Merged revisions 77890 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/trunk

........
  r77890 | antoine.pitrou | 2010-01-31 23:26:04 +0100 (dim., 31 janv. 2010) | 7 lines

  - Issue #6939: Fix file I/O objects in the `io` module to keep the original
    file position when calling `truncate()`.  It would previously change the
    file position to the given argument, which goes against the tradition of
    ftruncate() and other truncation APIs.  Patch by Pascal Chambon.
........

12 files changed, 97 insertions, 47 deletions

diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index a4beb2b..8960ce9 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -856,7 +856,7 @@ class BytesIO(BufferedIOBase):
         elif pos < 0:
             raise ValueError("negative truncate position %r" % (pos,))
         del self._buffer[pos:]
-        return self.seek(pos)
+        return pos
 
     def readable(self):
         return True
@@ -1215,8 +1215,7 @@ class BufferedRandom(BufferedWriter, BufferedReader):
         if pos is None:
             pos = self.tell()
         # Use seek to flush the read buffer.
-        self.seek(pos)
-        return BufferedWriter.truncate(self)
+        return BufferedWriter.truncate(self, pos)
 
     def read(self, n=None):
         if n is None:
@@ -1717,8 +1716,7 @@ class TextIOWrapper(TextIOBase):
         self.flush()
         if pos is None:
             pos = self.tell()
-        self.seek(pos)
-        return self.buffer.truncate()
+        return self.buffer.truncate(pos)
 
     def detach(self):
         if self.buffer is None:
diff --git a/Lib/test/test_fileio.py b/Lib/test/test_fileio.py
index d35549f..8348f6e 100644
--- a/Lib/test/test_fileio.py
+++ b/Lib/test/test_fileio.py
@@ -328,6 +328,17 @@ class OtherFileTests(unittest.TestCase):
             f.close()
             self.fail("no error for invalid mode: %s" % bad_mode)
 
+    def testTruncate(self):
+        f = _FileIO(TESTFN, 'w')
+        f.write(bytes(bytearray(range(10))))
+        self.assertEqual(f.tell(), 10)
+        f.truncate(5)
+        self.assertEqual(f.tell(), 10)
+        self.assertEqual(f.seek(0, os.SEEK_END), 5)
+        f.truncate(15)
+        self.assertEqual(f.tell(), 5)
+        self.assertEqual(f.seek(0, os.SEEK_END), 15)
+
     def testTruncateOnWindows(self):
         def bug801631():
             # SF bug <http://www.python.org/sf/801631>
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index fd7f404..fe1a2b8 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -229,6 +229,11 @@ class IOTest(unittest.TestCase):
 
     def write_ops(self, f):
         self.assertEqual(f.write(b"blah."), 5)
+        f.truncate(0)
+        self.assertEqual(f.tell(), 5)
+        f.seek(0)
+
+        self.assertEqual(f.write(b"blah."), 5)
         self.assertEqual(f.seek(0), 0)
         self.assertEqual(f.write(b"Hello."), 6)
         self.assertEqual(f.tell(), 6)
@@ -239,8 +244,9 @@ class IOTest(unittest.TestCase):
         self.assertEqual(f.write(b"h"), 1)
         self.assertEqual(f.seek(-1, 2), 13)
         self.assertEqual(f.tell(), 13)
+
         self.assertEqual(f.truncate(12), 12)
-        self.assertEqual(f.tell(), 12)
+        self.assertEqual(f.tell(), 13)
         self.assertRaises(TypeError, f.seek, 0.0)
 
     def read_ops(self, f, buffered=False):
@@ -285,7 +291,7 @@ class IOTest(unittest.TestCase):
         self.assertEqual(f.tell(), self.LARGE + 2)
         self.assertEqual(f.seek(0, 2), self.LARGE + 2)
         self.assertEqual(f.truncate(self.LARGE + 1), self.LARGE + 1)
-        self.assertEqual(f.tell(), self.LARGE + 1)
+        self.assertEqual(f.tell(), self.LARGE + 2)
         self.assertEqual(f.seek(0, 2), self.LARGE + 1)
         self.assertEqual(f.seek(-1, 2), self.LARGE)
         self.assertEqual(f.read(2), b"x")
@@ -980,7 +986,7 @@ class BufferedWriterTest(unittest.TestCase, CommonBufferedTests):
             bufio = self.tp(raw, 8)
             bufio.write(b"abcdef")
             self.assertEqual(bufio.truncate(3), 3)
-            self.assertEqual(bufio.tell(), 3)
+            self.assertEqual(bufio.tell(), 6)
         with self.open(support.TESTFN, "rb", buffering=0) as f:
             self.assertEqual(f.read(), b"abc")
 
@@ -1366,6 +1372,14 @@ class BufferedRandomTest(BufferedReaderTest, BufferedWriterTest):
             self.assertEqual(s,
                 b"A" + b"B" * overwrite_size + b"A" * (9 - overwrite_size))
 
+    def test_truncate_after_read_or_write(self):
+        raw = self.BytesIO(b"A" * 10)
+        bufio = self.tp(raw, 100)
+        self.assertEqual(bufio.read(2), b"AA") # the read buffer gets filled
+        self.assertEqual(bufio.truncate(), 2)
+        self.assertEqual(bufio.write(b"BB"), 2) # the write buffer increases
+        self.assertEqual(bufio.truncate(), 4)
+
     def test_misbehaved_io(self):
         BufferedReaderTest.test_misbehaved_io(self)
         BufferedWriterTest.test_misbehaved_io(self)
diff --git a/Lib/test/test_largefile.py b/Lib/test/test_largefile.py
index 7fd3e0e..1c6297a 100644
--- a/Lib/test/test_largefile.py
+++ b/Lib/test/test_largefile.py
@@ -122,14 +122,14 @@ class LargeFileTest(unittest.TestCase):
             newsize -= 1
             f.seek(42)
             f.truncate(newsize)
-            self.assertEqual(f.tell(), newsize)  # else wasn't truncated
+            self.assertEqual(f.tell(), 42)
             f.seek(0, 2)
             self.assertEqual(f.tell(), newsize)
             # XXX truncate(larger than true size) is ill-defined
             # across platform; cut it waaaaay back
             f.seek(0)
             f.truncate(1)
-            self.assertEqual(f.tell(), 1)       # else pointer moved
+            self.assertEqual(f.tell(), 0)       # else pointer moved
             f.seek(0)
             self.assertEqual(len(f.read()), 1)  # else wasn't truncated
 
diff --git a/Lib/test/test_memoryio.py b/Lib/test/test_memoryio.py
index 9777631..99dfe6c 100644
--- a/Lib/test/test_memoryio.py
+++ b/Lib/test/test_memoryio.py
@@ -73,7 +73,7 @@ class MemoryTestMixin:
         self.assertEqual(f.seek(0), 0)
         self.assertEqual(f.write(t("h")), 1)
         self.assertEqual(f.truncate(12), 12)
-        self.assertEqual(f.tell(), 12)
+        self.assertEqual(f.tell(), 1)
 
     def test_write(self):
         buf = self.buftype("hello world\n")
@@ -121,7 +121,8 @@ class MemoryTestMixin:
         self.assertEqual(memio.getvalue(), buf[:6])
         self.assertEqual(memio.truncate(4), 4)
         self.assertEqual(memio.getvalue(), buf[:4])
-        self.assertEqual(memio.tell(), 4)
+        self.assertEqual(memio.tell(), 6)
+        memio.seek(0, 2)
         memio.write(buf)
         self.assertEqual(memio.getvalue(), buf[:4] + buf)
         pos = memio.tell()
diff --git a/Misc/ACKS b/Misc/ACKS
index 3ee0d9f..b991960 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -123,6 +123,7 @@ Donn Cave
 Charles Cazabon
 Per Cederqvist
 Octavian Cerna
+Pascal Chambon
 Hye-Shik Chang
 Jeffrey Chang
 Mitch Chapman
diff --git a/Misc/NEWS b/Misc/NEWS
index 0abe5c2..02cdfbe 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -239,6 +239,11 @@ C-API
 Library
 -------
 
+- Issue #6939: Fix file I/O objects in the `io` module to keep the original
+  file position when calling `truncate()`.  It would previously change the
+  file position to the given argument, which goes against the tradition of
+  ftruncate() and other truncation APIs.  Patch by Pascal Chambon.
+
 - Issue #7610: Reworked implementation of the internal
   :class:`zipfile.ZipExtFile` class used to represent files stored inside
   an archive.  The new implementation is significantly faster and can
diff --git a/Modules/_io/bytesio.c b/Modules/_io/bytesio.c
index 5ca878d..1482d82 100644
--- a/Modules/_io/bytesio.c
+++ b/Modules/_io/bytesio.c
@@ -412,7 +412,7 @@ PyDoc_STRVAR(truncate_doc,
 "truncate([size]) -> int.  Truncate the file to at most size bytes.\n"
 "\n"
 "Size defaults to the current file position, as returned by tell().\n"
-"Returns the new size.  Imply an absolute seek to the position size.");
+"The current file position is unchanged.  Returns the new size.\n");
 
 static PyObject *
 bytesio_truncate(bytesio *self, PyObject *args)
@@ -451,7 +451,6 @@ bytesio_truncate(bytesio *self, PyObject *args)
         if (resize_buffer(self, size) < 0)
             return NULL;
     }
-    self->pos = size;
 
     return PyLong_FromSsize_t(size);
 }
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index f02fe8a..a785e79 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -758,8 +758,10 @@ fileio_tell(fileio *self, PyObject *args)
 static PyObject *
 fileio_truncate(fileio *self, PyObject *args)
 {
-	PyObject *posobj = NULL;
+	PyObject *posobj = NULL; /* the new size wanted by the user */
+#ifndef MS_WINDOWS
 	Py_off_t pos;
+#endif
 	int ret;
 	int fd;
 
@@ -774,58 +776,86 @@ fileio_truncate(fileio *self, PyObject *args)
 
 	if (posobj == Py_None || posobj == NULL) {
 		/* Get the current position. */
-                posobj = portable_lseek(fd, NULL, 1);
-                if (posobj == NULL)
+		posobj = portable_lseek(fd, NULL, 1);
+		if (posobj == NULL)
 			return NULL;
-        }
-        else {
-		/* Move to the position to be truncated. */
-                posobj = portable_lseek(fd, posobj, 0);
-        }
-	if (posobj == NULL)
-		return NULL;
-
-#if defined(HAVE_LARGEFILE_SUPPORT)
-	pos = PyLong_AsLongLong(posobj);
-#else
-	pos = PyLong_AsLong(posobj);
-#endif
-	if (pos == -1 && PyErr_Occurred())
-		return NULL;
+	}
+	else {
+		Py_INCREF(posobj);
+	}
 
 #ifdef MS_WINDOWS
 	/* MS _chsize doesn't work if newsize doesn't fit in 32 bits,
 	   so don't even try using it. */
 	{
+		PyObject *oldposobj, *tempposobj;
 		HANDLE hFile;
+	
+		/* we save the file pointer position */
+		oldposobj = portable_lseek(fd, NULL, 1); 
+		if (oldposobj == NULL) {
+			Py_DECREF(posobj);
+			return NULL;
+		}
+
+		/* we then move to the truncation position */
+		tempposobj = portable_lseek(fd, posobj, 0);
+		if (tempposobj == NULL) {
+			Py_DECREF(oldposobj);
+			Py_DECREF(posobj);
+			return NULL;
+		}
+		Py_DECREF(tempposobj);
 
 		/* Truncate.  Note that this may grow the file! */
 		Py_BEGIN_ALLOW_THREADS
 		errno = 0;
 		hFile = (HANDLE)_get_osfhandle(fd);
-		ret = hFile == (HANDLE)-1;
+		ret = hFile == (HANDLE)-1; /* testing for INVALID_HANDLE value */
 		if (ret == 0) {
 			ret = SetEndOfFile(hFile) == 0;
 			if (ret)
 				errno = EACCES;
 		}
 		Py_END_ALLOW_THREADS
+
+		/* we restore the file pointer position in any case */
+		tempposobj = portable_lseek(fd, oldposobj, 0);
+		Py_DECREF(oldposobj);
+		if (tempposobj == NULL) {
+			Py_DECREF(posobj);
+			return NULL;
+		}
+		Py_DECREF(tempposobj);
 	}
 #else
+
+#if defined(HAVE_LARGEFILE_SUPPORT)
+	pos = PyLong_AsLongLong(posobj);
+#else
+	pos = PyLong_AsLong(posobj);
+#endif
+	if (PyErr_Occurred()){
+		Py_DECREF(posobj);
+		return NULL;
+	}
+
 	Py_BEGIN_ALLOW_THREADS
 	errno = 0;
 	ret = ftruncate(fd, pos);
 	Py_END_ALLOW_THREADS
+
 #endif /* !MS_WINDOWS */
 
 	if (ret != 0) {
+		Py_DECREF(posobj);
 		PyErr_SetFromErrno(PyExc_IOError);
 		return NULL;
 	}
 
 	return posobj;
 }
-#endif
+#endif /* HAVE_FTRUNCATE */
 
 static char *
 mode_string(fileio *self)
diff --git a/Modules/_io/iobase.c b/Modules/_io/iobase.c
index d4757ed..271a41e 100644
--- a/Modules/_io/iobase.c
+++ b/Modules/_io/iobase.c
@@ -102,8 +102,8 @@ iobase_tell(PyObject *self, PyObject *args)
 PyDoc_STRVAR(iobase_truncate_doc,
     "Truncate file to size bytes.\n"
     "\n"
-    "Size defaults to the current IO position as reported by tell().  Return\n"
-    "the new size.");
+    "File pointer is left unchanged.  Size defaults to the current IO\n"
+    "position as reported by tell().  Returns the new size.");
 
 static PyObject *
 iobase_truncate(PyObject *self, PyObject *args)
diff --git a/Modules/_io/stringio.c b/Modules/_io/stringio.c
index c19c4c0..13e3b58 100644
--- a/Modules/_io/stringio.c
+++ b/Modules/_io/stringio.c
@@ -350,7 +350,7 @@ PyDoc_STRVAR(stringio_truncate_doc,
     "Truncate size to pos.\n"
     "\n"
     "The pos argument defaults to the current file position, as\n"
-    "returned by tell().  Imply an absolute seek to pos.\n"
+    "returned by tell().  The current file position is unchanged.\n"
     "Returns the new absolute position.\n");
 
 static PyObject *
@@ -390,7 +390,6 @@ stringio_truncate(stringio *self, PyObject *args)
             return NULL;
         self->string_size = size;
     }
-    self->pos = size;
 
     return PyLong_FromSsize_t(size);
 }
diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
index ba28d59..89d922c 100644
--- a/Modules/_io/textio.c
+++ b/Modules/_io/textio.c
@@ -2318,15 +2318,7 @@ textiowrapper_truncate(textio *self, PyObject *args)
         return NULL;
     Py_DECREF(res);
 
-    if (pos != Py_None) {
-        res = PyObject_CallMethodObjArgs((PyObject *) self,
-                                          _PyIO_str_seek, pos, NULL);
-        if (res == NULL)
-            return NULL;
-        Py_DECREF(res);
-    }
-
-    return PyObject_CallMethodObjArgs(self->buffer, _PyIO_str_truncate, NULL);
+    return PyObject_CallMethodObjArgs(self->buffer, _PyIO_str_truncate, pos, NULL);
 }
 
 static PyObject *