Lib/tempfile.py

"""Temporary files.

This module provides generic, low- and high-level interfaces for
creating temporary files and directories.  The interfaces listed
as "safe" just below can be used without fear of race conditions.
Those listed as "unsafe" cannot, and are provided for backward
compatibility only.

This module also provides some data items to the user:

  TMP_MAX  - maximum number of names that will be tried before
             giving up.
  template - the default prefix for all temporary names.
             You may change this to control the default prefix.
  tempdir  - If this is set to a string before the first use of
             any routine from this module, it will be considered as
             another candidate location to store temporary files.
"""

__all__ = [
    "NamedTemporaryFile", "TemporaryFile", # high level safe interfaces
    "mkstemp", "mkdtemp",                  # low level safe interfaces
    "mktemp",                              # deprecated unsafe interface
    "TMP_MAX", "gettempprefix",            # constants
    "tempdir", "gettempdir"
   ]


# Imports.

import os as _os
import errno as _errno
from random import Random as _Random

if _os.name == 'mac':
    import Carbon.Folder as _Folder
    import Carbon.Folders as _Folders

try:
    import fcntl as _fcntl
except ImportError:
    def _set_cloexec(fd):
        pass
else:
    def _set_cloexec(fd):
        try:
            flags = _fcntl.fcntl(fd, _fcntl.F_GETFD, 0)
        except IOError:
            pass
        else:
            # flags read successfully, modify
            flags |= _fcntl.FD_CLOEXEC
            _fcntl.fcntl(fd, _fcntl.F_SETFD, flags)


try:
    import thread as _thread
except ImportError:
    import dummy_thread as _thread
_allocate_lock = _thread.allocate_lock

_text_openflags = _os.O_RDWR | _os.O_CREAT | _os.O_EXCL
if hasattr(_os, 'O_NOINHERIT'):
    _text_openflags |= _os.O_NOINHERIT
if hasattr(_os, 'O_NOFOLLOW'):
    _text_openflags |= _os.O_NOFOLLOW

_bin_openflags = _text_openflags
if hasattr(_os, 'O_BINARY'):
    _bin_openflags |= _os.O_BINARY

if hasattr(_os, 'TMP_MAX'):
    TMP_MAX = _os.TMP_MAX
else:
    TMP_MAX = 10000

template = "tmp"

tempdir = None

# Internal routines.

_once_lock = _allocate_lock()

if hasattr(_os, "lstat"):
    _stat = _os.lstat
elif hasattr(_os, "stat"):
    _stat = _os.stat
else:
    # Fallback.  All we need is something that raises os.error if the
    # file doesn't exist.
    def _stat(fn):
        try:
            f = open(fn)
        except IOError:
            raise _os.error
        f.close()

def _exists(fn):
    try:
        _stat(fn)
    except _os.error:
        return False
    else:
        return True

class _RandomNameSequence:
    """An instance of _RandomNameSequence generates an endless
    sequence of unpredictable strings which can safely be incorporated
    into file names.  Each string is six characters long.  Multiple
    threads can safely use the same instance at the same time.

    _RandomNameSequence is an iterator."""

    characters = ("abcdefghijklmnopqrstuvwxyz" +
                  "ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
                  "0123456789-_")

    def __init__(self):
        self.mutex = _allocate_lock()
        self.rng = _Random()
        self.normcase = _os.path.normcase

    def __iter__(self):
        return self

    def next(self):
        m = self.mutex
        c = self.characters
        choose = self.rng.choice

        m.acquire()
        try:
            letters = [choose(c) for dummy in "123456"]
        finally:
            m.release()

        return self.normcase(''.join(letters))

def _candidate_tempdir_list():
    """Generate a list of candidate temporary directories which
    _get_default_tempdir will try."""

    dirlist = []

    # First, try the environment.
    for envname in 'TMPDIR', 'TEMP', 'TMP':
        dirname = _os.getenv(envname)
        if dirname: dirlist.append(dirname)

    # Failing that, try OS-specific locations.
    if _os.name == 'mac':
        try:
            fsr = _Folder.FSFindFolder(_Folders.kOnSystemDisk,
                                              _Folders.kTemporaryFolderType, 1)
            dirname = fsr.as_pathname()
            dirlist.append(dirname)
        except _Folder.error:
            pass
    elif _os.name == 'riscos':
        dirname = _os.getenv('Wimp$ScrapDir')
        if dirname: dirlist.append(dirname)
    elif _os.name == 'nt':
        dirlist.extend([ r'c:\temp', r'c:\tmp', r'\temp', r'\tmp' ])
    else:
        dirlist.extend([ '/tmp', '/var/tmp', '/usr/tmp' ])

    # As a last resort, the current directory.
    try:
        dirlist.append(_os.getcwd())
    except (AttributeError, _os.error):
        dirlist.append(_os.curdir)

    return dirlist

def _get_default_tempdir():
    """Calculate the default directory to use for temporary files.
    This routine should be called exactly once.

    We determine whether or not a candidate temp dir is usable by
    trying to create and write to a file in that directory.  If this
    is successful, the test file is deleted.  To prevent denial of
    service, the name of the test file must be randomized."""

    namer = _RandomNameSequence()
    dirlist = _candidate_tempdir_list()
    flags = _text_openflags

    for dir in dirlist:
        if dir != _os.curdir:
            dir = _os.path.normcase(_os.path.abspath(dir))
        # Try only a few names per directory.
        for seq in xrange(100):
            name = namer.next()
            filename = _os.path.join(dir, name)
            try:
                fd = _os.open(filename, flags, 0600)
                fp = _os.fdopen(fd, 'w')
                fp.write('blat')
                fp.close()
                _os.unlink(filename)
                del fp, fd
                return dir
            except (OSError, IOError), e:
                if e[0] != _errno.EEXIST:
                    break # no point trying more names in this directory
                pass
    raise IOError, (_errno.ENOENT,
                    ("No usable temporary directory found in %s" % dirlist))

_name_sequence = None

def _get_candidate_names():
    """Common setup sequence for all user-callable interfaces."""

    global _name_sequence
    if _name_sequence is None:
        _once_lock.acquire()
        try:
            if _name_sequence is None:
                _name_sequence = _RandomNameSequence()
        finally:
            _once_lock.release()
    return _name_sequence


def _mkstemp_inner(dir, pre, suf, flags):
    """Code common to mkstemp, TemporaryFile, and NamedTemporaryFile."""

    names = _get_candidate_names()

    for seq in xrange(TMP_MAX):
        name = names.next()
        file = _os.path.join(dir, pre + name + suf)
        try:
            fd = _os.open(file, flags, 0600)
            _set_cloexec(fd)
            return (fd, _os.path.abspath(file))
        except OSError, e:
            if e.errno == _errno.EEXIST:
                continue # try again
            raise

    raise IOError, (_errno.EEXIST, "No usable temporary file name found")


# User visible interfaces.

def gettempprefix():
    """Accessor for tempdir.template."""
    return template

tempdir = None

def gettempdir():
    """Accessor for tempdir.tempdir."""
    global tempdir
    if tempdir is None:
        _once_lock.acquire()
        try:
            if tempdir is None:
                tempdir = _get_default_tempdir()
        finally:
            _once_lock.release()
    return tempdir

def mkstemp(suffix="", prefix=template, dir=None, text=False):
    """mkstemp([suffix, [prefix, [dir, [text]]]])
    User-callable function to create and return a unique temporary
    file.  The return value is a pair (fd, name) where fd is the
    file descriptor returned by os.open, and name is the filename.

    If 'suffix' is specified, the file name will end with that suffix,
    otherwise there will be no suffix.

    If 'prefix' is specified, the file name will begin with that prefix,
    otherwise a default prefix is used.

    If 'dir' is specified, the file will be created in that directory,
    otherwise a default directory is used.

    If 'text' is specified and true, the file is opened in text
    mode.  Else (the default) the file is opened in binary mode.  On
    some operating systems, this makes no difference.

    The file is readable and writable only by the creating user ID.
    If the operating system uses permission bits to indicate whether a
    file is executable, the file is executable by no one. The file
    descriptor is not inherited by children of this process.

    Caller is responsible for deleting the file when done with it.
    """

    if dir is None:
        dir = gettempdir()

    if text:
        flags = _text_openflags
    else:
        flags = _bin_openflags

    return _mkstemp_inner(dir, prefix, suffix, flags)


def mkdtemp(suffix="", prefix=template, dir=None):
    """mkdtemp([suffix, [prefix, [dir]]])
    User-callable function to create and return a unique temporary
    directory.  The return value is the pathname of the directory.

    Arguments are as for mkstemp, except that the 'text' argument is
    not accepted.

    The directory is readable, writable, and searchable only by the
    creating user.

    Caller is responsible for deleting the directory when done with it.
    """

    if dir is None:
        dir = gettempdir()

    names = _get_candidate_names()

    for seq in xrange(TMP_MAX):
        name = names.next()
        file = _os.path.join(dir, prefix + name + suffix)
        try:
            _os.mkdir(file, 0700)
            return file
        except WindowsError, e:
            if e.errno == 183: # ERROR_ALREADY_EXISTS
                continue # try again
            raise
        except OSError, e:
            if e.errno == _errno.EEXIST:
                continue # try again
            raise

    raise IOError, (_errno.EEXIST, "No usable temporary directory name found")

def mktemp(suffix="", prefix=template, dir=None):
    """mktemp([suffix, [prefix, [dir]]])
    User-callable function to return a unique temporary file name.  The
    file is not created.

    Arguments are as for mkstemp, except that the 'text' argument is
    not accepted.

    This function is unsafe and should not be used.  The file name
    refers to a file that did not exist at some point, but by the time
    you get around to creating it, someone else may have beaten you to
    the punch.
    """

##    from warnings import warn as _warn
##    _warn("mktemp is a potential security risk to your program",
##          RuntimeWarning, stacklevel=2)

    if dir is None:
        dir = gettempdir()

    names = _get_candidate_names()
    for seq in xrange(TMP_MAX):
        name = names.next()
        file = _os.path.join(dir, prefix + name + suffix)
        if not _exists(file):
            return file

    raise IOError, (_errno.EEXIST, "No usable temporary filename found")

class _TemporaryFileWrapper:
    """Temporary file wrapper

    This class provides a wrapper around files opened for
    temporary use.  In particular, it seeks to automatically
    remove the file when it is no longer needed.
    """

    def __init__(self, file, name):
        self.file = file
        self.name = name
        self.close_called = False

    def __getattr__(self, name):
        file = self.__dict__['file']
        a = getattr(file, name)
        if type(a) != type(0):
            setattr(self, name, a)
        return a

    # NT provides delete-on-close as a primitive, so we don't need
    # the wrapper to do anything special.  We still use it so that
    # file.name is useful (i.e. not "(fdopen)") with NamedTemporaryFile.
    if _os.name != 'nt':

        # Cache the unlinker so we don't get spurious errors at
        # shutdown when the module-level "os" is None'd out.  Note
        # that this must be referenced as self.unlink, because the
        # name TemporaryFileWrapper may also get None'd out before
        # __del__ is called.
        unlink = _os.unlink

        def close(self):
            if not self.close_called:
                self.close_called = True
                self.file.close()
                self.unlink(self.name)

        def __del__(self):
            self.close()

def NamedTemporaryFile(mode='w+b', bufsize=-1, suffix="",
                       prefix=template, dir=None):
    """Create and return a temporary file.
    Arguments:
    'prefix', 'suffix', 'dir' -- as for mkstemp.
    'mode' -- the mode argument to os.fdopen (default "w+b").
    'bufsize' -- the buffer size argument to os.fdopen (default -1).
    The file is created as mkstemp() would do it.

    Returns an object with a file-like interface; the name of the file
    is accessible as file.name.  The file will be automatically deleted
    when it is closed.
    """

    if dir is None:
        dir = gettempdir()

    if 'b' in mode:
        flags = _bin_openflags
    else:
        flags = _text_openflags

    # Setting O_TEMPORARY in the flags causes the OS to delete
    # the file when it is closed.  This is only supported by Windows.
    if _os.name == 'nt':
        flags |= _os.O_TEMPORARY

    (fd, name) = _mkstemp_inner(dir, prefix, suffix, flags)
    file = _os.fdopen(fd, mode, bufsize)
    return _TemporaryFileWrapper(file, name)

if _os.name != 'posix' or _os.sys.platform == 'cygwin':
    # On non-POSIX and Cygwin systems, assume that we cannot unlink a file
    # while it is open.
    TemporaryFile = NamedTemporaryFile

else:
    def TemporaryFile(mode='w+b', bufsize=-1, suffix="",
                      prefix=template, dir=None):
        """Create and return a temporary file.
        Arguments:
        'prefix', 'suffix', 'directory' -- as for mkstemp.
        'mode' -- the mode argument to os.fdopen (default "w+b").
        'bufsize' -- the buffer size argument to os.fdopen (default -1).
        The file is created as mkstemp() would do it.

        Returns an object with a file-like interface.  The file has no
        name, and will cease to exist when it is closed.
        """

        if dir is None:
            dir = gettempdir()

        if 'b' in mode:
            flags = _bin_openflags
        else:
            flags = _text_openflags

        (fd, name) = _mkstemp_inner(dir, prefix, suffix, flags)
        try:
            _os.unlink(name)
            return _os.fdopen(fd, mode, bufsize)
        except:
            _os.close(fd)
            raise