wsgi proxy and 'hop by hop'

The WSGI proxy implementation passes hop-by-hop related headers (like transfer-encoding, connection, etc) through unchanged. According to PEP 3333 these however do not apply to WSGI:

http://legacy.python.org/dev/peps/pep-3333/

Indeed Waitress gives an exception when you try, and mod_wsgi seems to choke on such requests.

Since the WSGI proxy should be a conformant WSGI implementation, it should remove these hop by hop headers. This won't affect chunking, as if the proxy is proxying a chunked response, WSGI will return the chunks one by one in its iterator result. A WSGI server can then add them back again (I've seen Waitress does).