Listing 1: The Compression Function

using System;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
using System.IO;
using System.IO.Compression;

public partial class UserDefinedFunctions
{
  // Set the function characteristics.
  [Microsoft.SqlServer.Server.SqlFunction(IsDeterministic=true,
    DataAccess=DataAccessKind.None)]
// BEGIN CALLOUT A
    public static SqlBytes fn_compress(SqlBytes blob)
// END CALLOUT A
    {
      if (blob.IsNull)
        return blob;
// BEGIN CALLOUT B
      // Retrieve the BLOB's data.
      byte[] blobData = blob.Buffer;
// END CALLOUT B
// BEGIN CALLOUT C
      // Prepare for compression.
      MemoryStream compressedData = new MemoryStream();
        DeflateStream compressor = new DeflateStream(compressedData, 
        CompressionMode.Compress, true);
      // Write the uncompressed data using a DeflateStream compressor.
      compressor.Write(blobData, 0, blobData.Length);
      // Close the compressor to allow all the compressed bytes to be written.
      compressor.Flush();
      compressor.Close();
      compressor = null;
// END CALLOUT C
      // Return the compressed blob.
      return new SqlBytes(compressedData);
    }
};