# Copyright (C) 2010, 2011 Sebastian Thiel (byronimo@gmail.com) and contributors

#

# This module is part of GitDB and is released under

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

import binascii

import os

import mmap

import sys

import time

import errno

from io import BytesIO

from smmap import (

StaticWindowMapManager,

SlidingWindowMapManager,

SlidingWindowMapBuffer

)

# initialize our global memory manager instance

# Use it to free cached (and unused) resources.

mman = SlidingWindowMapManager()

# END handle mman

import hashlib

try:

from struct import unpack_from

except ImportError:

from struct import unpack, calcsize

__calcsize_cache = dict()

def unpack_from(fmt, data, offset=0):

try:

size = __calcsize_cache[fmt]

except KeyError:

size = calcsize(fmt)

__calcsize_cache[fmt] = size

# END exception handling

return unpack(fmt, data[offset: offset + size])

# END own unpack_from implementation

#{ Aliases

hex_to_bin = binascii.a2b_hex

bin_to_hex = binascii.b2a_hex

# errors

ENOENT = errno.ENOENT

# os shortcuts

exists = os.path.exists

mkdir = os.mkdir

chmod = os.chmod

isdir = os.path.isdir

isfile = os.path.isfile

rename = os.rename

dirname = os.path.dirname

basename = os.path.basename

join = os.path.join

read = os.read

write = os.write

close = os.close

fsync = os.fsync

def _retry(func, *args, **kwargs):

# Wrapper around functions, that are problematic on "Windows". Sometimes

# the OS or someone else has still a handle to the file

if sys.platform == "win32":

for _ in range(10):

try:

return func(*args, **kwargs)

except Exception:

time.sleep(0.1)

return func(*args, **kwargs)

else:

return func(*args, **kwargs)

def remove(*args, **kwargs):

return _retry(os.remove, *args, **kwargs)

# Backwards compatibility imports

from gitdb.const import (

NULL_BIN_SHA,

NULL_HEX_SHA

)

#} END Aliases

#{ compatibility stuff ...

class _RandomAccessBytesIO:

"""Wrapper to provide required functionality in case memory maps cannot or may

not be used. This is only really required in python 2.4"""

__slots__ = '_sio'

def __init__(self, buf=''):

self._sio = BytesIO(buf)

def __getattr__(self, attr):

return getattr(self._sio, attr)

def __len__(self):

return len(self.getvalue())

def __getitem__(self, i):

return self.getvalue()[i]

def __getslice__(self, start, end):

return self.getvalue()[start:end]

def byte_ord(b):

"""

Return the integer representation of the byte string. This supports Python

3 byte arrays as well as standard strings.

"""

try:

return ord(b)

except TypeError:

return b

#} END compatibility stuff ...

#{ Routines

def make_sha(source=b''):

"""A python2.4 workaround for the sha/hashlib module fiasco

**Note** From the dulwich project """

try:

return hashlib.sha1(source)

except NameError:

import sha

sha1 = sha.sha(source)

return sha1

def allocate_memory(size):

""":return: a file-protocol accessible memory block of the given size"""

if size == 0:

return _RandomAccessBytesIO(b'')

# END handle empty chunks gracefully

try:

return mmap.mmap(-1, size) # read-write by default

except OSError:

# setup real memory instead

# this of course may fail if the amount of memory is not available in

# one chunk - would only be the case in python 2.4, being more likely on

# 32 bit systems.

return _RandomAccessBytesIO(b"\0" * size)

# END handle memory allocation

def file_contents_ro(fd, stream=False, allow_mmap=True):

""":return: read-only contents of the file represented by the file descriptor fd

:param fd: file descriptor opened for reading

:param stream: if False, random access is provided, otherwise the stream interface

is provided.

:param allow_mmap: if True, its allowed to map the contents into memory, which

allows large files to be handled and accessed efficiently. The file-descriptor

will change its position if this is False"""

try:

if allow_mmap:

# supports stream and random access

try:

return mmap.mmap(fd, 0, access=mmap.ACCESS_READ)

except OSError:

# python 2.4 issue, 0 wants to be the actual size

return mmap.mmap(fd, os.fstat(fd).st_size, access=mmap.ACCESS_READ)

# END handle python 2.4

except OSError:

pass

# END exception handling

# read manually

contents = os.read(fd, os.fstat(fd).st_size)

if stream:

return _RandomAccessBytesIO(contents)

return contents

def file_contents_ro_filepath(filepath, stream=False, allow_mmap=True, flags=0):

"""Get the file contents at filepath as fast as possible

:return: random access compatible memory of the given filepath

:param stream: see ``file_contents_ro``

:param allow_mmap: see ``file_contents_ro``

:param flags: additional flags to pass to os.open

:raise OSError: If the file could not be opened

**Note** for now we don't try to use O_NOATIME directly as the right value needs to be

shared per database in fact. It only makes a real difference for loose object

databases anyway, and they use it with the help of the ``flags`` parameter"""

fd = os.open(filepath, os.O_RDONLY | getattr(os, 'O_BINARY', 0) | flags)

try:

return file_contents_ro(fd, stream, allow_mmap)

finally:

close(fd)

# END assure file is closed

def sliding_ro_buffer(filepath, flags=0):

"""

:return: a buffer compatible object which uses our mapped memory manager internally

ready to read the whole given filepath"""

return SlidingWindowMapBuffer(mman.make_cursor(filepath), flags=flags)

def to_hex_sha(sha):

""":return: hexified version of sha"""

if len(sha) == 40:

return sha

return bin_to_hex(sha)

def to_bin_sha(sha):

if len(sha) == 20:

return sha

return hex_to_bin(sha)

#} END routines

#{ Utilities

class LazyMixin:

"""

Base class providing an interface to lazily retrieve attribute values upon

first access. If slots are used, memory will only be reserved once the attribute

is actually accessed and retrieved the first time. All future accesses will

return the cached value as stored in the Instance's dict or slot.

"""

__slots__ = tuple()

def __getattr__(self, attr):

"""

Whenever an attribute is requested that we do not know, we allow it

to be created and set. Next time the same attribute is requested, it is simply

returned from our dict/slots. """

self._set_cache_(attr)

# will raise in case the cache was not created

return object.__getattribute__(self, attr)

def _set_cache_(self, attr):

"""

This method should be overridden in the derived class.

It should check whether the attribute named by attr can be created

and cached. Do nothing if you do not know the attribute or call your subclass

The derived class may create as many additional attributes as it deems

necessary in case a git command returns more information than represented

in the single attribute."""

pass

class LockedFD:

"""

This class facilitates a safe read and write operation to a file on disk.

If we write to 'file', we obtain a lock file at 'file.lock' and write to

that instead. If we succeed, the lock file will be renamed to overwrite

the original file.

When reading, we obtain a lock file, but to prevent other writers from

succeeding while we are reading the file.

This type handles error correctly in that it will assure a consistent state

on destruction.

**note** with this setup, parallel reading is not possible"""

__slots__ = ("_filepath", '_fd', '_write')

def __init__(self, filepath):

"""Initialize an instance with the givne filepath"""

self._filepath = filepath

self._fd = None

self._write = None # if True, we write a file

def __del__(self):

# will do nothing if the file descriptor is already closed

if self._fd is not None:

self.rollback()

def _lockfilepath(self):

return "%s.lock" % self._filepath

def open(self, write=False, stream=False):

"""

Open the file descriptor for reading or writing, both in binary mode.

:param write: if True, the file descriptor will be opened for writing. Other

wise it will be opened read-only.

:param stream: if True, the file descriptor will be wrapped into a simple stream

object which supports only reading or writing

:return: fd to read from or write to. It is still maintained by this instance

and must not be closed directly

:raise IOError: if the lock could not be retrieved

:raise OSError: If the actual file could not be opened for reading

**note** must only be called once"""

if self._write is not None:

raise AssertionError("Called %s multiple times" % self.open)

self._write = write

# try to open the lock file

binary = getattr(os, 'O_BINARY', 0)

lockmode = os.O_WRONLY | os.O_CREAT | os.O_EXCL | binary

try:

fd = os.open(self._lockfilepath(), lockmode, int("600", 8))

if not write:

os.close(fd)

else:

self._fd = fd

# END handle file descriptor

except OSError as e:

raise OSError("Lock at %r could not be obtained" % self._lockfilepath()) from e

# END handle lock retrieval

# open actual file if required

if self._fd is None:

# we could specify exclusive here, as we obtained the lock anyway

try:

self._fd = os.open(self._filepath, os.O_RDONLY | binary)

except:

# assure we release our lockfile

remove(self._lockfilepath())

raise

# END handle lockfile

# END open descriptor for reading

if stream:

# need delayed import

from gitdb.stream import FDStream

return FDStream(self._fd)

else:

return self._fd

# END handle stream

def commit(self):

"""When done writing, call this function to commit your changes into the

actual file.

The file descriptor will be closed, and the lockfile handled.

**Note** can be called multiple times"""

self._end_writing(successful=True)

def rollback(self):

"""Abort your operation without any changes. The file descriptor will be

closed, and the lock released.

**Note** can be called multiple times"""

self._end_writing(successful=False)

def _end_writing(self, successful=True):

"""Handle the lock according to the write mode """

if self._write is None:

raise AssertionError("Cannot end operation if it wasn't started yet")

if self._fd is None:

return

os.close(self._fd)

self._fd = None

lockfile = self._lockfilepath()

if self._write and successful:

# on windows, rename does not silently overwrite the existing one

if sys.platform == "win32":

if isfile(self._filepath):

remove(self._filepath)

# END remove if exists

# END win32 special handling

os.rename(lockfile, self._filepath)

# assure others can at least read the file - the tmpfile left it at rw--

# We may also write that file, on windows that boils down to a remove-

# protection as well

chmod(self._filepath, int("644", 8))

else:

# just delete the file so far, we failed

remove(lockfile)

# END successful handling

#} END utilities