requests: Do not leak header modifications when calling request.

The requests() function takes a headers dict argument
(call-by-reference). This object is then modified in the function. For
instance the host is added and authentication information. Such behavior
is not expected. It is also problematic:

- Modifications of the header dictionary will be visible on the caller
  site.
- When reusing the same (supposedly read-only) headers object for
  differenct calls, the second call will apparently re-use wrong headers
  from the previous call and may fail.

This patch should also fix #839. Unfortunately the copy operation does
not preserve the key order and we have to touch the existing test cases.

Signed-off-by: Richard Weickelt <richard@weickelt.de>

python-ecosys/requests/requests/__init__.py

@@ -46,6 +46,8 @@ def request(
 ):
     if headers is None:
         headers = {}
+    else:
+        headers = headers.copy()
 
     redirect = None  # redirection url, None means no redirection
     chunked_data = data and getattr(data, "__next__", None) and not getattr(data, "__len__", None)

python-ecosys/requests/test_requests.py

@@ -102,11 +102,11 @@ def test_post_chunked_data():
 
 def test_overwrite_get_headers():
     response = requests.request(
-        "GET", "http://example.com", headers={"Connection": "keep-alive", "Host": "test.com"}
+        "GET", "http://example.com", headers={"Host": "test.com", "Connection": "keep-alive"}
     )
 
     assert response.raw._write_buffer.getvalue() == (
-        b"GET / HTTP/1.0\r\n" + b"Host: test.com\r\n" + b"Connection: keep-alive\r\n\r\n"
+        b"GET / HTTP/1.0\r\n" + b"Connection: keep-alive\r\n" + b"Host: test.com\r\n\r\n"
     ), format_message(response)
 
 
@@ -145,6 +145,14 @@ def test_overwrite_post_chunked_data_headers():
     ), format_message(response)
 
 
+def test_do_not_modify_headers_argument():
+    global do_not_modify_this_dict
+    do_not_modify_this_dict = {}
+    requests.request("GET", "http://example.com", headers=do_not_modify_this_dict)
+
+    assert do_not_modify_this_dict == {}, do_not_modify_this_dict
+
+
 test_simple_get()
 test_get_auth()
 test_get_custom_header()
@@ -153,3 +161,4 @@ test_post_chunked_data()
 test_overwrite_get_headers()
 test_overwrite_post_json_headers()
 test_overwrite_post_chunked_data_headers()
+test_do_not_modify_headers_argument()