crixalis/lib/plugins/compression.js

'use strict';

/**
 * Compression plugin.
 * Provides gzip and deflate on the fly compression for response
 * @module Crixalis
 * @submodule compression
 * @for Controller
 */

var define = require('../controller').define,
	zlib   = require('zlib');

module.exports = function () {
	/**
	 * Default compression method. Supported values are __gzip__ and __deflate__.
	 * @property defaultCompression
	 * @type String
	 * @default gzip
	 */
	define('property', 'defaultCompression', 'gzip');

	/**
	 * Detect best supported by client compression format
	 * @method compression
	 * @return {String}
	 */
	define('method', 'compression', function () {
		var codings = this.codings,
			i, l;

		/* Select compression type */
		for (i = 0, l = codings.length; i < l; i++) {
			switch (codings[i]) {
				case '*':
					return this.defaultCompression;

				case 'gzip':
					return 'gzip';

				case 'deflate':
					return 'deflate';
			}
		}

		/* Nothing selected */
		return undefined;
	});

	/**
	 * Apply compression to response body
	 * @event compression
	 */
	define('handler', 'compression', function () {
		var that    = this,
			type    = this.compression(),
			length  = 0,
			buffers = [],
			compressor;

		switch (type) {
			case 'gzip':
				compressor = zlib.createGzip();
				break;

			case 'deflate':
				compressor = zlib.createDeflate();
				break;

			default:
				/* Compression not supported by client or disabled for this request */
				process.nextTick(function () {
					that._response();
				});
				return;
		}

		compressor.on('error', function (error) {
			that.error(error, true);
		});

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

		compressor.on('end', function () {
			var output, b, i, j, l, k;

			compressor.removeAllListeners();

			switch (buffers.length) {
				case 0:
					output = new Buffer(0);
					break;

				case 1:
					output = buffers[0];
					break;

				default:
					output = new Buffer(length);

					for (i = 0, j = 0, l = buffers.length; i < l; i++) {
						b = buffers[i];
						k = b.length;
						b.copy(output, j, 0, k);
						j += k;
					}
			}

			/* Set headers */
			that.headers['Content-Length']   = length;
			that.headers['Content-Encoding'] = type;
			that.headers['Vary']             = 'Accept-Encoding';

			that.body = output;

			/* Respond to client */
			that._response();
		});

		compressor.write(this.body);
		compressor.end();
	});
};