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[PR #1087] Fix async extraction of 7Zip archives with LZMA compression #1513

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opened 2026-01-29 22:20:55 +00:00 by claunia · 0 comments
claunia commented 2026-01-29 22:20:55 +00:00
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Original Pull Request: https://github.com/adamhathcock/sharpcompress/pull/1087

State: closed
Merged: No

Async extraction of large 7z files fails with DataErrorException in LzmaStream.ReadAsync. The LZMA decoder has state corruption bugs in its async implementation (in LzmaStream.ReadAsync, Decoder.CodeAsync, and OutWindow operations).

Changes

  • Added SyncOnlyStream wrapper in SevenZipArchive.cs: Forces async operations to use synchronous equivalents, bypassing buggy LZMA async code paths while maintaining async API surface
  • Modified SevenZipReader.GetEntryStream(): Wraps each entry's decompression stream in SyncOnlyStream
  • Modified SevenZipReader.GetEntries(): Creates fresh streams per entry instead of sharing LZMA streams across multiple files

Example

The following code now works correctly for large 7z files:

using var archive = ArchiveFactory.Open(archivePath);

foreach (var entry in archive.Entries)
{
    if (entry.IsDirectory) continue;
    
    using var sourceStream = await entry.OpenEntryStreamAsync(token);
    await using var targetStream = new FileStream(targetPath, options);
    await sourceStream.CopyToAsync(targetStream, token);  // No longer throws DataErrorException
}

Technical Notes

This is a workaround. The proper fix requires repairing the LZMA decoder's async state machine, which requires deep changes to the decoder implementation. The SyncOnlyStream wrapper ensures correctness at minimal performance cost for the 7Zip use case.

Original prompt

This section details on the original issue you should resolve

<issue_title>decompressing big .7z file throws error</issue_title>
<issue_description>lib version 0.42.1
under .net 10

code:

public class SharpCompressExtractor : IArchiveExtractor
{
    public async Task<IReadOnlyCollection<FileInfo>> ExtractAsync(
        string archivePath,
        string destinationDirectory,
        CancellationToken token)
    {
        if (!File.Exists(archivePath))
        {
            throw new FileNotFoundException($"Nie znaleziono archiwum: {archivePath}");
        }

        var extractedFiles = new List<FileInfo>();

        using var archive = ArchiveFactory.Open(archivePath);

        foreach (var entry in archive.Entries)
        {
            if (entry.IsDirectory)
            {
                continue;
            }

            token.ThrowIfCancellationRequested();

            var targetPath = Path.Combine(destinationDirectory, entry.Key);

            var targetDir = Path.GetDirectoryName(targetPath);

            if (!string.IsNullOrEmpty(targetDir) && !Directory.Exists(targetDir))
            {
                Directory.CreateDirectory(targetDir);
            }

            using var sourceStream = await entry.OpenEntryStreamAsync(token);

            var fileOptions = new FileStreamOptions
            {
                Mode = FileMode.Create,
                Access = FileAccess.Write,
                Share = FileShare.None,
                BufferSize = 1_024 * 1_024,
                Options = FileOptions.Asynchronous
            };

            await using var targetStream = new FileStream(targetPath, fileOptions);

            await sourceStream.CopyToAsync(targetStream, token);

            var fileInfo = new FileInfo(targetPath);

            extractedFiles.Add(fileInfo);
        }

        return extractedFiles;
    }
}

usage

            try
            {
                var files = await fileExtractor.ExtractAsync(
    "C:\\whitelist\\20251223.7z",
    "c:/whitelist/out",
    CancellationToken.None);
            }
            catch (Exception ex)
            {
                
            }

Data Error

at SharpCompress.Compressors.LZMA.LzmaStream.d__52.MoveNext()
at SharpCompress.Compressors.LZMA.LzmaStream.d__56.MoveNext()
at System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable`1.ConfiguredValueTaskAwaiter.GetResult()
at SharpCompress.IO.ReadOnlySubStream.d__24.MoveNext()
at System.IO.Stream.<g__Core|30_0>d.MoveNext()
at SharpCompressExtractor.d__0.MoveNext() in SharpCompressExtractor.cs

file : probably any from https://www.podatki.gov.pl/narzedzia/white-list/

but for sure exist for this url: https://plikplaski.mf.gov.pl/pliki//20251223.7z

this file perfectly uncompress under win11 using native extractor or 7zip manager
</issue_description>

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

@adamhathcock Sounds like the fix I did for https://github.com/adamhathcock/sharpcompress/pull/1081

I can validate next week though.</comment_new>

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

**Original Pull Request:** https://github.com/adamhathcock/sharpcompress/pull/1087 **State:** closed **Merged:** No --- Async extraction of large 7z files fails with `DataErrorException` in `LzmaStream.ReadAsync`. The LZMA decoder has state corruption bugs in its async implementation (in `LzmaStream.ReadAsync`, `Decoder.CodeAsync`, and `OutWindow` operations). ## Changes - **Added `SyncOnlyStream` wrapper in `SevenZipArchive.cs`**: Forces async operations to use synchronous equivalents, bypassing buggy LZMA async code paths while maintaining async API surface - **Modified `SevenZipReader.GetEntryStream()`**: Wraps each entry's decompression stream in `SyncOnlyStream` - **Modified `SevenZipReader.GetEntries()`**: Creates fresh streams per entry instead of sharing LZMA streams across multiple files ## Example The following code now works correctly for large 7z files: ```csharp using var archive = ArchiveFactory.Open(archivePath); foreach (var entry in archive.Entries) { if (entry.IsDirectory) continue; using var sourceStream = await entry.OpenEntryStreamAsync(token); await using var targetStream = new FileStream(targetPath, options); await sourceStream.CopyToAsync(targetStream, token); // No longer throws DataErrorException } ``` ## Technical Notes This is a workaround. The proper fix requires repairing the LZMA decoder's async state machine, which requires deep changes to the decoder implementation. The `SyncOnlyStream` wrapper ensures correctness at minimal performance cost for the 7Zip use case. <!-- START COPILOT ORIGINAL PROMPT --> <details> <summary>Original prompt</summary> > > ---- > > *This section details on the original issue you should resolve* > > <issue_title>decompressing big .7z file throws error</issue_title> > <issue_description>lib version 0.42.1 > under .net 10 > > code: > > ``` > public class SharpCompressExtractor : IArchiveExtractor > { > public async Task<IReadOnlyCollection<FileInfo>> ExtractAsync( > string archivePath, > string destinationDirectory, > CancellationToken token) > { > if (!File.Exists(archivePath)) > { > throw new FileNotFoundException($"Nie znaleziono archiwum: {archivePath}"); > } > > var extractedFiles = new List<FileInfo>(); > > using var archive = ArchiveFactory.Open(archivePath); > > foreach (var entry in archive.Entries) > { > if (entry.IsDirectory) > { > continue; > } > > token.ThrowIfCancellationRequested(); > > var targetPath = Path.Combine(destinationDirectory, entry.Key); > > var targetDir = Path.GetDirectoryName(targetPath); > > if (!string.IsNullOrEmpty(targetDir) && !Directory.Exists(targetDir)) > { > Directory.CreateDirectory(targetDir); > } > > using var sourceStream = await entry.OpenEntryStreamAsync(token); > > var fileOptions = new FileStreamOptions > { > Mode = FileMode.Create, > Access = FileAccess.Write, > Share = FileShare.None, > BufferSize = 1_024 * 1_024, > Options = FileOptions.Asynchronous > }; > > await using var targetStream = new FileStream(targetPath, fileOptions); > > await sourceStream.CopyToAsync(targetStream, token); > > var fileInfo = new FileInfo(targetPath); > > extractedFiles.Add(fileInfo); > } > > return extractedFiles; > } > } > ``` > > usage > ``` > try > { > var files = await fileExtractor.ExtractAsync( > "C:\\whitelist\\20251223.7z", > "c:/whitelist/out", > CancellationToken.None); > } > catch (Exception ex) > { > > } > ``` > > Data Error > > at SharpCompress.Compressors.LZMA.LzmaStream.<DecodeChunkHeaderAsync>d__52.MoveNext() > at SharpCompress.Compressors.LZMA.LzmaStream.<ReadAsync>d__56.MoveNext() > at System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable`1.ConfiguredValueTaskAwaiter.GetResult() > at SharpCompress.IO.ReadOnlySubStream.<ReadAsync>d__24.MoveNext() > at System.IO.Stream.<<CopyToAsync>g__Core|30_0>d.MoveNext() > at SharpCompressExtractor.<ExtractAsync>d__0.MoveNext() in SharpCompressExtractor.cs > > file : probably any from https://www.podatki.gov.pl/narzedzia/white-list/ > > but for sure exist for this url: https://plikplaski.mf.gov.pl/pliki//20251223.7z > > this file perfectly uncompress under win11 using native extractor or 7zip manager > </issue_description> > > ## Comments on the Issue (you are @copilot in this section) > > <comments> > <comment_new><author>@adamhathcock</author><body> > Sounds like the fix I did for https://github.com/adamhathcock/sharpcompress/pull/1081 > > I can validate next week though.</body></comment_new> > </comments> > </details> <!-- START COPILOT CODING AGENT SUFFIX --> - Fixes adamhathcock/sharpcompress#1086 <!-- START COPILOT CODING AGENT TIPS --> --- 💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more [Copilot coding agent tips](https://gh.io/copilot-coding-agent-tips) in the docs.
claunia added the pull-request label 2026-01-29 22:20:55 +00:00
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Reference: starred/sharpcompress#1513
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