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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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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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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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def read_pack_header(f):
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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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(num_objects,) = struct.unpack_from(">L", header, 8)
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return (version, num_objects)
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def read_pack_tail(f):
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def unpack_object(map):
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bytes = take_msb_bytes(map, 0)
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type = (bytes[0] >> 4) & 0x07
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size = bytes[0] & 0x0f
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for i, byte in enumerate(bytes[1:]):
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size += (byte & 0x7f) << ((i * 7) + 4)
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raw_base = len(bytes)
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if type == 6: # offset delta
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bytes = take_msb_bytes(map, raw_base)
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assert not (bytes[-1] & 0x80)
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delta_base_offset = bytes[0] & 0x7f
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for byte in bytes[1:]:
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delta_base_offset += 1
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delta_base_offset <<= 7
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delta_base_offset += (byte & 0x7f)
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uncomp, comp_len = read_zlib(map, raw_base, size)
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assert size == len(uncomp)
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return type, (delta_base_offset, uncomp), comp_len+raw_base
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elif type == 7: # ref delta
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basename = map[raw_base:raw_base+20]
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uncomp, comp_len = read_zlib(map, raw_base+20, size)
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assert size == len(uncomp)
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return type, (basename, uncomp), comp_len+raw_base+20
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uncomp, comp_len = read_zlib(map, raw_base, size)
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assert len(uncomp) == size
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return type, uncomp, comp_len+raw_base
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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.
388
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.
394
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)
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self._header_size = 12
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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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(version, self._num_objects) = \
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f.seek(self._size-20)
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(self._stored_checksum,) = read_pack_tail(f)
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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')
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map = simple_mmap(f, 0, self._size)
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return hashlib.sha1(map[:-20]).digest()
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def iterobjects(self):
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offset = self._header_size
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f = open(self._filename, 'rb')
426
for i in range(len(self)):
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map = simple_mmap(f, offset, self._size-offset)
428
(type, obj, total_size) = unpack_object(map)
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yield offset, type, obj
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def iterentries(self, ext_resolve_ref=None):
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postponed = defaultdict(list)
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class Postpone(Exception):
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"""Raised to postpone delta resolving."""
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def get_ref_text(sha):
445
return ext_resolve_ref(sha)
448
raise Postpone, (sha, )
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todo = list(self.iterobjects())
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(offset, type, obj) = todo.pop(0)
452
at[offset] = (type, obj)
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assert isinstance(offset, int)
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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, ):
460
postponed[sha].append((offset, type, obj))
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shafile = ShaFile.from_raw_string(type, obj)
463
sha = shafile.sha().digest()
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found[sha] = (type, obj)
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yield sha, offset, shafile.crc32()
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todo += postponed.get(sha, [])
468
raise KeyError([sha_to_hex(h) for h in postponed.keys()])
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def sorted_entries(self, resolve_ext_ref=None):
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ret = list(self.iterentries(resolve_ext_ref))
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def create_index_v1(self, filename):
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entries = self.sorted_entries()
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write_pack_index_v1(filename, entries, self.calculate_checksum())
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def create_index_v2(self, filename):
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entries = self.sorted_entries()
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write_pack_index_v2(filename, entries, self.calculate_checksum())
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def get_stored_checksum(self):
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return self._stored_checksum
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return (self.calculate_checksum() == self.get_stored_checksum())
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def get_object_at(self, offset):
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"""Given an offset in to the packfile return the object that is there.
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Using the associated index the location of an object can be looked up, and
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then the packfile can be asked directly for that object using this
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assert isinstance(offset, long) or isinstance(offset, int),\
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"offset was %r" % offset
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assert offset >= self._header_size
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size = os.path.getsize(self._filename)
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assert size == self._size, "Pack data %s has changed size, I don't " \
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"like that" % self._filename
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f = open(self._filename, 'rb')
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map = simple_mmap(f, offset, size-offset)
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return unpack_object(map)[:2]
510
class SHA1Writer(object):
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def __init__(self, f):
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self.sha1 = hashlib.sha1("")
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def write(self, data):
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self.sha1.update(data)
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sha = self.sha1.digest()
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assert len(sha) == 20
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sha = self.write_sha()
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def write_pack_object(f, type, object):
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"""Write pack object to a file.
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:param f: File to write to
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:param o: Object to write
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if type == 6: # ref delta
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(delta_base_offset, object) = object
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elif type == 7: # offset delta
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(basename, object) = object
547
c = (type << 4) | (size & 15)
550
f.write(chr(c | 0x80))
554
if type == 6: # offset delta
555
ret = [delta_base_offset & 0x7f]
556
delta_base_offset >>= 7
557
while delta_base_offset:
558
delta_base_offset -= 1
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ret.insert(0, 0x80 | (delta_base_offset & 0x7f))
560
delta_base_offset >>= 7
561
f.write("".join([chr(x) for x in ret]))
562
elif type == 7: # ref delta
563
assert len(basename) == 20
565
f.write(zlib.compress(object))
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def write_pack(filename, objects, num_objects):
570
f = open(filename + ".pack", 'w')
572
entries, data_sum = write_pack_data(f, objects, num_objects)
576
write_pack_index_v2(filename + ".idx", entries, data_sum)
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def write_pack_data(f, objects, num_objects, window=10):
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"""Write a new pack file.
582
:param filename: The filename of the new pack file.
583
:param objects: List of objects to write.
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:return: List with (name, offset, crc32 checksum) entries, pack checksum
586
recency = list(objects)
587
# FIXME: Somehow limit delta depth
588
# FIXME: Make thin-pack optional (its not used when cloning a pack)
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# Build a list of objects ordered by the magic Linus heuristic
590
# This helps us find good objects to diff against us
593
magic.append( (o._num_type, "filename", 1, -len(o.as_raw_string()[1]), o) )
595
# Build a map of objects and their index in magic - so we can find preceeding objects
598
for i in range(len(magic)):
599
offs[magic[i][4]] = i
603
f.write("PACK") # Pack header
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f.write(struct.pack(">L", 2)) # Pack version
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f.write(struct.pack(">L", num_objects)) # Number of objects in pack
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sha1 = o.sha().digest()
609
orig_t, raw = o.as_raw_string()
612
#for i in range(offs[o]-window, window):
613
# if i < 0 or i >= len(offs): continue
615
# if b._num_type != orig_t: continue
616
# _, base = b.as_raw_string()
617
# delta = create_delta(base, raw)
618
# if len(delta) < len(winner):
620
# t = 6 if magic[i][2] == 1 else 7
621
offset = write_pack_object(f, t, winner)
622
entries.append((sha1, offset, crc32))
623
return entries, f.write_sha()
626
def write_pack_index_v1(filename, entries, pack_checksum):
627
"""Write a new pack index file.
629
:param filename: The filename of the new pack index file.
630
:param entries: List of tuples with object name (sha), offset_in_pack, and
632
:param pack_checksum: Checksum of the pack file.
634
f = open(filename, 'w')
636
fan_out_table = defaultdict(lambda: 0)
637
for (name, offset, entry_checksum) in entries:
638
fan_out_table[ord(name[0])] += 1
640
for i in range(0x100):
641
f.write(struct.pack(">L", fan_out_table[i]))
642
fan_out_table[i+1] += fan_out_table[i]
643
for (name, offset, entry_checksum) in entries:
644
f.write(struct.pack(">L20s", offset, name))
645
assert len(pack_checksum) == 20
646
f.write(pack_checksum)
650
def create_delta(base_buf, target_buf):
651
"""Use python difflib to work out how to transform base_buf to target_buf"""
652
assert isinstance(base_buf, str)
653
assert isinstance(target_buf, str)
656
def encode_size(size):
666
out_buf += encode_size(len(base_buf))
667
out_buf += encode_size(len(target_buf))
668
# write out delta opcodes
669
seq = difflib.SequenceMatcher(a=base_buf, b=target_buf)
670
for opcode, i1, i2, j1, j2 in seq.get_opcodes():
671
# Git patch opcodes don't care about deletes!
672
#if opcode == "replace" or opcode == "delete":
674
if opcode == "equal":
675
# If they are equal, unpacker will use data from base_buf
676
# Write out an opcode that says what range to use
682
scratch += chr(o >> i)
687
scratch += chr(s >> i)
691
if opcode == "replace" or opcode == "insert":
692
# If we are replacing a range or adding one, then we just
693
# output it to the stream (prefixed by its size)
698
out_buf += target_buf[o:o+127]
702
out_buf += target_buf[o:o+s]
706
def apply_delta(src_buf, delta):
707
"""Based on the similar function in git's patch-delta.c."""
708
assert isinstance(src_buf, str), "was %r" % (src_buf,)
709
assert isinstance(delta, str)
714
return ord(ret), delta
715
def get_delta_header_size(delta):
719
cmd, delta = pop(delta)
720
size |= (cmd & ~0x80) << i
725
src_size, delta = get_delta_header_size(delta)
726
dest_size, delta = get_delta_header_size(delta)
727
assert src_size == len(src_buf), "%d vs %d" % (src_size, len(src_buf))
729
cmd, delta = pop(delta)
734
x, delta = pop(delta)
735
cp_off |= x << (i * 8)
738
if cmd & (1 << (4+i)):
739
x, delta = pop(delta)
740
cp_size |= x << (i * 8)
743
if (cp_off + cp_size < cp_size or
744
cp_off + cp_size > src_size or
745
cp_size > dest_size):
747
out += src_buf[cp_off:cp_off+cp_size]
752
raise ApplyDeltaError("Invalid opcode 0")
755
raise ApplyDeltaError("delta not empty: %r" % delta)
757
if dest_size != len(out):
758
raise ApplyDeltaError("dest size incorrect")
763
def write_pack_index_v2(filename, entries, pack_checksum):
764
"""Write a new pack index file.
766
:param filename: The filename of the new pack index file.
767
:param entries: List of tuples with object name (sha), offset_in_pack, and
769
:param pack_checksum: Checksum of the pack file.
771
f = open(filename, 'w')
773
f.write('\377tOc') # Magic!
774
f.write(struct.pack(">L", 2))
775
fan_out_table = defaultdict(lambda: 0)
776
for (name, offset, entry_checksum) in entries:
777
fan_out_table[ord(name[0])] += 1
779
for i in range(0x100):
780
f.write(struct.pack(">L", fan_out_table[i]))
781
fan_out_table[i+1] += fan_out_table[i]
782
for (name, offset, entry_checksum) in entries:
784
for (name, offset, entry_checksum) in entries:
785
f.write(struct.pack(">l", entry_checksum))
786
for (name, offset, entry_checksum) in entries:
787
# FIXME: handle if MSBit is set in offset
788
f.write(struct.pack(">L", offset))
789
# FIXME: handle table for pack files > 8 Gb
790
assert len(pack_checksum) == 20
791
f.write(pack_checksum)
797
def __init__(self, basename):
798
self._basename = basename
799
self._data_path = self._basename + ".pack"
800
self._idx_path = self._basename + ".idx"
805
return self.idx.objects_sha1()
809
if self._data is None:
810
self._data = PackData(self._data_path)
811
assert len(self.idx) == len(self._data)
812
assert self.idx.get_stored_checksums()[0] == self._data.get_stored_checksum()
817
if self._idx is None:
818
self._idx = PackIndex(self._idx_path)
822
if self._data is not None:
826
def __eq__(self, other):
827
return type(self) == type(other) and self.idx == other.idx
830
"""Number of entries in this pack."""
834
return "Pack(%r)" % self._basename
837
"""Iterate over all the sha1s of the objects in this pack."""
838
return iter(self.idx)
841
return self.idx.check() and self.data.check()
843
def get_stored_checksum(self):
844
return self.data.get_stored_checksum()
846
def __contains__(self, sha1):
847
"""Check whether this pack contains a particular SHA1."""
848
return (self.idx.object_index(sha1) is not None)
850
def get_raw(self, sha1, resolve_ref=None):
851
if resolve_ref is None:
852
resolve_ref = self.get_raw
853
offset = self.idx.object_index(sha1)
857
type, obj = self.data.get_object_at(offset)
858
assert isinstance(offset, int)
859
return resolve_object(offset, type, obj, resolve_ref,
860
self.data.get_object_at)
862
def __getitem__(self, sha1):
863
"""Retrieve the specified SHA1."""
864
type, uncomp = self.get_raw(sha1)
865
return ShaFile.from_raw_string(type, uncomp)
867
def iterobjects(self):
868
for offset, type, obj in self.data.iterobjects():
869
assert isinstance(offset, int)
870
yield ShaFile.from_raw_string(
871
*resolve_object(offset, type, obj, self.get_raw,
872
self.data.get_object_at))
875
def load_packs(path):
876
if not os.path.exists(path):
878
for name in os.listdir(path):
879
if name.startswith("pack-") and name.endswith(".pack"):
880
yield Pack(os.path.join(path, name[:-len(".pack")]))
added
removed
dulwich/pack.py
