Check checksum when reading TAR archives

[rzikm]

fixes #117455.

TarReader now throws when encountering checksum failures.

Draft beause there are test failures and discussion is needed.

[rzikm]

There seem to be two test files where we expect to progress even with invalid checksum?

node-tar/bad-cksum.tar - this one seems to be extracted correctly with GNU tar but will fail with bsdtar on windows

node-tar$ tar xf bad-cksum.ta
r -C test/
tar: Skipping to next header
tar: Exiting with failure status due to previous errors
node-tar$ ls test/
one-byte.txt
node-tar$ cat test/one-byte.txt
a

❯ tar xf .\bad-cksum.tar -C .\test\
tar.exe: Damaged tar archive
tar.exe: Retrying...
tar.exe: Damaged tar archive
tar.exe: Retrying..

golang_tar/issue12435.tar - this file seems to be garbage, null bytes in checksum.

System.Formats.Tar.Tests.TarWriter_Tests.Verify_Compatibility_RegularFile_EmptyFile_NoSizeStored tests seems to be editing some header data, so might just need fixing the checksum in the test data.

[dotnet-policy-service]

Added needs-breaking-change-doc-created label because this PR has the breaking-change label.

When you commit this breaking change:

1. Create and link to this PR and the issue a matching issue in the dotnet/docs repo using the breaking change documentation template, then remove this needs-breaking-change-doc-created label.
2. Ask a committer to mail the .NET Breaking Change Notification DL.

Tagging @dotnet/compat for awareness of the breaking change.

[Copilot]

Pull Request Overview

This PR adds checksum validation to TAR archive reading to improve data integrity. The TarReader now throws InvalidDataException when encountering checksum failures instead of silently ignoring them.

Key changes:

• Adds checksum validation logic to the TAR header reading process
• Updates tests to expect exceptions instead of null returns for invalid checksums
• Adds new error message resource for checksum validation failures

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/libraries/System.Formats.Tar/src/System/Formats/Tar/TarHeader.Read.cs	Implements checksum validation and adds helper method to calculate header checksums
src/libraries/System.Formats.Tar/src/Resources/Strings.resx	Adds new error message resource for checksum validation failures
src/libraries/System.Formats.Tar/tests/TarReader/TarReader.Tests.cs	Adds comprehensive test for invalid checksum scenarios
src/libraries/System.Formats.Tar/tests/TarReader/TarReader.File.Tests.cs	Updates existing tests to expect exceptions for checksum failures
src/libraries/System.Formats.Tar/tests/TarReader/TarReader.File.Async.Tests.cs	Updates async tests to expect exceptions for checksum failures
src/libraries/System.Formats.Tar/tests/TarWriter/TarWriter.Tests.cs	Fixes checksum in existing test to maintain validity
src/libraries/System.Formats.Tar/tests/TarTestsBase.cs	Removes "bad-cksum" test case from exclusion list