Issue 23759: urllib.parse: make coap:// known

The CoAP protocol (RFC 7252) registers the new URI schemes coap and coaps. They adhere to the generic RFC3986 rules, and use netloc and relative URIs.

Therefore, please add the 'coap' and 'coaps' schemes to the uses_relative and uses_netloc lists in urllib.parse.

I'm not sure about uses_params; the CoAP protocol in itself does not do anything special with the ';' character in URIs, so probably it should not be included there. (But then again, neither does RFC2616 mention ";" in the context of addresses, and it is included in uses_params).

I would like to see these hard-coded white lists of URL schemes eliminated as much as possible. Here’s some related issues:

* Issue 16134: rtmp, rtmpe, rtmps, rtmpt
* Issue 18828: redis, also proposing to urljoin() arbitrary schemes
* Issue 15009: yelp
* Issue 22852: Proposing that urlunsplit() and urlunparse() restore empty netloc, query, and fragment components properly for arbitary schemes
* Issue 23636: scgi

I too would like to see this issue dealt with generically.  I believe the last time we discussed it the barrier was backward compatibility and which RFCs we actually support :(.  Fixing it generically will require a well thought out and well researched proposal.

i wholeheartedly agree that a generic solution would be preferable, but as you pointed out, that needs to be well-researched. until there is a concrete plan for that, please don't let the ideal solution get in the way of a practical update of the uri scheme list.

I'm also +1 to handling this generically and agree that a well thought out and researched proposal would be required.

I did mention in #18228 (http://bugs.python.org/issue18828#msg238363) that I think that a short term solution to this problem could be to simply add documentation around manually adding schemes as required to uses_relative.