Merge pull request #1237 from adamhathcock/copilot/fix-zip-extraction-error

Fix DataErrorException when extracting LZMA-compressed zero-byte ZIP entries

src/SharpCompress/Common/Zip/ZipFilePart.Async.cs

@@ -158,6 +158,20 @@ internal abstract partial class ZipFilePart
                     .ReadFullyAsync(props, 0, propsSize, cancellationToken)
                     .ConfigureAwait(false);
 
+                // When the uncompressed size is known to be zero, skip remaining compressed
+                // bytes (required for streaming reads) and return an empty stream.
+                // Bit1 (EOS marker flag) means the output size is not stored in the header
+                // (the LZMA stream itself contains an end-of-stream marker instead), so we
+                // only short-circuit when the size is explicitly known to be zero.
+                if (
+                    !FlagUtility.HasFlag(Header.Flags, HeaderFlags.Bit1)
+                    && Header.UncompressedSize == 0
+                )
+                {
+                    await stream.SkipAsync(cancellationToken).ConfigureAwait(false);
+                    return Stream.Null;
+                }
+
                 context = context with
                 {
                     Properties = props,

src/SharpCompress/Common/Zip/ZipFilePart.cs

@@ -149,6 +149,21 @@ internal abstract partial class ZipFilePart : FilePart
                 reader.ReadUInt16(); // LZMA version
                 var propsLength = reader.ReadUInt16();
                 var props = reader.ReadBytes(propsLength);
+
+                // When the uncompressed size is known to be zero, skip remaining compressed
+                // bytes (required for streaming reads) and return an empty stream.
+                // Bit1 (EOS marker flag) means the output size is not stored in the header
+                // (the LZMA stream itself contains an end-of-stream marker instead), so we
+                // only short-circuit when the size is explicitly known to be zero.
+                if (
+                    !FlagUtility.HasFlag(Header.Flags, HeaderFlags.Bit1)
+                    && Header.UncompressedSize == 0
+                )
+                {
+                    stream.Skip();
+                    return Stream.Null;
+                }
+
                 context = context with
                 {
                     Properties = props,

tests/SharpCompress.Test/Zip/ZipArchiveTests.cs

@@ -896,4 +896,18 @@ public class ZipArchiveTests : ArchiveTests
         const int expected = (S_IFREG | 0b110_100_100) << 16; // 0644 mode regular file
         Assert.Equal(expected, firstEntry.Attrib);
     }
+
+    [Fact]
+    public void Zip_LZMA_ZeroSizeEntry_CanExtract()
+    {
+        using var archive = ArchiveFactory.OpenArchive(
+            Path.Combine(TEST_ARCHIVES_PATH, "Zip.lzma.empty.zip")
+        );
+        var entries = archive.Entries.Where(x => !x.IsDirectory).ToList();
+        Assert.Single(entries);
+        Assert.Equal(0, entries[0].Size);
+        var outStream = new MemoryStream();
+        entries[0].WriteTo(outStream);
+        Assert.Equal(0, outStream.Length);
+    }
 }

tests/SharpCompress.Test/Zip/ZipReaderTests.cs

@@ -543,4 +543,27 @@ public class ZipReaderTests : ReaderTests
         // Should iterate through all entries, not just the first one
         Assert.True(count > 1, $"Expected more than 1 entry, but got {count}");
     }
+
+    [Fact]
+    public void Zip_LZMA_ZeroSizeEntry_CanExtract_Streaming()
+    {
+        var path = Path.Combine(TEST_ARCHIVES_PATH, "Zip.lzma.empty.zip");
+        using var fileStream = File.OpenRead(path);
+        using Stream stream = new ForwardOnlyStream(fileStream);
+        using var reader = ReaderFactory.OpenReader(stream);
+
+        var count = 0;
+        while (reader.MoveToNextEntry())
+        {
+            if (!reader.Entry.IsDirectory)
+            {
+                count++;
+                Assert.Equal(0, reader.Entry.Size);
+                var outStream = new MemoryStream();
+                reader.WriteEntryTo(outStream);
+                Assert.Equal(0, outStream.Length);
+            }
+        }
+        Assert.Equal(1, count);
+    }
 }