In an ancient version of directories, we needed a MAC on each entry. In modern times, the entire dirnode comes with a digital signature, so the MAC on each entry is redundant.
With this patch, we no longer check those MACs when reading directories, but we still produce them so that older readers will accept directories that we write.
I get confused about whether a given argument or return value is a uri-as-string or uri-as-object. This patch adds a lot of assertions that it is one or the other, and also changes CheckerResults to take objects not strings.
In the future, I hope that we generally use Python objects except when importing into or exporting from the Python interpreter e.g. over the wire, the UI, or a stored file.
Removed the Checker service, removed checker results storage (both in-memory
and the tiny stub of sqlite-based storage). Added ICheckable, all
check/verify is now done by calling the check() method on filenodes and
dirnodes (immutable files, literal files, mutable files, and directory
instances).
Checker results are returned in a Results instance, with an html() method for
display. Checker results have been temporarily removed from the wui directory
listing until we make some other fixes.
Also fixed client.create_node_from_uri() to create LiteralFileNodes properly,
since they have different checking behavior. Previously we were creating full
FileNodes with LIT uris inside, which were downloadable but not checkable.
Now upload or encode methods take a required argument named "convergence" which can be either None, indicating no convergent encryption at all, or a string, which is the "added secret" to be mixed in to the content hash key. If you want traditional convergent encryption behavior, set the added secret to be the empty string.
This patch also renames "content hash key" to "convergent encryption" in a argument names and variable names. (A different and larger renaming is needed in order to clarify that Tahoe supports immutable files which are not encrypted content-hash-key a.k.a. convergent encryption.)
This patch also changes a few unit tests to use non-convergent encryption, because it doesn't matter for what they are testing and non-convergent encryption is slightly faster.
Unfinished bits: doc in webapi.txt, test handling of badly formed JSON, return reasonable HTTP response, examination of the effect of this patch on code coverage -- but I'm committing it anyway because MikeB can use it and I'm being called to dinner...
