TarReader rejects GNU sparse 1.0 entries whose sparse map exceeds 1 KiB

[pawlos]

Description

TarReader rejects valid GNU sparse format 1.0 (PAX) entries whose embedded sparse map is longer than about 1 KiB. Reading the entry's DataStream, or extracting it with TarFile.ExtractToDirectory, throws InvalidDataException: The TAR archive is corrupted or invalid.. GNU tar writes such maps for any moderately fragmented sparse file: a file with 76 data regions already produces a 1062-byte map.

Reproduction Steps

using System;
using System.Formats.Tar;
using System.IO;

// Both archives were written by tar (--format=pax --sparse --sparse-version=1.0).
foreach (string path in new[] { "sparse72.tar", "sparse76.tar" })
{
    string dir = Directory.CreateTempSubdirectory().FullName;
    try
    {
        TarFile.ExtractToDirectory(path, dir, overwriteFiles: true);
        Console.WriteLine($"{path}: OK");
    }
    catch (Exception ex)
    {
        Console.WriteLine($"{path}: {ex}");
    }
    finally
    {
        Directory.Delete(dir, recursive: true);
    }
}

sparse_files.zip

Expected behavior

Both archives are read and extracted without issues.

Actual behavior

InvalidDataException is thrown on a sparse file whose embedded sparse map is longer than about 1 KiB

Regression?

No. GNU sparse 1.0 reading is new in .NET 11

Known Workarounds

None

Configuration

.NET 11.0.0-rc.1.26425.128, linux-x64

Other information

• Other implementations read both archives correctly: GNU tar, Python tarfile
• The GNU sparse 1.0 format specification does not limit the sparse map size: https://www.gnu.org/software/tar/manual/html_node/PAX-1.html
• The exception is thrown from GnuSparseStream.ParseSparseMapCoreAsync / ReadLineAsync.
• Observed threshold: a 1006-byte sparse map (73 entries) works; a 1062-byte map (77 entries) fails.

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