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Make DeflateStream write out headers and footers #118570

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fde5a97
Make DeflateStream write out headers and footers
rzikm Aug 11, 2025
aa5f184
Remove semicolons on empty line
rzikm Aug 11, 2025
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29 changes: 16 additions & 13 deletions src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateZLib/DeflateStream.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,13 @@ public partial class DeflateStream : Stream
private volatile bool _activeAsyncOperation;
private bool _wroteBytes;

// Some deflaters (e.g. ZLib) write more than zero bytes for zero byte inputs.
// This round-trips and we should be ok with this, but our legacy managed deflater
// always wrote zero output for zero input and upstack code (e.g. ZipArchiveEntry)
// took dependencies on it. Thus, if we are opened from ZipArchiveEntry, we make
// sure to only "flush" when we actually had some input.
private bool _noFlushOnEmpty;

internal DeflateStream(Stream stream, CompressionMode mode, long uncompressedSize) : this(stream, mode, leaveOpen: false, ZLibNative.Deflate_DefaultWindowBits, uncompressedSize)
{
}
Expand All @@ -46,6 +53,12 @@ public DeflateStream(Stream stream, CompressionLevel compressionLevel, bool leav
{
}

// internal constructor to use from ZipArchiveEntry
internal DeflateStream(Stream stream, CompressionLevel compressionLevel, bool leaveOpen, bool noFlushOnEmpty) : this(stream, compressionLevel, leaveOpen)
{
_noFlushOnEmpty = noFlushOnEmpty;
}

/// <summary>
/// Initializes a new instance of the <see cref="DeflateStream"/> class by using the specified stream, compression options, and optionally leaves the stream open.
/// </summary>
Expand All @@ -62,7 +75,7 @@ internal DeflateStream(Stream stream, ZLibCompressionOptions compressionOptions,
ArgumentNullException.ThrowIfNull(stream);
ArgumentNullException.ThrowIfNull(compressionOptions);

InitializeDeflater(stream, (ZLibNative.CompressionLevel)compressionOptions.CompressionLevel, (CompressionStrategy)compressionOptions.CompressionStrategy, leaveOpen, windowBits);
InitializeDeflater(stream, (ZLibNative.CompressionLevel)compressionOptions.CompressionLevel, (CompressionStrategy)compressionOptions.CompressionStrategy, leaveOpen, windowBits);
}

/// <summary>
Expand Down Expand Up @@ -616,12 +629,7 @@ private void PurgeBuffers(bool disposing)
return;

Debug.Assert(_deflater != null && _buffer != null);
// Some deflaters (e.g. ZLib) write more than zero bytes for zero byte inputs.
// This round-trips and we should be ok with this, but our legacy managed deflater
// always wrote zero output for zero input and upstack code (e.g. ZipArchiveEntry)
// took dependencies on it. Thus, make sure to only "flush" when we actually had
// some input:
if (_wroteBytes)
if (_wroteBytes || !_noFlushOnEmpty)
{
// Compress any bytes left
WriteDeflaterOutput();
Expand Down Expand Up @@ -663,12 +671,7 @@ private async ValueTask PurgeBuffersAsync()
return;

Debug.Assert(_deflater != null && _buffer != null);
// Some deflaters (e.g. ZLib) write more than zero bytes for zero byte inputs.
// This round-trips and we should be ok with this, but our legacy managed deflater
// always wrote zero output for zero input and upstack code (e.g. ZipArchiveEntry)
// took dependencies on it. Thus, make sure to only "flush" when we actually had
// some input.
if (_wroteBytes)
if (_wroteBytes || !_noFlushOnEmpty)
{
// Compress any bytes left
await WriteDeflaterOutputAsync(default).ConfigureAwait(false);
Expand Down
3 changes: 1 addition & 2 deletions src/libraries/System.IO.Compression/src/System/IO/Compression/ZipArchiveEntry.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -719,7 +719,7 @@ private CheckSumAndSizeWriteStream GetDataCompressor(Stream backingStream, bool
case CompressionMethodValues.Deflate:
case CompressionMethodValues.Deflate64:
default:
compressorStream = new DeflateStream(backingStream, _compressionLevel, leaveBackingStreamOpen);
compressorStream = new DeflateStream(backingStream, _compressionLevel, leaveBackingStreamOpen, true);
break;

}
Expand Down Expand Up @@ -975,7 +975,6 @@ private bool WriteLocalFileHeaderInitialize(bool isEmptyFile, bool forceWrite, o
CompressionMethod = CompressionMethodValues.Stored;
compressedSizeTruncated = 0;
uncompressedSizeTruncated = 0;
Debug.Assert(_compressedSize == 0);
Debug.Assert(_uncompressedSize == 0);
Debug.Assert(_crc32 == 0);
}
Expand Down
19 changes: 17 additions & 2 deletions src/libraries/System.IO.Compression/tests/CompressionStreamUnitTests.Deflate.cs
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Expand Up @@ -156,11 +156,11 @@ public void StreamTruncation_IsDetected(TestScenario testScenario)
break;

case TestScenario.Read:
while (ZipFileTestBase.ReadAllBytes(decompressor, buffer, 0, buffer.Length) != 0) { };
while (ZipFileTestBase.ReadAllBytes(decompressor, buffer, 0, buffer.Length) != 0) { }
break;

case TestScenario.ReadAsync:
while (await ZipFileTestBase.ReadAllBytesAsync(decompressor, buffer, 0, buffer.Length) != 0) { };
while (await ZipFileTestBase.ReadAllBytesAsync(decompressor, buffer, 0, buffer.Length) != 0) { }
break;

case TestScenario.ReadByte:
Expand Down Expand Up @@ -219,5 +219,20 @@ public override Task WriteAsync(byte[] buffer, int offset, int count, Cancellati
return base.WriteAsync(buffer, offset, count, cancellationToken);
}
}

[Fact]
public void EmptyDeflateStream_WritesOutput()
{
using (var ms = new MemoryStream())
{
using (var deflateStream = new DeflateStream(ms, CompressionMode.Compress, leaveOpen: true))
{
// Write nothing
}

// DeflateStream should now write output even for empty streams
Assert.True(ms.Length > 0, "Empty DeflateStream should write finalization data");
}
}
}
}
34 changes: 30 additions & 4 deletions src/libraries/System.IO.Compression/tests/CompressionStreamUnitTests.Gzip.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -126,7 +126,7 @@ public async Task ConcatenatedEmptyGzipStreams()
[InlineData(10, TestScenario.ReadAsync, 1000, 2000)]
[InlineData(10, TestScenario.Copy, 1000, 2000)]
[InlineData(10, TestScenario.CopyAsync, 1000, 2000)]
[InlineData(2, TestScenario.Copy, 1000, 0x2000-30)]
[InlineData(2, TestScenario.Copy, 1000, 0x2000 - 30)]
[InlineData(2, TestScenario.CopyAsync, 1000, 0x2000 - 30)]
[InlineData(1000, TestScenario.Read, 1, 1)]
[InlineData(1000, TestScenario.ReadAsync, 1, 1)]
Expand Down Expand Up @@ -315,7 +315,7 @@ public void StreamCorruption_IsDetected()
{
Assert.Throws<InvalidDataException>(() =>
{
while (ZipFileTestBase.ReadAllBytes(decompressor, buffer, 0, buffer.Length) != 0);
while (ZipFileTestBase.ReadAllBytes(decompressor, buffer, 0, buffer.Length) != 0) ;
});
}
}
Expand Down Expand Up @@ -377,11 +377,11 @@ public void StreamTruncation_IsDetected(TestScenario testScenario)
break;

case TestScenario.Read:
while (ZipFileTestBase.ReadAllBytes(decompressor, buffer, 0, buffer.Length) != 0) { };
while (ZipFileTestBase.ReadAllBytes(decompressor, buffer, 0, buffer.Length) != 0) { }
break;

case TestScenario.ReadAsync:
while (await ZipFileTestBase.ReadAllBytesAsync(decompressor, buffer, 0, buffer.Length) != 0) { };
while (await ZipFileTestBase.ReadAllBytesAsync(decompressor, buffer, 0, buffer.Length) != 0) { }
break;

case TestScenario.ReadByte:
Expand Down Expand Up @@ -441,5 +441,31 @@ public override Task WriteAsync(byte[] buffer, int offset, int count, Cancellati
return base.WriteAsync(buffer, offset, count, cancellationToken);
}
}

[Fact]
public void EmptyGZipStream_WritesHeaderAndFooter()
{
// Test that an empty GZip stream still writes the required headers and footers
using (var ms = new MemoryStream())
{
using (var gzipStream = new GZipStream(ms, CompressionMode.Compress, leaveOpen: true))
{
// Write nothing
}

// At minimum it should have the GZip signature (0x1f 0x8b) and other required data
Assert.True(ms.Length > 0, "Empty GZip stream should write headers and footers");

// Verify the compressed data can be decompressed successfully
ms.Seek(0, SeekOrigin.Begin);
using (var decompressStream = new GZipStream(ms, CompressionMode.Decompress))
using (var resultStream = new MemoryStream())
{
decompressStream.CopyTo(resultStream);
Assert.Equal(0, resultStream.Length);
}
}
}

}
}
10 changes: 5 additions & 5 deletions src/libraries/System.IO.Compression/tests/ZipArchive/zip_InvalidParametersAndStrangeFiles.cs
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Expand Up @@ -195,7 +195,7 @@ public static async Task LargeArchive_DataDescriptor_Read_NonZip64_FileLengthGre
Stream source = await OpenEntryStream(async, e);
byte[] buffer = new byte[s_bufferSize];
int read = await source.ReadAsync(buffer, 0, buffer.Length); // We don't want to inflate this large archive entirely
// just making sure it read successfully
// just making sure it read successfully
Assert.Equal(s_bufferSize, read);
foreach (byte b in buffer)
{
Expand Down Expand Up @@ -564,7 +564,7 @@ public static async Task UpdateZipArchive_AddFileTo_ZipWithCorruptedFile(bool as
byte[] buffer2 = new byte[1024];
file.Seek(0, SeekOrigin.Begin);

while (await s.ReadAsync(buffer1, 0, buffer1.Length) != 0 )
while (await s.ReadAsync(buffer1, 0, buffer1.Length) != 0)
{
await file.ReadAsync(buffer2, 0, buffer2.Length);
Assert.Equal(buffer1, buffer2);
Expand Down Expand Up @@ -820,7 +820,7 @@ public static IEnumerable<object[]> EmptyFiles()
[MemberData(nameof(EmptyFiles))]
public async Task ReadArchive_WithEmptyDeflatedFile(byte[] fileBytes, bool async)
{
using (var testStream = new MemoryStream(fileBytes))
using (var testStream = new MemoryStream(fileBytes.ToArray()))
{
const string ExpectedFileName = "xl/customProperty2.bin";

Expand All @@ -834,7 +834,7 @@ public async Task ReadArchive_WithEmptyDeflatedFile(byte[] fileBytes, bool async
byte[] fileContent = testStream.ToArray();

// compression method should not have changed
Assert.Equal(firstEntryCompressionMethod, fileBytes[8]);
Assert.Equal(firstEntryCompressionMethod, fileContent[8]);

testStream.Seek(0, SeekOrigin.Begin);
// second attempt: open archive with zero-length file that is compressed (Deflate = 0x8)
Expand Down Expand Up @@ -1418,7 +1418,7 @@ public async Task ZipArchive_InvalidExtraFieldData_Async(byte validVersionToExtr
// for first.bin would normally be skipped (because it hasn't changed) but it needs to be rewritten
// because the central directory headers will be rewritten with a valid value and the local file header
// needs to match.
await using (ZipArchive updatedArchive = await ZipArchive.CreateAsync(updatedStream, ZipArchiveMode.Update, leaveOpen: true, entryNameEncoding: null))
await using (ZipArchive updatedArchive = await ZipArchive.CreateAsync(updatedStream, ZipArchiveMode.Update, leaveOpen: true, entryNameEncoding: null))
{
ZipArchiveEntry newEntry = updatedArchive.CreateEntry("second.bin", CompressionLevel.NoCompression);

Expand Down
105 changes: 41 additions & 64 deletions src/libraries/System.IO.Compression/tests/ZipArchive/zip_UpdateTests.cs
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Expand Up @@ -92,62 +92,39 @@ public static async Task EmptyEntryTest(ZipArchiveMode mode, bool async)
string data2 = "more test data written to file.";
DateTimeOffset lastWrite = new DateTimeOffset(1992, 4, 5, 12, 00, 30, new TimeSpan(-5, 0, 0));

var baseline = new LocalMemoryStream();
ZipArchive archive = await CreateZipArchive(async, baseline, mode);

await AddEntry(archive, "data1.txt", data1, lastWrite, async);

ZipArchiveEntry e = archive.CreateEntry("empty.txt");
e.LastWriteTime = lastWrite;

Stream s = await OpenEntryStream(async, e);
await DisposeStream(async, s);

await AddEntry(archive, "data2.txt", data2, lastWrite, async);

await DisposeZipArchive(async, archive);

var test = new LocalMemoryStream();
archive = await CreateZipArchive(async, test, mode);

await AddEntry(archive, "data1.txt", data1, lastWrite, async);

e = archive.CreateEntry("empty.txt");
e.LastWriteTime = lastWrite;

await AddEntry(archive, "data2.txt", data2, lastWrite, async);

await DisposeZipArchive(async, archive);

//compare
Assert.True(ArraysEqual(baseline.ToArray(), test.ToArray()), "Arrays didn't match");

//second test, this time empty file at end
baseline = baseline.Clone();
archive = await CreateZipArchive(async, baseline, mode);
async Task<byte[]> WriteTestArchive(bool openEntryStream, bool emptyEntryAtTheEnd)
{
var archiveStream = new LocalMemoryStream();
ZipArchive archive = await CreateZipArchive(async, archiveStream, mode);

await AddEntry(archive, "data1.txt", data1, lastWrite, async);
await AddEntry(archive, "data1.txt", data1, lastWrite, async);

e = archive.CreateEntry("empty.txt");
e.LastWriteTime = lastWrite;
ZipArchiveEntry e = archive.CreateEntry("empty.txt");
e.LastWriteTime = lastWrite;

s = await OpenEntryStream(async, e);
await DisposeStream(async, s);

await DisposeZipArchive(async, archive);
if (openEntryStream)
{
Stream s = await OpenEntryStream(async, e);
await DisposeStream(async, s);
}

test = test.Clone();
archive = await CreateZipArchive(async, test, mode);
if (!emptyEntryAtTheEnd)
{
await AddEntry(archive, "data2.txt", data2, lastWrite, async);
}

await AddEntry(archive, "data1.txt", data1, lastWrite, async);
await DisposeZipArchive(async, archive);

e = archive.CreateEntry("empty.txt");
e.LastWriteTime = lastWrite;
return archiveStream.ToArray();
}

await DisposeZipArchive(async, archive);
var baseline = await WriteTestArchive(openEntryStream: false, emptyEntryAtTheEnd: false);
var test = await WriteTestArchive(openEntryStream: true, emptyEntryAtTheEnd: false);
Assert.Equal(baseline, test);

//compare
Assert.True(ArraysEqual(baseline.ToArray(), test.ToArray()), "Arrays didn't match after update");
baseline = await WriteTestArchive(openEntryStream: false, emptyEntryAtTheEnd: true);
test = await WriteTestArchive(openEntryStream: true, emptyEntryAtTheEnd: true);
Assert.Equal(baseline, test);
}

[Theory]
Expand Down Expand Up @@ -474,10 +451,10 @@ public async Task Update_PerformMinimalWritesWhenNoFilesChanged(bool async)

public static IEnumerable<object[]> Get_Update_PerformMinimalWritesWhenFixedLengthEntryHeaderFieldChanged_Data()
{
yield return [ 49, 1, 1, ];
yield return [ 40, 3, 2, ];
yield return [ 30, 5, 3, ];
yield return [ 0, 8, 1, ];
yield return [49, 1, 1,];
yield return [40, 3, 2,];
yield return [30, 5, 3,];
yield return [0, 8, 1,];
}

[Theory]
Expand Down Expand Up @@ -657,9 +634,9 @@ public static IEnumerable<object[]> Get_Update_PerformMinimalWritesWhenEntryData

public static IEnumerable<object[]> Get_PerformMinimalWritesWithDataAndHeaderChanges_Data()
{
yield return [ 0, 0 ];
yield return [ 20, 40 ];
yield return [ 30, 10 ];
yield return [0, 0];
yield return [20, 40];
yield return [30, 10];
}

[Theory]
Expand Down Expand Up @@ -914,11 +891,11 @@ public async Task Update_PerformMinimalWritesWhenArchiveCommentChanged_Async()

public static IEnumerable<object[]> Get_Update_PerformMinimalWritesWhenEntriesModifiedAndDeleted_Data()
{
yield return [ -1, 40 ];
yield return [ -1, 49 ];
yield return [ -1, 0 ];
yield return [ 42, 40 ];
yield return [ 38, 40 ];
yield return [-1, 40];
yield return [-1, 49];
yield return [-1, 0];
yield return [42, 40];
yield return [38, 40];
}

[Theory]
Expand Down Expand Up @@ -1109,10 +1086,10 @@ public async Task Update_PerformMinimalWritesWhenEntriesModifiedAndDeleted_Async

public static IEnumerable<object[]> Get_Update_PerformMinimalWritesWhenEntriesModifiedAndAdded_Data()
{
yield return [ 1 ];
yield return [ 5 ];
yield return [ 10 ];
yield return [ 12 ];
yield return [1];
yield return [5];
yield return [10];
yield return [12];
}

[Theory]
Expand Down