# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
# Spack Project Developers. See the top-level COPYRIGHT file for details.
#
# SPDX-License-Identifier: (Apache-2.0 OR MIT)
import os
import re
import shutil
import subprocess
import sys
import tempfile
from llnl.util import lang, tty
from ..path import system_path_filter
if sys.platform == "win32":
from win32file import CreateHardLink
is_windows = sys.platform == "win32"
def symlink(source_path: str, link_path: str, allow_broken_symlinks: bool = not is_windows):
"""
Create a link.
On non-Windows and Windows with System Administrator
privleges this will be a normal symbolic link via
os.symlink.
On Windows without privledges the link will be a
junction for a directory and a hardlink for a file.
On Windows the various link types are:
Symbolic Link: A link to a file or directory on the
same or different volume (drive letter) or even to
a remote file or directory (using UNC in its path).
Need System Administrator privileges to make these.
Hard Link: A link to a file on the same volume (drive
letter) only. Every file (file's data) has at least 1
hard link (file's name). But when this method creates
a new hard link there will be 2. Deleting all hard
links effectively deletes the file. Don't need System
Administrator privileges.
Junction: A link to a directory on the same or different
volume (drive letter) but not to a remote directory. Don't
need System Administrator privileges.
Parameters:
source_path (str): The real file or directory that the link points to.
Must be absolute OR relative to the link.
link_path (str): The path where the link will exist.
allow_broken_symlinks (bool): On Linux or Mac, don't raise an exception if the source_path
doesn't exist. This will still raise an exception on Windows.
"""
source_path = os.path.normpath(source_path)
win_source_path = source_path
link_path = os.path.normpath(link_path)
# Never allow broken links on Windows.
if sys.platform == "win32" and allow_broken_symlinks:
raise ValueError("allow_broken_symlinks parameter cannot be True on Windows.")
if not allow_broken_symlinks:
# Perform basic checks to make sure symlinking will succeed
if os.path.lexists(link_path):
raise AlreadyExistsError(
f"Link path ({link_path}) already exists. Cannot create link."
)
if not os.path.exists(source_path):
if os.path.isabs(source_path) and not allow_broken_symlinks:
# An absolute source path that does not exist will result in a broken link.
raise SymlinkError(
f"Source path ({source_path}) is absolute but does not exist. Resulting "
f"link would be broken so not making link."
)
else:
# os.symlink can create a link when the given source path is relative to
# the link path. Emulate this behavior and check to see if the source exists
# relative to the link path ahead of link creation to prevent broken
# links from being made.
link_parent_dir = os.path.dirname(link_path)
relative_path = os.path.join(link_parent_dir, source_path)
if os.path.exists(relative_path):
# In order to work on windows, the source path needs to be modified to be
# relative because hardlink/junction dont resolve relative paths the same
# way as os.symlink. This is ignored on other operating systems.
win_source_path = relative_path
elif not allow_broken_symlinks:
raise SymlinkError(
f"The source path ({source_path}) is not relative to the link path "
f"({link_path}). Resulting link would be broken so not making link."
)
# Create the symlink
if sys.platform == "win32" and not _windows_can_symlink():
_windows_create_link(win_source_path, link_path)
else:
os.symlink(source_path, link_path, target_is_directory=os.path.isdir(source_path))
def islink(path: str) -> bool:
"""Override os.islink to give correct answer for spack logic.
For Non-Windows: a link can be determined with the os.path.islink method.
Windows-only methods will return false for other operating systems.
For Windows: spack considers symlinks, hard links, and junctions to
all be links, so if any of those are True, return True.
Args:
path (str): path to check if it is a link.
Returns:
bool - whether the path is any kind link or not.
"""
return any([os.path.islink(path), _windows_is_junction(path), _windows_is_hardlink(path)])
def _windows_is_hardlink(path: str) -> bool:
"""Determines if a path is a windows hard link. This is accomplished
by looking at the number of links using os.stat. A non-hard-linked file
will have a st_nlink value of 1, whereas a hard link will have a value
larger than 1. Note that both the original and hard-linked file will
return True because they share the same inode.
Args:
path (str): Windows path to check for a hard link
Returns:
bool - Whether the path is a hard link or not.
"""
if sys.platform != "win32" or os.path.islink(path) or not os.path.exists(path):
return False
return os.stat(path).st_nlink > 1
def _windows_is_junction(path: str) -> bool:
"""Determines if a path is a windows junction. A junction can be
determined using a bitwise AND operation between the file's
attribute bitmask and the known junction bitmask (0x400).
Args:
path (str): A non-file path
Returns:
bool - whether the path is a junction or not.
"""
if sys.platform != "win32" or os.path.islink(path) or os.path.isfile(path):
return False
import ctypes.wintypes
get_file_attributes = ctypes.windll.kernel32.GetFileAttributesW # type: ignore[attr-defined]
get_file_attributes.argtypes = (ctypes.wintypes.LPWSTR,)
get_file_attributes.restype = ctypes.wintypes.DWORD
invalid_file_attributes = 0xFFFFFFFF
reparse_point = 0x400
file_attr = get_file_attributes(str(path))
if file_attr == invalid_file_attributes:
return False
return file_attr & reparse_point > 0
@lang.memoized
def _windows_can_symlink() -> bool:
"""
Determines if windows is able to make a symlink depending on
the system configuration and the level of the user's permissions.
"""
if sys.platform != "win32":
tty.warn("windows_can_symlink method can't be used on non-Windows OS.")
return False
tempdir = tempfile.mkdtemp()
dpath = os.path.join(tempdir, "dpath")
fpath = os.path.join(tempdir, "fpath.txt")
dlink = os.path.join(tempdir, "dlink")
flink = os.path.join(tempdir, "flink.txt")
import llnl.util.filesystem as fs
fs.touchp(fpath)
try:
os.symlink(dpath, dlink)
can_symlink_directories = os.path.islink(dlink)
except OSError:
can_symlink_directories = False
try:
os.symlink(fpath, flink)
can_symlink_files = os.path.islink(flink)
except OSError:
can_symlink_files = False
# Cleanup the test directory
shutil.rmtree(tempdir)
return can_symlink_directories and can_symlink_files
def _windows_create_link(source: str, link: str):
"""
Attempts to create a Hard Link or Junction as an alternative
to a symbolic link. This is called when symbolic links cannot
be created.
"""
if sys.platform != "win32":
raise SymlinkError("windows_create_link method can't be used on non-Windows OS.")
elif os.path.isdir(source):
_windows_create_junction(source=source, link=link)
elif os.path.isfile(source):
_windows_create_hard_link(path=source, link=link)
else:
raise SymlinkError(
f"Cannot create link from {source}. It is neither a file nor a directory."
)
def _windows_create_junction(source: str, link: str):
"""Duly verify that the path and link are eligible to create a junction,
then create the junction.
"""
if sys.platform != "win32":
raise SymlinkError("windows_create_junction method can't be used on non-Windows OS.")
elif not os.path.exists(source):
raise SymlinkError("Source path does not exist, cannot create a junction.")
elif os.path.lexists(link):
raise AlreadyExistsError("Link path already exists, cannot create a junction.")
elif not os.path.isdir(source):
raise SymlinkError("Source path is not a directory, cannot create a junction.")
import subprocess
cmd = ["cmd", "/C", "mklink", "/J", link, source]
proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
out, err = proc.communicate()
tty.debug(out.decode())
if proc.returncode != 0:
err = err.decode()
tty.error(err)
raise SymlinkError("Make junction command returned a non-zero return code.", err)
def _windows_create_hard_link(path: str, link: str):
"""Duly verify that the path and link are eligible to create a hard
link, then create the hard link.
"""
if sys.platform != "win32":
raise SymlinkError("windows_create_hard_link method can't be used on non-Windows OS.")
elif not os.path.exists(path):
raise SymlinkError(f"File path {path} does not exist. Cannot create hard link.")
elif os.path.lexists(link):
raise AlreadyExistsError(f"Link path ({link}) already exists. Cannot create hard link.")
elif not os.path.isfile(path):
raise SymlinkError(f"File path ({link}) is not a file. Cannot create hard link.")
else:
tty.debug(f"Creating hard link {link} pointing to {path}")
CreateHardLink(link, path)
def readlink(path: str):
"""Spack utility to override of os.readlink method to work cross platform"""
if _windows_is_hardlink(path):
return _windows_read_hard_link(path)
elif _windows_is_junction(path):
return _windows_read_junction(path)
else:
return os.readlink(path)
def _windows_read_hard_link(link: str) -> str:
"""Find all of the files that point to the same inode as the link"""
if sys.platform != "win32":
raise SymlinkError("Can't read hard link on non-Windows OS.")
link = os.path.abspath(link)
fsutil_cmd = ["fsutil", "hardlink", "list", link]
proc = subprocess.Popen(fsutil_cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
out, err = proc.communicate()
if proc.returncode != 0:
raise SymlinkError(f"An error occurred while reading hard link: {err.decode()}")
# fsutil response does not include the drive name, so append it back to each linked file.
drive, link_tail = os.path.splitdrive(os.path.abspath(link))
links = set([os.path.join(drive, p) for p in out.decode().splitlines()])
links.remove(link)
if len(links) == 1:
return links.pop()
elif len(links) > 1:
# TODO: How best to handle the case where 3 or more paths point to a single inode?
raise SymlinkError(f"Found multiple paths pointing to the same inode {links}")
else:
raise SymlinkError("Cannot determine hard link source path.")
def _windows_read_junction(link: str):
"""Find the path that a junction points to."""
if sys.platform != "win32":
raise SymlinkError("Can't read junction on non-Windows OS.")
link = os.path.abspath(link)
link_basename = os.path.basename(link)
link_parent = os.path.dirname(link)
fsutil_cmd = ["dir", "/a:l", link_parent]
proc = subprocess.Popen(fsutil_cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
out, err = proc.communicate()
if proc.returncode != 0:
raise SymlinkError(f"An error occurred while reading junction: {err.decode()}")
matches = re.search(rf"<JUNCTION>\s+{link_basename} \[(.*)]", out.decode())
if matches:
return matches.group(1)
else:
raise SymlinkError("Could not find junction path.")
@system_path_filter
def resolve_link_target_relative_to_the_link(link):
"""
os.path.isdir uses os.path.exists, which for links will check
the existence of the link target. If the link target is relative to
the link, we need to construct a pathname that is valid from
our cwd (which may not be the same as the link's directory)
"""
target = readlink(link)
if os.path.isabs(target):
return target
link_dir = os.path.dirname(os.path.abspath(link))
return os.path.join(link_dir, target)
class SymlinkError(RuntimeError):
"""Exception class for errors raised while creating symlinks,
junctions and hard links
"""
class AlreadyExistsError(SymlinkError):
"""Link path already exists."""
