posix: always seek to EOF when opening a file in append mode
Python 3 already does this, so skip it there.
Consider the program:
#include <stdio.h>
int main() {
FILE *f = fopen("narf", "w");
fprintf(f, "narf\n");
fclose(f);
f = fopen("narf", "a");
printf("%ld\n", ftell(f));
fprintf(f, "troz\n");
printf("%ld\n", ftell(f));
return 0;
}
on macOS, FreeBSD, and Linux with glibc, this program prints
5
10
but on musl libc (Alpine Linux and probably others) this prints
0
10
By my reading of
https://pubs.opengroup.org/onlinepubs/
009695399/functions/fopen.html
this is technically correct, specifically:
> Opening a file with append mode (a as the first character in the
> mode argument) shall cause all subsequent writes to the file to be
> forced to the then current end-of-file, regardless of intervening
> calls to fseek().
in other words, the file position doesn't really matter in append-mode
files, and we can't depend on it being at all meaningful unless we
perform a seek() before tell() after open(..., 'a'). Experimentally
after a .write() we can do a .tell() and it'll always be reasonable,
but I'm unclear from reading the specification if that's a smart thing
to rely on. This matches what we do on Windows and what Python 3 does
for free, so let's just be consistent. Thanks to Yuya for the idea.
from __future__ import absolute_import, print_function
import os
import stat
import subprocess
import sys
if subprocess.call(['python', '%s/hghave' % os.environ['TESTDIR'],
'cacheable']):
sys.exit(80)
print_ = print
def print(*args, **kwargs):
"""print() wrapper that flushes stdout buffers to avoid py3 buffer issues
We could also just write directly to sys.stdout.buffer the way the
ui object will, but this was easier for porting the test.
"""
print_(*args, **kwargs)
sys.stdout.flush()
from mercurial import (
extensions,
hg,
localrepo,
pycompat,
ui as uimod,
util,
vfs as vfsmod,
)
if pycompat.ispy3:
xrange = range
class fakerepo(object):
def __init__(self):
self._filecache = {}
class fakevfs(object):
def join(self, p):
return p
vfs = fakevfs()
def unfiltered(self):
return self
def sjoin(self, p):
return p
@localrepo.repofilecache('x', 'y')
def cached(self):
print('creating')
return 'string from function'
def invalidate(self):
for k in self._filecache:
try:
delattr(self, pycompat.sysstr(k))
except AttributeError:
pass
def basic(repo):
print("* neither file exists")
# calls function
repo.cached
repo.invalidate()
print("* neither file still exists")
# uses cache
repo.cached
# create empty file
f = open('x', 'w')
f.close()
repo.invalidate()
print("* empty file x created")
# should recreate the object
repo.cached
f = open('x', 'w')
f.write('a')
f.close()
repo.invalidate()
print("* file x changed size")
# should recreate the object
repo.cached
repo.invalidate()
print("* nothing changed with either file")
# stats file again, reuses object
repo.cached
# atomic replace file, size doesn't change
# hopefully st_mtime doesn't change as well so this doesn't use the cache
# because of inode change
f = vfsmod.vfs(b'.')(b'x', b'w', atomictemp=True)
f.write(b'b')
f.close()
repo.invalidate()
print("* file x changed inode")
repo.cached
# create empty file y
f = open('y', 'w')
f.close()
repo.invalidate()
print("* empty file y created")
# should recreate the object
repo.cached
f = open('y', 'w')
f.write('A')
f.close()
repo.invalidate()
print("* file y changed size")
# should recreate the object
repo.cached
f = vfsmod.vfs(b'.')(b'y', b'w', atomictemp=True)
f.write(b'B')
f.close()
repo.invalidate()
print("* file y changed inode")
repo.cached
f = vfsmod.vfs(b'.')(b'x', b'w', atomictemp=True)
f.write(b'c')
f.close()
f = vfsmod.vfs(b'.')(b'y', b'w', atomictemp=True)
f.write(b'C')
f.close()
repo.invalidate()
print("* both files changed inode")
repo.cached
def fakeuncacheable():
def wrapcacheable(orig, *args, **kwargs):
return False
def wrapinit(orig, *args, **kwargs):
pass
originit = extensions.wrapfunction(util.cachestat, '__init__', wrapinit)
origcacheable = extensions.wrapfunction(util.cachestat, 'cacheable',
wrapcacheable)
for fn in ['x', 'y']:
try:
os.remove(fn)
except OSError:
pass
basic(fakerepo())
util.cachestat.cacheable = origcacheable
util.cachestat.__init__ = originit
def test_filecache_synced():
# test old behavior that caused filecached properties to go out of sync
os.system('hg init && echo a >> a && hg ci -qAm.')
repo = hg.repository(uimod.ui.load())
# first rollback clears the filecache, but changelog to stays in __dict__
repo.rollback()
repo.commit(b'.')
# second rollback comes along and touches the changelog externally
# (file is moved)
repo.rollback()
# but since changelog isn't under the filecache control anymore, we don't
# see that it changed, and return the old changelog without reconstructing
# it
repo.commit(b'.')
def setbeforeget(repo):
os.remove('x')
os.remove('y')
repo.__class__.cached.set(repo, 'string set externally')
repo.invalidate()
print("* neither file exists")
print(repo.cached)
repo.invalidate()
f = open('x', 'w')
f.write('a')
f.close()
print("* file x created")
print(repo.cached)
repo.__class__.cached.set(repo, 'string 2 set externally')
repo.invalidate()
print("* string set externally again")
print(repo.cached)
repo.invalidate()
f = open('y', 'w')
f.write('b')
f.close()
print("* file y created")
print(repo.cached)
def antiambiguity():
filename = 'ambigcheck'
# try some times, because reproduction of ambiguity depends on
# "filesystem time"
for i in xrange(5):
fp = open(filename, 'w')
fp.write('FOO')
fp.close()
oldstat = os.stat(filename)
if oldstat[stat.ST_CTIME] != oldstat[stat.ST_MTIME]:
# subsequent changing never causes ambiguity
continue
repetition = 3
# repeat changing via checkambigatclosing, to examine whether
# st_mtime is advanced multiple times as expected
for i in xrange(repetition):
# explicit closing
fp = vfsmod.checkambigatclosing(open(filename, 'a'))
fp.write('FOO')
fp.close()
# implicit closing by "with" statement
with vfsmod.checkambigatclosing(open(filename, 'a')) as fp:
fp.write('BAR')
newstat = os.stat(filename)
if oldstat[stat.ST_CTIME] != newstat[stat.ST_CTIME]:
# timestamp ambiguity was naturally avoided while repetition
continue
# st_mtime should be advanced "repetition * 2" times, because
# all changes occurred at same time (in sec)
expected = (oldstat[stat.ST_MTIME] + repetition * 2) & 0x7fffffff
if newstat[stat.ST_MTIME] != expected:
print("'newstat[stat.ST_MTIME] %s is not %s (as %s + %s * 2)" %
(newstat[stat.ST_MTIME], expected,
oldstat[stat.ST_MTIME], repetition))
# no more examination is needed regardless of result
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
print('basic:')
print()
basic(fakerepo())
print()
print('fakeuncacheable:')
print()
fakeuncacheable()
test_filecache_synced()
print()
print('setbeforeget:')
print()
setbeforeget(fakerepo())
print()
print('antiambiguity:')
print()
antiambiguity()