CLOUD-X

Remote Desktops and Applications through Web Browsers

Edgar Fabi´an Hern´andez-Ventura and Jorge Buenabad-Ch´avez

Departamento de Computaci´on, CINVESTAV-IPN, Ciudad de M´exico, D.F., Mexico

Keywords:

Remote desktops, Web browsers, Cloud computing.

Abstract:

Cloud computing is gaining general acceptance and we believe it will broaden its user base signiﬁcantly once

users can run their favourite applications in the Cloud through web browsers and with the same interface that

each such application is used in a desktop or laptop computer. This paper presents CloudX, a new architecture

based on web browser techonologies for the X Window system. X Window is the de facto standard for

window display in Unix-like operating systems. CloudX translates X Window commands to web browser

display commands using AJAX and SVG (Scalar Vector Graphics) technologies. CloudX does not require any

extension to the X Window system nor any plugin to the web browser.

1 INTRODUCTION

There has been a lot of hype around Cloud computing

in recent years, both in industry and in the research

community; and rightly so. For small and medium en-

terprises (SMEs) and individual entrepreneurs alike,

Cloud computing is quite the panacea in IT. Having

access to a sound IT infrastructure, at a reasonable

price, with 24/7 or so availability, and immediate use

from anywhere and any device, fosters both creativity

and entrepreneurship. Certainly, the cost and hassle

of deploying and maintaining a solid IT infrastructure

was a hindrance for many a good idea to develop.

We think the user base of Cloud computing

will broaden signiﬁcantly once users can run their

favourite applications in the Cloud through web

browsers and with the same interface that each such

application is used in a desktop or laptop computer.

It is possible to run applications with a rich GUI

remotely and with good performance using remote

desktop technologysuch as Cytrix (Citrix Inc., 2010b)

and NX (NoMachine, 2010). However, doing so is not

as ﬂexible as doing it through a web browser. Using

remote desktop technology would involve installing a

client software in each computer and mobile device

with which a user works, and it may not be available

for some software-hardware platforms. Also, its in-

stallation may require privileges (c.f. Ipod, Ipad) that

users may not have or may not want to exercise for

lack of relevant knowledge.

This paper presents Cloud-X, a new web-browser-

based architecture for the X Window system. X Win-

dow is the de facto standard for window display in

Unix-like operating systems. It consists of a general,

hardware-independentset of commandsto buildGUIs

and a network protocol for communication between

an application and remote display hardware. Cloud-

X translates X Window commands to browser dis-

play commands using AJAX and SVG (Scalar Vector

Graphics) technologies. It does not require any exten-

sion to the X Window system nor any plugin to the

web browser.

The remainder of the paper is organized as fol-

lows. Section 2 presents background material to X

Window and SVG. Section 3 presents the design of

Cloud-X. Section 4 presents related work and we con-

clude in Section 5.

2 BACKGROUND TO X WINDOW

AND SVG TECHNOLOGIES

2.1 X Window (X11)

“The X Window system [typically referred to as X11

for its current major version being 11] is a computer

software system and network protocol that provides

a basis for graphical user interfaces (GUI) for net-

worked computers. It creates a hardware abstraction

layer where software is written to use a generalized

set of commands, allowing for device independence

234

Fabián Hernández-Ventura E. and Buenabad-Chávez J..

CLOUD-X - Remote Desktops and Applications through Web Browsers.

DOI: 10.5220/0003611302340237

In Proceedings of the 6th International Conference on Software and Database Technologies (ICSOFT-2011), pages 234-237

ISBN: 978-989-8425-76-8

 2011 SCITEPRESS (Science and Technology Publications, Lda.)

and reuse of programs on any computer that imple-

ments X” (Wikipedia, 2011). It was developed in

1984 at MIT by Bob Scheiﬂer and Jim Gettys (Schei-

ﬂer et al., 1988).

The basic idea of the X11 protocol is as follows,

see Figure 1. Applications are clients that request an

X server to display their interfaces through requests

sent over a network. The server executes the requests

in the display hardware. The server also captures in-

put events from the user both through the mouse and

through the keyboard, and sends them back to the ap-

plication over the network. The application responds

to events by sending more requests to the X server,

and so on.

XServer

(Display)

(Application)

Client

Responses

Events

Errors

Requests

Figure 1: X11 base protocol.

In PCs and workstations using a Unix-like operat-

ing system, X11 works the same: a client application

and the X server run completely separate, but on the

same machine.

2.1.1 Display Capabilities

The server handles 127 different request codes, corre-

sponding to the core X11 protocol. The client sends

requests to create, manipulate and destroy server re-

sources. These resources will affect the GUI dis-

played to the user and include: windows, pointer, key-

board, fonts, pixmaps, graphical contexts and palettes

(colormaps). There are also requests to manage win-

dow properties, text manipulation and to subscribe to

events generated from the user.

2.1.2 Event Capabilities

The event capabilities of X11 include: cursors man-

agement, resource management, color mapping, inter-

client communication (the ability of different X11

applications to communicate with one another) and

input and output buffering, among others (Brain,

1992).

2.2 SVG

SVG (Scalable Vector Graphics) is a family of speci-

ﬁcations in XML for describing two-dimensionalvec-

tor graphics, both static and dynamic. The speciﬁca-

tion has been under development by the World Wide

Web Consortium (W3C) since 1999 (SVG Working

Group, 2010a).

Being deﬁned in XML text ﬁles, SVG images can

be searched, indexed, scripted, compressed, and cre-

ated and edited with a texteditor. There are also draw-

ing applications that support SVG ﬁle formats like

Inkscape (Inkscape, 2011).

All major modern web browsers support and ren-

der SVG markup directly with some limitations. It

is expected that in 2011 all major browsers comply

with at least 80% of the speciﬁcation of the SVG test

suite (SVG Working Group, 2010b).

2.2.1 Display Capabilities

SVG graphical objects can be vectorial graphics,

raster images (PNG, JPEG) and text. Graphical Ob-

jects can be modiﬁed in several ways while being dis-

played. They can be grouped together, the style with

which they were drawn can be changed, they can be

transformed in size, rotated, etc. This allows inter-

esting and complex ways of display and animation,

making SVG an excellent tool for web design and vi-

sualization.

2.2.2 Events Capabilities

SVG images are composed of graphical objects.

These objects offer different ways to interact with the

user. They can have hiperlinks to new pages or gener-

ate events by change of focus, mouse click, scrolling

or zooming.

Each event is handled by a deﬁned function that

may run a script, or perhaps start, stop or alter an ani-

mation. This is very important for the implementation

of Cloud-X. There is no need to develop a new mech-

anism for mouse or keyboard input. We just use the

event handlers already implemented for SVG in the

browser with no additional plugins required.

3 CLOUD-X

Cloud-X was conceived out of the need for visual-

izing already developed desktop software with rich

GUI, but remotely through the cloud. In our search,

we observed that the web browser is the most widely

used software to connectto the cloud, and was already

installed in almost any device (including tablets and

smartphones).

Although different technologies are available for

drawing in web browsers, like Java applets or Flash,

we wanted our software to be as non-invasive as pos-

CLOUD-X - Remote Desktops and Applications through Web Browsers

235

sible, and also to be standard complying. After study-

ing SVG, we made it our choice as we found it ideal

for displaying interfaces, and because it is based on

open standards. The latter guarantees (to some ex-

tent) long term support and usability in browsers that

implement those standards. Almost any major web

browser has SVG support or plans to implement it

in the short term. This eliminates the need of addi-

tional software like Oracle Java, Adobe Flash, Mi-

crosoft Silverlight, etc. All we got left to do was the

communication part.

Investigating the way Linux displays its graphics,

we found out that X11 already catered for remote dis-

play. Both ends of the connection were already there:

the applications already programmed to display their

interfaces remotely and web browsers with features

to display them. However, the communication can-

not be completed without software that translate mes-

sages between X11 and SVG.

Cloud-X makes such translation. It is a web ap-

plication programmed in Java and uses Tomcat Web

Server to provide dynamic web pages to an applica-

tion’s GUI using SVG and AJAX.

3.1 Overview

Figure 2 shows Cloud-X. Recall that: X11 works with

a client/server model, an application is the client, and

when an application requires to display a GUI it sends

a series of X11 commands to an X server. Cloud-

X translates them and writes an SVG ﬁle. The ﬁle

is created in a web server to make it available to the

web browser which then displays its content. In the

web browser, the user will interact with the GUI and

generate events. Cloud-X translates these events to

X11 events and sends them back to the application.

Application

WidgetToolkit

Xlib

Cloud-X

WebServer

Browser

Screen,

Keyboardand

PointingDevice

RemoteDesktop

Cloud-XServer

UserDevice

X11

HTTP

Figure 2: Cloud-X Architecture.

When only part of a GUI needs to be updated (for

instance edited text or closed subwindows), instead of

sending a completely new SVG ﬁle, AJAX is used to

refresh immediately only that part in the user’s web

browser. This is very convenient as the browser only

has to keep track of the currently displayed graphi-

cal objects, leaving to Cloud-X the task of manag-

ing what objects to show, and what objects to hide

or eliminate from memory. Cloud-X is composed of

four modules: the Access Controller, the Resources

Manager, the Events Manager and the Communica-

tion Manager.

3.2 From X Window to SVG and Vice

Versa

Cloud-X will map X Window commands and events

into “equivalent” SVG commandsand events and vice

versa, as outlined shortly. Assume a user connected to

a remoteweb server through a web browser, and about

to click on an icon in order to start running the Emacs

editor on a Linux remote host. The Emacs GUI inter-

face will be displayed within the web browser. (We

are ommitting some details of the communication: the

initial connection to the remote web server, in which

Cloud-X runs, and the communication to show the

ﬁrst display to the user.) The following events will

take place:

1. Cloud-X opens a secure shell channel with the

remote host where Emacs will run, and starts an

X11-forward session so that the display output of

Emacs will be forwarded to Cloud-X. (Note that

both the web server, Cloud-X and Emacs may run

in the same host.)

2. Emacs (through Xlib) starts the handshake proto-

col with the Cloud-X server, which involves ask-

ing the characteristics of the display and the X

server it is dealing with, e.g.: colours available,

display size, etc.

3. Cloud-X sends the web browser a simple SVG ﬁle

for the web browser to start displaying a blank

GUI and thus overlap some processing.

4. Emacs will then display its GUI, which involves

the following. It will ﬁrst send X11 requests to

create the necessary resources in the X Server, ac-

tually the Cloud-X server. Emacs will then send a

request to show its GUI (XmapWindow). On re-

ceiving this request, Cloud-X will generate a new

SVG ﬁle with the GUI and will push it into the

web browser.

5. Among other events, Emacs will request from

X server to be informed of keyboard and mouse

events, for instance, when Ctrl-S is entered. For

each event, Cloud-X will generate a handler func-

tion that is written in an SVG ﬁle and that is

pushed into the web browser. When the user inter-

action involves any such event, the relevant han-

dler function will send a message to Cloud-X,

which will translate it into an X11 response to

send to Emacs.

6. Emacs will eventually update part of its GUI (for

example, displaying the

File

menu), sending the

ICSOFT 2011 - 6th International Conference on Software and Data Technologies

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relevant X11 requests. Cloud-X will parse each

request, translate it into a single update to the

SVG ﬁle (in the web browser) corresponding to

the entire Emacs GUI, and then will push each

update into the web browser. The latter will then

update the user display.

We are currently implementing the above func-

tionality. After trying it out, we will design and imple-

ment the functionality relating to displaying streams

(sound and video), printing and ﬁle sharing.

4 RELATED WORK

The purpose of our work is to use web browsers

to display rich GUIS of applications running re-

motely. The work more similar to ours that we know

of is the Broadway extension to the GTK+ toolkit

library developed by Alexander Larsson (Larsson,

2010). Broadway extension is only for GTK+ soft-

ware. Cloud-X works for any X11 application includ-

ing GTK+, Qt, MOTIF, etc.

Rich GUI applications can be run remotely

through Remote Desktop technology, but not within

a web browser. There are various Remote Desktop

clients available. NX is an optimization of the X

Window system and protocol that connects to Linux

desktops (NoMachine, 2010). Virtual Network Com-

puting (VNC) has multi-platform compatibility given

by the underlying protocol, the Remote FrameBuffer

(RFB) protocol, which works directly with the screen

buffer and just sends the raw pixel data.

The Remote Desktop Protocol (RDP) (Microsoft,

2010) and Independent Computing Architecture

(ICA) (Citrix Inc., 2010a) are proprietary network

protocols for the Microsoft Windows operating sys-

tem. The commercial products Citrix XenAppp

client uses ICA (Citrix Inc., 2010b). ICA and RDP

send

GDI+

commands in ciphered packages through a

TCP/IP network.

GDI+

(Graphical Device Interface)

is the core Windows API for GUI drawing.

All these technologies require certain resources

and system permissions to install their clients, and as

mentioned earlier, they do not show the display within

web browsers.

5 CONCLUSIONS AND FUTURE

WORK

Web browsers run on a wide variety of devices and

operating systems and will soon be compliant to the

SVG standard. Through Cloud-X, web browsers will

be able to display rich GUIs of X11 applications run-

ning remotely. Cloud-X offers two main advantages:

i) immediate use of hundreds of applications already

developed for Unix-like operating systems based on

Xlib, and ii) development of new Cloud applications

without the need to develop new display technology.

Cloud-X can also be used as the base technology

to offer a complete operating system in the Cloud.

When a new user needs an account and resources to

work with, the system administrator can install a copy

of Linux in a powerful server with all the software re-

quired. The user can then access this new desktop en-

vironmentfromany devicewith a web browser,elimi-

nating the need of providingeach user with a powerful

machine.

ACKNOWLEDGEMENTS

Edgar Hern´andez-Ventura would like to thank

CONACyT for the scholarship granted to carry out

his MSc studies.

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