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noVNC: HTML5 VNC Client

Description

noVNC is a VNC client implemented using HTML5 technologies, specifically Canvas and WebSocket (supports 'wss://' encryption).

For browsers that do not have builtin WebSocket support, the project includes web-socket-js, a WebSocket emulator using Adobe Flash .

In addition, as3crypto has been added to web-socket-js to implement WebSocket SSL/TLS encryption, i.e. the "wss://" URI scheme.

Running in Chrome before and after connecting:

Requirements

Until there is VNC server support for WebSocket connections, you need to use a WebSocket to TCP socket proxy. There is a python proxy included ('wsproxy'). One advantage of using the proxy is that it has builtin support for SSL/TLS encryption (i.e. "wss://").

There a few reasons why a proxy is required:

WebSocket is not a pure socket protocol. There is an initial HTTP like handshake to allow easy hand-off by web servers and allow some origin policy exchange. Also, each WebSocket frame begins with 0 ('\x00') and ends with 255 ('\xff').
Javascript itself does not have the ability to handle pure byte strings (Unicode encoding messes with it) even though you can read them with WebSocket. The python proxy encodes the data so that the Javascript client can base64 decode the data into an array.
When using the web-socket-js as a fallback, WebSocket 'onmessage' events may arrive out of order. In order to compensate for this the client asks the proxy (using the initial query string) to add sequence numbers to each packet.

Usage

To encrypt the traffic using the WebSocket 'wss://' URI scheme you need to generate a certificate for the proxy to load. You can generate a self-signed certificate using openssl. The common name should be the hostname of the server where the proxy will be running:

openssl req -new -x509 -days 365 -nodes -out self.pem -keyout self.pem
run a VNC server.

vncserver :1
run the python proxy:

`./utils/wsproxy.py -f source_port target_addr:target_port

./utils/wsproxy.py -f 8787 localhost:5901
run the mini python web server to serve the directory:

./utils/web.py PORT

./utils/web.py 8080
Point your web browser at http://localhost:8080/vnc.html (or whatever port you used above to run the web server).
Specify the host and port where the proxy is running and the password that the vnc server is using (if any). Hit the Connect button and enjoy!

Browser Support

In the following table Jaunty is Ubuntu 9.04 and WinXP is Windows XP.

Linux (Ubuntu 9.04)

OS	Browser	Status	Notes
Jaunty	Chrome 5.0.375.29	Excellent	Very fast. Native WebSockets.
Jaunty	Firefox 3.5	Good	Large full-color images are somewhat slow from web-socket-js overhead.
Jaunty	Opera 10.60	Poor	web-socket-js problems, mouse/keyboard issues. See note 1
Jaunty	Arora 0.5	Good	Broken putImageData so large full-color images are slow. Uses web-socket-js.
Jaunty	Konqueror 4.2.2	Broken	web-socket-js never loads

WinXP	Chrome 5.0.375.99	Excellent	Very fast. Native WebSockets.
WinXP	Firefox 3.0.19	Good	Some overhead from web-socket-js.
WinXP	Safari 5.0	Fair	Fast. Native WebSockets. Broken 'wss://' (SSL) - weird client header
WinXP	IE 6, 7, 8	Non-starter	No basic Canvas support. Javascript painfully slow.

Note 1: Opera interacts poorly with web-socket-js. After two disconnects the browser tab or Flash often hang. Although Javascript is faster than Firefox 3.5, the high variability of web-socket-js performance results in overall performance being lower. Middle mouse clicks and keyboard events need some work to work properly under Opera.

Integration

The client is designed to be easily integrated with existing web structure and style.

At a minimum you must include the vnc.js and default_controls.js scripts and call their load() functions. For example:

<head>
    <script src='include/vnc.js'></script>
    <script src="include/default_controls.js"></script>
</head>
<body>
    <div id='vnc'>Loading</div>
</body>
<script>
    window.onload = function () {
        DefaultControls.load('vnc');
        RFB.load(); };
</script>

See vnc.html and vnc_auto.html for examples. The file include/plain.css has a list of stylable elements.

The vnc.js also includes other scripts within the include sub-directory. The VNC_uri_prefix variable can be use override the URL path to the directory that contains the include sub-directory.

Troubleshooting

You will need console logging support in the browser. Recent Chrome and Opera versions have built in support. Firefox has a nice extension called "firebug" that gives console logging support.

First, load the noVNC page with logging=debug added to the query string. For example vnc.html?logging=debug.

Then, activate the console logger in your browser. With Chrome it can be activate using Ctrl+Shift+J and then switching to the "Console" tab. With firefox+firebug, it can be activated using Ctrl+F12.

Now reproduce the problem. The console log output will give more information about what is going wrong and where in the code the problem is located. If you file a issue/bug, it can be very helpful to copy the last page of console output leading up the problem into the issue report.

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