SQL Server

Decompress Large Text File in Blocks

See more Compression Examples

Decompresses a large text file in blocks, and compares the restored (decompressed) file with the original to make sure it's correct. 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
    DECLARE @iTmp0 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.

    -- First, let's compress a text file.
    -- We'll then decompress in blocks, and compare the decompressed with the original file.

    -- Compress a text file:
    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', 'deflate'

    EXEC sp_OAMethod @compress, 'CompressFile', @success OUT, 'qa_data/hamlet.xml', 'qa_data/hamlet_compressed.dat'
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @compress, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @compress
        RETURN
      END

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

    -- Examine the uncompressed and compressed sizes:
    DECLARE @originalPath nvarchar(4000)
    SELECT @originalPath = 'qa_data/hamlet.xml'
    -- Note: The FileSize method returns a signed 32-bit integer.  If the file is potentially larger than 2GB, call FileSizeStr instead to return
    -- the size of the file as a string, then convert to an integer value.

    EXEC sp_OAMethod @fac, 'FileSize', @iTmp0 OUT, @originalPath
    PRINT 'uncompressed size: ' + @iTmp0

    EXEC sp_OAMethod @fac, 'FileSize', @iTmp0 OUT, 'qa_data/hamlet_compressed.dat'
    PRINT 'compressed size: ' + @iTmp0

    -- Decompress in blocks..
    DECLARE @facSrc int
    EXEC @hr = sp_OACreate 'Chilkat.FileAccess', @facSrc OUT

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

    EXEC sp_OAMethod @facSrc, 'OpenForRead', @success OUT, 'qa_data/hamlet_compressed.dat'

    -- 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.
    DECLARE @restoredPath nvarchar(4000)
    SELECT @restoredPath = 'qa_output/hamlet_restored.xml'
    EXEC sp_OAMethod @facDest, 'OpenForWrite', @success OUT, @restoredPath
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @facDest, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @compress
        EXEC @hr = sp_OADestroy @fac
        EXEC @hr = sp_OADestroy @facSrc
        EXEC @hr = sp_OADestroy @facDest
        RETURN
      END

    DECLARE @decompressedStr nvarchar(4000)

    -- 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, 'DecompressString', @decompressedStr OUT, @compressedBytes

        EXEC sp_OAMethod @facDest, 'AppendText', @success OUT, @decompressedStr, 'utf-8'

        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

    -- Examine the size of the restored file.

    EXEC sp_OAMethod @fac, 'FileSize', @iTmp0 OUT, @restoredPath
    PRINT 'restored size: ' + @iTmp0

    -- Compare the contents of the original with the restored.
    DECLARE @bEqualContents int
    EXEC sp_OAMethod @fac, 'FileContentsEqual', @bEqualContents OUT, @restoredPath, @originalPath

    PRINT 'Contents Equal: ' + @bEqualContents

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


END
GO