Rework check_header_validity for bytes/str subclasses

requests/utils.py

@@ -1030,26 +1030,22 @@ def check_header_validity(header):
 
     :param header: tuple, in the format (name, value).
     """
-    name, value = header
-
-    supported_types = tuple(HEADER_VALIDATORS.keys())
-    for part in header:
-        if not isinstance(part, supported_types):
+    for n, part in enumerate(header):
+        if isinstance(part, str):
+            validator = HEADER_VALIDATORS[str][n]
+        elif isinstance(part, bytes):
+            validator = HEADER_VALIDATORS[bytes][n]
+        else:
             raise InvalidHeader(
-                f"Header part ({part!r}) from {{{name!r}: {value!r}}} must be "
-                f"of type str or bytes, not {type(part)}"
+                f"Header part ({part!r}) from {header} "
+                f"must be of type str or bytes, not {type(part)}"
             )
 
-    _validate_header_part(name, "name", HEADER_VALIDATORS[type(name)][0])
-    _validate_header_part(value, "value", HEADER_VALIDATORS[type(value)][1])
-
-
-def _validate_header_part(header_part, header_kind, validator):
-    if not validator.match(header_part):
-        raise InvalidHeader(
-            f"Invalid leading whitespace, reserved character(s), or return"
-            f"character(s) in header {header_kind}: {header_part!r}"
-        )
+        if not validator.match(part):
+            raise InvalidHeader(
+                f"Invalid leading whitespace, reserved character(s), "
+                f"or return character(s) in header: {part!r}"
+            )
 
 
 def urldefragauth(url):

tests/test_requests.py

@@ -1747,6 +1747,26 @@ def test_header_no_leading_space(self, httpbin, invalid_header):
         with pytest.raises(InvalidHeader):
             requests.get(httpbin("get"), headers=invalid_header)
 
+    def test_header_with_subclass_types(self, httpbin):
+        """If the subclasses does not behave *exactly* like
+        the base bytes/str classes, this is not supported.
+        This test is for backwards compatibility.
+        """
+
+        class MyString(str):
+            pass
+
+        class MyBytes(bytes):
+            pass
+
+        r_str = requests.get(httpbin("get"), headers={MyString("x-custom"): "myheader"})
+        assert r_str.request.headers["x-custom"] == "myheader"
+
+        r_bytes = requests.get(
+            httpbin("get"), headers={MyBytes(b"x-custom"): b"myheader"}
+        )
+        assert r_bytes.request.headers["x-custom"] == b"myheader"
+
     @pytest.mark.parametrize("files", ("foo", b"foo", bytearray(b"foo")))
     def test_can_send_objects_with_files(self, httpbin, files):
         data = {"a": "this is a string"}