gh-142533: Apply PR feedback about redundant code changes

* Remove redundant validation checks
* Drop unnecessary return statement
* Remove unnecessary debug code

Author: tadejmagajna

Lib/http/server.py

@@ -552,7 +552,6 @@ def send_response_only(self, code, message=None):
                     message = ''
             if not hasattr(self, '_headers_buffer'):
                 self._headers_buffer = []
-            _validate_header_string(message)
             self._headers_buffer.append(("%s %d %s\r\n" %
                     (self.protocol_version, code, message)).encode(
                         'latin-1', 'strict'))

Lib/test/test_httpservers.py

@@ -1052,19 +1052,6 @@ def test_header_buffering_of_send_response_only(self):
         handler.end_headers()
         self.assertEqual(output.numWrites, 1)
 
-    def test_send_response_only_rejects_crlf_message(self):
-        input = BytesIO(b'GET / HTTP/1.1\r\n\r\n')
-        output = AuditableBytesIO()
-        handler = SocketlessRequestHandler()
-        handler.rfile = input
-        handler.wfile = output
-        handler.request_version = 'HTTP/1.1'
-
-        with self.assertRaises(ValueError) as ctx:
-            handler.send_response_only(418, 'value\r\nSet-Cookie: custom=true')
-        self.assertIn('Invalid header name/value: contains CR or LF',
-                      str(ctx.exception))
-
     def test_header_buffering_of_send_header(self):
 
         input = BytesIO(b'GET / HTTP/1.1\r\n\r\n')

Lib/wsgiref/headers.py

@@ -33,19 +33,14 @@ def __init__(self, headers=None):
         if type(headers) is not list:
             raise TypeError("Headers must be a list of name/value tuples")
         self._headers = headers
-        if __debug__:
-            for k, v in headers:
-                self._validate_header_string(k)
-                self._validate_header_string(v)
 
     def _validate_header_string(self, value):
         """Validate header type and value."""
-        if type(value) is str:
-            if '\r' in value or '\n' in value:
-                raise ValueError('Invalid header name/value: contains CR or LF')
-            return value
-        raise AssertionError("Header names/values must be"
-            " of type str (got {0})".format(repr(value)))
+        if not isinstance(value, str):
+            raise AssertionError("Header names/values must be"
+                " of type str (got {0})".format(repr(value)))
+        if '\r' in value or '\n' in value:
+            raise ValueError('Invalid header name/value: contains CR or LF')
 
     def __len__(self):
         """Return the total number of headers, including duplicates."""
@@ -54,17 +49,18 @@ def __len__(self):
     def __setitem__(self, name, val):
         """Set the value of a header."""
         del self[name]
-        self._headers.append(
-            (self._validate_header_string(name),
-             self._validate_header_string(val)))
+        self._validate_header_string(name)
+        self._validate_header_string(val)
+        self._headers.append((name, val))
 
     def __delitem__(self,name):
         """Delete all occurrences of a header, if present.
 
         Does *not* raise an exception if the header is missing.
         """
-        name = self._validate_header_string(name.lower())
-        self._headers[:] = [kv for kv in self._headers if kv[0].lower() != name]
+        self._headers[:] = [
+            kv for kv in self._headers if kv[0].lower() != name.lower()
+        ]
 
     def __getitem__(self,name):
         """Get the first header value for 'name'
@@ -90,15 +86,13 @@ def get_all(self, name):
         fields deleted and re-inserted are always appended to the header list.
         If no fields exist with the given name, returns an empty list.
         """
-        name = self._validate_header_string(name.lower())
-        return [kv[1] for kv in self._headers if kv[0].lower()==name]
+        return [kv[1] for kv in self._headers if kv[0].lower()==name.lower()]
 
 
     def get(self,name,default=None):
         """Get the first header value for 'name', or return 'default'"""
-        name = self._validate_header_string(name.lower())
         for k,v in self._headers:
-            if k.lower()==name:
+            if k.lower()==name.lower():
                 return v
         return default
 
@@ -151,8 +145,9 @@ def setdefault(self,name,value):
         and value 'value'."""
         result = self.get(name)
         if result is None:
-            self._headers.append((self._validate_header_string(name),
-                self._validate_header_string(value)))
+            self._validate_header_string(name)
+            self._validate_header_string(value)
+            self._headers.append((name, value))
             return value
         else:
             return result
@@ -173,15 +168,16 @@ def add_header(self, _name, _value, **_params):
         *not* handle '(charset, language, value)' tuples: all values must be
         strings or None.
         """
+        self._validate_header_string(_name)
         parts = []
         if _value is not None:
-            _value = self._validate_header_string(_value)
+            self._validate_header_string(_value)
             parts.append(_value)
         for k, v in _params.items():
-            k = self._validate_header_string(k)
+            self._validate_header_string(k)
             if v is None:
                 parts.append(k.replace('_', '-'))
             else:
-                v = self._validate_header_string(v)
+                self._validate_header_string(v)
                 parts.append(_formatparam(k.replace('_', '-'), v))
-        self._headers.append((self._validate_header_string(_name), "; ".join(parts)))
+        self._headers.append((_name, "; ".join(parts)))