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noVNC: HTML5 VNC Client

Description

noVNC is a VNC client implemented using HTML5 technologies, specifically Canvas and WebSockets (supports 'wss://' encryption). noVNC is licensed under the LGPLv3.

Special thanks to Sentry Data Systems for sponsoring ongoing development of this project (and for employing me).

Notable commits, announcements and news are posted to @noVNC

Screenshots

Running in Chrome before and after connecting:

 

See more screenshots here.

Browser Requirements

  • HTML5 Canvas: Except for Internet Explorer, most browsers have had Canvas support for quite some time. Internet Explorer 9 will have Canvas support (finally).

  • HTML5 WebSockets: For browsers that do not have builtin WebSockets support, the project includes web-socket-js, a WebSockets emulator using Adobe Flash.

  • Fast Javascript Engine: noVNC avoids using new Javascript functionality so it will run on older browsers, but decode and rendering happen in Javascript, so a slow Javascript engine will mean noVNC is painfully slow.

  • I maintain a more detailed list of browser compatibility here.

Server Requirements

Unless you are using a VNC server with support for WebSockets connections (only my fork of libvncserver currently), you need to use a WebSockets 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:

  1. WebSockets 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 WebSockets frame begins with 0 ('\x00') and ends with 255 ('\xff').

  2. Javascript itself does not have the ability to handle pure byte arrays. The python proxy encodes the data as base64 so that the Javascript client can decode the data as an integer array.

Quick Start

  • Use the launch script to start a mini-webserver and the WebSockets proxy. The --vnc option is used to specify the location of a running VNC server:

    ./utils/launch.sh --vnc localhost:5901

  • Point your browser to the cut-and-paste URL that is output by the launch script. Enter a password if the VNC server has one configured. Hit the Connect button and enjoy!

Advanced usage

  • To encrypt the traffic using the WebSocket 'wss://' URI scheme you need to generate a certificate for the proxy to load. By default the proxy loads a certificate file name self.pem but the --cert=CERT option can override the file name. You can generate a self-signed certificate using openssl. When asked for the common name, use the hostname of the server where the proxy will be running:

    openssl req -new -x509 -days 365 -nodes -out self.pem -keyout self.pem

  • tightvnc provide a nice startup script that can be used to run a separate X desktop that is served by VNC. To install and run the server under Ubuntu you would do something like this:

    sudo apt-get install tightvncserver

    vncserver :1

    The VNC server will run in the background. The port that it runs on is the display number + 5900 (i.e. 5901 in the case above).

  • x11vnc can be used to share your current X desktop. Note that if you run noVNC on the X desktop you are connecting to via VNC you will get a neat hall of mirrors effect, but the the client and server will fight over the mouse.

    sudo apt-get install x11vnc

    x11vnc -forever -display :0

    Without the -forever option, x11vnc will exit after the first disconnect. The -display option indicates the exiting X display to share. The port that it runs on is the display number + 5900 (i.e. 5900 in the case above).

  • To run the python proxy directly without using launch script (to pass additional options for example):

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

    ./utils/wsproxy.py -f 8787 localhost:5901

  • To run the mini python web server without the launch script:

    ./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.

  • If you are using python 2.3 or 2.4 and you want wsproxy to support 'wss://' (TLS) then see the wsproxy README for instructions on building the ssl module.

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 ui.js scripts and call UI.load(). For example:

<head>
    <script src='include/vnc.js'></script>
    <script src="include/ui.js"></script>
</head>
<body>
    <div id='vnc'>Loading</div>

    <script>
        window.onload = function () {
            UI.load('vnc');
        }
    </script>
</body>

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 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 is very helpful for me to have the last page of console output leading up the problem in the issue report. Other helpful issue/bug information: browser version, OS version, noVNC git version, and VNC server name/version.