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126 lines
4 KiB
Python
126 lines
4 KiB
Python
import hashlib
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import random
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import string
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import struct
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class RandomContentFile(object):
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def __init__(self, size, seed):
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self.seed = seed
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self.random = random.Random(self.seed)
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self.offset = 0
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self.buffer = ''
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self.size = size
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self.hash = hashlib.md5()
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self.digest_size = self.hash.digest_size
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self.digest = None
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def seek(self, offset):
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assert offset == 0
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self.random.seed(self.seed)
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self.offset = offset
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self.buffer = ''
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def tell(self):
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return self.offset
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def _generate(self):
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# generate and return a chunk of pseudorandom data
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# 256 bits = 32 bytes at a time
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size = 1*1024*1024
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l = [self.random.getrandbits(64) for _ in xrange(size/8)]
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s = struct.pack((size/8)*'Q', *l)
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return s
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def read(self, size=-1):
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if size < 0:
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size = self.size - self.offset
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r = []
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random_count = min(size, self.size - self.offset - self.digest_size)
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if random_count > 0:
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while len(self.buffer) < random_count:
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self.buffer += self._generate()
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self.offset += random_count
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size -= random_count
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data, self.buffer = self.buffer[:random_count], self.buffer[random_count:]
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if self.hash is not None:
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self.hash.update(data)
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r.append(data)
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digest_count = min(size, self.size - self.offset)
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if digest_count > 0:
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if self.digest is None:
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self.digest = self.hash.digest()
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self.hash = None
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self.offset += digest_count
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size -= digest_count
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data = self.digest[:digest_count]
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r.append(data)
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return ''.join(r)
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class FileVerifier(object):
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def __init__(self):
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self.size = 0
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self.hash = hashlib.md5()
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self.buf = ''
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def write(self, data):
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self.size += len(data)
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self.buf += data
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digsz = -1*self.hash.digest_size
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new_data, self.buf = self.buf[0:digsz], self.buf[digsz:]
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self.hash.update(new_data)
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def valid(self):
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"""
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Returns True if this file looks valid. The file is valid if the end
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of the file has the md5 digest for the first part of the file.
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"""
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return self.buf == self.hash.digest()
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def files(mean, stddev, seed=None):
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"""
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Yields file-like objects with effectively random contents, where
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the size of each file follows the normal distribution with `mean`
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and `stddev`.
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Beware, the file-likeness is very shallow. You can use boto's
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`key.set_contents_from_file` to send these to S3, but they are not
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full file objects.
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The last 128 bits are the MD5 digest of the previous bytes, for
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verifying round-trip data integrity. For example, if you
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re-download the object and place the contents into a file called
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``foo``, the following should print two identical lines:
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python -c 'import sys, hashlib; data=sys.stdin.read(); print hashlib.md5(data[:-16]).hexdigest(); print "".join("%02x" % ord(c) for c in data[-16:])' <foo
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Except for objects shorter than 16 bytes, where the second line
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will be proportionally shorter.
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"""
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rand = random.Random(seed)
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while True:
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while True:
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size = int(rand.normalvariate(mean, stddev))
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if size >= 0:
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break
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yield RandomContentFile(size=size, seed=rand.getrandbits(32))
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def names(mean, stddev, charset=None, seed=None):
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"""
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Yields strings that are somewhat plausible as file names, where
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the lenght of each filename follows the normal distribution with
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`mean` and `stddev`.
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"""
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if charset is None:
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charset = string.ascii_lowercase
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rand = random.Random(seed)
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while True:
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while True:
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length = int(rand.normalvariate(mean, stddev))
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if length >= 0:
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break
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name = ''.join(rand.choice(charset) for _ in xrange(length))
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yield name
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