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Introduction

BZip2 is a commonly used general purpose data compression algorithm.

RB-BZip2 is a BZip2 binding for Realbasic and Xojo projects.

Hilights

• Read and write compressed file or memory streams using a simple BinaryStream work-alike.

Getting started

This project provides several different ways to use BZip2.

Utility methods

The easiest way to use this project are the utility methods in the BZip2 module:

• Compress
• Decompress

These methods are overloaded with several useful variations on input and output parameters. All variations follow either this signature:

 function(source, destination, options[...]) As Boolean

or this signature:

 function(source, options[...]) As MemoryBlock

where source is a MemoryBlock, FolderItem, or an object which implements the Readable interface; and destination (when provided) is a FolderItem or an object which implements the Writeable interface. Methods which do not have a Destination parameter return output as a MemoryBlock instead. Refer to the examples below for demonstrations of some of these functions.

BZ2Stream class

The second way to use BZip2 is with the BZ2Stream class. The BZ2Stream is a BinaryStream work-alike, and implements both the Readable and Writeable interfaces. Anything written to a BZ2Stream is compressed and emitted to the output stream (another Writeable); reading from a BZ2Stream decompresses data from the input stream (another Readable).

Instances of BZ2Stream can be created from MemoryBlocks, FolderItems, and objects that implement the Readable and/or Writeable interfaces. For example, creating an in-memory compression stream from a zero-length MemoryBlock and writing a string to it:

  Dim output As New MemoryBlock(0)
  Dim z As New BZip2.BZ2Stream(output) ' zero-length creates a compressor
  z.Write("Hello, world!")
  z.Close

The string will be processed through the compressor and written to the output MemoryBlock. To create a decompressor pass a MemoryBlock whose size is > 0 (continuing from above):

  z = New BZip2.BZ2Stream(output) ' output contains the compressed string
  MsgBox(z.Read(64)) ' read the decompressed string

Compressor and Decompressor classes

The third and final way to use this project is through the Compressor and Decompressor classes. These classes provide a low-level wrapper to the BZip2 API. All compression and decompression done using the BZ2Stream class or the utility methods is ultimately carried out by an instance of Compressor and Decompressor, respectively.

More examples

This example compresses and decompresses a MemoryBlock:

  Dim data As MemoryBlock = "Potentially very large MemoryBlock goes here!"
  Dim comp As MemoryBlock = BZip2.Compress(data)
  Dim dcmp As MemoryBlock = BZip2.Decompress(comp)

This example bzips a file:

  Dim src As FolderItem = GetOpenFolderItem("") ' a file to be bzipped
  Dim dst As FolderItem = src.Parent.Child(src.Name + ".bz2")
  If BZip2.Compress(src, dst) Then 
    MsgBox("Compression succeeded!")
  Else
    MsgBox("Compression failed!")
  End If

This example opens an existing bzip2 file and decompresses it into a MemoryBlock:

  Dim f As FolderItem = GetOpenFolderItem("") ' the bzip file to open
  Dim data As MemoryBlock = BZip2.Decompress(f)
  If data <> Nil Then
    MsgBox("Decompression succeeded!")
  Else
    MsgBox("Decompression failed!")
  End If

How to incorporate bzip2 into your Realbasic/Xojo project

Import the BZip2 module

1. Download the RB-bzip2 project either in ZIP archive format or by cloning the repository with your Git client.
2. Open the RB-bzip2 project in REALstudio or Xojo. Open your project in a separate window.
3. Copy the BZip2 module into your project and save.

Ensure the bzip2 shared library is installed

bzip2 is installed by default on many Unix-like operating systems, however it may need to be installed separately.

Windows does not have it installed by default, you will need to ship the DLL with your application. You can use pre-built DLL available here (Win32x86), or you can build them yourself from source.

RB-bzip2 will raise a PlatformNotSupportedException when used if all required DLLs/SOs/DyLibs are not available at runtime.