upcoming deprecation in webish.py

[warner]

Our shiny new ​deprecations builder is running Tahoe tests against git trunk for both Twisted and Foolscap. It's yielded our first early warning signs:

.../allmydata/webish.py:44: DeprecationWarning: twisted.web.http.Request.channel was deprecated in Twisted 16.2.0. Call directly into the Request object instead.
.../allmydata/webish.py:45: DeprecationWarning: twisted.web.http.Request.channel was deprecated in Twisted 16.2.0. Call directly into the Request object instead.
.../nevow/appserver.py:229: DeprecationWarning: twisted.web.http.Request.channel was deprecated in Twisted 16.2.0. Call directly into the Request object instead.

It looks like our cut/paste/override copy of twisted.web.http.Request.requestReceived is out of date, and is using things that Twisted will be deprecating in the next release (the current release, 16.1.0, doesn't produce complaints).

Nominally we could just make our local requestReceived method look more like Twisted's current copy (in this case, changing self.client = self.channel.transport.getPeer() into = self._channel.getPeer()), but it might be good to rethink this, and find a way to get rid of our custom subclass. Especially because then we'd be using a clearly-marked-as-private attribute.

This might also tie into removing Nevow (#1963).

[warner]

This might have been reverted in current Twisted trunk.. at least the buildbot isn't complaining anymore. I know they had some regressions with .channel that affected Autobahn, so they're currently rethinking how they arrange the Request object.

We should still fix our code to stop poking around inside requestReceived, of course.

[exarkun]

As of Twisted 18.4.0 client and host attributes are set by Request.__init__ so these two lines can simply be deleted - if the Twisted dependency is bumped up to 18.4.0 which is nearly two years old at this point (and will almost certainly be more than two years old by the time this change is released) and thus seems reasonable.

[exarkun]

​https://github.com/tahoe-lafs/tahoe-lafs/pull/686

[GitHub <noreply@…>]

In 3de23ddf/trunk:

Merge pull request #686 from tahoe-lafs/2771.remove-channel-use

Remove Request.channel use

Fixes: ticket:2771