Question

I need to compress a buffer in Node.js with zlib at the extreme compression level. The outputted header should be 78 DA. Unless I’m missing something, the Node.js documentation doesn’t really describe how to use the zlib.Deflate class. It doesn’t accept any parameters.

http://nodejs.org/api/zlib.html#zlib_class_zlib_deflate

Answer 1

Use zlib. createGzip/createDeflate to get an instance of the compressor you need, with options in an object.

If you want to do this all in-memory:

var zlib = require('zlib');

// create a new gzip object
var gzip = zlib.createGzip({
    level: 9 // maximum compression
}), buffers=[], nread=0;

// attach event handlers...

gzip.on('error', function(err) {
    gzip.removeAllListeners();
    gzip=null;
});

gzip.on('data', function(chunk) {
    buffers.push(chunk);
    nread += chunk.length;
});


gzip.on('end', function() {
    var buffer;
    switch (buffers.length) {
        case 0: // no data.  return empty buffer
            buffer = new Buffer(0);
            break;
        case 1: // only one chunk of data.  return it.
            buffer = buffers[0];
            break;
        default: // concatenate the chunks of data into a single buffer.
            buffer = new Buffer(nread);
            var n = 0;
            buffers.forEach(function(b) {
                var l = b.length;
                b.copy(buffer, n, 0, l);
                n += l;
            });
            break;
    }

    gzip.removeAllListeners();
    gzip=null;

    // do something with `buffer` here!
});

// and finally, give it data to compress
gzip.write(inputBuffer);
gzip.end();

Of course, if you’re dealing with large amounts of data, stream the output to a file rather than buffering everything in memory.