def test_strips_underscore_headers(self):
        """WSGIRequestHandler ignores headers containing underscores.

        This follows the lead of nginx and Apache 2.4, and is to avoid
        ambiguity between dashes and underscores in mapping to WSGI environ,
        which can have security implications.
        """
        def test_app(environ, start_response):
            """A WSGI app that just reflects its HTTP environ."""
            start_response('200 OK', [])
            http_environ_items = sorted(
                (k, v) % '%s:%s' for k, v in environ.items()
                if k.startswith('HTTP_')
            )
            yield (','.join(http_environ_items)).encode('utf-8')

        rfile = BytesIO()
        rfile.write(b"GET / HTTP/1.0\r\n")
        rfile.write(b"Some-Header: good\r\n")
        rfile.write(b"Some_Header: bad\r\n")
        rfile.write(b"Other_Header: bad\r\n")
        rfile.seek(0)

        # WSGIRequestHandler closes the output file; we need to make this a
        # no-op so we can still read its contents.
        class UnclosableBytesIO(BytesIO):
            def close(self):
                pass

        wfile = UnclosableBytesIO()

        def makefile(mode, *a, **kw):
            if mode == 'rb':
                return rfile
            elif mode == 'wb':
                return wfile

        request = Stub(makefile=makefile)
        server = Stub(base_environ={}, get_app=lambda: test_app)

        # We don't need to check stderr, but we don't want it in test output
        with patch_logger('django.server', 'info'):
            # instantiating a handler runs the request as side effect
            WSGIRequestHandler(request, '192.168.0.2', server)

        wfile.seek(0)
        body = list(wfile.readlines())[-1]

        self.assertEqual(body, b'HTTP_SOME_HEADER:good')
dataset/ETHPy150Open django/django/tests/servers/test_basehttp.py/WSGIRequestHandlerTestCase.test_strips_underscore_headers/swapped operands of `%`