Return a bounded substream when data descriptors are used in seekable…

… zips

src/SharpCompress/Common/Zip/SeekableZipFilePart.cs

@@ -1,17 +1,20 @@
 using System.IO;
 using SharpCompress.Common.Zip.Headers;
+using SharpCompress.IO;
 
 namespace SharpCompress.Common.Zip
 {
     internal class SeekableZipFilePart : ZipFilePart
     {
         private bool _isLocalHeaderLoaded;
         private readonly SeekableZipHeaderFactory _headerFactory;
+        private readonly DirectoryEntryHeader _directoryEntryHeader;
 
         internal SeekableZipFilePart(SeekableZipHeaderFactory headerFactory, DirectoryEntryHeader header, Stream stream)
             : base(header, stream)
         {
             _headerFactory = headerFactory;
+            _directoryEntryHeader = header;
         }
 
         internal override Stream GetCompressedStream()
@@ -36,6 +39,15 @@ private void LoadLocalHeader()
         protected override Stream CreateBaseStream()
         {
             BaseStream.Position = Header.DataStartPosition.Value;
+
+            if ((Header.CompressedSize == 0)
+                && FlagUtility.HasFlag(Header.Flags, HeaderFlags.UsePostDataDescriptor)
+                && (_directoryEntryHeader?.HasData == true)
+                && (_directoryEntryHeader?.CompressedSize != 0))
+            {
+                return new ReadOnlySubStream(BaseStream, _directoryEntryHeader.CompressedSize);
+            }
+
             return BaseStream;
         }
     }

tests/SharpCompress.Test/Zip/ZipArchiveTests.cs

@@ -536,5 +536,24 @@ public void Zip_BadLocalExtra_Read()
                 Assert.Null(ex);
             }
         }
-    }
+
+        [Fact]
+        public void Zip_NoCompression_DataDescriptors_Read()
+        {
+            string zipPath = Path.Combine(TEST_ARCHIVES_PATH, "Zip.none.datadescriptors.zip");
+
+            using (ZipArchive za = ZipArchive.Open(zipPath))
+            {
+                var firstEntry = za.Entries.First(x => x.Key == "first.txt");
+                var buffer = new byte[4096];
+
+                using (var memoryStream = new MemoryStream())
+                using (var firstStream = firstEntry.OpenEntryStream())
+                {
+                    firstStream.CopyTo(memoryStream);
+                    Assert.Equal(199, memoryStream.Length);
+                }
+            }
+        }
+   }
 }