add get_version() method to Referenceable objects, describe our versioning scheme

[warner]

Zooko and I hammered out a versioning scheme on the mailing list: ​http://allmydata.org/pipermail/tahoe-dev/2008-November/000879.html has the discussion.

The action items are:

• add remote_get_version methods to our four main Referenceable objects:
  • storage server
  • introducer server
  • helper
  • chk-upload-helper
• add web pages for the URLs referenced therein
• add code to call storage.get_version and stash it somewhere
  • add code to upload to respect max-immutable-share-size
• add code to introducer client to get_version and require v1
• add code to helper client to get_version and require v1

[warner]

Mostly done, in 0eb6b324a4fcda2f, bf06492a90a3cc49, 0fab511be531c6f3, and 3e25efc010876b42. The URLs used as protocol identifiers are:

• ​http://allmydata.org/tahoe/protocols/storage/v1
• ​http://allmydata.org/tahoe/protocols/introducer/v1
• ​http://allmydata.org/tahoe/protocols/helper/v1
• ​http://allmydata.org/tahoe/protocols/helper/chk-upload/v1

The version information is attached to the RemoteReference, in the form of a VersionedRemoteReference wrapper with a .version attribute.

The upload code has been modified to look for maximum-immutable-share-size and skip any servers which can't handle the share we want to give them. This still needs tests, though.

[zooko]

Oh, it according to the most recent comment, this might not be thoroughly tested. What shall we do with this ticket?

[warner]

89683a39062edc6e adds the test (confirm that the upload code honors maximum-immutable-share-size), so I think we can close this one completely now.