Chilkat Examples

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(Node.js) Decompress Large Text File in Blocks

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

Install Chilkat for Node.js and Electron using npm at

Chilkat npm packages for Node.js

Chilkat npm packages for Electron

on Windows, Linux, MacOSX, and ARM

var os = require('os');
if (os.platform() == 'win32') {  
    if (os.arch() == 'ia32') {
        var chilkat = require('@chilkat/ck-node21-win-ia32');
    } else {
        var chilkat = require('@chilkat/ck-node21-win64'); 
    }
} else if (os.platform() == 'linux') {
    if (os.arch() == 'arm') {
        var chilkat = require('@chilkat/ck-node21-arm');
    } else if (os.arch() == 'x86') {
        var chilkat = require('@chilkat/ck-node21-linux32');
    } else {
        var chilkat = require('@chilkat/ck-node21-linux64');
    }
} else if (os.platform() == 'darwin') {
    if (os.arch() == 'arm64') {
        var chilkat = require('@chilkat/ck-node21-mac-m1');
    } else {
        var chilkat = require('@chilkat/ck-node21-macosx');
    }
}

function chilkatExample() {

    // 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";

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

    var decompressedStr;

    var i = 0;
    while (i < numBlocks) {
        compressedBytes = facSrc.ReadBlock(i,blockSize);
        if (i == 0) {
            decompressedStr = compress.BeginDecompressString(compressedBytes);
        }
        else {
            decompressedStr = compress.MoreDecompressString(compressedBytes);
        }

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

        i = i+1;
    }

    // At the very end, flush any remaining content, if any.
    decompressedStr = compress.EndDecompressString();
    facDest.AppendText(decompressedStr,"utf-8");

    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();

 

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