SQL Server

Decompress Large Binary File in Blocks

See more Compression Examples

Decompresses a large binary file in blocks. SQL Server

-- 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 requires the Chilkat API to have been previously unlocked.
    -- See Global Unlock Sample for sample code.

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

    DECLARE @facDest int
    EXEC @hr = sp_OACreate 'Chilkat.FileAccess', @facDest OUT

    -- Open a previously compressed file for decompressing.
    -- See Compress Large File in Blocks

    EXEC sp_OAMethod @facSrc, 'OpenForRead', @success OUT, 'c:/temp/qa_output/compressedBmp.dat'
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @facSrc, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @facSrc
        EXEC @hr = sp_OADestroy @facDest
        RETURN
      END

    -- If we compress in 32K chunks, find out how many blocks there will be.
    DECLARE @blockSize int
    SELECT @blockSize = 32768
    DECLARE @numBlocks int
    EXEC sp_OAMethod @facSrc, 'GetNumBlocks', @numBlocks OUT, @blockSize

    -- Open an output file for the decompressed data.
    EXEC sp_OAMethod @facDest, 'OpenForWrite', @success OUT, 'c:/temp/qa_output/decompressed.bmp'
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @facDest, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @facSrc
        EXEC @hr = sp_OADestroy @facDest
        RETURN
      END

    DECLARE @compress int
    EXEC @hr = sp_OACreate 'Chilkat.Compression', @compress OUT

    EXEC sp_OASetProperty @compress, 'Algorithm', 'deflate'

    -- Assuming numBlocks > 1
    EXEC sp_OASetProperty @compress, 'FirstChunk', 1
    EXEC sp_OASetProperty @compress, 'LastChunk', 0

    DECLARE @i int
    SELECT @i = 0
    WHILE @i < @numBlocks
      BEGIN
        EXEC sp_OAMethod @facSrc, 'ReadBlock', @compressedBytes OUT, @i, @blockSize

        EXEC sp_OAMethod @compress, 'DecompressBytes', @decompressedBytes OUT, @compressedBytes
        EXEC sp_OAMethod @facDest, 'FileWrite', @success OUT, @decompressedBytes

        SELECT @i = @i + 1

        EXEC sp_OASetProperty @compress, 'FirstChunk', 0
        IF @i = (@numBlocks - 1)
          BEGIN
            EXEC sp_OASetProperty @compress, 'LastChunk', 1
          END
      END

    EXEC sp_OAMethod @facSrc, 'FileClose', NULL
    EXEC sp_OAMethod @facDest, 'FileClose', NULL


    PRINT 'Finished decompressing file.'

    EXEC @hr = sp_OADestroy @facSrc
    EXEC @hr = sp_OADestroy @facDest
    EXEC @hr = sp_OADestroy @compress


END
GO