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platform_utils.py
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platform_utils.py
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# -*- coding:utf-8 -*-
#
# Copyright (C) 2016 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import errno
import os
import platform
import select
import shutil
import stat
from pyversion import is_python3
if is_python3():
from queue import Queue
else:
from Queue import Queue
from threading import Thread
def isWindows():
""" Returns True when running with the native port of Python for Windows,
False when running on any other platform (including the Cygwin port of
Python).
"""
# Note: The cygwin port of Python returns "CYGWIN_NT_xxx"
return platform.system() == "Windows"
class FileDescriptorStreams(object):
""" Platform agnostic abstraction enabling non-blocking I/O over a
collection of file descriptors. This abstraction is required because
fctnl(os.O_NONBLOCK) is not supported on Windows.
"""
@classmethod
def create(cls):
""" Factory method: instantiates the concrete class according to the
current platform.
"""
if isWindows():
return _FileDescriptorStreamsThreads()
else:
return _FileDescriptorStreamsNonBlocking()
def __init__(self):
self.streams = []
def add(self, fd, dest, std_name):
""" Wraps an existing file descriptor as a stream.
"""
self.streams.append(self._create_stream(fd, dest, std_name))
def remove(self, stream):
""" Removes a stream, when done with it.
"""
self.streams.remove(stream)
@property
def is_done(self):
""" Returns True when all streams have been processed.
"""
return len(self.streams) == 0
def select(self):
""" Returns the set of streams that have data available to read.
The returned streams each expose a read() and a close() method.
When done with a stream, call the remove(stream) method.
"""
raise NotImplementedError
def _create_stream(fd, dest, std_name):
""" Creates a new stream wrapping an existing file descriptor.
"""
raise NotImplementedError
class _FileDescriptorStreamsNonBlocking(FileDescriptorStreams):
""" Implementation of FileDescriptorStreams for platforms that support
non blocking I/O.
"""
class Stream(object):
""" Encapsulates a file descriptor """
def __init__(self, fd, dest, std_name):
self.fd = fd
self.dest = dest
self.std_name = std_name
self.set_non_blocking()
def set_non_blocking(self):
import fcntl
flags = fcntl.fcntl(self.fd, fcntl.F_GETFL)
fcntl.fcntl(self.fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)
def fileno(self):
return self.fd.fileno()
def read(self):
return self.fd.read(4096)
def close(self):
self.fd.close()
def _create_stream(self, fd, dest, std_name):
return self.Stream(fd, dest, std_name)
def select(self):
ready_streams, _, _ = select.select(self.streams, [], [])
return ready_streams
class _FileDescriptorStreamsThreads(FileDescriptorStreams):
""" Implementation of FileDescriptorStreams for platforms that don't support
non blocking I/O. This implementation requires creating threads issuing
blocking read operations on file descriptors.
"""
def __init__(self):
super(_FileDescriptorStreamsThreads, self).__init__()
# The queue is shared accross all threads so we can simulate the
# behavior of the select() function
self.queue = Queue(10) # Limit incoming data from streams
def _create_stream(self, fd, dest, std_name):
return self.Stream(fd, dest, std_name, self.queue)
def select(self):
# Return only one stream at a time, as it is the most straighforward
# thing to do and it is compatible with the select() function.
item = self.queue.get()
stream = item.stream
stream.data = item.data
return [stream]
class QueueItem(object):
""" Item put in the shared queue """
def __init__(self, stream, data):
self.stream = stream
self.data = data
class Stream(object):
""" Encapsulates a file descriptor """
def __init__(self, fd, dest, std_name, queue):
self.fd = fd
self.dest = dest
self.std_name = std_name
self.queue = queue
self.data = None
self.thread = Thread(target=self.read_to_queue)
self.thread.daemon = True
self.thread.start()
def close(self):
self.fd.close()
def read(self):
data = self.data
self.data = None
return data
def read_to_queue(self):
""" The thread function: reads everything from the file descriptor into
the shared queue and terminates when reaching EOF.
"""
for line in iter(self.fd.readline, b''):
self.queue.put(_FileDescriptorStreamsThreads.QueueItem(self, line))
self.fd.close()
self.queue.put(_FileDescriptorStreamsThreads.QueueItem(self, None))
def symlink(source, link_name):
"""Creates a symbolic link pointing to source named link_name.
Note: On Windows, source must exist on disk, as the implementation needs
to know whether to create a "File" or a "Directory" symbolic link.
"""
if isWindows():
import platform_utils_win32
source = _validate_winpath(source)
link_name = _validate_winpath(link_name)
target = os.path.join(os.path.dirname(link_name), source)
if isdir(target):
platform_utils_win32.create_dirsymlink(_makelongpath(source), link_name)
else:
platform_utils_win32.create_filesymlink(_makelongpath(source), link_name)
else:
return os.symlink(source, link_name)
def _validate_winpath(path):
path = os.path.normpath(path)
if _winpath_is_valid(path):
return path
raise ValueError("Path \"%s\" must be a relative path or an absolute "
"path starting with a drive letter".format(path))
def _winpath_is_valid(path):
"""Windows only: returns True if path is relative (e.g. ".\\foo") or is
absolute including a drive letter (e.g. "c:\\foo"). Returns False if path
is ambiguous (e.g. "x:foo" or "\\foo").
"""
assert isWindows()
path = os.path.normpath(path)
drive, tail = os.path.splitdrive(path)
if tail:
if not drive:
return tail[0] != os.sep # "\\foo" is invalid
else:
return tail[0] == os.sep # "x:foo" is invalid
else:
return not drive # "x:" is invalid
def _makelongpath(path):
"""Return the input path normalized to support the Windows long path syntax
("\\\\?\\" prefix) if needed, i.e. if the input path is longer than the
MAX_PATH limit.
"""
if isWindows():
# Note: MAX_PATH is 260, but, for directories, the maximum value is actually 246.
if len(path) < 246:
return path
if path.startswith(u"\\\\?\\"):
return path
if not os.path.isabs(path):
return path
# Append prefix and ensure unicode so that the special longpath syntax
# is supported by underlying Win32 API calls
return u"\\\\?\\" + os.path.normpath(path)
else:
return path
def rmtree(path):
"""shutil.rmtree(path) wrapper with support for long paths on Windows.
Availability: Unix, Windows."""
if isWindows():
shutil.rmtree(_makelongpath(path), onerror=handle_rmtree_error)
else:
shutil.rmtree(path)
def handle_rmtree_error(function, path, excinfo):
# Allow deleting read-only files
os.chmod(path, stat.S_IWRITE)
function(path)
def rename(src, dst):
"""os.rename(src, dst) wrapper with support for long paths on Windows.
Availability: Unix, Windows."""
if isWindows():
# On Windows, rename fails if destination exists, see
# https://docs.python.org/2/library/os.html#os.rename
try:
os.rename(_makelongpath(src), _makelongpath(dst))
except OSError as e:
if e.errno == errno.EEXIST:
os.remove(_makelongpath(dst))
os.rename(_makelongpath(src), _makelongpath(dst))
else:
raise
else:
os.rename(src, dst)
def remove(path):
"""Remove (delete) the file path. This is a replacement for os.remove that
allows deleting read-only files on Windows, with support for long paths and
for deleting directory symbolic links.
Availability: Unix, Windows."""
if isWindows():
longpath = _makelongpath(path)
try:
os.remove(longpath)
except OSError as e:
if e.errno == errno.EACCES:
os.chmod(longpath, stat.S_IWRITE)
# Directory symbolic links must be deleted with 'rmdir'.
if islink(longpath) and isdir(longpath):
os.rmdir(longpath)
else:
os.remove(longpath)
else:
raise
else:
os.remove(path)
def walk(top, topdown=True, onerror=None, followlinks=False):
"""os.walk(path) wrapper with support for long paths on Windows.
Availability: Windows, Unix.
"""
if isWindows():
return _walk_windows_impl(top, topdown, onerror, followlinks)
else:
return os.walk(top, topdown, onerror, followlinks)
def _walk_windows_impl(top, topdown, onerror, followlinks):
try:
names = listdir(top)
except Exception as err:
if onerror is not None:
onerror(err)
return
dirs, nondirs = [], []
for name in names:
if isdir(os.path.join(top, name)):
dirs.append(name)
else:
nondirs.append(name)
if topdown:
yield top, dirs, nondirs
for name in dirs:
new_path = os.path.join(top, name)
if followlinks or not islink(new_path):
for x in _walk_windows_impl(new_path, topdown, onerror, followlinks):
yield x
if not topdown:
yield top, dirs, nondirs
def listdir(path):
"""os.listdir(path) wrapper with support for long paths on Windows.
Availability: Windows, Unix.
"""
return os.listdir(_makelongpath(path))
def rmdir(path):
"""os.rmdir(path) wrapper with support for long paths on Windows.
Availability: Windows, Unix.
"""
os.rmdir(_makelongpath(path))
def isdir(path):
"""os.path.isdir(path) wrapper with support for long paths on Windows.
Availability: Windows, Unix.
"""
return os.path.isdir(_makelongpath(path))
def islink(path):
"""os.path.islink(path) wrapper with support for long paths on Windows.
Availability: Windows, Unix.
"""
if isWindows():
import platform_utils_win32
return platform_utils_win32.islink(_makelongpath(path))
else:
return os.path.islink(path)
def readlink(path):
"""Return a string representing the path to which the symbolic link
points. The result may be either an absolute or relative pathname;
if it is relative, it may be converted to an absolute pathname using
os.path.join(os.path.dirname(path), result).
Availability: Windows, Unix.
"""
if isWindows():
import platform_utils_win32
return platform_utils_win32.readlink(_makelongpath(path))
else:
return os.readlink(path)
def realpath(path):
"""Return the canonical path of the specified filename, eliminating
any symbolic links encountered in the path.
Availability: Windows, Unix.
"""
if isWindows():
current_path = os.path.abspath(path)
path_tail = []
for c in range(0, 100): # Avoid cycles
if islink(current_path):
target = readlink(current_path)
current_path = os.path.join(os.path.dirname(current_path), target)
else:
basename = os.path.basename(current_path)
if basename == '':
path_tail.append(current_path)
break
path_tail.append(basename)
current_path = os.path.dirname(current_path)
path_tail.reverse()
result = os.path.normpath(os.path.join(*path_tail))
return result
else:
return os.path.realpath(path)