BF: set_readonly helper to set or reset file to/from readonly mode

Author: yarikoptic

bin/heudiconv

@@ -53,6 +53,14 @@ from random import sample
 MIN_VERSIONS = {
     'datalad': '0.7'
 }
+
+# Some variables for reuse
+import stat
+
+ALL_CAN_WRITE = (stat.S_IWUSR | stat.S_IWGRP | stat.S_IWOTH)
+ALL_CAN_READ = (stat.S_IRUSR | stat.S_IRGRP | stat.S_IROTH)
+assert ALL_CAN_READ >> 1 == ALL_CAN_WRITE  # Assumption in the code
+
 PY3 = sys.version_info[0] >= 3
 
 import logging
@@ -305,6 +313,35 @@ def find_files(regex, topdir=curdir, exclude=None, exclude_vcs=True, dirs=False)
 find_files.__doc__ %= (_VCS_REGEX,)
 
 
+def set_readonly(path, read_only=True):
+    """Make file read only or writeable while preserving "access levels"
+
+    So if file was not readable by "others" it should remain not readable
+    by others
+
+    Parameters
+    ----------
+    path : str
+    read_only : bool, optional
+      If True (default) - would make it read-only. If False, would make it
+      writeable for levels where it is readable
+    """
+    # get current permissions
+    perms = stat.S_IMODE(os.lstat(path).st_mode)
+    # set new permissions
+    if read_only:
+        new_perms = perms & (~ALL_CAN_WRITE)
+    else:
+        # need to set only for those which had read bit set
+        # read bit is <<1 away from write bit
+        whocanread = perms & ALL_CAN_READ
+        thosecanwrite = whocanread >> 1
+        new_perms = perms | thosecanwrite
+    # apply and return those target permissions
+    os.chmod(path, new_perms)
+    return new_perms
+
+
 def group_dicoms_into_seqinfos(
         files, file_filter=None, dcmfilter=None, grouping='studyUID'
 ):

tests/test_main.py

@@ -1,6 +1,7 @@
 import csv
 import os
 import pytest
+import stat
 import sys
 
 from mock import patch
@@ -194,4 +195,23 @@ def test__find_subj_ses():
     assert heudiconv._find_subj_ses('950_bids_test4/sub-phantom1sid1/fmap/sub-phantom1sid1_acq-3mm_phasediff.json') == ('phantom1sid1', None)
     assert heudiconv._find_subj_ses('sub-s1/ses-s1/fmap/sub-s1_ses-s1_acq-3mm_phasediff.json') == ('s1', 's1')
     assert heudiconv._find_subj_ses('sub-s1/ses-s1/fmap/sub-s1_ses-s1_acq-3mm_phasediff.json') == ('s1', 's1')
-    assert heudiconv._find_subj_ses('fmap/sub-01-fmap_acq-3mm_acq-3mm_phasediff.nii.gz') == ('01', None)
+    assert heudiconv._find_subj_ses('fmap/sub-01-fmap_acq-3mm_acq-3mm_phasediff.nii.gz') == ('01', None)
+
+
+def test_make_readonly(tmpdir):
+    # we could test it all without torturing a poor file, but for going all
+    # the way, let's do it on a file
+    path = tmpdir.join('f')
+    pathname = str(path)
+    with open(pathname, 'w'):
+        pass
+    for orig, ro, rw in [
+        (0o600, 0o400, 0o600),  # fully returned
+        (0o624, 0o404, 0o606),  # it will not get write bit where it is not readable
+        (0o1777, 0o1555, 0o1777),  # and other bits should be preserved
+    ]:
+        os.chmod(pathname, orig)
+        assert heudiconv.set_readonly(pathname) == ro
+        assert stat.S_IMODE(os.lstat(pathname).st_mode) == ro
+        # and it should go back if we set it back to non-read_only
+        assert heudiconv.set_readonly(pathname, read_only=False) == rw