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-rw-r--r--genbackupdatalib/generator.py44
1 files changed, 13 insertions, 31 deletions
diff --git a/genbackupdatalib/generator.py b/genbackupdatalib/generator.py
index 8cf349c..227b6a4 100644
--- a/genbackupdatalib/generator.py
+++ b/genbackupdatalib/generator.py
@@ -14,49 +14,31 @@
# along with this program. If not, see <http://www.gnu.org/licenses/>.
-import random
import struct
+import Crypto.Cipher.ARC4
+
class DataGenerator(object):
'''Generate random binary data.'''
- # We generate data by using a blob of suitable size. The output
- # sequence repeats the blob, where each repetition is preceded by
- # a 64-bit counter.
- #
- # We need to be relatively prime with obnam's chunk size, which
- # defaults to 64 KiB (65536 bytes). This is so that obnam does not
- # notice a lot of duplicated data, resulting in unrealistically
- # high amounts of compression in the backup store.
- #
- # Ideally, we would not generate any repeating data, but the random
- # number generator is not fast enough for that. We need to generate
- # data about as fast as the disk can write it, and the random number
- # generator is orders of magnitude slower than that.
-
- _blob_size = 65521
- _blob_size = 1021
+ _data = 'x' * 1024**2
def __init__(self, seed):
- self._random = random.Random(seed)
- self._blob = self._generate_blob()
- self._counter = 0
+ key = struct.pack('!Q', seed)
+ self._arc4 = Crypto.Cipher.ARC4.new(key)
self._buffer = ''
- def _generate_blob(self):
- return ''.join(chr(self._random.randint(0, 255))
- for i in range(self._blob_size))
-
def generate(self, size):
- while size > len(self._buffer):
- self._buffer += self._generate_more_data()
+ while len(self._buffer) < size:
+ self._buffer += self._generate_junk()
+ return self._split_off_data(size)
+
+ def _generate_junk(self):
+ return self._arc4.encrypt(self._data)
+
+ def _split_off_data(self, size):
data = self._buffer[:size]
self._buffer = self._buffer[size:]
return data
-
- def _generate_more_data(self):
- self._counter += 1
- return struct.pack('!Q', self._counter) + self._blob
-