Fix recorder producing Content-Type in both content_type and headers

responses/_recorder.py

@@ -145,16 +145,19 @@ def _on_request(
         request.params = self._parse_request_params(request.path_url)  # type: ignore[attr-defined]
         request.req_kwargs = kwargs  # type: ignore[attr-defined]
         requests_response = _real_send(adapter, request, **kwargs)
+        content_type = requests_response.headers.get("Content-Type", _UNSET)
         headers_values = {
-            key: value for key, value in requests_response.headers.items()
+            key: value
+            for key, value in requests_response.headers.items()
+            if key.lower() != "content-type"
         }
         responses_response = Response(
             method=str(request.method),
             url=str(requests_response.request.url),
             status=requests_response.status_code,
             body=requests_response.text,
             headers=headers_values,
-            content_type=requests_response.headers.get("Content-Type", _UNSET),
+            content_type=content_type,
         )
         self._registry.add(responses_response)
         return requests_response

responses/tests/test_recorder.py

@@ -122,6 +122,30 @@ def run():
 
         assert data == get_data(httpserver.host, httpserver.port)
 
+    def test_recorder_excludes_content_type_from_headers(self, httpserver):
+        """Content-Type should be in content_type, not duplicated in headers."""
+        httpserver.expect_request("/json").respond_with_data(
+            '{"message": "hello"}',
+            status=200,
+            content_type="application/json; charset=UTF-8",
+        )
+        url = httpserver.url_for("/json")
+
+        @_recorder.record(file_path=self.out_file)
+        def record():
+            requests.get(url)
+
+        record()
+
+        with open(self.out_file) as file:
+            data = yaml.safe_load(file)
+
+        rsp = data["responses"][0]["response"]
+        assert rsp["content_type"] == "application/json; charset=UTF-8"
+        headers = rsp.get("headers") or {}
+        assert "Content-Type" not in headers
+        assert "content-type" not in headers
+
     def prepare_server(self, httpserver):
         httpserver.expect_request("/500").respond_with_data(
             "500 Internal Server Error",
@@ -238,3 +262,4 @@ def _parse_resp_f(file_path):
             assert responses.registered()[3].content_type == "text/plain"
 
         run()
+