How to decompress File

Following code explain how to decompress file

Public Sub DecompressGivenFile(ByVal srcFile As String, ByVal destFile As String)
       
        Dim sourceStream As FileStream = Nothing
        Dim destinationStream As FileStream = Nothing
        Dim decompressedStream As GZipStream = Nothing
        Dim quartetBuffer As Byte() = Nothing

        Try
          
            sourceStream = New FileStream(sourceFile, FileMode.Open)
            decompressedStream = New GZipStream(sourceStream, CompressionMode.Decompress, True)
          
            quartetBuffer = New Byte(4) {}
            Dim position As Integer = CType(sourceStream.Length, Integer) - 4
            sourceStream.Position = position
            sourceStream.Read(quartetBuffer, 0, 4)
            sourceStream.Position = 0
            Dim checkLength As Integer = BitConverter.ToInt32(quartetBuffer, 0)

            Dim buffer(checkLength + 100) As Byte
            Dim offset As Integer = 0
            Dim total As Integer = 0

          
            While True
                Dim bytesRead As Integer = decompressedStream.Read(buffer, offset, 100)
                If bytesRead = 0 Then
                    Exit While
                End If
                offset += bytesRead
                total += bytesRead
            End While

           
            destinationStream = New FileStream(destinationFile, FileMode.Create)
            destinationStream.Write(buffer, 0, total)
            destinationStream.Flush()

        Catch ex As ApplicationException
            MessageBox.Show(ex.Message, "An Error occured during compression", MessageBoxButtons.OK, MessageBoxIcon.Error)       
        End Try
 End Sub