers (a
+            # CaseInsensitiveDict) is not lost in the plain-dict rebuild.
+            request_headers = {
+                k: request_headers[k] for k in headers if k in request_headers
+            }
 
         valid = _compare_with_regex(request_headers)
 
diff --git a/responses/tests/test_matchers.py b/responses/tests/test_matchers.py
index fc4fbc6f..5b56838b 100644
--- a/responses/tests/test_matchers.py
+++ b/responses/tests/test_matchers.py
@@ -857,6 +857,26 @@ def run():
     assert_reset()
 
 
+def test_request_matches_headers_case_insensitive_field_names():
+    # HTTP header names are case-insensitive (and HTTP/2 lower-cases them), so
+    # the default matcher must match regardless of the field-name casing.
+    @responses.activate
+    def run():
+        url = "http://example.com/"
+        responses.add(
+            method=responses.GET,
+            url=url,
+            json={"success": True},
+            match=[matchers.header_matcher({"X-Custom": "token"})],
+        )
+
+        resp = requests.get(url, headers={"x-custom": "token"})
+        assert_response(resp, body='{"success": true}', content_type="application/json")
+
+    run()
+    assert_reset()
+
+
 def test_request_header_value_mismatch_raises():
     @responses.activate
     def run():

From 8da842acc4e4bfe14167552273f53905607bccf9 Mon Sep 17 00:00:00 2001
From: Andrew Chen <48723787+chuenchen309@users.noreply.github.com>
Date: Sun, 19 Jul 2026 05:16:22 +0800
Subject: [PATCH 2/2] Add CHANGES entry for the header_matcher
 case-insensitivity fix

---
 CHANGES | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/CHANGES b/CHANGES
index dcdce261..1ec7c55a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -5,6 +5,10 @@
   registered URL's own query string) discarding blank-valued query params
   (``b=``), which caused requests with an extra or missing blank param to
   match incorrectly. See #804
+* Fixed the default `header_matcher` (``strict_match=False``) matching header
+  field names case-sensitively, so a request whose header casing differed from
+  the matcher spec (for example lowercase names over HTTP/2) failed to match.
+  See #805
 
 0.26.2
 ------