#6077: on Windows, fix truncation of a tempfile.TemporaryFile opened in "wt+" mode:

files opened with os.open() stop on the first \x1a (Ctrl-Z) unless os.O_BINARY is used.

Will backport to 3.1

Lib/tempfile.py

@@ -169,7 +169,6 @@ def _get_default_tempdir():
 
     namer = _RandomNameSequence()
     dirlist = _candidate_tempdir_list()
-    flags = _text_openflags
 
     for dir in dirlist:
         if dir != _os.curdir:
@@ -179,7 +178,7 @@ def _get_default_tempdir():
             name = next(namer)
             filename = _os.path.join(dir, name)
             try:
-                fd = _os.open(filename, flags, 0o600)
+                fd = _os.open(filename, _bin_openflags, 0o600)
                 fp = _io.open(fd, 'wb')
                 fp.write(b'blat')
                 fp.close()
@@ -434,10 +433,7 @@ def NamedTemporaryFile(mode='w+b', buffering=-1, encoding=None,
     if dir is None:
         dir = gettempdir()
 
-    if 'b' in mode:
-        flags = _bin_openflags
-    else:
-        flags = _text_openflags
+    flags = _bin_openflags
 
     # Setting O_TEMPORARY in the flags causes the OS to delete
     # the file when it is closed.  This is only supported by Windows.
@@ -475,10 +471,7 @@ else:
         if dir is None:
             dir = gettempdir()
 
-        if 'b' in mode:
-            flags = _bin_openflags
-        else:
-            flags = _text_openflags
+        flags = _bin_openflags
 
         (fd, name) = _mkstemp_inner(dir, prefix, suffix, flags)
         try:

Lib/test/test_tempfile.py

@@ -309,8 +309,12 @@ class test__mkstemp_inner(TC):
         if not has_textmode:
             return            # ugh, can't use SkipTest.
 
-        self.do_create(bin=0).write(b"blat\n")
-        # XXX should test that the file really is a text file
+        # A text file is truncated at the first Ctrl+Z byte
+        f = self.do_create(bin=0)
+        f.write(b"blat\x1a")
+        f.write(b"extra\n")
+        os.lseek(f.fd, 0, os.SEEK_SET)
+        self.assertEquals(os.read(f.fd, 20), b"blat")
 
 test_classes.append(test__mkstemp_inner)
 
@@ -761,6 +765,10 @@ class test_SpooledTemporaryFile(TC):
         f.write("xyzzy\n")
         f.seek(0)
         self.assertEqual(f.read(), "abc\ndef\nxyzzy\n")
+        # Check that Ctrl+Z doesn't truncate the file
+        f.write("foo\x1abar\n")
+        f.seek(0)
+        self.assertEqual(f.read(), "abc\ndef\nxyzzy\nfoo\x1abar\n")
 
     def test_text_newline_and_encoding(self):
         f = tempfile.SpooledTemporaryFile(mode='w+', max_size=10,

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 3.2 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #6077: On Windows, files opened with tempfile.TemporaryFile in "wt+"
+  mode would appear truncated on the first '0x1a' byte (aka. Ctrl+Z).
+
 - Issue #7085: Fix crash when importing some extensions in a thread
   on MacOSX 10.6.