Skip to content

C
cpython
Commit f1827cfa authored by Tim Peters's avatar Tim Peters
Browse files
Options

SF bug 801631: file.truncate fault on windows. 

file_truncate():  C doesn't define what fflush(fp) does if fp is open
for update, and the preceding I/O operation on fp was input.  On Windows,
fflush() actually changes the current file position then.  Because
Windows doesn't support ftruncate() directly, this not only caused
Python's file.truncate() to change the file position (contra our docs),
it also caused the file not to change size.

Repaired by getting the initial file position at the start, restoring
it at the end, and tossing all the complicated micro-efficiency checks
trying to avoid "provably unnecessary" seeks.  file.truncate() can't
be a frequent operation, and seeking to the current file position has
got to be cheap anyway.

Bugfix candidate.
parent a26c16c8
Hide whitespace changes
Inline Side-by-side
Showing with 98 additions and 74 deletions
Lib/test/test_file.py
View file @ f1827cfa
......@@ -132,3 +132,31 @@ else:
raise TestFailed, 'file.writelines([]) on a closed file should raise a ValueError'
os.unlink(TESTFN)
def bug801631():
# SF bug <http://www.python.org/sf/801631>
# "file.truncate fault on windows"
f = file(TESTFN, 'wb')
f.write('12345678901') # 11 bytes
f.close()
f = file(TESTFN,'rb+')
data = f.read(5)
if data != '12345':
raise TestFailed("Read on file opened for update failed %r" % data)
if f.tell() != 5:
raise TestFailed("File pos after read wrong %d" % f.tell())
f.truncate()
if f.tell() != 5:
raise TestFailed("File pos after ftruncate wrong %d" % f.tell())
f.close()
size = os.path.getsize(TESTFN)
if size != 5:
raise TestFailed("File size after ftruncate wrong %d" % size)
try:
bug801631()
finally:
os.unlink(TESTFN)
Misc/NEWS
View file @ f1827cfa
......@@ -94,6 +94,10 @@ Tests
Windows
-------
- file.truncate() could misbehave if the file was open for update
(modes r+, rb+, w+, wb+), and the most recent file operation before
the truncate() call was an input operation. SF bug 801631.
Mac
----
......
Objects/fileobject.c
View file @ f1827cfa
......@@ -96,7 +96,7 @@ dircheck(PyFileObject* f)
#else
char *msg = "Is a directory";
#endif
PyObject *exc = PyObject_CallFunction(PyExc_IOError, "(is)",
PyObject *exc = PyObject_CallFunction(PyExc_IOError, "(is)",
EISDIR, msg);
PyErr_SetObject(PyExc_IOError, exc);
Py_XDECREF(exc);
......@@ -137,7 +137,7 @@ fill_file_fields(PyFileObject *f, FILE *fp, char *name, char *mode,
#endif
Py_INCREF(Py_None);
f->f_encoding = Py_None;
if (f->f_name == NULL || f->f_mode == NULL)
return NULL;
f->f_fp = fp;
......@@ -189,8 +189,8 @@ open_the_file(PyFileObject *f, char *name, char *mode)
#endif
#ifdef MS_WINDOWS
if (PyUnicode_Check(f->f_name)) {
PyObject *wmode;
wmode = PyUnicode_DecodeASCII(mode, strlen(mode), NULL);
PyObject *wmode;
wmode = PyUnicode_DecodeASCII(mode, strlen(mode), NULL);
if (f->f_name && wmode) {
Py_BEGIN_ALLOW_THREADS
/* PyUnicode_AS_UNICODE OK without thread
......@@ -529,18 +529,33 @@ file_seek(PyFileObject *f, PyObject *args)
static PyObject *
file_truncate(PyFileObject *f, PyObject *args)
{
int ret;
Py_off_t newsize;
PyObject *newsizeobj;
PyObject *newsizeobj = NULL;
Py_off_t initialpos;
int ret;
if (f->f_fp == NULL)
return err_closed();
newsizeobj = NULL;
if (!PyArg_UnpackTuple(args, "truncate", 0, 1, &newsizeobj))
return NULL;
/* Get current file position. If the file happens to be open for
* update and the last operation was an input operation, C doesn't
* define what the later fflush() will do, but we promise truncate()
* won't change the current position (and fflush() *does* change it
* then at least on Windows). The easiest thing is to capture
* current pos now and seek back to it at the end.
*/
Py_BEGIN_ALLOW_THREADS
errno = 0;
initialpos = _portable_ftell(f->f_fp);
Py_END_ALLOW_THREADS
if (initialpos == -1)
goto onioerror;
/* Set newsize to current postion if newsizeobj NULL, else to the
specified value. */
* specified value.
*/
if (newsizeobj != NULL) {
#if !defined(HAVE_LARGEFILE_SUPPORT)
newsize = PyInt_AsLong(newsizeobj);
......@@ -552,17 +567,13 @@ file_truncate(PyFileObject *f, PyObject *args)
if (PyErr_Occurred())
return NULL;
}
else {
/* Default to current position. */
Py_BEGIN_ALLOW_THREADS
errno = 0;
newsize = _portable_ftell(f->f_fp);
Py_END_ALLOW_THREADS
if (newsize == -1)
goto onioerror;
}
else /* default to current position */
newsize = initialpos;
/* Flush the file. */
/* Flush the stream. We're mixing stream-level I/O with lower-level
* I/O, and a flush may be necessary to synch both platform views
* of the current file state.
*/
Py_BEGIN_ALLOW_THREADS
errno = 0;
ret = fflush(f->f_fp);
......@@ -574,66 +585,47 @@ file_truncate(PyFileObject *f, PyObject *args)
/* MS _chsize doesn't work if newsize doesn't fit in 32 bits,
so don't even try using it. */
{
Py_off_t current; /* current file position */
HANDLE hFile;
int error;
/* current <- current file postion. */
if (newsizeobj == NULL)
current = newsize;
else {
Py_BEGIN_ALLOW_THREADS
errno = 0;
current = _portable_ftell(f->f_fp);
Py_END_ALLOW_THREADS
if (current == -1)
goto onioerror;
}
/* Move to newsize. */
if (current != newsize) {
Py_BEGIN_ALLOW_THREADS
errno = 0;
error = _portable_fseek(f->f_fp, newsize, SEEK_SET)
!= 0;
Py_END_ALLOW_THREADS
if (error)
goto onioerror;
}
/* Have to move current pos to desired endpoint on Windows. */
Py_BEGIN_ALLOW_THREADS
errno = 0;
ret = _portable_fseek(f->f_fp, newsize, SEEK_SET) != 0;
Py_END_ALLOW_THREADS
if (ret)
goto onioerror;
/* Truncate. Note that this may grow the file! */
Py_BEGIN_ALLOW_THREADS
errno = 0;
hFile = (HANDLE)_get_osfhandle(fileno(f->f_fp));
error = hFile == (HANDLE)-1;
if (!error) {
error = SetEndOfFile(hFile) == 0;
if (error)
ret = hFile == (HANDLE)-1;
if (ret == 0) {
ret = SetEndOfFile(hFile) == 0;
if (ret)
errno = EACCES;
}
Py_END_ALLOW_THREADS
if (error)
if (ret)
goto onioerror;
/* Restore original file position. */
if (current != newsize) {
Py_BEGIN_ALLOW_THREADS
errno = 0;
error = _portable_fseek(f->f_fp, current, SEEK_SET)
!= 0;
Py_END_ALLOW_THREADS
if (error)
goto onioerror;
}
}
#else
Py_BEGIN_ALLOW_THREADS
errno = 0;
ret = ftruncate(fileno(f->f_fp), newsize);
Py_END_ALLOW_THREADS
if (ret != 0) goto onioerror;
if (ret != 0)
goto onioerror;
#endif /* !MS_WINDOWS */
/* Restore original file position. */
Py_BEGIN_ALLOW_THREADS
errno = 0;
ret = _portable_fseek(f->f_fp, initialpos, SEEK_SET) != 0;
Py_END_ALLOW_THREADS
if (ret)
goto onioerror;
Py_INCREF(Py_None);
return Py_None;
......@@ -866,7 +858,7 @@ file_readinto(PyFileObject *f, PyObject *args)
while (ntodo > 0) {
Py_BEGIN_ALLOW_THREADS
errno = 0;
nnow = Py_UniversalNewlineFread(ptr+ndone, ntodo, f->f_fp,
nnow = Py_UniversalNewlineFread(ptr+ndone, ntodo, f->f_fp,
(PyObject *)f);
Py_END_ALLOW_THREADS
if (nnow == 0) {
......@@ -1137,8 +1129,8 @@ get_line(PyFileObject *f, int n)
if (skipnextlf ) {
skipnextlf = 0;
if (c == '\n') {
/* Seeing a \n here with
* skipnextlf true means we
/* Seeing a \n here with
* skipnextlf true means we
* saw a \r before.
*/
newlinetypes |= NEWLINE_CRLF;
......@@ -1734,8 +1726,8 @@ get_newlines(PyFileObject *f, void *closure)
case NEWLINE_CR|NEWLINE_LF|NEWLINE_CRLF:
return Py_BuildValue("(sss)", "\r", "\n", "\r\n");
default:
PyErr_Format(PyExc_SystemError,
"Unknown newlines value 0x%x\n",
PyErr_Format(PyExc_SystemError,
"Unknown newlines value 0x%x\n",
f->f_newlinetypes);
return NULL;
}
......@@ -1745,7 +1737,7 @@ get_newlines(PyFileObject *f, void *closure)
static PyGetSetDef file_getsetlist[] = {
{"closed", (getter)get_closed, NULL, "True if the file is closed"},
#ifdef WITH_UNIVERSAL_NEWLINES
{"newlines", (getter)get_newlines, NULL,
{"newlines", (getter)get_newlines, NULL,
"end-of-line convention used in this file"},
#endif
{0},
......@@ -1760,8 +1752,8 @@ drop_readahead(PyFileObject *f)
}
}
/* Make sure that file has a readahead buffer with at least one byte
(unless at EOF) and no more than bufsize. Returns negative value on
/* Make sure that file has a readahead buffer with at least one byte
(unless at EOF) and no more than bufsize. Returns negative value on
error */
static int
readahead(PyFileObject *f, int bufsize)
......@@ -1769,7 +1761,7 @@ readahead(PyFileObject *f, int bufsize)
int chunksize;
if (f->f_buf != NULL) {
if( (f->f_bufend - f->f_bufptr) >= 1)
if( (f->f_bufend - f->f_bufptr) >= 1)
return 0;
else
drop_readahead(f);
......@@ -1796,8 +1788,8 @@ readahead(PyFileObject *f, int bufsize)
}
/* Used by file_iternext. The returned string will start with 'skip'
uninitialized bytes followed by the remainder of the line. Don't be
horrified by the recursive call: maximum recursion depth is limited by
uninitialized bytes followed by the remainder of the line. Don't be
horrified by the recursive call: maximum recursion depth is limited by
logarithmic buffer growth to about 50 even when reading a 1gb line. */
static PyStringObject *
......@@ -1809,11 +1801,11 @@ readahead_get_line_skip(PyFileObject *f, int skip, int bufsize)
int len;
if (f->f_buf == NULL)
if (readahead(f, bufsize) < 0)
if (readahead(f, bufsize) < 0)
return NULL;
len = f->f_bufend - f->f_bufptr;
if (len == 0)
if (len == 0)
return (PyStringObject *)
PyString_FromStringAndSize(NULL, skip);
bufptr = memchr(f->f_bufptr, '\n', len);
......@@ -1822,7 +1814,7 @@ readahead_get_line_skip(PyFileObject *f, int skip, int bufsize)
len = bufptr - f->f_bufptr;
s = (PyStringObject *)
PyString_FromStringAndSize(NULL, skip+len);
if (s == NULL)
if (s == NULL)
return NULL;
memcpy(PyString_AS_STRING(s)+skip, f->f_bufptr, len);
f->f_bufptr = bufptr;
......@@ -2079,7 +2071,7 @@ PyFile_WriteObject(PyObject *v, PyObject *f, int flags)
return -1;
}
#ifdef Py_USING_UNICODE
if ((flags & Py_PRINT_RAW) &&
if ((flags & Py_PRINT_RAW) &&
PyUnicode_Check(v) && enc != Py_None) {
char *cenc = PyString_AS_STRING(enc);
value = PyUnicode_AsEncodedString(v, cenc, "strict");
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment
GitLab Nexedi Edition | About GitLab | About Nexedi | 沪ICP备2021021310号-2 | 沪ICP备2021021310号-7