added unit tests to test various permutations of the rename function, and
some sanity checks on the rename-form function.
also added a guard to prevent '/' in from_/to_name in rename calls.
By writing something like "25 75 100" into a file named 'encoding_parameters'
in the central Introducer's base directory, all clients which use that
introducer will be advised to use 25-out-of-100 encoding for files (i.e.
100 shares will be produced, 25 are required to reconstruct, and the upload
process will be happy if it can find homes for at least 75 shares). The
default values are "3 7 10". For small meshes, the defaults are probably
good, but for larger ones it may be appropriate to increase the number of
shares.
This will make it easier to change RIBucketWriter in the future to reduce the wire
protocol to just open/write(offset,data)/close, and do all the structuring on the
client end. The ultimate goal is to store each bucket in a single file, to reduce
the considerable filesystem-quantization/inode overhead on the storage servers.
Also include the encoder portion of Bob Ippolito's simplejson-1.7.1 as
allmydata.util.json_encoder . simplejson is distributed under a more liberal
license than Tahoe (looks to be modified BSD), so redistributing it should be ok.
To use this, write a number like 10MB or 5Gb or 5000000000 to a file
named 'sizelimit' in the client's base directory. The node will not grant
leases for shares that would take it much beyond this many bytes of
storage. Note that metadata is not included in the allocation count until
a restart, so the actual space consumed may grow beyond the limit if
the node is not restarted very frequently and the amount of metadata is
significant.
If the error occurs before any data has been sent, we can give a sensible
error message (code 500, stack trace, etc). This will cover most of the error
cases. The ones that aren't covered are when we run out of good peers after
successfully decoding the first segment, either because they go away or
because their shares are corrupt.
