From 0e86a5842d0fadff37c299e8a1c03535c6727b19 Mon Sep 17 00:00:00 2001
From: Antoine Pitrou <solipsis@pitrou.net>
Date: Fri, 25 Nov 2011 18:03:09 +0100
Subject: [PATCH] Issue #9957: SpooledTemporaryFile.truncate() now accepts an
 optional size parameter, as other file-like objects. Patch by Ryan Kelly.

---
 Lib/tempfile.py           |  9 +++++++--
 Lib/test/test_tempfile.py | 21 +++++++++++++++++++++
 Misc/NEWS                 |  4 +++-
 3 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/Lib/tempfile.py b/Lib/tempfile.py
index 3ec6b4a3da9..e3afa3b0ac0 100644
--- a/Lib/tempfile.py
+++ b/Lib/tempfile.py
@@ -578,8 +578,13 @@ class SpooledTemporaryFile:
     def tell(self):
         return self._file.tell()
 
-    def truncate(self):
-        self._file.truncate()
+    def truncate(self, size=None):
+        if size is None:
+            self._file.truncate()
+        else:
+            if size > self._max_size:
+                self.rollover()
+            self._file.truncate(size)
 
     def write(self, s):
         file = self._file
diff --git a/Lib/test/test_tempfile.py b/Lib/test/test_tempfile.py
index 014fca01a99..5b0bca797e9 100644
--- a/Lib/test/test_tempfile.py
+++ b/Lib/test/test_tempfile.py
@@ -846,6 +846,27 @@ class test_SpooledTemporaryFile(TC):
                 pass
         self.assertRaises(ValueError, use_closed)
 
+    def test_truncate_with_size_parameter(self):
+        # A SpooledTemporaryFile can be truncated to zero size
+        f = tempfile.SpooledTemporaryFile(max_size=10)
+        f.write(b'abcdefg\n')
+        f.seek(0)
+        f.truncate()
+        self.assertFalse(f._rolled)
+        self.assertEqual(f._file.getvalue(), b'')
+        # A SpooledTemporaryFile can be truncated to a specific size
+        f = tempfile.SpooledTemporaryFile(max_size=10)
+        f.write(b'abcdefg\n')
+        f.truncate(4)
+        self.assertFalse(f._rolled)
+        self.assertEqual(f._file.getvalue(), b'abcd')
+        # A SpooledTemporaryFile rolls over if truncated to large size
+        f = tempfile.SpooledTemporaryFile(max_size=10)
+        f.write(b'abcdefg\n')
+        f.truncate(20)
+        self.assertTrue(f._rolled)
+        if has_stat:
+            self.assertEqual(os.fstat(f.fileno()).st_size, 20)
 
 test_classes.append(test_SpooledTemporaryFile)
 
diff --git a/Misc/NEWS b/Misc/NEWS
index f78a31eec70..93169e4608b 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -386,10 +386,12 @@ Core and Builtins
 - Issue #12380: The rjust, ljust and center methods of bytes and bytearray
   now accept a bytearray argument.
 
-
 Library
 -------
 
+- Issue #9957: SpooledTemporaryFile.truncate() now accepts an optional size
+  parameter, as other file-like objects.  Patch by Ryan Kelly.
+
 - Issue #13458: Fix a memory leak in the ssl module when decoding a
   certificate with a subjectAltName.  Patch by Robert Xiao.