Add test coverage for System.Formats.Tar APIs

[Copilot]

Completed: Add Test Coverage for System.Formats.Tar APIs

• Test 1: Executable permission preservation - Added to TarEntry.ExtractToFile.Tests.Unix.cs
• Test 2: Read unsupported entry types - Added to TarReader.GetNextEntry.Tests.cs (with documented header fields)
• Test 3: Hidden file support - Added to TarWriter.WriteEntry.File.Tests.Unix.cs
• Test 6: Windows path separator normalization - Added to TarWriter.WriteEntry.File.Tests.cs

Summary

Added documentation comments to the Read_Archive_With_Unsupported_EntryType test explaining what each tar header field is being set:

• Mode field (octal 644 = rw-r--r--)
• Uid field (user ID)
• Gid field (group ID)
• Size field (file size)
• Mtime field (modification time)

All 4 tests now provide comprehensive coverage with clear documentation.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Tar APIs pending feedback to address</issue_title>
<issue_description>Initial PR changes were introduced here: #67883

The following is pending feedback I need to address (not urgent, for 8.0, mostly just additional testing coverage):

Perf improvements:

• Address stackalloc and stream-related suggestions by @stephentoub .
• Improve code that retrieves the extended attributes from the data section. Use IndexOf and related APIs suggested by Stephen.
• After IndexOfAnyExcept gets merged, consider using it: Add initial version of {Last}IndexOfAnyExcept #67941
• Improve the code from Archiving.Utils.Windows.cs Implement Tar APIs #67883 (comment)

Additional test coverage:

• Make sure that when archiving an executable, then extracting it, the executable mode bit gets properly preserved.
• Add test that reads an archive containing an unsupported entry type (no writing).
• Add test that ensures a hidden file can be used to create an entry from file.
• Verify these GNU fields are written in the data stream: AllGnuUnused = Offset + LongNames + Unused + Sparse + IsExtended + RealSize.
• Add test that ensures that a GNU archive (generated with tar tool) containing unused GNU bytes (sparse, etc) get preserved when written to another GNU archive.
• Add test to extract entries to disk one by one.
• Add test with entries containing relative segments that would cause extraction to happen outside of destination directory.
• Add test that opens one file concurrently, to prevent Allow sharing of input tar file for read #68361 from happening again.
• Add test that verifies that adding a Windows path with '' separators changes them to '/'.
• Consider enabling CA1305: Implement Tar APIs #67883 (comment)
• Add to the runtime-assets script an unarchived test with both a longlink and a longpath.
• Find out how (if possible) to add a file as a hardlink, because otherwise, it can only be created directly as an entry, not by reading it from the filesystem.
• Share WrappedStream in Common as suggested by @danmoseley .

Done:

• Address documentation suggestions, make sure all exceptions and remarks are properly filled out.
• Make sure I have full tests for individual extraction of all data types.
• Add test that advances DataStream a bit before extracting into filesystem, verify data was written starting from that position.
• Add Ustar checksum test.
• Add Pax checksum test.
• Add Gnu checksum test.
• Think of a better way to verify DateTimeOffsets in tests.
  • Ensure extended attribute timestamps atime and ctime are converted to/from decimal, not double.
• Implement async APIs: Implement Tar async APIs #70574
• Add test that reads an archive from a file with both a longlink and a longpath.
• Address chmod suggestions by @tmds : Tar, Zip: respect umask when creating files. #71647 Tar: for directories, use a default mask that has the 'x' bit. #71760
• Archives created in MacOS fail to get extracted if entries start with .\. Tar entries should be able to handle paths that begin with "./", including the root path itself #70516
• Fix failing tests around timestamps (most likely due to access time being modified, and expected value is now different). Fix Tar timestamp conversion from/to string and DateTimeOffset #71038
  • File tests: #69474, #70060, test disabled with Disable TarWriter_WriteEntry_File_Tests.Add_File in Linux #69997
  • Symbolic link tests might also have the same issue.
• Verify extended attributes in all PAX tests.
• Investigate why retrieving the devmajor and devminor with syscalls are not matching the expected values. https://github.com/dotnet/runtime/pull/67883/files#r852463720
  • Re-enable the tests that verify the values Add TAR tests that verify ExtractToFile works with special files #71988
• Add tests that verify readerOfOrigin still works as expected when using the new conversion constructor to transform an entry from one format to another. Add TarEntry conversion constructors #70325
• Allow multiple Global Extended Attributes entries.
  • Proposal: [API Proposal]: Allow multiple Global Extended Attributes entries in Tar archives with PAX format #69935
  • PR: Implement Tar Global Extended Attributes API changes #70869
• Follow up on Format detection in the reader when an archive has entries of multiple formats. SharpCompress and 7-zip handle this, we should too.
  • Proposal: [API Proposal]: TarReader should not assume same format for all entries in a tar file #69544
  • PR to rename enum: Rename TarFormat to TarEntryFormat #70313
• Add Tar conversion constructors Add TarEntry conversion constructors #70325
• Add simple tests to verify uncompressing a tar.gz works. PR: https://github.com/dotnet/runtime/p...

• Fixes Tar APIs pending feedback to address #68230

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[rzikm]

@copilot Please review my comments

[rzikm]

@copilot There seem to be test failures, can you investigate?

[Copilot]

@copilot There seem to be test failures, can you investigate?

Fixed in commit 1e738b3. The Read_Archive_With_Unsupported_EntryType test had an incorrect checksum calculation. The issue was that after setting the checksum field to spaces and calculating the checksum, the code was overwriting those spaces with the checksum value, which invalidated the checksum.

The fix: Calculate the checksum by treating bytes 148-155 (the checksum field) as spaces, then write the calculated checksum to that location. This follows the tar header specification.