The method wsgiref.validate:InputWrapper.readline doesn't take any
arguments.  It should take an optional size argument.  Though this isn't
part of the WSGI specification, the cgi module uses this argument when
parsing the body, and in practice no applications that use
cgi.FieldStorage (which is most applications) are compatible with
wsgiref.validate as a result.  Simply adding a *args that is passed to
the underlying file fixes this.