From e4db231760c11037126a5dfeff35d3ca40c970ed Mon Sep 17 00:00:00 2001
From: Silas Sewell <silas@sewell.org>
Date: Thu, 23 Aug 2018 09:02:38 -0400
Subject: [PATCH] bpo-34472: Add data descriptor signature to zipfile (GH-8871)

This makes streamed zips compatible with MacOS Archive Utility and
other applications.
---
 Lib/zipfile.py                                              | 6 ++++--
 Misc/ACKS                                                   | 1 +
 .../next/Library/2018-08-23-09-25-08.bpo-34472.cGyYrO.rst   | 3 +++
 3 files changed, 8 insertions(+), 2 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2018-08-23-09-25-08.bpo-34472.cGyYrO.rst

diff --git a/Lib/zipfile.py b/Lib/zipfile.py
index 89df90b25209f8..4a6b40ee441c6f 100644
--- a/Lib/zipfile.py
+++ b/Lib/zipfile.py
@@ -159,6 +159,8 @@ class LargeZipFile(Exception):
 _CD64_DIRECTORY_SIZE = 8
 _CD64_OFFSET_START_CENTDIR = 9
 
+_DD_SIGNATURE = 0x08074b50
+
 _EXTRA_FIELD_STRUCT = struct.Struct('<HH')
 
 def _strip_extra(extra, xids):
@@ -1118,8 +1120,8 @@ def close(self):
         # Write updated header info
         if self._zinfo.flag_bits & 0x08:
             # Write CRC and file sizes after the file data
-            fmt = '<LQQ' if self._zip64 else '<LLL'
-            self._fileobj.write(struct.pack(fmt, self._zinfo.CRC,
+            fmt = '<LLQQ' if self._zip64 else '<LLLL'
+            self._fileobj.write(struct.pack(fmt, _DD_SIGNATURE, self._zinfo.CRC,
                 self._zinfo.compress_size, self._zinfo.file_size))
             self._zipfile.start_dir = self._fileobj.tell()
         else:
diff --git a/Misc/ACKS b/Misc/ACKS
index a29ff6020bbfc3..96563f62a1a860 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1468,6 +1468,7 @@ Roger D. Serwy
 Jerry Seutter
 Pete Sevander
 Denis Severson
+Silas Sewell
 Ian Seyer
 Dmitry Shachnev
 Anish Shah
diff --git a/Misc/NEWS.d/next/Library/2018-08-23-09-25-08.bpo-34472.cGyYrO.rst b/Misc/NEWS.d/next/Library/2018-08-23-09-25-08.bpo-34472.cGyYrO.rst
new file mode 100644
index 00000000000000..208ec0bf7431e4
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-08-23-09-25-08.bpo-34472.cGyYrO.rst
@@ -0,0 +1,3 @@
+Improved compatibility for streamed files in :mod:`zipfile`. Previously an
+optional signature was not being written and certain ZIP applications were
+not supported. Patch by Silas Sewell.