Creating an In-Memory Tar Archive from SQL Server varbinary(max) Files Using .NET 8

Below is an example of how you can achieve this using the .NET native APIs in .NET 8. The System.Formats.Tar namespace now provides the TarWriter and TarEntry classes, so you don't necessarily need a third-party library like SharpZipLib.

Keep in mind that when creating a TarEntry, you’ll need to specify the entry type (typically RegularFile) and set the DataStream. Also, the tar header requires the size of the entry. If you have a stream that supports seeking, you can set the Length property (or use other means to set the size) before writing the entry.

Below is a sample implementation based on your pseudocode:

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CSHARPCopied
using System;
using System.Data.SqlClient;
using System.Formats.Tar;
using System.IO;
using System.Threading.Tasks;

public class TarFileService
{
    public async Task CreateTarFromDatabaseFilesAsync()
    {
        // Create a MemoryStream to store the .tar archive in memory
        using var tarStream = new MemoryStream();
        // Create the TarWriter to write tar entries to tarStream.
        // Use leaveOpen: true if you plan to write tarStream further after disposing tarWriter.
        await using var tarWriter = new TarWriter(tarStream, leaveOpen: true);
        
        // Open a connection to SQL Server
        await using var connection = new SqlConnection("YourConnectionString");
        await connection.OpenAsync();
        var command = new SqlCommand("SELECT FileName, FileData FROM FilesTable", connection);
        
        // Execute the reader to get files from the database
        await using var reader = await command.ExecuteReaderAsync();

        while (await reader.ReadAsync())
        {
            var fileName = reader.GetString(0);
            // GetStream returns a Stream for the varbinary(MAX) column containing file data.
            using Stream fileDataStream = reader.GetStream(1);

            // If possible, get the length of the data (this is required for correct tar headers)
            long size = fileDataStream.CanSeek ? fileDataStream.Length : 0;

            // Create a TarEntry for a regular file.
            // The constructor takes the entry type and the name.
            var entry = new TarEntry(TarEntryType.RegularFile, fileName)
            {
                // Setting the DataStream to the file data read from SQL.
                DataStream = fileDataStream
            };

            // Optionally, set the entry's size if the API requires it.
            // entry.DataStream must support length, or you might need to copy to a MemoryStream first.
            // For example, if !CanSeek, you might load the stream into a MemoryStream so its length is known.

            // Write the entry to the tar archive.
            tarWriter.WriteEntry(entry);
        }

        // At this point, tarStream contains the complete tar archive.
        // For example, to write it to an HTTP Response stream:
        tarStream.Seek(0, SeekOrigin.Begin);
        // await tarStream.CopyToAsync(response.Body); // response.Body is your HTTP response stream.
    }
}

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Key Points

• .NET Native API:
  .NET 8 includes System.Formats.Tar, which provides native support to create and extract tar archives without third-party libraries.

• TarEntry Construction:
  Create a new TarEntry by specifying the entry type (e.g., TarEntryType.RegularFile) and the file name. Then set its DataStream property to the file data stream obtained from the SQL reader.

• Stream Length Considerations:
  The tar header records the size of each file. Ensure that your stream’s length is known (ideally the stream supports seeking) or load the data into a MemoryStream first to determine its length.

By following this approach, you can construct a tar archive on the fly using files stored in SQL Server without extra dependencies.