Allow str/bytes subclasses to be used as header parts

requests/_internal_utils.py

@@ -14,9 +14,11 @@
 _VALID_HEADER_VALUE_RE_BYTE = re.compile(rb"^\S[^\r\n]*$|^$")
 _VALID_HEADER_VALUE_RE_STR = re.compile(r"^\S[^\r\n]*$|^$")
 
+_HEADER_VALIDATORS_STR = (_VALID_HEADER_NAME_RE_STR, _VALID_HEADER_VALUE_RE_STR)
+_HEADER_VALIDATORS_BYTE = (_VALID_HEADER_NAME_RE_BYTE, _VALID_HEADER_VALUE_RE_BYTE)
 HEADER_VALIDATORS = {
-    bytes: (_VALID_HEADER_NAME_RE_BYTE, _VALID_HEADER_VALUE_RE_BYTE),
-    str: (_VALID_HEADER_NAME_RE_STR, _VALID_HEADER_VALUE_RE_STR),
+    bytes: _HEADER_VALIDATORS_BYTE,
+    str: _HEADER_VALIDATORS_STR,
 }
 
 

requests/utils.py

@@ -25,7 +25,7 @@
 from .__version__ import __version__
 
 # to_native_string is unused here, but imported here for backwards compatibility
-from ._internal_utils import HEADER_VALIDATORS, to_native_string  # noqa: F401
+from ._internal_utils import _HEADER_VALIDATORS_BYTE, _HEADER_VALIDATORS_STR, HEADER_VALIDATORS, to_native_string  # noqa: F401
 from .compat import (
     Mapping,
     basestring,
@@ -1031,20 +1031,23 @@ def check_header_validity(header):
     :param header: tuple, in the format (name, value).
     """
     name, value = header
+    _validate_header_part(header, name, 0)
+    _validate_header_part(header, value, 1)
 
-    for part in header:
-        if type(part) not in HEADER_VALIDATORS:
-            raise InvalidHeader(
-                f"Header part ({part!r}) from {{{name!r}: {value!r}}} must be "
-                f"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, header_part, header_validator_index):
+    if isinstance(header_part, str):
+        validator = _HEADER_VALIDATORS_STR[header_validator_index]
+    elif isinstance(header_part, bytes):
+        validator = _HEADER_VALIDATORS_BYTE[header_validator_index]
+    else:
+        raise InvalidHeader(
+            f"Header part ({header_part!r}) from {header} "
+            f"must be of type str or bytes, not {type(header_part)}"
+        )
 
-def _validate_header_part(header_part, header_kind, validator):
     if not validator.match(header_part):
+        header_kind = 'name' if header_validator_index == 0 else 'value'
         raise InvalidHeader(
             f"Invalid leading whitespace, reserved character(s), or return"
             f"character(s) in header {header_kind}: {header_part!r}"

tests/test_requests.py

@@ -1752,6 +1752,29 @@ 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"
+
+        r_mixed = requests.get(httpbin("get"), headers={MyString("x-custom"): MyBytes(b"myheader")})
+        assert r_mixed.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"}