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# This module is part of GitDB and is released under

# the New BSD License: https://opensource.org/license/bsd-3-clause/

"""Contains basic c-functions which usually contain performance critical code

Keeping this code separate from the beginning makes it easier to out-source

it into c later, if required"""

import zlib

from gitdb.util import byte_ord

decompressobj = zlib.decompressobj

import mmap

from itertools import islice

from functools import reduce

from gitdb.const import NULL_BYTE, BYTE_SPACE

from gitdb.utils.encoding import force_text

from gitdb.typ import (

str_blob_type,

str_commit_type,

str_tree_type,

str_tag_type,

)

from io import StringIO

# INVARIANTS

OFS_DELTA = 6

REF_DELTA = 7

delta_types = (OFS_DELTA, REF_DELTA)

type_id_to_type_map = {

0: b'', # EXT 1

1: str_commit_type,

2: str_tree_type,

3: str_blob_type,

4: str_tag_type,

5: b'', # EXT 2

OFS_DELTA: "OFS_DELTA", # OFFSET DELTA

REF_DELTA: "REF_DELTA" # REFERENCE DELTA

}

type_to_type_id_map = {

str_commit_type: 1,

str_tree_type: 2,

str_blob_type: 3,

str_tag_type: 4,

"OFS_DELTA": OFS_DELTA,

"REF_DELTA": REF_DELTA,

}

# used when dealing with larger streams

chunk_size = 1000 * mmap.PAGESIZE

__all__ = ('is_loose_object', 'loose_object_header_info', 'msb_size', 'pack_object_header_info',

'write_object', 'loose_object_header', 'stream_copy', 'apply_delta_data',

'is_equal_canonical_sha', 'connect_deltas', 'DeltaChunkList', 'create_pack_object_header')

#{ Structures

def _set_delta_rbound(d, size):

"""Truncate the given delta to the given size

:param size: size relative to our target offset, may not be 0, must be smaller or equal

to our size

:return: d"""

d.ts = size

# NOTE: data is truncated automatically when applying the delta

# MUST NOT DO THIS HERE

return d

def _move_delta_lbound(d, bytes):

"""Move the delta by the given amount of bytes, reducing its size so that its

right bound stays static

:param bytes: amount of bytes to move, must be smaller than delta size

:return: d"""

if bytes == 0:

return

d.to += bytes

d.so += bytes

d.ts -= bytes

if d.data is not None:

d.data = d.data[bytes:]

# END handle data

return d

def delta_duplicate(src):

return DeltaChunk(src.to, src.ts, src.so, src.data)

def delta_chunk_apply(dc, bbuf, write):

"""Apply own data to the target buffer

:param bbuf: buffer providing source bytes for copy operations

:param write: write method to call with data to write"""

if dc.data is None:

# COPY DATA FROM SOURCE

write(bbuf[dc.so:dc.so + dc.ts])

else:

# APPEND DATA

# what's faster: if + 4 function calls or just a write with a slice ?

# Considering data can be larger than 127 bytes now, it should be worth it

if dc.ts < len(dc.data):

write(dc.data[:dc.ts])

else:

write(dc.data)

# END handle truncation

# END handle chunk mode

class DeltaChunk:

"""Represents a piece of a delta, it can either add new data, or copy existing

one from a source buffer"""

__slots__ = (

'to', # start offset in the target buffer in bytes

'ts', # size of this chunk in the target buffer in bytes

'so', # start offset in the source buffer in bytes or None

'data', # chunk of bytes to be added to the target buffer,

# DeltaChunkList to use as base, or None

)

def __init__(self, to, ts, so, data):

self.to = to

self.ts = ts

self.so = so

self.data = data

def __repr__(self):

return "DeltaChunk(%i, %i, %s, %s)" % (self.to, self.ts, self.so, self.data or "")

#{ Interface

def rbound(self):

return self.to + self.ts

def has_data(self):

""":return: True if the instance has data to add to the target stream"""

return self.data is not None

#} END interface

def _closest_index(dcl, absofs):

""":return: index at which the given absofs should be inserted. The index points

to the DeltaChunk with a target buffer absofs that equals or is greater than

absofs.

**Note:** global method for performance only, it belongs to DeltaChunkList"""

lo = 0

hi = len(dcl)

while lo < hi:

mid = (lo + hi) / 2

dc = dcl[mid]

if dc.to > absofs:

hi = mid

elif dc.rbound() > absofs or dc.to == absofs:

return mid

else:

lo = mid + 1

# END handle bound

# END for each delta absofs

return len(dcl) - 1

def delta_list_apply(dcl, bbuf, write):

"""Apply the chain's changes and write the final result using the passed

write function.

:param bbuf: base buffer containing the base of all deltas contained in this

list. It will only be used if the chunk in question does not have a base

chain.

:param write: function taking a string of bytes to write to the output"""

for dc in dcl:

delta_chunk_apply(dc, bbuf, write)

# END for each dc

def delta_list_slice(dcl, absofs, size, ndcl):

""":return: Subsection of this list at the given absolute offset, with the given

size in bytes.

:return: None"""

cdi = _closest_index(dcl, absofs) # delta start index

cd = dcl[cdi]

slen = len(dcl)

lappend = ndcl.append

if cd.to != absofs:

tcd = DeltaChunk(cd.to, cd.ts, cd.so, cd.data)

_move_delta_lbound(tcd, absofs - cd.to)

tcd.ts = min(tcd.ts, size)

lappend(tcd)

size -= tcd.ts

cdi += 1

# END lbound overlap handling

while cdi < slen and size:

# are we larger than the current block

cd = dcl[cdi]

if cd.ts <= size:

lappend(DeltaChunk(cd.to, cd.ts, cd.so, cd.data))

size -= cd.ts

else:

tcd = DeltaChunk(cd.to, cd.ts, cd.so, cd.data)

tcd.ts = size

lappend(tcd)

size -= tcd.ts

break

# END hadle size

cdi += 1

# END for each chunk

class DeltaChunkList(list):

"""List with special functionality to deal with DeltaChunks.

There are two types of lists we represent. The one was created bottom-up, working

towards the latest delta, the other kind was created top-down, working from the

latest delta down to the earliest ancestor. This attribute is queryable

after all processing with is_reversed."""

__slots__ = tuple()

def rbound(self):

""":return: rightmost extend in bytes, absolute"""

if len(self) == 0:

return 0

return self[-1].rbound()

def lbound(self):

""":return: leftmost byte at which this chunklist starts"""

if len(self) == 0:

return 0

return self[0].to

def size(self):

""":return: size of bytes as measured by our delta chunks"""

return self.rbound() - self.lbound()

def apply(self, bbuf, write):

"""Only used by public clients, internally we only use the global routines

for performance"""

return delta_list_apply(self, bbuf, write)

def compress(self):

"""Alter the list to reduce the amount of nodes. Currently we concatenate

add-chunks

:return: self"""

slen = len(self)

if slen < 2:

return self

i = 0

first_data_index = None

while i < slen:

dc = self[i]

i += 1

if dc.data is None:

if first_data_index is not None and i - 2 - first_data_index > 1:

# if first_data_index is not None:

nd = StringIO() # new data

so = self[first_data_index].to # start offset in target buffer

for x in range(first_data_index, i - 1):

xdc = self[x]

nd.write(xdc.data[:xdc.ts])

# END collect data

del(self[first_data_index:i - 1])

buf = nd.getvalue()

self.insert(first_data_index, DeltaChunk(so, len(buf), 0, buf))

slen = len(self)

i = first_data_index + 1

# END concatenate data

first_data_index = None

continue

# END skip non-data chunks

if first_data_index is None:

first_data_index = i - 1

# END iterate list

# if slen_orig != len(self):

# print "INFO: Reduced delta list len to %f %% of former size" % ((float(len(self)) / slen_orig) * 100)

return self

def check_integrity(self, target_size=-1):

"""Verify the list has non-overlapping chunks only, and the total size matches

target_size

:param target_size: if not -1, the total size of the chain must be target_size

:raise AssertionError: if the size doesn't match"""

if target_size > -1:

assert self[-1].rbound() == target_size

assert reduce(lambda x, y: x + y, (d.ts for d in self), 0) == target_size

# END target size verification

if len(self) < 2:

return

# check data

for dc in self:

assert dc.ts > 0

if dc.has_data():

assert len(dc.data) >= dc.ts

# END for each dc

left = islice(self, 0, len(self) - 1)

right = iter(self)

right.next()

# this is very pythonic - we might have just use index based access here,

# but this could actually be faster

for lft, rgt in zip(left, right):

assert lft.rbound() == rgt.to

assert lft.to + lft.ts == rgt.to

# END for each pair

class TopdownDeltaChunkList(DeltaChunkList):

"""Represents a list which is generated by feeding its ancestor streams one by

one"""

__slots__ = tuple()

def connect_with_next_base(self, bdcl):

"""Connect this chain with the next level of our base delta chunklist.

The goal in this game is to mark as many of our chunks rigid, hence they

cannot be changed by any of the upcoming bases anymore. Once all our

chunks are marked like that, we can stop all processing

:param bdcl: data chunk list being one of our bases. They must be fed in

consecutively and in order, towards the earliest ancestor delta

:return: True if processing was done. Use it to abort processing of

remaining streams if False is returned"""

nfc = 0 # number of frozen chunks

dci = 0 # delta chunk index

slen = len(self) # len of self

ccl = list() # temporary list

while dci < slen:

dc = self[dci]

dci += 1

# all add-chunks which are already topmost don't need additional processing

if dc.data is not None:

nfc += 1

continue

# END skip add chunks

# copy chunks

# integrate the portion of the base list into ourselves. Lists

# dont support efficient insertion ( just one at a time ), but for now

# we live with it. Internally, its all just a 32/64bit pointer, and

# the portions of moved memory should be smallish. Maybe we just rebuild

# ourselves in order to reduce the amount of insertions ...

del(ccl[:])

delta_list_slice(bdcl, dc.so, dc.ts, ccl)

# move the target bounds into place to match with our chunk

ofs = dc.to - dc.so

for cdc in ccl:

cdc.to += ofs

# END update target bounds

if len(ccl) == 1:

self[dci - 1] = ccl[0]

else:

# maybe try to compute the expenses here, and pick the right algorithm

# It would normally be faster than copying everything physically though

# TODO: Use a deque here, and decide by the index whether to extend

# or extend left !

post_dci = self[dci:]

del(self[dci - 1:]) # include deletion of dc

self.extend(ccl)

self.extend(post_dci)

slen = len(self)

dci += len(ccl) - 1 # deleted dc, added rest

# END handle chunk replacement

# END for each chunk

if nfc == slen:

return False

# END handle completeness

return True

#} END structures

#{ Routines

def is_loose_object(m):

"""

:return: True the file contained in memory map m appears to be a loose object.

Only the first two bytes are needed"""

b0, b1 = map(ord, m[:2])

word = (b0 << 8) + b1

return b0 == 0x78 and (word % 31) == 0

def loose_object_header_info(m):

"""

:return: tuple(type_string, uncompressed_size_in_bytes) the type string of the

object as well as its uncompressed size in bytes.

:param m: memory map from which to read the compressed object data"""

decompress_size = 8192 # is used in cgit as well

hdr = decompressobj().decompress(m, decompress_size)

type_name, size = hdr[:hdr.find(NULL_BYTE)].split(BYTE_SPACE)

return type_name, int(size)

def pack_object_header_info(data):

"""

:return: tuple(type_id, uncompressed_size_in_bytes, byte_offset)

The type_id should be interpreted according to the ``type_id_to_type_map`` map

The byte-offset specifies the start of the actual zlib compressed datastream

:param m: random-access memory, like a string or memory map"""

c = byte_ord(data[0]) # first byte

i = 1 # next char to read

type_id = (c >> 4) & 7 # numeric type

size = c & 15 # starting size

s = 4 # starting bit-shift size

while c & 0x80:

c = byte_ord(data[i])

i += 1

size += (c & 0x7f) << s

s += 7

# END character loop

# end performance at expense of maintenance ...

return (type_id, size, i)

def create_pack_object_header(obj_type, obj_size):

"""

:return: string defining the pack header comprised of the object type

and its incompressed size in bytes

:param obj_type: pack type_id of the object

:param obj_size: uncompressed size in bytes of the following object stream"""

c = 0 # 1 byte

hdr = bytearray() # output string

c = (obj_type << 4) | (obj_size & 0xf)

obj_size >>= 4

while obj_size:

hdr.append(c | 0x80)

c = obj_size & 0x7f

obj_size >>= 7

# END until size is consumed

hdr.append(c)

# end handle interpreter

return hdr

def msb_size(data, offset=0):

"""

:return: tuple(read_bytes, size) read the msb size from the given random

access data starting at the given byte offset"""

size = 0

i = 0

l = len(data)

hit_msb = False

while i < l:

c = data[i + offset]

size |= (c & 0x7f) << i * 7

i += 1

if not c & 0x80:

hit_msb = True

break

# END check msb bit

# END while in range

# end performance ...

if not hit_msb:

raise AssertionError("Could not find terminating MSB byte in data stream")

return i + offset, size

def loose_object_header(type, size):

"""

:return: bytes representing the loose object header, which is immediately

followed by the content stream of size 'size'"""

return ('%s %i\0' % (force_text(type), size)).encode('ascii')

def write_object(type, size, read, write, chunk_size=chunk_size):

"""

Write the object as identified by type, size and source_stream into the

target_stream

:param type: type string of the object

:param size: amount of bytes to write from source_stream

:param read: read method of a stream providing the content data

:param write: write method of the output stream

:param close_target_stream: if True, the target stream will be closed when

the routine exits, even if an error is thrown

:return: The actual amount of bytes written to stream, which includes the header and a trailing newline"""

tbw = 0 # total num bytes written

# WRITE HEADER: type SP size NULL

tbw += write(loose_object_header(type, size))

tbw += stream_copy(read, write, size, chunk_size)

return tbw

def stream_copy(read, write, size, chunk_size):

"""

Copy a stream up to size bytes using the provided read and write methods,

in chunks of chunk_size

**Note:** its much like stream_copy utility, but operates just using methods"""

dbw = 0 # num data bytes written

# WRITE ALL DATA UP TO SIZE

while True:

cs = min(chunk_size, size - dbw)

# NOTE: not all write methods return the amount of written bytes, like

# mmap.write. Its bad, but we just deal with it ... perhaps its not

# even less efficient

# data_len = write(read(cs))

# dbw += data_len

data = read(cs)

data_len = len(data)

dbw += data_len

write(data)

if data_len < cs or dbw == size:

break

# END check for stream end

# END duplicate data

return dbw

def connect_deltas(dstreams):

"""

Read the condensed delta chunk information from dstream and merge its information

into a list of existing delta chunks

:param dstreams: iterable of delta stream objects, the delta to be applied last

comes first, then all its ancestors in order

:return: DeltaChunkList, containing all operations to apply"""

tdcl = None # topmost dcl

dcl = tdcl = TopdownDeltaChunkList()

for dsi, ds in enumerate(dstreams):

# print "Stream", dsi

db = ds.read()

delta_buf_size = ds.size

# read header

i, base_size = msb_size(db)

i, target_size = msb_size(db, i)

# interpret opcodes

tbw = 0 # amount of target bytes written

while i < delta_buf_size:

c = ord(db[i])

i += 1

if c & 0x80:

cp_off, cp_size = 0, 0

if (c & 0x01):

cp_off = ord(db[i])

i += 1

if (c & 0x02):

cp_off |= (ord(db[i]) << 8)

i += 1

if (c & 0x04):

cp_off |= (ord(db[i]) << 16)

i += 1

if (c & 0x08):

cp_off |= (ord(db[i]) << 24)

i += 1

if (c & 0x10):

cp_size = ord(db[i])

i += 1

if (c & 0x20):

cp_size |= (ord(db[i]) << 8)

i += 1

if (c & 0x40):

cp_size |= (ord(db[i]) << 16)

i += 1

if not cp_size:

cp_size = 0x10000

rbound = cp_off + cp_size

if (rbound < cp_size or

rbound > base_size):

break

dcl.append(DeltaChunk(tbw, cp_size, cp_off, None))

tbw += cp_size

elif c:

# NOTE: in C, the data chunks should probably be concatenated here.

# In python, we do it as a post-process

dcl.append(DeltaChunk(tbw, c, 0, db[i:i + c]))

i += c

tbw += c

else:

raise ValueError("unexpected delta opcode 0")

# END handle command byte

# END while processing delta data

dcl.compress()

# merge the lists !

if dsi > 0:

if not tdcl.connect_with_next_base(dcl):

break

# END handle merge

# prepare next base

dcl = DeltaChunkList()

# END for each delta stream

return tdcl

def apply_delta_data(src_buf, src_buf_size, delta_buf, delta_buf_size, write):

"""

Apply data from a delta buffer using a source buffer to the target file

:param src_buf: random access data from which the delta was created

:param src_buf_size: size of the source buffer in bytes

:param delta_buf_size: size for the delta buffer in bytes

:param delta_buf: random access delta data

:param write: write method taking a chunk of bytes

**Note:** transcribed to python from the similar routine in patch-delta.c"""

i = 0

db = delta_buf

while i < delta_buf_size:

c = db[i]

i += 1

if c & 0x80:

cp_off, cp_size = 0, 0

if (c & 0x01):

cp_off = db[i]

i += 1

if (c & 0x02):

cp_off |= (db[i] << 8)

i += 1

if (c & 0x04):

cp_off |= (db[i] << 16)

i += 1

if (c & 0x08):

cp_off |= (db[i] << 24)

i += 1

if (c & 0x10):

cp_size = db[i]

i += 1

if (c & 0x20):

cp_size |= (db[i] << 8)

i += 1

if (c & 0x40):

cp_size |= (db[i] << 16)

i += 1

if not cp_size:

cp_size = 0x10000

rbound = cp_off + cp_size

if (rbound < cp_size or

rbound > src_buf_size):

break

write(src_buf[cp_off:cp_off + cp_size])

elif c:

write(db[i:i + c])

i += c

else:

raise ValueError("unexpected delta opcode 0")

# END handle command byte

# END while processing delta data

# yes, lets use the exact same error message that git uses :)

assert i == delta_buf_size, "delta replay has gone wild"

def is_equal_canonical_sha(canonical_length, match, sha1):

"""

:return: True if the given lhs and rhs 20 byte binary shas

The comparison will take the canonical_length of the match sha into account,

hence the comparison will only use the last 4 bytes for uneven canonical representations

:param match: less than 20 byte sha

:param sha1: 20 byte sha"""

binary_length = canonical_length // 2

if match[:binary_length] != sha1[:binary_length]:

return False

if canonical_length - binary_length and \

(byte_ord(match[-1]) ^ byte_ord(sha1[len(match) - 1])) & 0xf0:

return False

# END handle uneven canonnical length

return True

#} END routines

try:

from gitdb_speedups._perf import connect_deltas

except ImportError:

pass

gitdb/gitdb/fun.py at master · gitpython-developers/gitdb · GitHub

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