(SQL Server) Chunked Compression Using CompressBd2 with FirstChunk and LastChunk

See more Compression Examples

This example demonstrates how to compress data in multiple segments using the CompressBd2 method together with the FirstChunk and LastChunk properties. Instead of compressing all data in a single call, the input is divided into smaller chunks and processed sequentially, which is useful when handling streaming data or large inputs.

The example shows how to correctly mark the first, middle, and final chunks so that the compression stream is properly initialized and finalized. The compressed output is accumulated in a separate BinData object without modifying the input chunks. Finally, the example decompresses the combined result to verify that the original data is restored correctly.

This approach is ideal for scenarios where data is received incrementally, such as reading from a network stream, processing large files in parts, or handling real-time data feeds.

Chilkat ActiveX Downloads

ActiveX for 32-bit and 64-bit Windows

-- Important: See this note about string length limitations for strings returned by sp_OAMethod calls.
--
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    -- Important: Do not use nvarchar(max).  See the warning about using nvarchar(max).
    DECLARE @sTmp0 nvarchar(4000)
    DECLARE @success int
    SELECT @success = 0

    -- This example assumes the Chilkat API has already been unlocked.
    -- See Global Unlock Sample for sample code.

    DECLARE @compress int
    EXEC @hr = sp_OACreate 'Chilkat.Compression', @compress OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    EXEC sp_OASetProperty @compress, 'Algorithm', 'zlib'

    -- This will accumulate the compressed output.
    DECLARE @bdOut int
    EXEC @hr = sp_OACreate 'Chilkat.BinData', @bdOut OUT

    -- ------------------------------------------------------------------
    -- Simulate input arriving in chunks.
    -- ------------------------------------------------------------------

    DECLARE @part1 nvarchar(4000)
    SELECT @part1 = 'The quick brown fox '
    DECLARE @part2 nvarchar(4000)
    SELECT @part2 = 'jumps over the lazy dog. '
    DECLARE @part3 nvarchar(4000)
    SELECT @part3 = 'This text is split into chunks.'

    -- ------------------------------------------------------------------
    -- Compress the first chunk
    -- ------------------------------------------------------------------

    EXEC sp_OASetProperty @compress, 'FirstChunk', 1
    EXEC sp_OASetProperty @compress, 'LastChunk', 0

    DECLARE @bdIn int
    EXEC @hr = sp_OACreate 'Chilkat.BinData', @bdIn OUT

    EXEC sp_OAMethod @bdIn, 'AppendString', @success OUT, @part1, 'utf-8'

    EXEC sp_OAMethod @compress, 'CompressBd2', @success OUT, @bdIn, @bdOut
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @compress, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @compress
        EXEC @hr = sp_OADestroy @bdOut
        EXEC @hr = sp_OADestroy @bdIn
        RETURN
      END

    -- ------------------------------------------------------------------
    -- Compress a middle chunk
    -- ------------------------------------------------------------------

    EXEC sp_OASetProperty @compress, 'FirstChunk', 0
    EXEC sp_OASetProperty @compress, 'LastChunk', 0

    EXEC sp_OAMethod @bdIn, 'Clear', @success OUT
    EXEC sp_OAMethod @bdIn, 'AppendString', @success OUT, @part2, 'utf-8'

    EXEC sp_OAMethod @compress, 'CompressBd2', @success OUT, @bdIn, @bdOut
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @compress, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @compress
        EXEC @hr = sp_OADestroy @bdOut
        EXEC @hr = sp_OADestroy @bdIn
        RETURN
      END

    -- ------------------------------------------------------------------
    -- Compress the final chunk
    -- ------------------------------------------------------------------

    EXEC sp_OASetProperty @compress, 'FirstChunk', 0
    EXEC sp_OASetProperty @compress, 'LastChunk', 1

    EXEC sp_OAMethod @bdIn, 'Clear', @success OUT
    EXEC sp_OAMethod @bdIn, 'AppendString', @success OUT, @part3, 'utf-8'

    EXEC sp_OAMethod @compress, 'CompressBd2', @success OUT, @bdIn, @bdOut
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @compress, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @compress
        EXEC @hr = sp_OADestroy @bdOut
        EXEC @hr = sp_OADestroy @bdIn
        RETURN
      END

    -- Get the final compressed result as base64 for display
    DECLARE @compressedBase64 nvarchar(4000)
    EXEC sp_OAMethod @bdOut, 'GetEncoded', @compressedBase64 OUT, 'base64'


    PRINT 'Compressed data (base64):'

    PRINT @compressedBase64

    -- ------------------------------------------------------------------
    -- Decompress to verify correctness
    -- ------------------------------------------------------------------

    DECLARE @bdDecompressed int
    EXEC @hr = sp_OACreate 'Chilkat.BinData', @bdDecompressed OUT

    EXEC sp_OASetProperty @compress, 'FirstChunk', 1
    EXEC sp_OASetProperty @compress, 'LastChunk', 1

    EXEC sp_OAMethod @compress, 'DecompressBd2', @success OUT, @bdOut, @bdDecompressed
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @compress, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @compress
        EXEC @hr = sp_OADestroy @bdOut
        EXEC @hr = sp_OADestroy @bdIn
        EXEC @hr = sp_OADestroy @bdDecompressed
        RETURN
      END

    -- Convert decompressed bytes back to a string
    DECLARE @resultText nvarchar(4000)
    EXEC sp_OAMethod @bdDecompressed, 'GetString', @resultText OUT, 'utf-8'


    PRINT 'Decompressed text:'

    PRINT @resultText

    EXEC @hr = sp_OADestroy @compress
    EXEC @hr = sp_OADestroy @bdOut
    EXEC @hr = sp_OADestroy @bdIn
    EXEC @hr = sp_OADestroy @bdDecompressed


END
GO