def test_union_empty(self): """Test that empty intervals are well behaved.""" a = Interval() b = Interval() c = a.union(b) d = b.union(a) self.assertEqual(a, b) self.assertEqual(b, c) self.assertEqual(c, d)
class File(object):
"""Holds data on what parts of a file have already been used."""
__metaclass__ = invariant.EnforceInvariant
def __init__(self, filename, size, subdir):
# Total size of the file
self.size = size
# Number of bytes in the file that have been used already.
self.used = 0
# Relative name of the file.
self.filename = filename
# Regions of the file in use.
self._extents = Interval()
# Subdir the file is currently in.
self.subdir = subdir
def _checkInvariant(self):
assert self.size >= self.used
assert len(self._extents) == self.used
@property
def free(self):
return self.size - self.used
@property
def path(self):
"""Returns the path of the padfile relative to the paddir."""
return (self.subdir, self.filename)
def getAllocation(self, requested):
"""Requests an allocation from the file of the given size. Raises OutOfPad
if the file is out of space."""
if requested > self.free:
raise OutOfPad("File %s has %i bytes but you requested %i." % \
(self.filename, self.free, requested))
alloc = Allocation()
for (start, length) in self._extents.iterExterior(self.size):
interval = Interval.fromAtom(start, min(requested - len(alloc), length))
seg = Allocation(self, interval)
alloc.unionUpdate(seg)
if len(alloc) >= requested:
assert len(alloc) == requested
break
assert len(alloc) == requested
return alloc
def commitAllocation(self, ival):
"""Mark the specified interval as used. Error if overlaps with currently
used area."""
self._extents = self._extents.union(ival)
self.used += len(ival)
def consumeEntireFile(self):
"""Mark the entire file as consumed. Used to prevent its use for encryption
while keeping it around for decryption."""
self.used = self.size
self._extents = Interval.fromAtom(0, self.size)
