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Avoid unnecessary array allocations in ZipArchive #123836

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Merged
stephentoub merged 1 commit into from
Feb 3, 2026
+37 −34
Merged

Avoid unnecessary array allocations in ZipArchive #123836

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18 changes: 6 additions & 12 deletions ...braries/System.IO.Compression/src/System/IO/Compression/DeflateManaged/InflaterManaged.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -615,10 +615,8 @@ private bool DecodeDynamicBlockHeader()
throw new InvalidDataException();
}

for (int j = 0; j < repeatCount; j++)
{
_codeList[_loopCounter++] = previousCode;
}
_codeList.AsSpan(_loopCounter, repeatCount).Fill(previousCode);
_loopCounter += repeatCount;
}
else if (_lengthCode == 17)
{
Expand All @@ -635,10 +633,8 @@ private bool DecodeDynamicBlockHeader()
throw new InvalidDataException();
}

for (int j = 0; j < repeatCount; j++)
{
_codeList[_loopCounter++] = 0;
}
_codeList.AsSpan(_loopCounter, repeatCount).Clear();
_loopCounter += repeatCount;
}
else
{
Expand All @@ -656,10 +652,8 @@ private bool DecodeDynamicBlockHeader()
throw new InvalidDataException();
}

for (int j = 0; j < repeatCount; j++)
{
_codeList[_loopCounter++] = 0;
}
_codeList.AsSpan(_loopCounter, repeatCount).Clear();
_loopCounter += repeatCount;
}
}
_state = InflaterState.ReadingTreeCodesBefore; // we want to read the next code.
Expand Down
16 changes: 12 additions & 4 deletions src/libraries/System.IO.Compression/src/System/IO/Compression/ZipArchive.Async.cs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Buffers;
using System.Collections.Generic;
using System.Diagnostics;
using System.Text;
Expand Down Expand Up @@ -199,31 +200,34 @@ private async Task ReadCentralDirectoryAsync(CancellationToken cancellationToken
{
cancellationToken.ThrowIfCancellationRequested();

byte[] arrayPoolArray = ArrayPool<byte>.Shared.Rent(ReadCentralDirectoryReadBufferSize);
try
{
ReadCentralDirectoryInitialize(out byte[] fileBuffer, out long numberOfEntries, out bool saveExtraFieldsAndComments, out bool continueReadingCentralDirectory, out int bytesRead, out int currPosition, out int bytesConsumed);
Memory<byte> fileBuffer = arrayPoolArray;

ReadCentralDirectoryInitialize(out long numberOfEntries, out bool saveExtraFieldsAndComments, out bool continueReadingCentralDirectory, out int bytesRead, out int currPosition, out int bytesConsumed);

// read the central directory
while (continueReadingCentralDirectory)
{
// the buffer read must always be large enough to fit the constant section size of at least one header
int currBytesRead = await _archiveStream.ReadAtLeastAsync(fileBuffer, ZipCentralDirectoryFileHeader.BlockConstantSectionSize, throwOnEndOfStream: false, cancellationToken).ConfigureAwait(false);

byte[] sizedFileBuffer = fileBuffer[0..currBytesRead];
ReadOnlyMemory<byte> sizedFileBuffer = fileBuffer[0..currBytesRead];
continueReadingCentralDirectory = currBytesRead >= ZipCentralDirectoryFileHeader.BlockConstantSectionSize;

while (currPosition + ZipCentralDirectoryFileHeader.BlockConstantSectionSize <= currBytesRead)
{
(bool result, bytesConsumed, ZipCentralDirectoryFileHeader? currentHeader) =
await ZipCentralDirectoryFileHeader.TryReadBlockAsync(sizedFileBuffer.AsMemory(currPosition), _archiveStream, saveExtraFieldsAndComments, cancellationToken).ConfigureAwait(false);
await ZipCentralDirectoryFileHeader.TryReadBlockAsync(sizedFileBuffer.Slice(currPosition), _archiveStream, saveExtraFieldsAndComments, cancellationToken).ConfigureAwait(false);

if (!ReadCentralDirectoryEndOfInnerLoopWork(result, currentHeader, bytesConsumed, ref continueReadingCentralDirectory, ref numberOfEntries, ref currPosition, ref bytesRead))
{
break;
}
}

ReadCentralDirectoryEndOfOuterLoopWork(ref currPosition, sizedFileBuffer);
ReadCentralDirectoryEndOfOuterLoopWork(ref currPosition, sizedFileBuffer.Span);
}

ReadCentralDirectoryPostOuterLoopWork(numberOfEntries);
Expand All @@ -232,6 +236,10 @@ private async Task ReadCentralDirectoryAsync(CancellationToken cancellationToken
{
throw new InvalidDataException(SR.Format(SR.CentralDirectoryInvalid, ex));
}
finally
{
ArrayPool<byte>.Shared.Return(arrayPoolArray);
}
}

// This function reads all the EOCD stuff it needs to find the offset to the start of the central directory
Expand Down
22 changes: 13 additions & 9 deletions src/libraries/System.IO.Compression/src/System/IO/Compression/ZipArchive.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@

// Zip Spec here: http://www.pkware.com/documents/casestudies/APPNOTE.TXT

using System.Buffers;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
Expand All @@ -15,6 +16,8 @@ namespace System.IO.Compression
{
public partial class ZipArchive : IDisposable, IAsyncDisposable
{
private const int ReadCentralDirectoryReadBufferSize = 4096;

private readonly Stream _archiveStream;
private ZipArchiveEntry? _archiveStreamOwner;
private readonly ZipArchiveMode _mode;
Expand Down Expand Up @@ -475,12 +478,8 @@ private void EnsureCentralDirectoryRead()
}
}

private void ReadCentralDirectoryInitialize(out byte[] fileBuffer, out long numberOfEntries, out bool saveExtraFieldsAndComments, out bool continueReadingCentralDirectory, out int bytesRead, out int currPosition, out int bytesConsumed)
private void ReadCentralDirectoryInitialize(out long numberOfEntries, out bool saveExtraFieldsAndComments, out bool continueReadingCentralDirectory, out int bytesRead, out int currPosition, out int bytesConsumed)
{
const int ReadCentralDirectoryReadBufferSize = 4096;

fileBuffer = new byte[ReadCentralDirectoryReadBufferSize];

// assume ReadEndOfCentralDirectory has been called and has populated _centralDirectoryStart

_archiveStream.Seek(_centralDirectoryStart, SeekOrigin.Begin);
Expand Down Expand Up @@ -550,19 +549,20 @@ private void ReadCentralDirectoryPostOuterLoopWork(long numberOfEntries)

private void ReadCentralDirectory()
{
byte[] arrayPoolArray = ArrayPool<byte>.Shared.Rent(ReadCentralDirectoryReadBufferSize);
try
{
ReadCentralDirectoryInitialize(out byte[] fileBuffer, out long numberOfEntries, out bool saveExtraFieldsAndComments, out bool continueReadingCentralDirectory, out int bytesRead, out int currPosition, out int bytesConsumed);
Span<byte> fileBuffer = arrayPoolArray.AsSpan();

Span<byte> fileBufferSpan = fileBuffer.AsSpan();
ReadCentralDirectoryInitialize(out long numberOfEntries, out bool saveExtraFieldsAndComments, out bool continueReadingCentralDirectory, out int bytesRead, out int currPosition, out int bytesConsumed);

// read the central directory
while (continueReadingCentralDirectory)
{
// the buffer read must always be large enough to fit the constant section size of at least one header
int currBytesRead = _archiveStream.ReadAtLeast(fileBufferSpan, ZipCentralDirectoryFileHeader.BlockConstantSectionSize, throwOnEndOfStream: false);
int currBytesRead = _archiveStream.ReadAtLeast(fileBuffer, ZipCentralDirectoryFileHeader.BlockConstantSectionSize, throwOnEndOfStream: false);

ReadOnlySpan<byte> sizedFileBuffer = fileBufferSpan.Slice(0, currBytesRead);
ReadOnlySpan<byte> sizedFileBuffer = fileBuffer.Slice(0, currBytesRead);
continueReadingCentralDirectory = currBytesRead >= ZipCentralDirectoryFileHeader.BlockConstantSectionSize;

while (currPosition + ZipCentralDirectoryFileHeader.BlockConstantSectionSize <= currBytesRead)
Expand All @@ -585,6 +585,10 @@ private void ReadCentralDirectory()
{
throw new InvalidDataException(SR.Format(SR.CentralDirectoryInvalid, ex));
}
finally
{
ArrayPool<byte>.Shared.Return(arrayPoolArray);
}
}

private void ReadEndOfCentralDirectoryInnerWork(ZipEndOfCentralDirectoryBlock eocd)
Expand Down
15 changes: 6 additions & 9 deletions src/libraries/System.IO.Compression/src/System/IO/Compression/ZipBlocks.Async.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -190,23 +190,20 @@ internal sealed partial class ZipCentralDirectoryFileHeader
// Data needs to come from two sources, and we must thus copy data into a single address space.
else
{
if (dynamicHeaderSize > StackAllocationThreshold)
{
arrayPoolBuffer = ArrayPool<byte>.Shared.Rent(dynamicHeaderSize);
}

byte[] collatedHeader = dynamicHeaderSize <= StackAllocationThreshold ? new byte[dynamicHeaderSize] : arrayPoolBuffer.AsSpan(0, dynamicHeaderSize).ToArray();
arrayPoolBuffer = ArrayPool<byte>.Shared.Rent(dynamicHeaderSize);
Memory<byte> collatedHeader = arrayPoolBuffer.AsMemory(0, dynamicHeaderSize);

buffer[FieldLocations.DynamicData..].CopyTo(collatedHeader);

Debug.Assert(bytesToRead == collatedHeader[remainingBufferLength..].Length);
int realBytesRead = await furtherReads.ReadAtLeastAsync(collatedHeader.AsMemory(remainingBufferLength..), bytesToRead, throwOnEndOfStream: false, cancellationToken).ConfigureAwait(false);
Debug.Assert(bytesToRead == collatedHeader.Length - remainingBufferLength);
int realBytesRead = await furtherReads.ReadAtLeastAsync(collatedHeader.Slice(remainingBufferLength), bytesToRead, throwOnEndOfStream: false, cancellationToken).ConfigureAwait(false);

if (realBytesRead != bytesToRead)
{
return (false, bytesRead, null);
}
dynamicHeader = collatedHeader;

dynamicHeader = collatedHeader.Span;
}

TryReadBlockFinalize(header, dynamicHeader, dynamicHeaderSize, uncompressedSizeSmall, compressedSizeSmall, diskNumberStartSmall, relativeOffsetOfLocalHeaderSmall, saveExtraFieldsAndComments, ref bytesRead, out Zip64ExtraField zip64);
Expand Down
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