Data Descriptor Lost UncompressedSize #147

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1. Numpsy commented on Jun 7, 2020

   

   Numpsy

   on Jun 7, 2020

   Contributor

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   example of a unit test that looks to hit the issue (or something very similar at least):

   [Test]
   [Category("Zip")]
   public void TestDescriptorUpdate()
   {
       MemoryStream msw = new MemoryStreamWithoutSeek();
       using (ZipOutputStream outStream = new ZipOutputStream(msw))
       {
           outStream.UseZip64 = UseZip64.Off;
           outStream.IsStreamOwner = false;
           outStream.PutNextEntry(new ZipEntry("StripedMarlin"));
           outStream.WriteByte(89);
   
           outStream.PutNextEntry(new ZipEntry("StripedMarlin2"));
           outStream.WriteByte(91);
       }
   
       var zipData = msw.ToArray();
       Assert.IsTrue(ZipTesting.TestArchive(zipData));
   
       using (var memoryStream = new MemoryStream(zipData))
       {
           using (var zipFile = new ZipFile(memoryStream, leaveOpen: true))
           {
               zipFile.BeginUpdate();
               zipFile.Delete("StripedMarlin");
               zipFile.CommitUpdate();
           }
   
           memoryStream.Position = 0;
   
           using (var zipFile = new ZipFile(memoryStream, leaveOpen: true))
           {
               Assert.That(zipFile.TestArchive(true), Is.True);
           }
       }
   }

   i tried debugging the zipfile update, and i'm wondering if there is an issue in the GetDescriptorSize function in ZipFile:

   private int GetDescriptorSize(ZipUpdate update)
   {
       int result = 0;
       if ((update.Entry.Flags & (int)GeneralBitFlags.Descriptor) != 0)
       {
           result = ZipConstants.DataDescriptorSize - 4;
           if (update.Entry.LocalHeaderRequiresZip64)
           {
               result = ZipConstants.Zip64DataDescriptorSize - 4;
           }
       }
       return result;
   }

   Where I don't know what those -4s are for?

   The test passes if those are removed, so i'm not sure if the issue isn't just that it's slicing the end off the descriptor when doing the update?
   (though i'm not sure if there should really be a descriptor there after the update at all, given that the size fields for the entry are known at this point)
2. Numpsy commented on Jun 7, 2020

   

   Numpsy

   on Jun 7, 2020

   Contributor

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   Actually, posted that and then saw the

   

   comment in CopyEntryDirect, which sounds a tad suspicious given that GetDescriptorSize takes 4 bytes off the size.