Lower change footprint

Author: tomchristie

h11/_connection.py

@@ -560,27 +560,27 @@ def _clean_up_response_headers_for_sending(self, response):
             # but the HTTP spec says that if our peer does this then we have
             # to fix it instead of erroring out, so we'll accord the user the
             # same respect).
-            headers = set_comma_header(headers, b"Content-Length", [])
+            headers = set_comma_header(headers, b"content-length", [])
             if self.their_http_version is None or self.their_http_version < b"1.1":
                 # Either we never got a valid request and are sending back an
                 # error (their_http_version is None), so we assume the worst;
                 # or else we did get a valid HTTP/1.0 request, so we know that
                 # they don't understand chunked encoding.
-                headers = set_comma_header(headers, b"Transfer-Encoding", [])
+                headers = set_comma_header(headers, b"transfer-encoding", [])
                 # This is actually redundant ATM, since currently we
                 # unconditionally disable keep-alive when talking to HTTP/1.0
                 # peers. But let's be defensive just in case we add
                 # Connection: keep-alive support later:
                 if self._request_method != b"HEAD":
                     need_close = True
             else:
-                headers = set_comma_header(headers, b"Transfer-Encoding", ["chunked"])
+                headers = set_comma_header(headers, b"transfer-encoding", ["chunked"])
 
         if not self._cstate.keep_alive or need_close:
             # Make sure Connection: close is set
             connection = set(get_comma_header(headers, b"connection"))
             connection.discard(b"keep-alive")
             connection.add(b"close")
-            headers = set_comma_header(headers, b"Connection", sorted(connection))
+            headers = set_comma_header(headers, b"connection", sorted(connection))
 
         response.headers = headers

h11/_headers.py

@@ -170,14 +170,12 @@ def get_comma_header(headers, name):
 
 def set_comma_header(headers, name, new_values):
     # The header name `name` is expected to be lower-case bytes.
-    raw_name = name
-    name = name.lower()
     new_headers = []
     for found_raw_name, found_name, found_raw_value in headers.raw_items:
         if found_name != name:
             new_headers.append((found_raw_name, found_raw_value))
     for new_value in new_values:
-        new_headers.append((raw_name, new_value))
+        new_headers.append((name.title(), new_value))
     return normalize_and_validate(new_headers)