Automatically rewind base stream position when decompression finishes by iremyux · Pull Request #121111 · dotnet/runtime

iremyux · 2025-10-27T10:37:39Z

Fixes automatic stream positioning issue when using compression streams with mixed-content data.

When using DeflateStream, GZipStream, ZLibStream or BrotliStream for decompression, the underlying stream position would advance past the end of compressed data due to internal buffering. This caused issues when reading additional content after decompression in mixed-format files.

Added automatic stream rewinding when decompression completes and the underlying stream supports seeking
The stream is now rewound to the exact end of compressed data by seeking back by the number of unconsumed bytes in the inflater/decoder buffer
Added _decompressionFinished flag to ensure rewinding happens only once, even with multiple Read/ReadAsync/CopyTo calls after decompression completes
Added new tests to verify stream rewinding behavior and prevention of multiple rewinds

Fixes #73770

Copilot

Pull Request Overview

This PR fixes an issue where DeflateStream, GZipStream, and ZLibStream would leave the underlying stream position past the end of compressed data due to internal buffering, making it impossible to read additional content after decompression in mixed-format files.

Key Changes:

Added automatic stream rewinding logic that repositions seekable streams to the exact end of compressed data when decompression finishes
Exposed internal method GetAvailableInput() in Inflater to track unconsumed buffered bytes
Added comprehensive test coverage for both sync and async decompression scenarios

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
`CompressionStreamUnitTests.Deflate.cs`	Added two test methods (`AutomaticStreamRewinds_WhenDecompressionFinishes` and async variant) to verify stream position is correctly restored after decompression
`Inflater.cs`	Added `GetAvailableInput()` method to expose the count of unconsumed bytes in the internal buffer
`DeflateStream.cs`	Implemented automatic stream rewinding in both `Dispose` and `DisposeAsync` by seeking backwards by the number of unconsumed bytes

src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateZLib/DeflateStream.cs

src/libraries/System.IO.Compression/tests/CompressionStreamUnitTests.Deflate.cs

src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateZLib/DeflateStream.cs

…zip and Zlib

src/libraries/System.IO.Compression.Brotli/src/System/IO/Compression/BrotliStream.cs

...raries/System.IO.Compression.Brotli/src/System/IO/Compression/dec/BrotliStream.Decompress.cs

Copilot

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateZLib/DeflateStream.cs

...raries/System.IO.Compression.Brotli/src/System/IO/Compression/dec/BrotliStream.Decompress.cs

src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateZLib/DeflateStream.cs

src/libraries/System.IO.Compression.Brotli/src/System/IO/Compression/BrotliStream.cs

…ession/BrotliStream.cs Co-authored-by: Copilot <[email protected]>

…DeflateZLib/DeflateStream.cs Co-authored-by: Copilot <[email protected]>

…et-runtime into 73770-stream-rewind

rzikm

LGTM, apart from unresolved Copilot comments about comment wording

rhuijben · 2025-11-25T06:49:11Z

Thanks, this solves a lot of issues I've had to work around in he past.
Too bad this will probably need a few years to be everywhere in stable releases.

Thanks!!

iremyux added 5 commits October 24, 2025 15:19

Rewind the DeflateStream when it is disposed in decompression mode

99cc990

Remove trailing whitespace

c7b2ed8

Change comment

2a435c4

Rewind when _leaveOpen is true

1357c5d

Add tests

731b4e8

iremyux self-assigned this Oct 27, 2025

Merge branch 'main' into 73770-stream-rewind

5ae51cd

github-actions bot added the area-System.IO.Compression label Oct 27, 2025

iremyux marked this pull request as ready for review October 27, 2025 11:25

Copilot AI review requested due to automatic review settings October 27, 2025 11:25

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iremyux requested a review from a team October 27, 2025 13:32

build-analysis bot mentioned this pull request Oct 27, 2025

The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

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rzikm reviewed Nov 3, 2025

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iremyux added 3 commits November 4, 2025 14:37

Adding TryRewindStream function and removing duplicate code

65f9ab0

Adding tests for Gzip and Zlib too

da66fbe

Move the test to the base instead of defining the same for Deflate, G…

38c5dc9

…zip and Zlib

This was referenced Nov 4, 2025

[wasm] OpenQA.Selenium.WebDriverTimeoutException: timeout: Timed out receiving message from renderer #117486

Open

System.Security.Cryptography.X509Certificates.Tests fails on Linux #120527

Closed

iremyux and others added 3 commits November 7, 2025 17:32

Merge branch 'dotnet:main' into 73770-stream-rewind

f192a78

Refactor stream rewind tests

c72075d

Add the rewinding logic to BrotliStream as well

52cbdb8

iremyux changed the title ~~Automatically rewind base stream position when DeflateStream decompression finishes~~ Automatically rewind base stream position when decompression finishes Nov 7, 2025

Merge branch 'main' into 73770-stream-rewind

08c0caf

rzikm reviewed Nov 10, 2025

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src/libraries/System.IO.Compression.Brotli/src/System/IO/Compression/BrotliStream.cs Outdated Show resolved Hide resolved

iremyux added 2 commits November 11, 2025 13:47

Update the test according to the current behavior of streams

f4806c9

Move rewinding to end of Read instead of Dispose

e5c7ff0

Merge branch 'main' into 73770-stream-rewind

2730924

iremyux requested a review from rzikm November 11, 2025 13:00

This was referenced Nov 11, 2025

Unable to pull image from mcr.microsoft.com #117164

Open

slow macOS - "##[error]The job running on agent Azure Pipelines 9 ran longer than the maximum time of 60 minutes." dotnet/dnceng#1883

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rzikm reviewed Nov 12, 2025

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...raries/System.IO.Compression.Brotli/src/System/IO/Compression/dec/BrotliStream.Decompress.cs Outdated Show resolved Hide resolved

iremyux added 3 commits November 17, 2025 21:06

Introduce the boolean to keep track if we rewound

8a499ee

Introduce the boolean to keep track if we rewound

d713505

Add test with multiple reads

5887a22

iremyux requested a review from Copilot November 23, 2025 19:21

Copilot started reviewing on behalf of iremyux November 23, 2025 19:22 View session

Copilot finished reviewing on behalf of iremyux November 23, 2025 19:24

Copilot AI reviewed Nov 23, 2025

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This was referenced Nov 23, 2025

SIGSEGV in System.Net.Quic.Functional.Tests #121575

Closed

Cose.Tests.TestKeyRing.CreateECDsa fails with "OSStatus error -50" #121902

Open

iremyux and others added 4 commits November 24, 2025 10:50

Update src/libraries/System.IO.Compression.Brotli/src/System/IO/Compr…

672a06e

…ession/BrotliStream.cs Co-authored-by: Copilot <[email protected]>

Update src/libraries/System.IO.Compression/src/System/IO/Compression/…

1bf173f

…DeflateZLib/DeflateStream.cs Co-authored-by: Copilot <[email protected]>

Make decompression finished flag volatile

a0795c5

Merge branch '73770-stream-rewind' of https://github.com/iremyux/dotn…

36fd431

…et-runtime into 73770-stream-rewind

rzikm approved these changes Nov 24, 2025

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build-analysis bot mentioned this pull request Nov 24, 2025

Cannot find 'arm64-v8a' device dotnet/dnceng#2284

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3 tasks

iremyux merged commit cf9869e into dotnet:main Nov 24, 2025
86 checks passed

dotnet-maestro bot mentioned this pull request Nov 25, 2025

[main] Source code updates from dotnet/runtime dotnet/dotnet#3448

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iremyux deleted the 73770-stream-rewind branch November 26, 2025 20:10

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Automatically rewind base stream position when decompression finishes#121111

Automatically rewind base stream position when decompression finishes#121111
iremyux merged 23 commits intodotnet:mainfrom
iremyux:73770-stream-rewind

iremyux commented Oct 27, 2025 •

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iremyux commented Oct 27, 2025 •

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