* emit lease expiry date in ISO-8601'ish format as well as Brian's format
* rename iso_utc_time_to_localseconds() to iso_utc_time_to_seconds()
* add iso_utc_date()
* simplify the body of iso_utc_time_to_seconds()
This walks slowly through all shares, examining their leases, deciding which
are still valid and which have expired. Once enabled, it will then remove the
expired leases, and delete shares which no longer have any valid leases. Note
that there is not yet a tahoe.cfg option to enable lease-deletion: the
current code is read-only. A subsequent patch will add a tahoe.cfg knob to
control this, as well as docs. Some other minor items included in this patch:
tahoe debug dump-share has a new --leases-only flag
storage sharefile/leaseinfo code is cleaned up
storage web status page (/storage) has more info, more tests coverage
space-left measurement on OS-X should be more accurate (it was off by 2048x)
(use stat .f_frsize instead of f_bsize)
The code for validating the share hash tree and the block hash tree has been rewritten to make sure it handles all cases, to share metadata about the file (such as the share hash tree, block hash trees, and UEB) among different share downloads, and not to require hashes to be stored on the server unnecessarily, such as the roots of the block hash trees (not needed since they are also the leaves of the share hash tree), and the root of the share hash tree (not needed since it is also included in the UEB). It also passes the latest tests including handling corrupted shares well.
ValidatedReadBucketProxy takes a share_hash_tree argument to its constructor, which is a reference to a share hash tree shared by all ValidatedReadBucketProxies for that immutable file download.
ValidatedReadBucketProxy requires the block_size and share_size to be provided in its constructor, and it then uses those to compute the offsets and lengths of blocks when it needs them, instead of reading those values out of the share. The user of ValidatedReadBucketProxy therefore has to have first used a ValidatedExtendedURIProxy to compute those two values from the validated contents of the URI. This is pleasingly simplifies safety analysis: the client knows which span of bytes corresponds to a given block from the validated URI data, rather than from the unvalidated data stored on the storage server. It also simplifies unit testing of verifier/repairer, because now it doesn't care about the contents of the "share size" and "block size" fields in the share. It does not relieve the need for share data v2 layout, because we still need to store and retrieve the offsets of the fields which come after the share data, therefore we still need to use share data v2 with its 8-byte fields if we want to store share data larger than about 2^32.
Specify which subset of the block hashes and share hashes you need while downloading a particular share. In the future this will hopefully be used to fetch only a subset, for network efficiency, but currently all of them are fetched, regardless of which subset you specify.
ReadBucketProxy hides the question of whether it has "started" or not (sent a request to the server to get metadata) from its user.
Download is optimized to do as few roundtrips and as few requests as possible, hopefully speeding up download a bit.
Nathan Wilcox observed that the storage server can rely on the size of the share file combined with the count of leases to unambiguously identify the location of the leases. This means that it can hold any size share data, even though the field nominally used to hold the size of the share data is only 32 bits wide.
With this patch, the storage server still writes the "size of the share data" field (just in case the server gets downgraded to an earlier version which requires that field, or the share file gets moved to another server which is of an earlier vintage), but it doesn't use it. Also, with this patch, the server no longer rejects requests to write shares which are >= 2^32 bytes in size, and it no longer rejects attempts to read such shares.
This fixes http://allmydata.org/trac/tahoe/ticket/346 (increase share-size field to 8 bytes, remove 12GiB filesize limit), although there remains open a question of how clients know that a given server can handle large shares (by using the new versioning scheme, probably).
Note that share size is also limited by another factor -- how big of a file we can store on the local filesystem on the server. Currently allmydata.com typically uses ext3 and I think we typically have block size = 4 KiB, which means that the largest file is about 2 TiB. Also, the hard drives themselves are only 1 TB, so the largest share is definitely slightly less than 1 TB, which means (when K == 3), the largest file is less than 3 TB.
This patch also refactors the creation of new sharefiles so that only a single fopen() is used.
This patch also helps with the unit-testing of repairer, since formerly it was unclear what repairer should expect to find if the "share data size" field was corrupted (some corruptions would have no effect, others would cause failure to download). Now it is clear that repairer is not required to notice if this field is corrupted since it has no effect on download. :-)
