When requesting a resource from an origin server, the request-target in request line should always starts with a back slash. But in SimpleHTTPServerTestCase in test_httpservers.py, almost all the requests are sent without the back slash though the handler handles it well. The request lines are like 'GET tmpXXXXX HTTP/1.1'. I add the back slashes.

Maybe in SimpleHTTPRequestHandler, we should reject such invalid request-targets and then return BAD_REQUEST. And then issue2254 won't happen.