gistfile1.js

var fs = require('fs');
var http = require('http');
var urlparser = require('url');
var k = process.binding('constants');

function Download(url,path, options,callback){
	/*
		existing options:
			- range: [start, end] specifies the Range of the part to be downloaded. start or end may be null to specify download "from beginning" or "to end" respecively.
			- continue: if not set to true file will be truncated before writing to it
	*/
	this.callback=callback;
	this.http.tx={
		headers: null,
		range: null,
		parsedUrl: urlparser.parse(url)
	};
		
	this.http.rx= {
			headers: null,
			status: null,
			range: null,
			bytes: 0,
			responseObject: null
	}
	this.http.state.current=this.http.state.clear;
	this.fs={
		fd: null,
		position: 0,
		target: null,
		fileSize: null,
		truncate: true,
		path: null
	}

	this.cache.buffer = new Buffer(this.cache.size),
	this.position= 0
	this.timer= {timerObject: null, bytesLastStatsUpdate: 0, timerInterval: 2000};
	//this.parseOptions(options || {});
	this.Download(url,path);
}

Download.prototype = {
	http: {
		state: {clear: 0, awaitingResponse: 1, downloading: 2, finished: 3},
		parseResponseHeaders: function(that){
			var rx=that.http.rx;
			var headers=rx.headers;
			that.fs.target=headers['content-length'] || null;
			console.log('target: ' + that.fs.target);
			if(headers['content-range'] && new RegExp("bytes \d+-\d+/((\d+)|\*)").test(headers['content-range'])){
				var s = headers['content-range'].substr(0,6).split('/')
				that.rx.range=s[0].split('-');
				that.fs.fileSize=s[1]!="*" ? s[1] : null;
			}
		}
	},
	cache: {
		size: 524288, //512kB
		flush: function(that){
			that.http.rx.responseObject.pause();
			fs.write(that.fs.fd,that.cache.buffer,0,that.cache.buffer.position,that.fs.position,function(err,written){
				if(that.http.state.current == that.http.state.finished){
					fs.close(this.fs.fd);
					delete this.cache;
				}
				else{
					that.http.rx.responseObject.resume()
				}
			});
			that.fs.position+=that.cache.position;
			that.cache.position=0;
		},
		append: function(that,chunk){
			chunk.position=0;
			if(Buffer.isBuffer(chunk)){
				console.log('is buffer!');
			}
			else{
				 console.log('not a buffer!');
			}
			while(that.cache.position+chunk.length-chunk.position>=that.cache.size){
				chunk.copy(that.cache.buffer,that.cache.position,chunk.position,that.cache.size-that.cache.position);
				chunk.position+=that.cache.size-that.cache.position;
				that.buffer.flush(that);
			}
			chunk.copy(that.cache.buffer,that.cache.position,chunk.size-chunk.position)
			that.cache.position+=chunk.size-chunk.position;
		
			if(that.http.rx.bytes==that.fs.target || that.http.state.current == that.http.state.finished){
				that.http.state.current=that.http.state.finished
				clearInterval(that.timer.timerObject);
				that.rx.responseObject.destroy();
			}
		}
	},
	Download: function (url,path){
		this.http.state.current = this.http.state.awaitingResponse;
		var options={host: this.http.tx.parsedUrl.host, port: this.http.tx.parsedUrl.port ||'80', path: this.http.tx.parsedUrl.pathname, method: 'GET'};
		if(this.http.tx.range && (options['Range'][0] || options['Range'][1])) options['Range'] = 'bytes='+(this.http.tx.range[0] || "") +"-"+(this.http.range[1] || "")
		var g=http.get(options);
		console.log('now waiting for a response');
		var that= this;
		g.on('response', function(res) {
			that.http.rx.responseObject = res;
			that.http.rx.responseObject.pause();
			that.http.rx.responseObject.setEncoding('binary');			

			console.log('got response: ' + that.http.rx.responseObject.statusCode);
			that.http.rx.headers=that.http.rx.responseObject.headers;
			that.http.parseResponseHeaders(that)
			that.http.rx.status=that.http.rx.responseObject.statusCode;
			that.http.state.current = that.http.state.downloading;
			res.on('data',function(chunk){that.http.rx.bytes+=chunk.length; that.cache.append(that,chunk)});
			that.openFile(path);
		});
		g.on('error', function(e) {
			console.log('got error while sending get request: ' + e.message);
			process.exit(2);
		});
		g.on('end', function() {
			this.http.state.current = this.http.state.finished;
			console.log('download complete');
		});
	},
	openFile: function(path){
		console.log('path: ' + path)
		var that=this;
		fs.open(path, k.O_WRONLY | k.O_CREAT | (this.fs.truncate ? 0 : k.O_TRUNC ) , 0777, function(err, fd){
			if(err){
				console.error("Got error while opening file: " + err.message);
				process.exit(1); 
			}
			that.fs.fd=fd;
			console.log('file sucessfully opened')
			that.http.rx.responseObject.resume();
			that.timer.timerObject=setInterval(function(){that.statsTick(that)},that.timer.timerInterval);
		});
	},
	statsTick: function(that){
		console.log('recieved: ' + that.http.rx.bytes + 'B of '+ that.fs.target + 'B, progress: ' + ( that.http.rx.bytes /that.fs.target*100).toPrecision(4) + '%, download-rate: '
			+ ((that.http.rx.bytes-that.timer.bytesLastStatsUpdate)/that.timer.timerInterval).toPrecision(4) + 'kB/s, connection status: ' + that.http.state.current);
		that.timer.bytesLastStatsUpdate = that.http.rx.bytes;
	}
}

var d = new Download('http://dl.google.com/earth/client/current/GoogleEarthLinux.bin', 'googleearth.bin');