class RestClient::Request

def maybe_convert_extension(ext)
  unless ext =~ /\A[a-zA-Z0-9_@-]+\z/
    # Don't look up strings unless they look like they could be a file
    # extension known to mime-types.
    #
    # There currently isn't any API public way to look up extensions
    # directly out of MIME::Types, but the type_for() method only strips
    # off after a period anyway.
    return ext
  end
  types = MIME::Types.type_for(ext)
  if types.empty?
    ext
  else
    types.first.content_type
  end
end