code: def _get_headers(environ):
      # type: (Dict[str, str]) -> Iterator[Tuple[str, str]]
      
      for key, value in environ.items():
          key = str(key)
          if key.startswith("HTTP_") and key not in (
              "HTTP_CONTENT_TYPE",
              "HTTP_CONTENT_LENGTH",
          ):
              yield key[5:].replace("_", "-").title(), value
          elif key in ("CONTENT_TYPE", "CONTENT_LENGTH"):
              yield key.replace("_", "-").title(), value
docs: Returns only proper HTTP headers.