Hi again,
first of all, sorry for not contributing to the discussion for such a long time. I was quite busy lately.
I tested the patch with Python 3.5.0a3. It works nicely for my use case. Thanks a lot!
I have one issue though: urllib's HTTPHandler and HTTPSHandler still try to enforce a Content-length to be set (by AbstractHTTPHandler.do_request_()). But for chunked transfer encoding, the Content-length must not be set. Using to this patch, HTTPConnection also checks for the Content-length in _send_request() and sets it if missing. AFAICS, HTTPConnection now does a far better job checking this then HTTPHandler and - most importantly - does it in a way that is compatible with chunked transfer encoding. So, I would suggest, that there is no need for HTTPHandler to care about the content length and that it should just leave this header alone.
E.g., I suggest that the "if not request.has_header('Content-length'): [...]" statement should completely be removed from AbstractHTTPHandler.do_request_() in urllib/request.py.