(DataFlex) Crypt2 Compression Example

The Chilkat Crypt2 class include a few methods for compression and decompression (inflate). These are legacy method that existed long before the Chilkat.Compression class was first introduced. These methods should be avoided in favor of using the Chilkat.Compression methods. The reason is that they are limited to bzip2, and the compressed output includes an 8-byte header that is composed of a magic number (0xB394A7E1) and the size of the original uncompressed data (4 bytes and thus limited to 4GB).

This example demonstrates compression and decompression, and also how to compress using Crypt2 and decompress using Chilkat.Compression. The Chilkat.Compression class does not emit any header, and supports other compression methods.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

Use ChilkatAx-9.5.0-win32.pkg

Procedure Test
    Handle hoCrypt
    Handle hoSb
    Integer i
    String sCompressedStr
    String sOriginalStr
    Handle hoCompress
    Variant vBd
    Handle hoBd
    String sTemp1

    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    Get Create (RefClass(cComChilkatCrypt2)) To hoCrypt
    If (Not(IsComObjectCreated(hoCrypt))) Begin
        Send CreateComObject of hoCrypt
    End

    Get Create (RefClass(cComChilkatStringBuilder)) To hoSb
    If (Not(IsComObjectCreated(hoSb))) Begin
        Send CreateComObject of hoSb
    End
    Move 0 To i
    While (i < 10)
        Get ComAppendInt Of hoSb i To iSuccess
        Get ComAppend Of hoSb " the quick brown fox jumps over the crazy dog" + (character(13)) + (character(10)) To iSuccess
        Move i + 1 To i
    Loop

    Showln "Before compression:"
    Get ComGetAsString Of hoSb To sTemp1
    Showln sTemp1

    // Before compression:
    // 0 the quick brown fox jumps over the crazy dog
    // 1 the quick brown fox jumps over the crazy dog
    // 2 the quick brown fox jumps over the crazy dog
    // 3 the quick brown fox jumps over the crazy dog
    // 4 the quick brown fox jumps over the crazy dog
    // 5 the quick brown fox jumps over the crazy dog
    // 6 the quick brown fox jumps over the crazy dog
    // 7 the quick brown fox jumps over the crazy dog
    // 8 the quick brown fox jumps over the crazy dog
    // 9 the quick brown fox jumps over the crazy dog

    Set ComEncodingMode Of hoCrypt To "base64"
    // Compress the utf-8 representation of the string.
    // Note: Choosing "Unicode" or "utf-16" is a poor choice for text that is mostly us-ascii.
    // The utf-8 representation will result in a smaller size.
    Set ComCharset Of hoCrypt To "utf-8"
    Get ComGetAsString Of hoSb To sTemp1
    Get ComCompressStringENC Of hoCrypt sTemp1 To sCompressedStr

    Showln "After compression:"
    Showln sCompressedStr

    // After compression:
    // 4aeUs+ABAABCWmgzMUFZJlNZT/+H9wAAN1mAABJAAH/gP/v/8CAAkDGExNBgjEMjCYFKqGoAaDygNDamyTYmKe6Ypqn0mqZpgmaZd/hv8fLz9McsU7kyTgmwnAmibU4pyJom5PxNqapxTBO1M05JuT4TrT+TRMCapqm9VzTmn+LuSKcKEgn/8P7g

    // Note: The compressed data includes an 8-byte header composed of a magic number (0xB394A7E1) and the original data byte count.
    // Therefore, the Crypt2 compress/inflate methods are considered legacy and should only be used for data already
    // compressed with these methods.  The Chilkat.Compression class is generalized, emits no headers, and can interoperate with
    // with other software systems without trouble.  

    // If we re-encode from base64 to hex, then we can see the header:
    Get ComReEncode Of hoCrypt sCompressedStr "base64" "hex" To sTemp1
    Showln sTemp1

    // The hex compressed string is:
    // E1A794B3E0010000425A68333141592653594...
    // We can see the 8-byte header in the hex:  magic number = 0xE1A794B3E (little-endian), and byte count = 0xE0010000 (little-endian)

    Get ComInflateStringENC Of hoCrypt sCompressedStr To sOriginalStr
    Showln "After inflate:"
    Showln sOriginalStr

    // ---------------------------------------------------------------------------
    // To inflate with Chilkat.Compression:

    Get Create (RefClass(cComChilkatCompression)) To hoCompress
    If (Not(IsComObjectCreated(hoCompress))) Begin
        Send CreateComObject of hoCompress
    End

    Set ComAlgorithm Of hoCompress To "bzip2"
    Set ComCharset Of hoCompress To "utf-8"
    Set ComEncodingMode Of hoCompress To "base64"

    Get Create (RefClass(cComChilkatBinData)) To hoBd
    If (Not(IsComObjectCreated(hoBd))) Begin
        Send CreateComObject of hoBd
    End
    Get ComAppendEncoded Of hoBd sCompressedStr "base64" To iSuccess
    // Remove the 1st 8 bytes.
    Get ComRemoveChunk Of hoBd 0 8 To iSuccess

    Get pvComObject of hoBd to vBd
    Get ComDecompressBd Of hoCompress vBd To iSuccess

    Showln "After decompression:"
    Get ComGetString Of hoBd "utf-8" To sTemp1
    Showln sTemp1


End_Procedure