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 macfs as _macfs
    import MACFS as _MACFS

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

try:
    import thread as _thread
    _allocate_lock = _thread.allocate_lock
except (ImportError, AttributeError):
    class _allocate_lock:
        def acquire(self):
            pass
        release = acquire

_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

if _os.name == 'nt':
    template = '~t' # cater to eight-letter limit
else:
    template = "tmp"

tempdir = None

# Internal routines.

_once_lock = _allocate_lock()

def _once(var, initializer):
    """Wrapper to execute an initialization operation just once,
    even if multiple threads reach the same point at the same time.

    var is the name (as a string) of the variable to be entered into
    the current global namespace.

    initializer is a callable which will return the appropriate initial
    value for variable.  It will be called only if variable is not
    present in the global namespace, or its current value is None.

    Do not call _once from inside an initializer routine, it will deadlock.
    """

    vars = globals()
    lock = _once_lock

    # Check first outside the lock.
    if var in vars and vars[var] is not None:
        return
    try:
        lock.acquire()
        # Check again inside the lock.
        if var in vars and vars[var] is not None:
            return
        vars[var] = initializer()
    finally:
        lock.release()

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
        r = self.rng

        try:
            m.acquire()
            letters = ''.join([r.choice(c), r.choice(c), r.choice(c),
                               r.choice(c), r.choice(c), r.choice(c)])
        finally:
            m.release()

        return self.normcase(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:
            refnum, dirid = _macfs.FindFolder(_MACFS.kOnSystemDisk,
                                              _MACFS.kTemporaryFolderType, 1)
            dirname = _macfs.FSSpec((refnum, dirid, '')).as_pathname()
            dirlist.append(dirname)
        except _macfs.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 through '_once' (see above) as we
    do not want multiple threads attempting this calculation simultaneously.

    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))

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

    _once('_name_sequence', _RandomNameSequence)
    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, 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

def gettempdir():
    """Accessor for tempdir.tempdir."""
    _once('tempdir', _get_default_tempdir)
    return tempdir

def mkstemp(suffix="", prefix=template, dir=gettempdir(), binary=1):
    """mkstemp([suffix, [prefix, [dir, [binary]]]])
    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 'binary' is specified and false, the file is opened in binary
    mode.  Otherwise, the file is opened in text 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 binary:
        flags = _bin_openflags
    else:
        flags = _text_openflags

    return _mkstemp_inner(dir, prefix, suffix, flags)


def mkdtemp(suffix="", prefix=template, dir=gettempdir()):
    """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 'binary' 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.
    """

    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 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=gettempdir()):
    """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 'binary' 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)

    names = _get_candidate_names()
    for seq in xrange(TMP_MAX):
        name = names.next()
        file = _os.path.join(dir, prefix + name + suffix)
        if not _os.path.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 = 0

    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 = 1
                self.file.close()
                self.unlink(self.name)

        def __del__(self):
            self.close()

def NamedTemporaryFile(mode='w+b', bufsize=-1, suffix="",
                       prefix=template, dir=gettempdir()):
    """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 a file object; the name of the file is accessible as
    file.name.  The file will be automatically deleted when it is
    closed.
    """

    bin = 'b' in mode
    if bin: 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':
    # On non-POSIX 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=gettempdir()):
        """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 a file object.  The file has no name, and will cease to
        exist when it is closed.
        """

        bin = 'b' in mode
        if bin: 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