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Add TODO and explanation for SyncOnlyStream workaround

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The SyncOnlyStream wrapper is necessary because the LZMA decoder has bugs in its async implementation that cause state corruption (IndexOutOfRangeException, DataErrorException) even with fresh, non-shared streams.

Without this wrapper, async operations on LZMA streams fail. The proper fix would be to repair the async bugs in LzmaStream.ReadAsync, Decoder.CodeAsync, and OutWindow async operations, but that requires deep changes to the decoder state machine.

Added detailed comments explaining this is a workaround and where the real fix should go.

Co-authored-by: adamhathcock <527620+adamhathcock@users.noreply.github.com>
This commit is contained in:
copilot-swe-agent[bot]
2025-12-19 13:47:49 +00:00
parent e57e87090f
commit 8fc8295a89
1 changed files with 14 additions and 8 deletions
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22
src/SharpCompress/Archives/SevenZip/SevenZipArchive.cs
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@@ -243,12 +243,13 @@ public class SevenZipArchive : AbstractArchive<SevenZipArchiveEntry, SevenZipVol
protected override EntryStream GetEntryStream()
{
// Create a fresh decompression stream for each file to avoid
// state corruption when multiple files share the same LZMA stream
// in async operations. This is less efficient but ensures correctness.
// Create a fresh decompression stream for each file (no state sharing).
// However, the LZMA decoder has bugs in its async implementation that cause
// state corruption even on fresh streams. The SyncOnlyStream wrapper
// works around these bugs by forcing async operations to use sync equivalents.
//
// Wrap in SyncOnlyStream to force all async operations to use
// synchronous equivalents, avoiding bugs in LZMA's async implementation
// TODO: Fix the LZMA decoder async bugs (in LzmaStream, Decoder, OutWindow)
// so this wrapper is no longer necessary.
var entry = _currentEntry.NotNull("currentEntry is not null");
if (entry.IsDirectory)
{
@@ -259,8 +260,13 @@ public class SevenZipArchive : AbstractArchive<SevenZipArchiveEntry, SevenZipVol
}
/// <summary>
/// A stream wrapper that forces all async operations to use synchronous equivalents.
/// This is used for 7Zip LZMA streams to avoid state corruption bugs in the async implementation.
/// WORKAROUND: Forces async operations to use synchronous equivalents.
/// This is necessary because the LZMA decoder has bugs in its async implementation
/// that cause state corruption (IndexOutOfRangeException, DataErrorException).
///
/// The proper fix would be to repair the LZMA decoder's async methods
/// (LzmaStream.ReadAsync, Decoder.CodeAsync, OutWindow async operations),
/// but that requires deep changes to the decoder state machine.
/// </summary>
private sealed class SyncOnlyStream : Stream
{
@@ -291,7 +297,7 @@ public class SevenZipArchive : AbstractArchive<SevenZipArchiveEntry, SevenZipVol
public override void Write(byte[] buffer, int offset, int count) =>
_baseStream.Write(buffer, offset, count);
// Force async operations to use sync equivalents
// Force async operations to use sync equivalents to avoid LZMA decoder bugs
public override Task<int> ReadAsync(
byte[] buffer,
int offset,