Lianja

Streaming Compression

See more Compression Examples

Compress and decompress using a stream. Lianja

llSuccess = .F.

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

loFac = createobject("CkFileAccess")
loCompress = createobject("CkCompression")
loCompress.Algorithm = "deflate"

loStreamC = createobject("CkStream")

// This example sets the source and sink of the stream to files.
// A stream can have use other streams as a source or sink,
// or the application can itself be the source/sink by directly
// reading or writing a stream.  (See below for an example of this..)
loStreamC.SourceFile = "qa_data/hamlet.xml"
loStreamC.SinkFile = "qa_output/hamlet_compressed.dat"

// Compress from source to sink.
llSuccess = loCompress.CompressStream(loStreamC)
if (llSuccess <> .T.) then
    ? loCompress.LastErrorText
    release loFac
    release loCompress
    release loStreamC
    return
endif

? "File-to-file deflate compression successful."
// 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.
? "Original size = " + str(loFac.FileSize(loStreamC.SourceFile))
? "Compressed size = " + str(loFac.FileSize(loStreamC.SinkFile))

// Now do file-to-file decompression
loStreamD = createobject("CkStream")
loStreamD.SourceFile = "qa_output/hamlet_compressed.dat"
loStreamD.SinkFile = "qa_output/hamlet_restored.xml"

// Decompress from source to sink.
llSuccess = loCompress.DecompressStream(loStreamD)
if (llSuccess <> .T.) then
    ? loCompress.LastErrorText
    release loFac
    release loCompress
    release loStreamC
    release loStreamD
    return
endif

? "File-to-file deflate decompression successful."

// Let's double-check to see that the files are equal in size and content:

llBFilesEqual = loFac.FileContentsEqual(loStreamC.SourceFile,loStreamD.SinkFile)
if (llBFilesEqual <> .T.) then
    ? "The output file is not equal to the input file!"
else
    ? "The file was successfully compressed and decompressed."
endif

// ---------------------------------------------------------------------
// Now let's decompress again, but this time w/ the application reading
// the decompressed data directly from a stream.
loStreamA = createobject("CkStream")

loStreamA.SourceFile = "qa_output/hamlet_compressed.dat"

// Start decompressing in a background thread.
loTask = loCompress.DecompressStreamAsync(loStreamA)
llSuccess = loTask.Run()

// Read decompressed data from streamA:

do while (loStreamA.EndOfStream <> .T.)
    if (loStreamA.DataAvailable = .T.) then
        lcDecompressedText = loStreamA.ReadString()
        ? lcDecompressedText
    endif

enddo

// Let's make sure the background task finished and that the decompress was successful.
// It should already be the case that the task is finished.
do while (loTask.Finished <> .T.)
    loTask.SleepMs(20)
enddo

// The decompressor may have finished, but it is possible that data
// remains to be flushed.  
if (loStreamA.DataAvailable = .T.) then
    lcDecompressedText = loStreamA.ReadString()
    ? lcDecompressedText
endif

// Did streamA succeed in reading the entire file?
if (loTask.TaskSuccess <> .T.) then
    ? "async decompress failed:"
    ? loTask.ResultErrorText
    llSuccess = .F.
endif

? "The async decompress was successful."


release loFac
release loCompress
release loStreamC
release loStreamD
release loStreamA