Configure FileStreamOptions with PreallocationSize and async access in ZipArchiveEntry extract methods#125260
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rzikm merged 5 commits intodotnet:mainfrom Mar 19, 2026
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Pull request overview
Improves ZipArchiveEntry extraction performance/behavior by configuring FileStreamOptions to (1) preallocate disk space based on the entry’s uncompressed size and (2) enable async file I/O when extracting via async APIs.
Changes:
- Set
FileStreamOptions.PreallocationSizefromZipArchiveEntry.Lengthduring extraction initialization. - Thread an
asyncflag into the shared initialization helper to setFileOptions.AsynchronousforExtractToFileAsync.
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Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
| src/libraries/System.IO.Compression.ZipFile/src/System/IO/Compression/ZipFileExtensions.ZipArchiveEntry.Extract.cs | Adds preallocation and async/sync option selection to the shared file-creation options. |
| src/libraries/System.IO.Compression.ZipFile/src/System/IO/Compression/ZipFileExtensions.ZipArchiveEntry.Extract.Async.cs | Passes the async flag so extracted file streams use async I/O. |
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...O.Compression.ZipFile/src/System/IO/Compression/ZipFileExtensions.ZipArchiveEntry.Extract.cs
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…n ZipArchiveEntry extract methods Set PreallocationSize based on the entry's uncompressed size to allow the file system to pre-allocate disk space, reducing fragmentation and improving write performance. Configure FileOptions.Asynchronous when extracting from async methods so that the FileStream uses async I/O. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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ZipArchiveEntry.Length throws InvalidOperationException when the entry has been opened for writing (e.g. in Update mode). Read it in a try/catch and fall back to 0 (no preallocation) to avoid regressing that scenario. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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...O.Compression.ZipFile/src/System/IO/Compression/ZipFileExtensions.ZipArchiveEntry.Extract.cs
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...O.Compression.ZipFile/src/System/IO/Compression/ZipFileExtensions.ZipArchiveEntry.Extract.cs
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stephentoub
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Mar 6, 2026
...O.Compression.ZipFile/src/System/IO/Compression/ZipFileExtensions.ZipArchiveEntry.Extract.cs
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stephentoub
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...O.Compression.ZipFile/src/System/IO/Compression/ZipFileExtensions.ZipArchiveEntry.Extract.cs
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iremyux
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Mar 12, 2026
...O.Compression.ZipFile/src/System/IO/Compression/ZipFileExtensions.ZipArchiveEntry.Extract.cs
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...O.Compression.ZipFile/src/System/IO/Compression/ZipFileExtensions.ZipArchiveEntry.Extract.cs
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...O.Compression.ZipFile/src/System/IO/Compression/ZipFileExtensions.ZipArchiveEntry.Extract.cs
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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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This was referenced Mar 18, 2026
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I see that we do not have new tests for the new behavior - is it intentional? |
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There is no way to functionally test the new behavior. |
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Set
PreallocationSizeonFileStreamOptionsbased on the entry's uncompressed size (ZipArchiveEntry.Length) to allow the file system to pre-allocate disk space, reducing fragmentation and improving write performance.Configure
FileOptions.Asynchronouswhen extracting from async methods (ExtractToFileAsync) so theFileStreamuses async I/O.