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# pack.py -- For dealing wih packed git objects.
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# Copyright (C) 2007 James Westby <jw+debian@jameswestby.net>
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# Copryight (C) 2008 Jelmer Vernooij <jelmer@samba.org>
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# The code is loosely based on that in the sha1_file.c file from git itself,
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# which is Copyright (C) Linus Torvalds, 2005 and distributed under the
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# This program is free software; you can redistribute it and/or
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# modify it under the terms of the GNU General Public License
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# as published by the Free Software Foundation; version 2
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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"""Classes for dealing with packed git objects.
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A pack is a compact representation of a bunch of objects, stored
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using deltas where possible.
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They have two parts, the pack file, which stores the data, and an index
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that tells you where the data is.
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To find an object you look in all of the index files 'til you find a
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match for the object name. You then use the pointer got from this as
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a pointer in to the corresponding packfile.
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from collections import defaultdict
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from itertools import imap, izip
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from errors import ApplyDeltaError
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supports_mmap_offset = (sys.version_info[0] >= 3 or
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(sys.version_info[0] == 2 and sys.version_info[1] >= 6))
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def take_msb_bytes(map, offset):
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while len(ret) == 0 or ret[-1] & 0x80:
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ret.append(ord(map[offset]))
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def read_zlib(data, offset, dec_size):
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obj = zlib.decompressobj()
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while obj.unused_data == "":
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add = data[base:base+1024]
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x += obj.decompress(add)
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assert len(x) == dec_size
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comp_len = fed-len(obj.unused_data)
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return sha.hexdigest()
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"""Convert a hex string to a binary sha string."""
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for i in range(0, len(hex), 2):
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ret += chr(int(hex[i:i+2], 16))
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"""Convert a binary sha string to a hex sha string."""
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ret += "%02x" % ord(i)
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MAX_MMAP_SIZE = 256 * 1024 * 1024
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def simple_mmap(f, offset, size, access=mmap.ACCESS_READ):
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"""Simple wrapper for mmap() which always supports the offset parameter.
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:param f: File object.
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:param offset: Offset in the file, from the beginning of the file.
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:param size: Size of the mmap'ed area
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:param access: Access mechanism.
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:return: MMAP'd area.
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if offset+size > MAX_MMAP_SIZE and not supports_mmap_offset:
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raise AssertionError("%s is larger than 256 meg, and this version "
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"of Python does not support the offset argument to mmap().")
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if supports_mmap_offset:
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return mmap.mmap(f.fileno(), size, access=access, offset=offset)
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class ArraySkipper(object):
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def __init__(self, array, offset):
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def __getslice__(self, i, j):
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return self.array[i+self.offset:j+self.offset]
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def __getitem__(self, i):
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return self.array[i+self.offset]
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return len(self.array) - self.offset
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return str(self.array[self.offset:])
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mem = mmap.mmap(f.fileno(), size+offset, access=access)
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return ArraySkipper(mem, offset)
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def resolve_object(offset, type, obj, get_ref, get_offset):
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"""Resolve an object, possibly resolving deltas when necessary."""
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if not type in (6, 7): # Not a delta
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if type == 6: # offset delta
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(delta_offset, delta) = obj
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assert isinstance(delta_offset, int)
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assert isinstance(delta, str)
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offset = offset-delta_offset
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type, base_obj = get_offset(offset)
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assert isinstance(type, int)
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elif type == 7: # ref delta
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(basename, delta) = obj
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assert isinstance(basename, str) and len(basename) == 20
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assert isinstance(delta, str)
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type, base_obj = get_ref(basename)
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assert isinstance(type, int)
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type, base_text = resolve_object(offset, type, base_obj, get_ref, get_offset)
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return type, apply_delta(base_text, delta)
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class PackIndex(object):
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"""An index in to a packfile.
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Given a sha id of an object a pack index can tell you the location in the
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packfile of that object if it has it.
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To do the loop it opens the file, and indexes first 256 4 byte groups
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with the first byte of the sha id. The value in the four byte group indexed
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is the end of the group that shares the same starting byte. Subtract one
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from the starting byte and index again to find the start of the group.
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The values are sorted by sha id within the group, so do the math to find
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the start and end offset and then bisect in to find if the value is present.
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def __init__(self, filename):
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"""Create a pack index object.
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Provide it with the name of the index file to consider, and it will map
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it whenever required.
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self._filename = filename
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# Take the size now, so it can be checked each time we map the file to
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# ensure that it hasn't changed.
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self._size = os.path.getsize(filename)
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self._file = open(filename, 'r')
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self._contents = simple_mmap(self._file, 0, self._size)
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if self._contents[:4] != '\377tOc':
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self._fan_out_table = self._read_fan_out_table(0)
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(self.version, ) = struct.unpack_from(">L", self._contents, 4)
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assert self.version in (2,), "Version was %d" % self.version
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self._fan_out_table = self._read_fan_out_table(8)
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self._name_table_offset = 8 + 0x100 * 4
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self._crc32_table_offset = self._name_table_offset + 20 * len(self)
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self._pack_offset_table_offset = self._crc32_table_offset + 4 * len(self)
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def __eq__(self, other):
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if type(self) != type(other):
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if self._fan_out_table != other._fan_out_table:
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for (name1, _, _), (name2, _, _) in izip(self.iterentries(), other.iterentries()):
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"""Return the number of entries in this pack index."""
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return self._fan_out_table[-1]
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def _unpack_entry(self, i):
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"""Unpack the i-th entry in the index file.
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:return: Tuple with object name (SHA), offset in pack file and
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CRC32 checksum (if known)."""
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if self.version == 1:
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(offset, name) = struct.unpack_from(">L20s", self._contents,
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(0x100 * 4) + (i * 24))
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return (name, offset, None)
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return (self._unpack_name(i), self._unpack_offset(i),
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self._unpack_crc32_checksum(i))
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def _unpack_name(self, i):
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if self.version == 1:
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return self._unpack_entry(i)[0]
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return struct.unpack_from("20s", self._contents,
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self._name_table_offset + i * 20)[0]
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def _unpack_offset(self, i):
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if self.version == 1:
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return self._unpack_entry(i)[1]
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return struct.unpack_from(">L", self._contents,
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self._pack_offset_table_offset + i * 4)[0]
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def _unpack_crc32_checksum(self, i):
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if self.version == 1:
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return struct.unpack_from(">L", self._contents,
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self._crc32_table_offset + i * 4)[0]
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return imap(sha_to_hex, self._itersha())
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for i in range(len(self)):
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yield self._unpack_name(i)
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def objects_sha1(self):
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return iter_sha1(self._itersha())
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def iterentries(self):
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"""Iterate over the entries in this pack index.
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Will yield tuples with object name, offset in packfile and crc32 checksum.
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for i in range(len(self)):
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yield self._unpack_entry(i)
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def _read_fan_out_table(self, start_offset):
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for i in range(0x100):
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ret.append(struct.unpack(">L", self._contents[start_offset+i*4:start_offset+(i+1)*4])[0])
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"""Check that the stored checksum matches the actual checksum."""
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return self.calculate_checksum() == self.get_stored_checksums()[1]
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def calculate_checksum(self):
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f = open(self._filename, 'r')
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return hashlib.sha1(self._contents[:-20]).digest()
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def get_stored_checksums(self):
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"""Return the SHA1 checksums stored for the corresponding packfile and
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this header file itself."""
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return str(self._contents[-40:-20]), str(self._contents[-20:])
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def object_index(self, sha):
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"""Return the index in to the corresponding packfile for the object.
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Given the name of an object it will return the offset that object lives
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at within the corresponding pack file. If the pack file doesn't have the
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object then None will be returned.
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size = os.path.getsize(self._filename)
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assert size == self._size, "Pack index %s has changed size, I don't " \
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"like that" % self._filename
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sha = hex_to_sha(sha)
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return self._object_index(sha)
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def _object_index(self, sha):
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"""See object_index"""
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start = self._fan_out_table[idx-1]
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end = self._fan_out_table[idx]
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file_sha = self._unpack_name(i)
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return self._unpack_offset(i)
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class PackData(object):
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"""The data contained in a packfile.
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Pack files can be accessed both sequentially for exploding a pack, and
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directly with the help of an index to retrieve a specific object.
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The objects within are either complete or a delta aginst another.
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The header is variable length. If the MSB of each byte is set then it
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indicates that the subsequent byte is still part of the header.
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For the first byte the next MS bits are the type, which tells you the type
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of object, and whether it is a delta. The LS byte is the lowest bits of the
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size. For each subsequent byte the LS 7 bits are the next MS bits of the
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size, i.e. the last byte of the header contains the MS bits of the size.
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For the complete objects the data is stored as zlib deflated data.
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The size in the header is the uncompressed object size, so to uncompress
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you need to just keep feeding data to zlib until you get an object back,
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or it errors on bad data. This is done here by just giving the complete
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buffer from the start of the deflated object on. This is bad, but until I
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get mmap sorted out it will have to do.
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Currently there are no integrity checks done. Also no attempt is made to try
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and detect the delta case, or a request for an object at the wrong position.
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It will all just throw a zlib or KeyError.
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def __init__(self, filename):
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"""Create a PackData object that represents the pack in the given filename.
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The file must exist and stay readable until the object is disposed of. It
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must also stay the same size. It will be mapped whenever needed.
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Currently there is a restriction on the size of the pack as the python
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mmap implementation is flawed.
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self._filename = filename
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assert os.path.exists(filename), "%s is not a packfile" % filename
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self._size = os.path.getsize(filename)
367
self._header_size = 12
368
assert self._size >= self._header_size, "%s is too small for a packfile" % filename
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def _read_header(self):
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f = open(self._filename, 'rb')
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f.seek(self._size-20)
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self._stored_checksum = f.read(20)
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assert header[:4] == "PACK"
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(version,) = struct.unpack_from(">L", header, 4)
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assert version in (2, 3), "Version was %d" % version
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(self._num_objects,) = struct.unpack_from(">L", header, 8)
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"""Returns the number of objects in this pack."""
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return self._num_objects
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def calculate_checksum(self):
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f = open(self._filename, 'rb')
391
map = simple_mmap(f, 0, self._size)
392
return hashlib.sha1(map[:-20]).digest()
396
def iterobjects(self):
397
offset = self._header_size
398
f = open(self._filename, 'rb')
399
for i in range(len(self)):
400
map = simple_mmap(f, offset, self._size-offset)
401
(type, obj, total_size) = self._unpack_object(map)
402
yield offset, type, obj
406
def iterentries(self, ext_resolve_ref=None):
409
postponed = defaultdict(list)
410
class Postpone(Exception):
411
"""Raised to postpone delta resolving."""
413
def get_ref_text(sha):
418
return ext_resolve_ref(sha)
421
raise Postpone, (sha, )
422
todo = list(self.iterobjects())
424
(offset, type, obj) = todo.pop(0)
425
at[offset] = (type, obj)
426
assert isinstance(offset, int)
427
assert isinstance(type, int)
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assert isinstance(obj, tuple) or isinstance(obj, str)
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type, obj = resolve_object(offset, type, obj, get_ref_text,
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except Postpone, (sha, ):
433
postponed[sha].append((offset, type, obj))
435
shafile = ShaFile.from_raw_string(type, obj)
436
sha = shafile.sha().digest()
437
found[sha] = (type, obj)
438
yield sha, offset, shafile.crc32()
439
todo += postponed.get(sha, [])
441
raise KeyError([sha_to_hex(h) for h in postponed.keys()])
443
def sorted_entries(self, resolve_ext_ref=None):
444
ret = list(self.iterentries(resolve_ext_ref))
448
def create_index_v1(self, filename):
449
entries = self.sorted_entries()
450
write_pack_index_v1(filename, entries, self.calculate_checksum())
452
def create_index_v2(self, filename):
453
entries = self.sorted_entries()
454
write_pack_index_v2(filename, entries, self.calculate_checksum())
456
def get_stored_checksum(self):
457
return self._stored_checksum
460
return (self.calculate_checksum() == self.get_stored_checksum())
462
def get_object_at(self, offset):
463
"""Given an offset in to the packfile return the object that is there.
465
Using the associated index the location of an object can be looked up, and
466
then the packfile can be asked directly for that object using this
469
assert isinstance(offset, long) or isinstance(offset, int),\
470
"offset was %r" % offset
471
assert offset >= self._header_size
472
size = os.path.getsize(self._filename)
473
assert size == self._size, "Pack data %s has changed size, I don't " \
474
"like that" % self._filename
475
f = open(self._filename, 'rb')
477
map = simple_mmap(f, offset, size-offset)
478
return self._unpack_object(map)[:2]
482
def _unpack_object(self, map):
483
bytes = take_msb_bytes(map, 0)
484
type = (bytes[0] >> 4) & 0x07
485
size = bytes[0] & 0x0f
486
for i, byte in enumerate(bytes[1:]):
487
size += (byte & 0x7f) << ((i * 7) + 4)
488
raw_base = len(bytes)
489
if type == 6: # offset delta
490
bytes = take_msb_bytes(map, raw_base)
491
assert not (bytes[-1] & 0x80)
492
delta_base_offset = bytes[0] & 0x7f
493
for byte in bytes[1:]:
494
delta_base_offset += 1
495
delta_base_offset <<= 7
496
delta_base_offset += (byte & 0x7f)
498
uncomp, comp_len = read_zlib(map, raw_base, size)
499
assert size == len(uncomp)
500
return type, (delta_base_offset, uncomp), comp_len+raw_base
501
elif type == 7: # ref delta
502
basename = map[raw_base:raw_base+20]
503
uncomp, comp_len = read_zlib(map, raw_base+20, size)
504
assert size == len(uncomp)
505
return type, (basename, uncomp), comp_len+raw_base+20
507
uncomp, comp_len = read_zlib(map, raw_base, size)
508
assert len(uncomp) == size
509
return type, uncomp, comp_len+raw_base
512
class SHA1Writer(object):
514
def __init__(self, f):
516
self.sha1 = hashlib.sha1("")
518
def write(self, data):
519
self.sha1.update(data)
523
sha = self.sha1.digest()
524
assert len(sha) == 20
529
sha = self.write_sha()
537
def write_pack_object(f, type, object):
538
"""Write pack object to a file.
540
:param f: File to write to
541
:param o: Object to write
544
if type == 6: # ref delta
545
(delta_base_offset, object) = object
546
elif type == 7: # offset delta
547
(basename, object) = object
549
c = (type << 4) | (size & 15)
552
f.write(chr(c | 0x80))
556
if type == 6: # offset delta
557
ret = [delta_base_offset & 0x7f]
558
delta_base_offset >>= 7
559
while delta_base_offset:
560
delta_base_offset -= 1
561
ret.insert(0, 0x80 | (delta_base_offset & 0x7f))
562
delta_base_offset >>= 7
563
f.write("".join([chr(x) for x in ret]))
564
elif type == 7: # ref delta
565
assert len(basename) == 20
567
f.write(zlib.compress(object))
571
def write_pack(filename, objects, num_objects):
572
f = open(filename + ".pack", 'w')
574
entries, data_sum = write_pack_data(f, objects, num_objects)
578
write_pack_index_v2(filename + ".idx", entries, data_sum)
581
def write_pack_data(f, objects, num_objects):
582
"""Write a new pack file.
584
:param filename: The filename of the new pack file.
585
:param objects: List of objects to write.
586
:return: List with (name, offset, crc32 checksum) entries, pack checksum
590
f.write("PACK") # Pack header
591
f.write(struct.pack(">L", 2)) # Pack version
592
f.write(struct.pack(">L", num_objects)) # Number of objects in pack
594
sha1 = o.sha().digest()
597
t, o = o.as_raw_string()
598
offset = write_pack_object(f, t, o)
599
entries.append((sha1, offset, crc32))
600
return entries, f.write_sha()
603
def write_pack_index_v1(filename, entries, pack_checksum):
604
"""Write a new pack index file.
606
:param filename: The filename of the new pack index file.
607
:param entries: List of tuples with object name (sha), offset_in_pack, and
609
:param pack_checksum: Checksum of the pack file.
611
f = open(filename, 'w')
613
fan_out_table = defaultdict(lambda: 0)
614
for (name, offset, entry_checksum) in entries:
615
fan_out_table[ord(name[0])] += 1
617
for i in range(0x100):
618
f.write(struct.pack(">L", fan_out_table[i]))
619
fan_out_table[i+1] += fan_out_table[i]
620
for (name, offset, entry_checksum) in entries:
621
f.write(struct.pack(">L20s", offset, name))
622
assert len(pack_checksum) == 20
623
f.write(pack_checksum)
627
def apply_delta(src_buf, delta):
628
"""Based on the similar function in git's patch-delta.c."""
629
assert isinstance(src_buf, str), "was %r" % (src_buf,)
630
assert isinstance(delta, str)
635
return ord(ret), delta
636
def get_delta_header_size(delta):
640
cmd, delta = pop(delta)
641
size |= (cmd & ~0x80) << i
646
src_size, delta = get_delta_header_size(delta)
647
dest_size, delta = get_delta_header_size(delta)
648
assert src_size == len(src_buf)
650
cmd, delta = pop(delta)
655
x, delta = pop(delta)
656
cp_off |= x << (i * 8)
659
if cmd & (1 << (4+i)):
660
x, delta = pop(delta)
661
cp_size |= x << (i * 8)
664
if (cp_off + cp_size < cp_size or
665
cp_off + cp_size > src_size or
666
cp_size > dest_size):
668
out += src_buf[cp_off:cp_off+cp_size]
673
raise ApplyDeltaError("Invalid opcode 0")
676
raise ApplyDeltaError("delta not empty: %r" % delta)
678
if dest_size != len(out):
679
raise ApplyDeltaError("dest size incorrect")
684
def write_pack_index_v2(filename, entries, pack_checksum):
685
"""Write a new pack index file.
687
:param filename: The filename of the new pack index file.
688
:param entries: List of tuples with object name (sha), offset_in_pack, and
690
:param pack_checksum: Checksum of the pack file.
692
f = open(filename, 'w')
694
f.write('\377tOc') # Magic!
695
f.write(struct.pack(">L", 2))
696
fan_out_table = defaultdict(lambda: 0)
697
for (name, offset, entry_checksum) in entries:
698
fan_out_table[ord(name[0])] += 1
700
for i in range(0x100):
701
f.write(struct.pack(">L", fan_out_table[i]))
702
fan_out_table[i+1] += fan_out_table[i]
703
for (name, offset, entry_checksum) in entries:
705
for (name, offset, entry_checksum) in entries:
706
f.write(struct.pack(">l", entry_checksum))
707
for (name, offset, entry_checksum) in entries:
708
# FIXME: handle if MSBit is set in offset
709
f.write(struct.pack(">L", offset))
710
# FIXME: handle table for pack files > 8 Gb
711
assert len(pack_checksum) == 20
712
f.write(pack_checksum)
718
def __init__(self, basename):
719
self._basename = basename
720
self._data_path = self._basename + ".pack"
721
self._idx_path = self._basename + ".idx"
726
return self.idx.objects_sha1()
730
if self._data is None:
731
self._data = PackData(self._data_path)
732
assert len(self.idx) == len(self._data)
733
assert self.idx.get_stored_checksums()[0] == self._data.get_stored_checksum()
738
if self._idx is None:
739
self._idx = PackIndex(self._idx_path)
743
if self._data is not None:
747
def __eq__(self, other):
748
return type(self) == type(other) and self.idx == other.idx
751
"""Number of entries in this pack."""
755
return "Pack(%r)" % self._basename
758
"""Iterate over all the sha1s of the objects in this pack."""
759
return iter(self.idx)
762
return self.idx.check() and self.data.check()
764
def get_stored_checksum(self):
765
return self.data.get_stored_checksum()
767
def __contains__(self, sha1):
768
"""Check whether this pack contains a particular SHA1."""
769
return (self.idx.object_index(sha1) is not None)
771
def get_raw(self, sha1, resolve_ref=None):
772
if resolve_ref is None:
773
resolve_ref = self.get_raw
774
offset = self.idx.object_index(sha1)
778
type, obj = self.data.get_object_at(offset)
779
assert isinstance(offset, int)
780
return resolve_object(offset, type, obj, resolve_ref,
781
self.data.get_object_at)
783
def __getitem__(self, sha1):
784
"""Retrieve the specified SHA1."""
785
type, uncomp = self.get_raw(sha1)
786
return ShaFile.from_raw_string(type, uncomp)
788
def iterobjects(self):
789
for offset, type, obj in self.data.iterobjects():
790
assert isinstance(offset, int)
791
yield ShaFile.from_raw_string(
792
*resolve_object(offset, type, obj, self.get_raw,
793
self.data.get_object_at))
796
def load_packs(path):
797
if not os.path.exists(path):
799
for name in os.listdir(path):
800
if name.startswith("pack-") and name.endswith(".pack"):
801
yield Pack(os.path.join(path, name[:-len(".pack")]))
added
removed
dulwich/dulwich/pack.py
