Tar: Only treat reparse points marked as junctions or symlinks as actual tar symlinks by rzikm · Pull Request #124753 · dotnet/runtime

rzikm · 2026-02-23T12:57:58Z

Problem

On Windows, TarWriter.ConstructEntryForWriting classifies ALL files with the ReparsePoint file attribute as symbolic links. This is incorrect for files with non-symlink reparse points such as:

Deduplicated files (IO_REPARSE_TAG_DEDUP) - content is transparently accessible
OneDrive synced files - content is transparently accessible
AppExecLinks (IO_REPARSE_TAG_APPEXECLINK) - content is NOT accessible as a regular file

Solution

Use FileSystemInfo.LinkTarget to distinguish symlinks and junctions from other reparse point types. LinkTarget returns non-null only for IO_REPARSE_TAG_SYMLINK and IO_REPARSE_TAG_MOUNT_POINT (verified in FileSystem.Windows.cs:GetImmediateLinkTarget).

Classification logic:

Symlinks/junctions (LinkTarget is not null) - TarEntryType.SymbolicLink with the link target path
Non-symlink directory reparse points (e.g., OneDrive dirs) - TarEntryType.Directory
Non-symlink file reparse points with Normal/Archive (e.g., dedup files) - Regular file entry, content read via FileStream
Non-symlink reparse points where FileStream fails (e.g., AppExecLinks) - IOException with TarUnsupportedFile message
Other reparse points (no Normal/Archive/Directory attributes) - IOException with TarUnsupportedFile message

Changes

TarWriter.Windows.cs: Core fix - use LinkTarget for symlink/junction detection, let other reparse points fall through to attribute-based classification, catch FileStream failures for opaque reparse points
TarHelpers.cs: Added GetRegularFileEntryTypeForFormat helper
TarWriter.Unix.cs: Use new helper (consistency)
New Windows-only tests: Junction and AppExecLink scenarios (sync + async)
Test infrastructure: Moved GetAppExecLinkPath to shared ReparsePointUtilities.cs
8 test files: Use GetRegularFileEntryTypeForFormat helper

Copilot

Pull request overview

This PR fixes a critical bug where TarWriter on Windows incorrectly classified all reparse points (including data deduplication, OneDrive placeholders, and AppExecLinks) as symbolic links. The fix leverages the FileSystemInfo.LinkTarget property which only returns a non-null value for true symbolic links (IO_REPARSE_TAG_SYMLINK) and junctions (IO_REPARSE_TAG_MOUNT_POINT), allowing other reparse point types to be correctly classified as regular files or directories.

Changes:

Modified TarWriter.Windows.cs to check LinkTarget property instead of just the ReparsePoint attribute
Extracted GetRegularFileEntryTypeForFormat helper to TarHelpers.cs to eliminate duplication
Added comprehensive tests for junctions and non-symlink reparse points (using AppExecLinks)
Moved GetAppExecLinkPath utility to shared ReparsePointUtilities.cs for reuse across test projects

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
TarWriter.Windows.cs	Core fix: checks `LinkTarget is not null` to distinguish symlinks/junctions from other reparse points; caches LinkTarget value to avoid redundant I/O
TarHelpers.cs	Adds `GetRegularFileEntryTypeForFormat` helper method to centralize V7 vs regular file type selection logic
TarWriter.Unix.cs	Refactored to use new helper method; removed unused `using` directives
TarWriter.WriteEntry.File.Tests.Windows.cs	New test file with junction test and non-symlink reparse point test (sync version)
TarWriter.WriteEntryAsync.File.Tests.Windows.cs	New test file with junction test and non-symlink reparse point test (async version)
System.Formats.Tar.Tests.csproj	Registers new Windows-specific test files
TarTestsBase.cs	Adds `GetRegularFileEntryTypeForFormat` helper for test code reuse
Various test files	Replace inline ternary expressions with `GetRegularFileEntryTypeForFormat` helper for consistency
ReparsePointUtilities.cs	Adds `GetAppExecLinkPath` method migrated from FileSystem tests for cross-project reuse
File/FileInfo SymbolicLinks.cs	Updated to use `MountHelper.GetAppExecLinkPath()` instead of local method
BaseSymbolicLinks.FileSystem.cs	Removed `GetAppExecLinkPath` (migrated to shared utilities); removed unused using directive

Copilot

Pull request overview

Copilot reviewed 18 out of 18 changed files in this pull request and generated no new comments.

…n Windows Only treat reparse points as symbolic links when FileSystemInfo.LinkTarget returns a non-null value, indicating the reparse point is a true symlink or junction. Other reparse points (e.g., deduplication, OneDrive) now fall through to be handled as regular files or directories. Added GetRegularFileEntryTypeForFormat helper to reduce duplication of the V7/regular file entry type check pattern across source and test files. Moved GetAppExecLinkPath to shared ReparsePointUtilities so it can be used by both FileSystem and Tar tests. Added tests verifying junctions are correctly written as symbolic link entries and that non-symlink reparse points are not misidentified. Fixes dotnet#82949 Co-authored-by: Copilot <[email protected]>

Copilot

Pull request overview

Copilot reviewed 20 out of 20 changed files in this pull request and generated 3 comments.

src/libraries/System.Formats.Tar/src/System/Formats/Tar/TarWriter.Windows.cs

src/libraries/Common/src/Interop/Windows/Kernel32/Interop.FindFirstFileEx.cs

Remove FindFirstFile/GetFindData interop and use FileSystemInfo.LinkTarget to detect symlinks and junctions. Non-symlink reparse points with file attributes (e.g., dedup, OneDrive) fall through to be classified as regular files or directories based on their attributes. Opaque reparse points (e.g., AppExecLinks) that cannot be read are caught at FileStream open and rethrown with TarUnsupportedFile message. Co-authored-by: Copilot <[email protected]>

rzikm · 2026-02-25T08:05:02Z

@copilot run the code review skill

alinpahontu2912 · 2026-02-25T12:01:15Z

src/libraries/Common/tests/System/IO/ReparsePointUtilities.cs

 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
+#if !NETFRAMEWORK


why do we need the guards for io.enumeration? i see it was not used previously

System.IO.Enumeration is not available on .NET Framework, the build results from the previous PR are not available but I expect the build to have failed on .NET Framework then.

Copilot AI review requested due to automatic review settings February 23, 2026 12:57

github-actions bot added the area-System.Formats.Tar label Feb 23, 2026

dotnet-policy-service bot assigned rzikm Feb 23, 2026

Copilot started reviewing on behalf of rzikm February 23, 2026 12:58 View session

Copilot AI reviewed Feb 23, 2026

View reviewed changes

This was referenced Feb 23, 2026

[android] Android.Device_Emulator.JIT.Test failing on emulators with CoreCLR #112633

Open

[android][clr] No peer certificates when executing System.Net.Http.Functional.Tests on Android emulator #124526

Open

rzikm force-pushed the fix/tar-reparse-point-82949 branch from a3c53f0 to fff18c6 Compare February 23, 2026 16:22

build-analysis bot mentioned this pull request Feb 23, 2026

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

Open

rzikm force-pushed the fix/tar-reparse-point-82949 branch from fff18c6 to e9aac36 Compare February 24, 2026 15:08

Copilot AI review requested due to automatic review settings February 24, 2026 15:08

Copilot started reviewing on behalf of rzikm February 24, 2026 15:09 View session

rzikm force-pushed the fix/tar-reparse-point-82949 branch 2 times, most recently from aaa64b5 to 926b2fd Compare February 24, 2026 15:14

Copilot AI reviewed Feb 24, 2026

View reviewed changes

rzikm force-pushed the fix/tar-reparse-point-82949 branch from 926b2fd to 1e1492f Compare February 24, 2026 15:30

Use GetFindData helper

814b786

Copilot AI review requested due to automatic review settings February 24, 2026 15:43

rzikm changed the title ~~Fix TarWriter treating non-symlink reparse points as symbolic links on Windows~~ Tar: Only treat reparse points marked as junctions or symlinks as actual tar symlinks Feb 24, 2026

Copilot started reviewing on behalf of rzikm February 24, 2026 15:44 View session

rzikm requested review from a team and removed request for a team February 24, 2026 15:48

Copilot AI reviewed Feb 24, 2026

View reviewed changes

build-analysis bot mentioned this pull request Feb 25, 2026

[FAIL] System.Net.Http.Functional.Tests.SocketsHttpHandler_HttpClientHandlerTest.LargeUriAndHeaders_Works #124487

Open

alinpahontu2912 reviewed Feb 25, 2026

View reviewed changes

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Tar: Only treat reparse points marked as junctions or symlinks as actual tar symlinks#124753

Tar: Only treat reparse points marked as junctions or symlinks as actual tar symlinks#124753
rzikm wants to merge 3 commits intodotnet:mainfrom
rzikm:fix/tar-reparse-point-82949

rzikm commented Feb 23, 2026 •

edited

Loading

Uh oh!

Copilot AI left a comment

Uh oh!

Copilot AI left a comment

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

rzikm commented Feb 25, 2026

Uh oh!

alinpahontu2912 Feb 25, 2026

Uh oh!

rzikm Feb 25, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Conversation

rzikm commented Feb 23, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Problem

Solution

Changes

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Uh oh!

Uh oh!

rzikm commented Feb 25, 2026

Uh oh!

alinpahontu2912 Feb 25, 2026

Choose a reason for hiding this comment

Uh oh!

rzikm Feb 25, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

rzikm commented Feb 23, 2026 •

edited

Loading