I still don’t think the test case is a reasonable example. According to <http://www.w3.org/Protocols/HTTP/AsImplemented.html>, HTTP 0.9 only supported GET, not CONNECT, and doesn’t include any header fields in the protocol (such as your X-Foo: bar). It would make more sense to me to adjust the check at <https://hg.python.org/cpython/file/69ea73015132/Lib/httplib.py#l813> to also check for version == "HTTP/0.9". That would probably eliminate the need to mess too much with the details of the LineAndFileWrapper class.

But if you wanted to parse the CONNECT response as a HTTP 0.9 response, I think you should not try to parse any header, because that will tend to skip over the start of the actual response.

Also, I assume the change to “configure” is unrelated.