Issue #26293: Fixed writing ZIP files that starts not from the start of the

file.  Offsets in ZIP file now are relative to the start of the archive in
conforming to the specification.

1 files changed, 15 insertions, 15 deletions

diff --git a/Lib/zipfile.py b/Lib/zipfile.py
index 44e653d620..3751e698be 100644
--- a/Lib/zipfile.py
+++ b/Lib/zipfile.py
@@ -1103,10 +1103,10 @@ class ZipFile:
                 # even if no files are added to the archive
                 self._didModify = True
                 try:
-                    self.start_dir = self.fp.tell()
+                    self.start_dir = self._start_disk = self.fp.tell()
                 except (AttributeError, OSError):
                     self.fp = _Tellable(self.fp)
-                    self.start_dir = 0
+                    self.start_dir = self._start_disk = 0
                     self._seekable = False
                 else:
                     # Some file-like objects can provide tell() but not seek()
@@ -1127,7 +1127,7 @@ class ZipFile:
                     # set the modified flag so central directory gets written
                     # even if no files are added to the archive
                     self._didModify = True
-                    self.start_dir = self.fp.tell()
+                    self.start_dir = self._start_disk = self.fp.tell()
             else:
                 raise ValueError("Mode must be 'r', 'w', 'x', or 'a'")
         except:
@@ -1171,17 +1171,18 @@ class ZipFile:
         offset_cd = endrec[_ECD_OFFSET]         # offset of central directory
         self._comment = endrec[_ECD_COMMENT]    # archive comment
 
-        # "concat" is zero, unless zip was concatenated to another file
-        concat = endrec[_ECD_LOCATION] - size_cd - offset_cd
+        # self._start_disk:  Position of the start of ZIP archive
+        # It is zero, unless ZIP was concatenated to another file
+        self._start_disk = endrec[_ECD_LOCATION] - size_cd - offset_cd
         if endrec[_ECD_SIGNATURE] == stringEndArchive64:
             # If Zip64 extension structures are present, account for them
-            concat -= (sizeEndCentDir64 + sizeEndCentDir64Locator)
+            self._start_disk -= (sizeEndCentDir64 + sizeEndCentDir64Locator)
 
         if self.debug > 2:
-            inferred = concat + offset_cd
-            print("given, inferred, offset", offset_cd, inferred, concat)
+            inferred = self._start_disk + offset_cd
+            print("given, inferred, offset", offset_cd, inferred, self._start_disk)
         # self.start_dir:  Position of start of central directory
-        self.start_dir = offset_cd + concat
+        self.start_dir = offset_cd + self._start_disk
         fp.seek(self.start_dir, 0)
         data = fp.read(size_cd)
         fp = io.BytesIO(data)
@@ -1221,7 +1222,7 @@ class ZipFile:
                             t>>11, (t>>5)&0x3F, (t&0x1F) * 2 )
 
             x._decodeExtra()
-            x.header_offset = x.header_offset + concat
+            x.header_offset = x.header_offset + self._start_disk
             self.filelist.append(x)
             self.NameToInfo[x.filename] = x
 
@@ -1685,11 +1686,10 @@ class ZipFile:
                 file_size = zinfo.file_size
                 compress_size = zinfo.compress_size
 
-            if zinfo.header_offset > ZIP64_LIMIT:
-                extra.append(zinfo.header_offset)
+            header_offset = zinfo.header_offset - self._start_disk
+            if header_offset > ZIP64_LIMIT:
+                extra.append(header_offset)
                 header_offset = 0xffffffff
-            else:
-                header_offset = zinfo.header_offset
 
             extra_data = zinfo.extra
             min_version = 0
@@ -1736,7 +1736,7 @@ class ZipFile:
         # Write end-of-zip-archive record
         centDirCount = len(self.filelist)
         centDirSize = pos2 - self.start_dir
-        centDirOffset = self.start_dir
+        centDirOffset = self.start_dir - self._start_disk
         requires_zip64 = None
         if centDirCount > ZIP_FILECOUNT_LIMIT:
             requires_zip64 = "Files count"