view tests/test-atomictempfile.py @ 40056:324b4b10351e

revlog: rewrite censoring logic

I was able to corrupt a revlog relatively easily with the existing
censoring code. The underlying problem is that the existing code
doesn't fully take delta chains into account. When copying revisions
that occur after the censored revision, the delta base can refer
to a censored revision. Then at read time, things blow up due to the
revision data not being a compressed delta.

This commit rewrites the revlog censoring code to take a higher-level
approach. We now create a new revlog instance pointing at temp files.
We iterate through each revision in the source revlog and insert
those revisions into the new revlog, replacing the censored revision's
data along the way.

The new implementation isn't as efficient as the old one. This is
because it will fully engage delta computation on insertion. But I
don't think it matters.

The new implementation is a bit hacky because it attempts to reload
the revlog instance with a new revlog index/data file. This is fragile.
But this is needed because the index (which could be backed by C) would
have a cached copy of the old, possibly changed data and that could
lead to problems accessing index or revision data later.

One benefit of the new approach is that we integrate with the
transaction. The old revlog is backed up and if the transaction is
rolled back, the original revlog is restored.

As part of this, we had to teach the transaction about the store
vfs. I'm not super keen about this. But this was the easiest way
to hook things up to the transaction. We /could/ just ignore the
transaction like we were doing before. But any file mutation should
be governed by transaction semantics, including undo during rollback.

Differential Revision: https://phab.mercurial-scm.org/D4869

from __future__ import absolute_import

import glob
import os
import shutil
import stat
import tempfile
import unittest

from mercurial import (
    pycompat,
    util,
)
atomictempfile = util.atomictempfile

if pycompat.ispy3:
    xrange = range

class testatomictempfile(unittest.TestCase):
    def setUp(self):
        self._testdir = tempfile.mkdtemp(b'atomictempfiletest')
        self._filename = os.path.join(self._testdir, b'testfilename')

    def tearDown(self):
        shutil.rmtree(self._testdir, True)

    def testsimple(self):
        file = atomictempfile(self._filename)
        self.assertFalse(os.path.isfile(self._filename))
        tempfilename = file._tempname
        self.assertTrue(tempfilename in glob.glob(
            os.path.join(self._testdir, b'.testfilename-*')))

        file.write(b'argh\n')
        file.close()

        self.assertTrue(os.path.isfile(self._filename))
        self.assertTrue(tempfilename not in glob.glob(
            os.path.join(self._testdir, b'.testfilename-*')))

    # discard() removes the temp file without making the write permanent
    def testdiscard(self):
        file = atomictempfile(self._filename)
        (dir, basename) = os.path.split(file._tempname)

        file.write(b'yo\n')
        file.discard()

        self.assertFalse(os.path.isfile(self._filename))
        self.assertTrue(basename not in os.listdir(b'.'))

    # if a programmer screws up and passes bad args to atomictempfile, they
    # get a plain ordinary TypeError, not infinite recursion
    def testoops(self):
        with self.assertRaises(TypeError):
            atomictempfile()

    # checkambig=True avoids ambiguity of timestamp
    def testcheckambig(self):
        def atomicwrite(checkambig):
            f = atomictempfile(self._filename, checkambig=checkambig)
            f.write(b'FOO')
            f.close()

        # try some times, because reproduction of ambiguity depends on
        # "filesystem time"
        for i in xrange(5):
            atomicwrite(False)
            oldstat = os.stat(self._filename)
            if oldstat[stat.ST_CTIME] != oldstat[stat.ST_MTIME]:
                # subsequent changing never causes ambiguity
                continue

            repetition = 3

            # repeat atomic write with checkambig=True, to examine
            # whether st_mtime is advanced multiple times as expected
            for j in xrange(repetition):
                atomicwrite(True)
            newstat = os.stat(self._filename)
            if oldstat[stat.ST_CTIME] != newstat[stat.ST_CTIME]:
                # timestamp ambiguity was naturally avoided while repetition
                continue

            # st_mtime should be advanced "repetition" times, because
            # all atomicwrite() occurred at same time (in sec)
            oldtime = (oldstat[stat.ST_MTIME] + repetition) & 0x7fffffff
            self.assertTrue(newstat[stat.ST_MTIME] == oldtime)
            # no more examination is needed, if assumption above is true
            break
        else:
            # This platform seems too slow to examine anti-ambiguity
            # of file timestamp (or test happened to be executed at
            # bad timing). Exit silently in this case, because running
            # on other faster platforms can detect problems
            pass

    def testread(self):
        with open(self._filename, 'wb') as f:
            f.write(b'foobar\n')
        file = atomictempfile(self._filename, mode=b'rb')
        self.assertTrue(file.read(), b'foobar\n')
        file.discard()

    def testcontextmanagersuccess(self):
        """When the context closes, the file is closed"""
        with atomictempfile(b'foo') as f:
            self.assertFalse(os.path.isfile(b'foo'))
            f.write(b'argh\n')
        self.assertTrue(os.path.isfile(b'foo'))

    def testcontextmanagerfailure(self):
        """On exception, the file is discarded"""
        try:
            with atomictempfile(b'foo') as f:
                self.assertFalse(os.path.isfile(b'foo'))
                f.write(b'argh\n')
                raise ValueError
        except ValueError:
            pass
        self.assertFalse(os.path.isfile(b'foo'))

if __name__ == '__main__':
    import silenttestrunner
    silenttestrunner.main(__name__)