Node.js

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. Node.js

NODEJS_PRELUDE

function chilkatExample() {

    var success = false;

    //  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:
    var compress = new chilkat.Compression();
    compress.Algorithm = "deflate";

    success = compress.CompressFile("qa_data/hamlet.xml","qa_data/hamlet_compressed.dat");
    if (success == false) {
        console.log(compress.LastErrorText);
        return;
    }

    var fac = new chilkat.FileAccess();

    //  Examine the uncompressed and compressed sizes:
    var 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.
    console.log("uncompressed size: " + fac.FileSize(originalPath));
    console.log("compressed size: " + fac.FileSize("qa_data/hamlet_compressed.dat"));

    //  Decompress in blocks..
    var facSrc = new chilkat.FileAccess();
    var facDest = new chilkat.FileAccess();

    facSrc.OpenForRead("qa_data/hamlet_compressed.dat");

    //  If we compress in 32K chunks, find out how many blocks there will be.
    var blockSize = 32768;
    var numBlocks = facSrc.GetNumBlocks(blockSize);

    //  Open an output file for the decompressed data.
    var restoredPath = "qa_output/hamlet_restored.xml";
    success = facDest.OpenForWrite(restoredPath);
    if (success == false) {
        console.log(facDest.LastErrorText);
        return;
    }

    var decompressedStr;

    //  Assuming numBlocks > 1
    compress.FirstChunk = true;
    compress.LastChunk = false;

    var i = 0;
    while (i < numBlocks) {
        compressedBytes = facSrc.ReadBlock(i,blockSize);
        decompressedStr = compress.DecompressString(compressedBytes);

        facDest.AppendText(decompressedStr,"utf-8");

        i = i+1;

        compress.FirstChunk = false;
        if (i == (numBlocks - 1)) {
            compress.LastChunk = true;
        }

    }

    facSrc.FileClose();
    facDest.FileClose();

    //  Examine the size of the restored file.
    console.log("restored size: " + fac.FileSize(restoredPath));

    //  Compare the contents of the original with the restored.
    var bEqualContents = fac.FileContentsEqual(restoredPath,originalPath);
    console.log("Contents Equal: " + bEqualContents);

}

chilkatExample();