From 29034baf58156e2462b0680e9092c0a3cccb0798 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Tue, 18 Sep 2018 23:28:34 +0300
Subject: [PATCH] [2.7] bpo-34341: Fix appending to ZIP archives with the ZIP64
 extension. (GH-8683). (GH-9400)

(cherry picked from commit 9bdb7be482aef8f60daa1d36606568a132dcb616)
---
 Lib/test/test_zipfile.py                      | 14 ++++++++++++
 Lib/zipfile.py                                | 22 +++++++++++++++++++
 .../2018-08-06-11-01-18.bpo-34341.E0b9p2.rst  |  2 ++
 3 files changed, 38 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2018-08-06-11-01-18.bpo-34341.E0b9p2.rst

diff --git a/Lib/test/test_zipfile.py b/Lib/test/test_zipfile.py
index 9c63aebbbe0e..4e545f140a83 100644
--- a/Lib/test/test_zipfile.py
+++ b/Lib/test/test_zipfile.py
@@ -812,6 +812,20 @@ class TestZip64InSmallFiles(unittest.TestCase):
             self.assertEqual(content, "%d" % (i**3 % 57))
         zipf2.close()
 
+    def test_append(self):
+        # Test that appending to the Zip64 archive doesn't change
+        # extra fields of existing entries.
+        with zipfile.ZipFile(TESTFN2, "w", allowZip64=True) as zipfp:
+            zipfp.writestr("strfile", self.data)
+        with zipfile.ZipFile(TESTFN2, "r", allowZip64=True) as zipfp:
+            zinfo = zipfp.getinfo("strfile")
+            extra = zinfo.extra
+        with zipfile.ZipFile(TESTFN2, "a", allowZip64=True) as zipfp:
+            zipfp.writestr("strfile2", self.data)
+        with zipfile.ZipFile(TESTFN2, "r", allowZip64=True) as zipfp:
+            zinfo = zipfp.getinfo("strfile")
+            self.assertEqual(zinfo.extra, extra)
+
     def tearDown(self):
         zipfile.ZIP64_LIMIT = self._limit
         zipfile.ZIP_FILECOUNT_LIMIT = self._filecount_limit
diff --git a/Lib/zipfile.py b/Lib/zipfile.py
index 3ab66cea69d8..0f890ac6f3ab 100644
--- a/Lib/zipfile.py
+++ b/Lib/zipfile.py
@@ -131,6 +131,27 @@ _CD64_NUMBER_ENTRIES_TOTAL = 7
 _CD64_DIRECTORY_SIZE = 8
 _CD64_OFFSET_START_CENTDIR = 9
 
+_EXTRA_FIELD_STRUCT = struct.Struct('<HH')
+
+def _strip_extra(extra, xids):
+    # Remove Extra Fields with specified IDs.
+    unpack = _EXTRA_FIELD_STRUCT.unpack
+    modified = False
+    buffer = []
+    start = i = 0
+    while i + 4 <= len(extra):
+        xid, xlen = unpack(extra[i : i + 4])
+        j = i + 4 + xlen
+        if xid in xids:
+            if i != start:
+                buffer.append(extra[start : i])
+            start = j
+            modified = True
+        i = j
+    if not modified:
+        return extra
+    return b''.join(buffer)
+
 def _check_zipfile(fp):
     try:
         if _EndRecData(fp):
@@ -1293,6 +1314,7 @@ class ZipFile(object):
                     extra_data = zinfo.extra
                     if extra:
                         # Append a ZIP64 field to the extra's
+                        extra_data = _strip_extra(extra_data, (1,))
                         extra_data = struct.pack(
                                 '<HH' + 'Q'*len(extra),
                                 1, 8*len(extra), *extra) + extra_data
diff --git a/Misc/NEWS.d/next/Library/2018-08-06-11-01-18.bpo-34341.E0b9p2.rst b/Misc/NEWS.d/next/Library/2018-08-06-11-01-18.bpo-34341.E0b9p2.rst
new file mode 100644
index 000000000000..46a9cde19c40
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-08-06-11-01-18.bpo-34341.E0b9p2.rst
@@ -0,0 +1,2 @@
+Appending to the ZIP archive with the ZIP64 extension no longer grows the
+size of extra fields of existing entries.
-- 
2.47.3