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

[Copilot]

Extracting a ZIP archive containing an LZMA-compressed entry with 0 uncompressed bytes throws DataErrorException from LzmaStream.Read().

Root cause

LZMA entries in ZIP always carry a 4-byte header (version + property length) plus 5-byte properties, followed by actual LZMA stream data — even for empty files. So CompressedSize > 0 while UncompressedSize == 0.

LzmaStream is constructed with outputSize=0, setting _availableBytes=0. The first Read() call immediately sets _endReached=true without running the decoder, then the end-of-stream check throws because _inputPosition (0, never incremented) ≠ _inputSize (> 0).

Fix

In ZipFilePart.CreateDecompressionStream (sync and async), after parsing the LZMA header, short-circuit when the output size is definitively zero — i.e., Bit1 (EOS-marker flag) is not set and UncompressedSize == 0:

// 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(); // drain remaining bytes — required to advance position in streaming reads
    return Stream.Null;
}

stream.Skip() is necessary because the stream at this point is a ReadOnlySubStream scoped to CompressedSize bytes; draining it keeps the underlying archive stream correctly positioned for sequential (non-seekable) reads.

Changes

• ZipFilePart.cs / ZipFilePart.Async.cs — early return for known-empty LZMA entries in both sync and async decompression paths
• Zip.lzma.empty.zip — new test archive containing a single LZMA-compressed zero-byte entry
• ZipArchiveTests — regression test via seekable ArchiveFactory.OpenArchive
• ZipReaderTests — regression test via streaming ReaderFactory.OpenReader with a forward-only stream

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Error when extract zip file contains 0-size entry</issue_title>
<issue_description>SharpCompress version: 0.46.3

Test code:

using SharpCompress.Archives;

try
{
    var zipFile = "test.zip";
    var outDir = "output";
    if (!Directory.Exists(outDir))
        Directory.CreateDirectory(outDir);
    using (var archive = ArchiveFactory.OpenArchive(zipFile))
    {
        archive.WriteToDirectory(outDir);
    }
    Console.WriteLine("Success");
}
catch (Exception ex)
{
    Console.WriteLine(ex.ToString());
}

Test zip file:
test.zip

Test output:

SharpCompress.Compressors.LZMA.DataErrorException: Data Error
   at SharpCompress.Compressors.LZMA.LzmaStream.Read(Byte[] buffer, Int32 offset, Int32 count) in D:\a\sharpcompress\sharpcompress\src\SharpCompress\Compressors\LZMA\LzmaStream.cs:line 305
   at System.IO.Stream.CopyTo(Stream destination, Int32 bufferSize)
   at SharpCompress.Archives.IArchiveEntryExtensions.WriteTo(IArchiveEntry archiveEntry, Stream streamToWriteTo, IProgress`1 progress) in D:\a\sharpcompress\sharpcompress\src\SharpCompress\Archives\IArchiveEntryExtensions.cs:line 28
   at SharpCompress.Archives.IArchiveEntryExtensions.<>c__DisplayClass8_0.<WriteToFile>b__0(String x, FileMode fm) in D:\a\sharpcompress\sharpcompress\src\SharpCompress\Archives\IArchiveEntryExtensions.cs:line 139
   at SharpCompress.Common.ExtractionMethods.WriteEntryToFile(IEntry entry, String destinationFileName, Action`2 openAndWrite) in D:\a\sharpcompress\sharpcompress\src\SharpCompress\Common\ExtractionMethods.cs:line 120
   at SharpCompress.Archives.IArchiveEntryExtensions.WriteToFile(IArchiveEntry entry, String destinationFileName) in D:\a\sharpcompress\sharpcompress\src\SharpCompress\Archives\IArchiveEntryExtensions.cs:line 133
   at SharpCompress.Archives.IArchiveEntryExtensions.<>c__DisplayClass6_0.<WriteToDirectory>b__0(String path) in D:\a\sharpcompress\sharpcompress\src\SharpCompress\Archives\IArchiveEntryExtensions.cs:line 109
   at SharpCompress.Common.ExtractionMethods.WriteEntryToDirectory(IEntry entry, String destinationDirectory, Action`1 write) in D:\a\sharpcompress\sharpcompress\src\SharpCompress\Common\ExtractionMethods.cs:line 85
   at SharpCompress.Archives.IArchiveEntryExtensions.WriteToDirectory(IArchiveEntry entry, String destinationDirectory) in D:\a\sharpcompress\sharpcompress\src\SharpCompress\Archives\IArchiveEntryExtensions.cs:line 106
   at SharpCompress.Archives.IArchiveExtensions.WriteToDirectoryInternal(IArchive archive, String destinationDirectory, IProgress`1 progress) in D:\a\sharpcompress\sharpcompress\src\SharpCompress\Archives\IArchiveExtensions.cs:line 61
   at SharpCompress.Archives.IArchiveExtensions.WriteToDirectory(IArchive archive, String destinationDirectory, IProgress`1 progress) in D:\a\sharpcompress\sharpcompress\src\SharpCompress\Archives\IArchiveExtensions.cs:line 30
   at Program.<Main>$(String[] args) in D:\Code\ConsoleApp2\ConsoleApp2\Program.cs:line 11
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes Error when extract zip file contains 0-size entry #1236

---

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[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Overview

The fix addresses a bug where extracting LZMA-compressed zero-byte ZIP entries throws a DataErrorException. The solution correctly short-circuits decompression when the uncompressed size is explicitly known to be zero (i.e., when Bit1 EOS marker flag is not set and UncompressedSize == 0).

Changes Reviewed

File	Lines	Description
src/SharpCompress/Common/Zip/ZipFilePart.cs	153-165	Added early return for zero-size LZMA entries (sync)
src/SharpCompress/Common/Zip/ZipFilePart.Async.cs	161-173	Added early return for zero-size LZMA entries (async)
tests/SharpCompress.Test/Zip/ZipArchiveTests.cs	900-912	Regression test for Archive API
tests/SharpCompress.Test/Zip/ZipReaderTests.cs	547-568	Regression test for Reader API (streaming)
tests/TestArchives/Archives/Zip.lzma.empty.zip	N/A	New test archive

Code Quality

• Logic: Correct - checks both !Bit1 (size stored in header) and UncompressedSize == 0
• Stream handling: Correct - uses stream.Skip() / stream.SkipAsync() to drain remaining bytes for forward-only streams
• Return value: Correct - returns Stream.Null for zero-size entries
• Documentation: Excellent - clear comments explaining the Bit1 flag behavior
• Tests: Comprehensive - covers both seekable (Archive API) and forward-only (Reader API) scenarios

Files Reviewed (5 files)

• src/SharpCompress/Common/Zip/ZipFilePart.cs
• src/SharpCompress/Common/Zip/ZipFilePart.Async.cs
• tests/SharpCompress.Test/Zip/ZipArchiveTests.cs
• tests/SharpCompress.Test/Zip/ZipReaderTests.cs
• tests/TestArchives/Archives/Zip.lzma.empty.zip

[Copilot]

Pull request overview

Fixes extraction of ZIP entries that are LZMA-compressed but have a known uncompressed size of 0 bytes, preventing DataErrorException during reads and adding regression coverage for both seekable and streaming readers.

Changes:

• Short-circuit LZMA decompression for entries with explicitly-known zero uncompressed size (sync + async paths).
• Add a new LZMA ZIP fixture containing a single zero-byte entry.
• Add regression tests for both ArchiveFactory.OpenArchive (seekable) and ReaderFactory.OpenReader (streaming/forward-only).

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/SharpCompress/Common/Zip/ZipFilePart.cs	Adds early-return logic for known-empty LZMA entries during decompression stream creation.
src/SharpCompress/Common/Zip/ZipFilePart.Async.cs	Async equivalent of the LZMA known-empty early-return logic.
tests/TestArchives/Archives/Zip.lzma.empty.zip	New test archive fixture containing a zero-byte LZMA-compressed entry.
tests/SharpCompress.Test/Zip/ZipArchiveTests.cs	Regression test covering extraction via seekable archive API.
tests/SharpCompress.Test/Zip/ZipReaderTests.cs	Regression test covering extraction via streaming reader API with a forward-only stream.

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