handle IPv6

[Brian Warner]

​Tahoe#867 is about supporting IPv6 in a tahoe grid. For that to work, we need v6 support in Foolscap. This depends upon getting v6 support in Twisted (for which you should look at ​Twisted#3014, still open as of august-2010).

Thanks to Zooko's persuasion in #60, FURLs with v6 addresses are likely to be tolerated (i.e. ignored) by current versions of Foolscap (0.2.6 or later, so everything since may-2008). In particular, any connection hint with more than one colon is ignored. So backwards compatibility shouldn't be a problem.

The FURL syntax for a v6 address would be pb://TUBID@ipv6:[fe80::1%lo0]:12345/SWISS, and the syntax for a v4+v6 FURL would be pb://TUBID@127.0.0.1:12345,ipv6:[::1]:12345/SWISS or pb://TUBID@ipv4:127.0.0.1:12345,ipv6:[::1]:12345/SWISS .

The new parsing rules will have a legacy-ipv4 rule that matches hints with a single colon, so anything else will be in the form TYPE:ADDRESS:PORT. (future schemes that don't have two-part address+port identifiers, like Tor hidden services or #151 I2P endpoints will need an extra colon, like i2p::I2PHASH.b32.i2p, to avoid being confused with legacy IPV4ADDR:PORT pairs).

Once the Twisted work is done, the foolscap-side work is a new parser in source:foolscap/referenceable.py (decode_location_hints) to spot the v6 addresses, then work in negotiate.TubConnector to stop ignoring non-ipv4 hints and call reactor.connectTCP6 or whatever the new API is. We'll also need code to parse the Tub.listenOn strports spec to handle v6, and something for setLocationAutomatically to take a v6 hint and construct a FURL from it.

[Brian Warner]

Twisted-12.0.0 (released 10-Feb-2012) appears to contain enough support (in reactor.listenTCP and reactor.connectTCP) to enable client/server handling of v6 address literals. I *think* that's enough to let us:

• use v6 address literals in Tub.listenOn
• connect to v6 address literals found in FURL connection hints

If we also extend Tub.setLocationAutomatically to learn how to detect v6 addresses on local interfaces, then we could get numeric v6 addresses in automatically-generated connection hints.

What Twisted doesn't handle yet is DNS resolution, so we can't yet tolerate is folks modifying their FURL's connection hints to replace the numeric IPv6 address with a DNS name (that has an A6 or AAAA record).

The Tub.listenOn and Listener code may need some work: I don't know if the current use of internet.TCPServer is v4-only or not.