(Node.js) Add Custom Extra Data to a Gzip File

This example demonstrates how to use the SetExtraData method to include custom binary data in the Gzip header using a hex-encoded string.

The hex string represents the raw bytes to embed in the Gzip metadata. When a compression method is called, this data is included in the Gzip header.

The example also shows how to retrieve the metadata using GetGzipInfo to verify that the extra data was successfully embedded. The retrieved value is returned as a Base64-encoded string.

Install Chilkat for Node.js and Electron using npm at Chilkat npm packages for Node.js Chilkat npm packages for Electron on Windows, Linux, MacOS

var os = require('os');
if (os.platform() == 'win32') {  
  var chilkat = require('@chilkat/ck-node23-win64'); 
} else if (os.platform() == 'linux') {
    if (os.arch() == 'arm') {
        var chilkat = require('@chilkat/ck-node23-linux-arm');
    } else if (os.arch() == 'arm64') {
        var chilkat = require('@chilkat/ck-node23-linux-arm64');
    } else {
        var chilkat = require('@chilkat/ck-node23-linux-x64');
    }
} else if (os.platform() == 'darwin') {
  var chilkat = require('@chilkat/ck-node23-mac-universal');
}

function chilkatExample() {

    var success = false;

    // This example demonstrates how to include custom extra data
    // in the Gzip header when compressing.

    // The extra data is provided as a hex-encoded string.

    var gzip = new chilkat.Gzip();
    var json = new chilkat.JsonObject();

    // Set extra data using a hex string.
    // This example represents 4 bytes: 00 01 02 03
    success = gzip.SetExtraData("00010203","hex");
    if (success == false) {
        console.log(gzip.LastErrorText);
        return;
    }

    // Compress a file so the extra data is embedded in the Gzip header:
    var inputFile = "example.txt";
    var outputFile = "example.txt.gz";

    success = gzip.CompressFile(inputFile,outputFile);
    if (success == false) {
        console.log(gzip.LastErrorText);
        return;
    }

    console.log("Gzip file created with extra data.");

    // (Optional) Retrieve the metadata to verify:
    success = gzip.GetGzipInfo(outputFile,json);
    if (success == false) {
        console.log(gzip.LastErrorText);
        return;
    }

    console.log("Metadata JSON:");
    console.log(json.Emit());

}

chilkatExample();