From f689f104aa89b2dc01e2ee259de8f5d3db3bdb95 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 23 Mar 2015 15:25:18 +0200
Subject: [PATCH] Issue #21560: An attempt to write a data of wrong type no
 longer cause GzipFile corruption.  Original patch by Wolfgang Maier.

---
 Lib/gzip.py           |  4 ++--
 Lib/test/test_gzip.py | 27 +++++++++++++++++++++++++++
 Misc/NEWS             |  3 +++
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/Lib/gzip.py b/Lib/gzip.py
index 49566fd242..83cc0773d7 100644
--- a/Lib/gzip.py
+++ b/Lib/gzip.py
@@ -238,9 +238,9 @@ class GzipFile(io.BufferedIOBase):
             data = data.tobytes()
 
         if len(data) > 0:
-            self.size = self.size + len(data)
+            self.fileobj.write(self.compress.compress(data))
+            self.size += len(data)
             self.crc = zlib.crc32(data, self.crc) & 0xffffffffL
-            self.fileobj.write( self.compress.compress(data) )
             self.offset += len(data)
 
         return len(data)
diff --git a/Lib/test/test_gzip.py b/Lib/test/test_gzip.py
index 7f24981ed4..41857c7f83 100644
--- a/Lib/test/test_gzip.py
+++ b/Lib/test/test_gzip.py
@@ -30,6 +30,14 @@ class TestGzip(unittest.TestCase):
     def tearDown(self):
         test_support.unlink(self.filename)
 
+    def write_and_read_back(self, data, mode='b'):
+        b_data = memoryview(data).tobytes()
+        with gzip.GzipFile(self.filename, 'w'+mode) as f:
+            l = f.write(data)
+        self.assertEqual(l, len(b_data))
+        with gzip.GzipFile(self.filename, 'r'+mode) as f:
+            self.assertEqual(f.read(), b_data)
+
     @test_support.requires_unicode
     def test_unicode_filename(self):
         unicode_filename = test_support.TESTFN_UNICODE
@@ -60,6 +68,25 @@ class TestGzip(unittest.TestCase):
         # Test multiple close() calls.
         f.close()
 
+    # The following test_write_xy methods test that write accepts
+    # the corresponding bytes-like object type as input
+    # and that the data written equals bytes(xy) in all cases.
+    def test_write_memoryview(self):
+        self.write_and_read_back(memoryview(data1 * 50))
+
+    def test_write_incompatible_type(self):
+        # Test that non-bytes-like types raise TypeError.
+        # Issue #21560: attempts to write incompatible types
+        # should not affect the state of the fileobject
+        with gzip.GzipFile(self.filename, 'wb') as f:
+            with self.assertRaises(UnicodeEncodeError):
+                f.write(u'\xff')
+            with self.assertRaises(TypeError):
+                f.write([1])
+            f.write(data1)
+        with gzip.GzipFile(self.filename, 'rb') as f:
+            self.assertEqual(f.read(), data1)
+
     def test_read(self):
         self.test_write()
         # Try reading.
diff --git a/Misc/NEWS b/Misc/NEWS
index 761f2fb07f..052e55cd77 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -21,6 +21,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #21560: An attempt to write a data of wrong type no longer cause
+  GzipFile corruption.  Original patch by Wolfgang Maier.
+
 - Issue #23647: Increase impalib's MAXLINE to accommodate modern mailbox sizes.
 
 - Issue #23539: If body is None, http.client.HTTPConnection.request now sets
-- 
2.50.1